Elevator Maintenance

By David Herres

Elevators have become an essential feature of most multistory buildings and are no longer limited only to tall buildings. Elevators provide an accessible and easy means of egress for employees and customers. In certain types of buildings elevators are required by the model building codes or Federal law.  When there is an elevator outage for any length of time in a commercial or industrial setting, it is usually a very serious problem because the entire operation can be impacted if not paralyzed altogether. Designers and elevator technicians must have the knowledge and expertise to create, install, and maintain systems that function around the clock for years with minimal interruption.

The elevator motion controller shuts down the system when a dangerous condition is sensed.

When a system failure does occur, facility maintenance personnel and/or outside elevator professionals must make repairs quickly and with minimal disruption to workflow and building operations. Where available, onsite electricians may perform initial troubleshooting and evaluation when there is a malfunction. For example, an onsite electrician may verify that there is power to the elevator disconnecting means and perform a visual inspection to ensure that nothing is blocking an elevator door. Typically, there is an elevator company on-call that will dispatch an elevator technician to troubleshoot more complex problems. Elevator maintenance and repair must conform to legal mandates, which vary widely in different states or jurisdictions, so the local situation should be researched and evaluated.

Elevators invariably include robust fail-safe interlock mechanisms that prevent the car from moving if any of a certain class of mechanical failures occur. An example is when a door fails to close securely, or the electrical circuit including the door sensor fails to inform the elevator motion controller that the door is closed. There are shut-down mechanisms for various types of elevators. For example, in a hydraulic (non-cable) elevator, the elevator will shut down when the oil reservoir temperature rises above a specific level.

In any elevator system alteration or repair, there is the potential for introducing unforeseen hazards including electric shock, fire, falling down an elevator shaft and injury due to malfunctioning elevator doors or door interlocks. Any uncontrolled movement of the elevator car can result in serious injury. When working on an elevator, a simple error can have disastrous consequences. Electricians should recognize their limitations and not attempt repairs if they are not trained to work on the elevator system. Safety interlock systems must never be left inoperable when an elevator is in service.

To illustrate, a tragic accident occurred on December 14, 2011 in a Madison Avenue, New York City elevator shaft when without warning an elevator car lurched upward, crushing a 41-year-old advertizing executive, causing her death. A lengthy investigation found the elevator maintenance company at fault because workers disabled the door interlock circuit, a common practice during maintenance, but failed to restore it once the maintenance work was complete.

AC motor controlled by a variable frequency drive.

Virtually all elevators are powered by electric motors. For many years, throughout the first half of the 20th century, DC motors were used exclusively because their speed could be easily and smoothly regulated, an important feature as the car slows approaching a scheduled floor stop. In the 1960’s, variable frequency drives (VFD’s) were developed, permitting smooth speed control for off-the-shelf AC induction motors. Pulse width modulation (PWM) was the method that enabled this speed control by varying the duty cycle rather than the voltage, which would indeed regulate speed but also cause overheating and short motor life. VFD’s also control torque and provide other automatic and manual control via a versatile user interface.

In the event of malfunction such as motor overheating or outright failure, electricians should become adept at diagnosing and repairing VFD’s, which are used in a great many applications including but not at all limited to elevators. Great care must be exercised because these systems usually operate at voltages higher than the usual 240 volts. Also, in opening an enclosure and making electrical measurements, even after the unit is powered down, large electrolytic capacitors that are capable of holding a lethal electrical charge may be encountered. Such work should not be attempted until instruction and training in this area has been completed and workers are aware of all hazards and protective procedures.

Elevator installations must conform to all NEC requirements that were in place at the time of the original construction when the elevator(s) were placed in service. Among the more important tasks of elevator maintenance workers is to examine existing installations to see if they conform to current NEC regulations. Of course, there is no obligation to immediately upgrade every installation as new Code revisions are enacted every three years, but in some cases the NEC will require updates when repairs are made. For example, Article 406 requires GFCI receptacles to be installed when receptacles are replaced in any location where GFCI protection is required by the current code. GFCI protection requirements have been expanded in the 2017 NEC. To learn more about 2017 NEC changes, sign up for a 2017 Code Changes course at jadelearning.com.  It is a simple matter to install GFCI receptacles in an elevator pit that was built before they existed, but the 2017 NEC does not permit the required lighting to be connected to the load side of a GFCI receptacle. The 2017 NEC also makes it clear that lighting and receptacles in elevator machine rooms must be on separate branch circuits. Old systems should be reworked to incorporate new requirements where this is feasible.

As in other electrical equipment and installations, new elevators must comply with the current NEC requirements, in this instance Article 620, Elevators, Dumbwaiters, Escalators, Moving Walks, Platform Lifts, and Stairway Chairlifts. Specific elevator rules in Article 620 address dedicated circuits in control and machine rooms, enclosing live parts, guarding of machinery, wiring methods in machine rooms, hoistways, pits and cars, GFCI requirements, and signage.

Elevators must also comply with the general requirements elsewhere in the Code. Examples of important Code-wide mandates are Over-Current Protection, Access and Working Space About Electrical Equipment, Conductor Ampacity, Grounding Requirements and Motor Installations. Keep up with the latest requirements by taking one of our on-line courses on the 2017 NEC.

 

Posted in 2017 NEC, 70E, Electrical Safety, Equipment, Uncategorized, Wiring Tagged with: , , ,

Oregon Electrical License Renewal: Act now to meet the 10/1 deadline

Fall is officially here, which means there’s not much time left to complete your Oregon electrician continuing education courses. JADE Learning will submit continuing education hours to the Oregon Building Codes Division every business day until Oct 1—ensuring you can complete your renewal on time, with no late penalties.

REMEMBER: Because Oct. 1 falls on a Sunday, you’ll want to complete your courses by 5:00 PM Eastern on Friday, Sept. 29, in order to have your credits reported before the deadline.

Get the continuing education you need, online, anytime. We’ve made it easy with courses specifically for renewing your Oregon electrical license, including:

  • Limited Journeyman Manufacturing Plant Electrician (PJ)
  • Limited Energy Technician Class A (LEA)
  • Limited Energy Technician Class B (LEB)
  • Limited Maintenance Electrician (LME)
  • Limited Renewable Energy Technician (LRT)
  • Limited Journeyman Sign Electrician (SIG)

We’ve been a trusted provider of electrical continuing education in Oregon since 2002. We’re here to support every step of your electrical license renewal in Oregon.

Courses we recommend to complete your renewal are:

Oregon electrical courses

Oregon electrical renewal courses for 2017

You can log in to your JADE Learning account or register a free account at any time day or night. All JADE Learning courses can be completed online from any device. Courses can be completed on a computer, laptop, tablet, or smartphone.

Our courses are tailored to the requirements for Oregon electrical license renewal below:

Oregon License chart

Oregon electrical license renewal 2017

Once you complete your Oregon electrical license continuing education, JADE Learning will submit your hours to the Oregon Building Codes Division every business day in September as the October 1 deadline approaches. We’ll also send an email notification so you know when your hours have been submitted. When the Oregon BCD posts the hours, they can be checked on the License Holder Search webpage.

After your hours are posted, you’re ready to renew your Oregon electrician license online. The cost to renew will be between $50 and $100, depending on your Oregon electrical license type. You can submit your Oregon electrician license renewal online before October 1, 2017, to keep your license active for another 3 years.

Get started now! Log in to your JADE Learning account or register a free account and begin taking online courses to satisfy your Oregon electrician continuing education requirements.

 

Posted in Uncategorized

Oregon Electrical Continuing Education in 3 Easy Steps

The Oregon electrical license renewal deadlines for Limited Journeyman Manufacturing Plant Electrician (PJ), Limited Energy Technician Class A (LEA), Limited Energy Class B (LEB), Limited Maintenance Electrician (LME), Limited Renewable Energy Technician (LRT), and Limited Journeyman Sign Electrician (SIG) are approaching on October 1, 2017.

The Oregon Building Codes Division (BCD) requirements for this renewal are as follows:

Oregon License chart

Oregon electrical license renewal 2017

The best continuing education package for Oregon Limited Journeyman Manufacturing Plant Electrician (PJ) renewal is JADE Learning’s 16 Hour Package for PJ Licensees. The online package includes the following Oregon licensed electrician continuing education courses:

  • 2017 NEC Changes Part 1
  • Lockout/Tagout (NFPA 70E)
  • OESC and Administrative Rules

Follow the suggestions in the chart below to get hours for your Oregon electrical license renewal.

Oregon electrical courses

Oregon electrical renewal courses for 2017

Follow these 3 easy steps to renew your Limited Journeyman Manufacturing Plant Electrician (PJ), Oregon Limited Energy Technician Class A (LEA), ​​Limited Energy Technician Class B (LEB), ​​​Limited Maintenance Electrician (LME), ​​Limited Renewable Energy Technician (LRT), or ​​Limited Journeyman Sign Electrician (SIG) license for the 2017 deadline:

Step 1: Continuing Education

Complete the appropriate recommended course(s) from the chart above to ensure all requirements for your specific Oregon electrical license type are met. You can log in to your JADE Learning account or register a free account at any time day or night. All JADE Learning courses can be completed online from any device. Courses can be completed on a computer, laptop, tablet, or smartphone. The Oregon 16 Hour Package for PJ Licensees is discounted to $149, until September 1, 2017. To receive the package discount, all courses in the package have to be paid for altogether upon completion.

Step 2: Check CE Hours

Wait for your Oregon electrical continuing education hours to be reported to the Oregon BCD. JADE Learning will submit hours to the Oregon Building Codes Division every business day in September as the October 1 deadline approaches. When licensee hours are reported, JADE Learning will send an email notification informing the licensee about the submittal of the hours. When the Oregon BCD posts the hours they can be checked on the License Holder Search webpage.

Step 3: Renew Oregon Electrician License Online

When you can confirm that your hours are posted, you are ready to renew your Oregon electrician license online. The cost to renew will be between $50 and $100, depending on your Oregon electrical license type. You can submit your Oregon electrician license renewal online before October 1, 2017, to keep an active license for another 3 years.

Get started now! Log in to your JADE Learning account or register a free account and begin taking online courses to satisfy your Oregon electrician continuing education requirements.

Please note that October 1, falls on a Sunday this year, so licensees should have hours completed by September 29, so that they can be reported on time.

Posted in 2017 NEC, Electrical Licensing, JADE Learning, Oregon Electrical License Renewal Tagged with: , , , , , , , , , , , , , , ,

North Carolina Electrical Contractor Classes for 2017

There are about 2,500 licensed electrical contractors in North Carolina whose licenses expire in the latter part of the year. Is your license about to expire? If so, sign up now to take the North Carolina electrical contractor continuing education class to renew your license on time.

The requirements set by the North Carolina State Board of Examiners of Electrical Contractors are as follows:

  • North Carolina Electrical contractors have to complete a total of 8 continuing education hours per year
  • North Carolina Electrical contractors have to complete at least half of the 8 hours in a classroom

What does this mean?

A licensed electrical contractor in North Carolina with the license type of Limited, Intermediate, Unlimited, or Residential dwelling will have to complete at least 4 hours of in-person classroom training per year. The other 4 hours can either be in-person classroom training or completed online with JADE Learning.

Let’s take a look at the different options that a North Carolina electrical contractor has to complete their electrical continuing education requirement:

  1. 8 hours of in-person class instruction and 8 hours of online course completion – this will give licensees 2 years of electrical continuing education for their North Carolina Electrical Contractor license.
  2. 8 hours of in-person class instruction – this will give licensees 1 year of electrical continuing education for their North Carolina Electrical Contractor license.
  3. 4 hours of in-person class instruction and 4 hours of online course completion – this will give licensees 1 year of electrical continuing education for their North Carolina Electrical Contractor license.

NC Class testimonial

Sign up for the 4 hour Feeders and Branch Circuits and the 4 hour 2014 NEC Applications classes now to fulfill your 2017 North Carolina electrical continuing education requirement or bank some hours for the 2018 renewal. With attendance, each licensee will receive a coupon with two discount codes, each worth $25 off any North Carolina online electrical continuing education course.

The next JADE Learning North Carolina electrical contractor renewal class will be on August 10th, 2017, in Raleigh, North Carolina.

For North Carolina electrical license holders that are also licensed in Georgia or Virginia, the two classroom courses, Feeders and Branch Circuits and 2014 NEC Applications can be reciprocated for electrical continuing education credits to Georgia and Virginia.

Other electrical continuing courses are available at: www.JadeLearning.com.

Posted in 2014 NEC, Branch Circuits, JADE Learning, North Carolina Classroom, State Requirements Tagged with: , , , , , , , ,

Fire Alarm Systems

Fire Alarm Systems

By David Herres

Fire alarm systems are at least an order of magnitude more challenging to understand than homeowner-type smoke alarms, even if individual smoke alarms within the home are wired together to work in concert. Fire alarm work must not be taken for granted because if a system should fail to respond to a smoke or heat event, humans could perish in a fiery inferno. The recent fire at a 24-story high-rise apartment building in London demonstrates how quickly a fire can spread- and its deadly consequences.  It is a little less dramatic, but the possibility of false alarm also presents hazards that should be recognized. Recurring false alarms make for complacency so that the occupants may disregard the real one and also divert fire department resources from real emergencies. To ensure their reliability, fire alarm systems must be installed and maintained by trained technicians.

The defining element in a fire alarm system is the control panel.

Fire Alarm Control Panel

The fire alarm control panel is the heart of the system, where technicians program and interact with initiating devices and indicating appliances as required.

If the control panel is located in an office or maintenance center, building management can quickly respond to alarm or trouble signals, but additional annunciator panels may be required in location(s) accessible to emergency responders. The purpose of an annunciator panel is to allow the emergency responders to quickly identify the location of the fire and provide information on the status of any interconnected fire safety systems.

The control panel contains a central processing unit, an alphanumeric readout that displays the system status (normal, trouble, or alarm), and responds to queries and programming instructions entered on a keypad. The control panel also contains back-up batteries, terminals for connecting conductors to remote devices, etc. This control panel can range in size from a small wall-mounted box set at eye level, to a heavy floor-to-ceiling steel enclosure for large occupancies with many zones.

The control panel is a highly intelligent unit with lots of functionality. A large part of its job is to coordinate interaction with other systems inside and beyond the confines of the building. The alarm system interacts with elevators so that occupants are not brought to a floor that is impacted and firefighters arriving at the scene can manually control the lift from inside the car. Additionally, the control panel places the system in alarm if the sprinkler system is activated. In essence, every sprinkler head is an alarm initiating device.

Where the fire alarm system is monitored by a central supervising station, if the system goes into alarm, a call is automatically placed to the designated supervisory station. Typically, two dedicated phone lines are required for monitoring and alarm transmission. The control panel makes test calls periodically to check the phone lines and goes into the trouble state, indicated by an audible signal and alphanumeric report at the control panel, if either of these lines is down. Where fire alarm systems are not monitored by a supervising station, a sign is typically required at each manual fire alarm box that reads, WHEN ALARM SOUNDS-CALL  FIRE DEPARTMENT.

Fire Detector

The remote elements of the fire alarm system fall into two major categories:

  • Initiating devices, including alarm heads and duct sensors that, detecting the presence of heat or smoke, perform the function of placing the system into alarm status.  Fire alarm heads and pull stations are initiating devices that automatically or manually report to the control panel, which responds by placing the system in the alarm state.
  • Indicating appliances, including horns, strobe lights, chimes and bells, serve to alert occupants and building personnel to the presence of fire.

These sensors and loads are wired in parallel, daisy-chain style, just like feed-through receptacles on a branch circuit, with each conductor terminated to a separate terminal on the device. Neither line is grounded, although for line integrity and ease of maintenance, it is often recommended that all zone wiring be run in electrical metallic tubing (EMT), which serves as an equipment-grounding conductor and provides physical protection. Alarm heads are designed to conduct only when fire is detected, placing the system into alarm status. How, you may wonder, can the system differentiate between normal operation and an open circuit? The answer is by means of an end-of-line resistor, typically 4.7K ohms, which is continuously read by the control panel when the line is intact.

Fire Alarm Pull Station

Regulatory statutes for fire alarm work differ widely. Some states mandate one or more levels of licensing for fire alarm professionals, while others make no mention of this type of work. New Hampshire falls into neither category with an optional licensing program that will become mandatory down the road. In all cases the local authority having jurisdiction or local fire department should be contacted if a fire alarm system is to be installed, modified, or removed from operation. Installation requirements for fire alarm systems are found in several documents:

NFPA 101 Life Safety Code, the ICC International Building Code, and the ICC International Fire Code specify which occupancies are required to have fire alarm systems. NFPA 72 National Fire Alarm and Signaling Code lays out system design requirements, including location and spacing of heads and pull stations, testing and maintenance procedures, minimum performance requirements and operational protocols.

NFPA 70 National Electric Code in Article 760, Fire Alarm Systems, specifies wiring requirements, both for power to the control console and zone wiring to initiating devices and to indicating appliances and phone lines used for automatic calling. Other fire alarm functions including guard’s tour, sprinkler water flow, elevator capture and shutdown, door release, smoke doors and damper control, fire doors and fan shutdown are covered by Article 760 where these functions are controlled and powered by the fire alarm system.

 

Posted in 2017 NEC, Alarm, Equipment, Fire Alarm, Technology Tagged with: , , , , ,

Electrical Safety Never Takes A Holiday

May is designated as Electrical Safety Month and many organizations and employers take advantage of the focus on electrical safety to emphasize the importance of following safe working practices when working around energized equipment. The month of May is fast passing and the Memorial Day holiday is approaching, but we must never allow our electrical safe working practices to take a holiday, not even a day off. Day in and day out the hazards associated with working around energized electrical equipment remain present. Those hazards never take a holiday, so neither can our electrical safety procedures. Designating May as Electrical Safety month is a good reminder, but electrical safety is important all year long.

A panelboard destroyed by an arc-flash event. (Not the one at the bowling alley).

An example is provided by a report of an electrical fire in a bowling alley. An untrained person was tasked with installing some filler blanks where circuit breakers were missing in a panelboard. A simple task that certainly needed to be done; if the filler blanks are not installed, the energized bus bars are exposed. What can go wrong? We all know the answer. A lot! Apparently, while installing the filler blanks a short circuit was created across the bus bars resulting in an arc flash. Fortunately, no serious injury resulted, but the panelboard was destroyed. The bowling alley was out of business for several days until the electrical system was repaired, so employees likely lost a few days wages as well. It could have been much worse.

The 2017 NEC includes many reminders to help us remember the importance of following safe work practices. Signage requirements in 110.16 are intended to WARN qualified persons of potential arc flash hazards. Article 690 requires numerous WARNING signs to remind us of the hazards specific to PV systems including new signage requirements for Rapid Shutdown systems. The entrance to rooms or enclosures containing equipment operating at over 1000 volts are required to be kept locked and marked with conspicuous DANGER-HIGH VOLTAGE-KEEP OUT signs to inform both qualified and unqualified persons of the hazard. These and the numerous other CAUTION, WARNING and DANGER signs required by the NEC are intended to provide that final opportunity to remember and follow safe working practices.

PV System Warning Sign required by 690.13

PV System Warning Sign required by 690.13

But, human nature often chooses an easier path. Even qualified persons are sometimes tempted to take shortcuts, but what makes a person qualified to work around energized electrical equipment in the first place? Experience? Training? Time?

The Standard for Electrical Safety in the Workplace (NFPA 70E) defines a qualified person as, “One who has demonstrated skills and knowledge related to the construction and operation of electrical equipment and installations and has received safety training to identify and avoid the hazards involved.” Obviously, the employee in the bowling alley was not able to identify and avoid the hazards involved.

Training is only part of the equation; an employee must demonstrate that the training had the desired effect by following safe working practices. The employee’s supervisor has a key role in verifying that the employee is applying what was learned in the classroom to real world situations. Was he or she paying attention during training, or were they sending text messages or thinking about their next work task? When did employees performing electrical work last receive training?

NFPA 70E requires retraining in safety-related work practices at least every three years. Three years is a long time. Even the most qualified person can develop bad habits, and we all need reminding from time to time. That is, after all, what all those warning signs in the NEC are about. What about unqualified persons? By definition, a qualified person is one who has received training and demonstrated the necessary skills. Does an unqualified person require training?

An unqualified person is still required by NFPA 70E to be “trained in, and be familiar with, any electrical safety-related practices necessary for their safety.”  Virtually any maintenance technician is exposed to some level of electrical hazard and should receive the training necessary to avoid those hazards. As demonstrated by the employee in the bowling alley, unqualified persons should never be permitted to work on energized electrical equipment.

Jade Learning provides on-site Electrical Safety Training based on NFPA 70E. Visit us online or contact us at 1-800-443-5233 for a quote. Some of our online continuing education courses also include an electrical safety component. May is a good reminder, but remember that electrical safety should never take a holiday.

Posted in 2017 NEC, 70E, Electrical Safety, Marking and Labeling, Photovoltaics Tagged with: , , ,

Article 90: Simple But Important Changes

When reading a book, how often do we skip past the introduction and start with the chapters that interest us? That happens to those of us that use the NEC as well, but understanding the introduction to the code in Article 90 is key to properly applying the technical requirements in the other chapters of the NEC. Changes in the Introduction may appear simple, but simple does not mean unimportant.

One thing that has not changed is the purpose of the NEC under 90.1. The stated purpose remains,  “the practical safeguarding of persons and property from the hazards arising from the use of electricity.”

An exhaust fan was removed, but the NM cable was not terminated in a box as required by 300.15.

There are limits to what any code or standard can do in protecting human beings from our own mistakes, but as we look at the changes that have been introduced this year in Article 90 and elsewhere in the NEC, we should keep in mind the purpose of the Code: the practical safeguarding of persons and property from electrical hazards. Fires, explosions, and electric shock continue to take lives and destroy property each year; as we study the changes in the 2017 we should think about the link between the change and the stated purpose of the NEC.

One such change appears in 90.2. Previous editions of the NEC stated that, “This Code covers the installation of electrical conductors, equipment, and raceways;” However, the requirements that apply when conductors or equipment are removed have sometimes been overlooked. For example, 590.2(D) requires the removal of temporary wiring upon completion of construction, 390.8 requires removal of circuit conductors in underfloor raceways when outlets are abandoned, and 110.12 requires unused openings in electrical equipment to be closed. Section 725.25 and requires the accessible portion of abandoned Class 2 and Class 3 cables to be removed while 800.25 requires the same for abandoned communications cables. In the 2017 NEC, 90.2 states that the code covers, “the installation and removal,” of electrical conductors, equipment and raceways.

The 2017 NEC covers the installation and removal of electrical conductors, equipment, and raceways.

The point of the change is that the removal of electrical conductors, equipment, and raceways be done in such a manner that the electrical system remains in compliance with the safety requirements of the NEC. Since the NEC is adopted by many states and local jurisdictions for regulatory purposes, clarifying that the code applies to both the installation and removal of conductors and equipment reinforces the importance that electrical work be performed by qualified persons and in compliance with the NEC regardless of whether the work involves the installation or removal of electrical conductors, equipment or raceways.

Another significant change is found in 90.3 Code Arrangement. For many years, the accepted arrangement was that Chapters 1-4 applied generally and Chapters 5, 6, and 7 applied to special occupancies, special equipment, or other special conditions. It was accepted that Chapters 5, 6, or 7 could modify the general requirements in Chapters 1-4. While this is true, in fact the requirements of Chapters 5, 6, and  7 may “supplement or modify” requirements within any of the 7 chapters- not just Chapters 1-4.

For example, an electric sign installed within a fountain must comply with the specific provisions found in 680.57, which modify the basic requirements for electric signs in Article 600. The disconnecting means for the sign must comply with both the sign disconnect requirements in 600.6 and the pool maintenance disconnecting means required by 680.13. Since Article 680 is written to address the specific hazards associated with electrical equipment around swimming pools and fountains, it is logical that the more specific requirements in Article 680 will supplement of modify the general requirements for signs in Article 600 just as Article 600 supplements or modifies the general requirements in Chapters 1-4.

Sign in fountain

The changes in 90.3, Code Arrangement, make it clear that the NEC is a comprehensive document. As we study the 2017 NEC changes, we cannot just pick out individual sections to apply independently of related requirements in other chapters. As stated in 90.1(B), compliance with the NEC and proper maintenance will result in an “installation that is essentially free from hazard.” The practical safeguarding of persons and property from electrical hazards should be our goal for every electrical installation. Jade Learning offers courses on the 2017 NEC changes as well as exam prep courses to help you learn your way through the NEC. Power your career by registering for a free account!

 

Posted in 2017 NEC, Conductors, Electrical Safety, Equipment, Pools and Spas, Wiring Tagged with: , , , , , , , ,

Feeder Conductor Ampacity

Feeders Part 3

Feeder Conductor Ampacity.

The conditions of use must be considered when determining the minimum size of a feeder conductor. A continuous load, such as the lighting load in a store building, generates heat in the feeder conductor that must be compensated for. Ambient temperatures above 86oF or more than 3 current-carrying conductors in a raceway or cable can have a similar heating effect.

215.2 Feeder with Scales

The conductor size required to serve the noncontinuous load plus 125% of the continuous load is compared to the conductor size required to compensate for ambient temperature and or more than 3 current-carrying conductors in a raceway. The larger size conductor must be used.

According to 215.2(A)(1) in the 2014 NEC the ampacity of feeder conductors must not be less than the ampacity required for the greater of (A) or (B) below:

(A)        100% of the noncontinuous load plus 125% of any continuous loads.

OR

(B)        100% of the maximum load served after the application of any ampacity adjustment or temperature correction factors.

The ampacity of the feeder conductors is also limited by the temperature rating of the circuit breaker or panelboard terminals as covered in 110.14(C). Equipment terminals for circuits rated over 100 amps will be rated at 750C. Higher temperature rated conductors are permitted to be used on these terminals, but the ampacity of the conductor used is limited to no more than the 750C ampacity in Table 310.15(B)(16) for the same size conductor.

For example, a 208Y/120 volt 4-wire 3-phase feeder supplies 100 amps of continuous nonlinear lighting load and 50 amps of noncontinuous load for general purpose receptacles in a retail store. All terminals and conductors are rated 75oC.

First, find the ampacity of the conductor needed to satisfy 125% of the continuous load plus 100% of the noncontinuous load.

100 Amps continuous X 125% = 125 Amps.

125 Amps + 50 Amps noncontinuous = 175 Amp conductor.

In the 75oC column of Table 310.15(B)(16), a 2/0 AWG THWN copper conductor has an allowable ampacity of 175 amps so this conductor meets the minimum required ampacity for the noncontinuous load plus 125% of the continuous load.

The conductor ampacity in Table 310.15(B)(16) is based on an ambient temperature of 86oF and not more than 3 current-carrying conductors in a raceway. If there are more than 3 current-carrying conductors in a raceway or cable, the ampacity of the conductor must be adjusted.

Ampacity adjustment

Where there are more than 3 current-carrying conductors in a raceway or cable, the ampacity of the conductor must be adjusted to prevent damage to conductor insulation caused by overheating.

Since the 208Y/120-volt, 4-wire feeder supplies nonlinear lighting loads, the neutral must be counted as a current carrying conductor per 310.15(B)(5). This means that there are 4 current-carrying conductors in the same raceway. The adjustment factor in Table 310.15(B)(3)(a) for 4-6 current-carrying conductors in the same raceway or cable is 80% or 0.80. The fastest way to find a conductor that will meet the adjusted ampacity requirement is to divide the load served by the adjustment factor (0.80). It is not required to multiply the continuous load by 125% before applying the adjustment factors in Table 310.15(B)(3)(a).

Load served = 100 Amps continuous + 50 Amps noncontinuous = 150 Amps.

150 Amps ÷ 0.80 = 187.5 Amps (Round up to 188 Amps).

In the 75oC column of Table 310.15(B)(16) a 3/0 THWN copper conductor has an allowable ampacity of 200 amps. To double check that this conductor is sufficient for the load served, multiply the conductor ampacity by the 80% adjustment factor (0.80) in Table 310.15(B)(3)(a).

200 Amps (From Table) X 0.80 adjustment factor = 160 Amps adjusted ampacity.

Load served = 100 Amps continuous + 50 Amps noncontinuous = 150 amps.

The adjusted ampacity of a 3/0 THWN copper conductor is adequate for the maximum load served. Since the ampacity adjustment resulted in a conductor larger than the 2/0 AWG THWN conductor required for the noncontinuous load plus 125% of the continuous load, the larger 3/0 THWN copper conductor must be used.

Adjustment factors for more than 3 current-carrying conductors in a raceway or cable also apply where single conductors or multiconductor cables are bundled together for more than 24 inches in length. Although not discussed in this article, conductor ampacity must also be adjusted for ambient temperatures other than 86oF. Ambient temperature correction factors are found in Table 310.15(B)(2)(a).

To learn more about the allowable ampacity of conductors and the NEC, register for one of our on-line courses at jadelearning.com or you can power your career to the next level by signing up for one of our exam prep courses!

Posted in 2014 NEC, Ampacity, Cables and Raceways, Calculations, Conductors, Electrical Exam Prep, Feeders, Inspection, Wiring Tagged with: , , , , ,

Feeders Part 2: Overcurrent Protection

The general rule in 215.3 is that a feeder overcurrent device shall have a rating not less than the noncontinuous load plus 125% of any continuous loads supplied by the feeder. Unless permitted for specific applications, such as motor circuits, the rating of the feeder overcurrent device is selected as close as practical to the allowable ampacity of the conductor. This allows the overcurrent device to protect the conductor from overheating due to overloads, as well as from ground-faults and short-circuits. However, the allowable ampacity of a conductor will seldom exactly match one of the standard ratings for fuses or inverse time circuit breakers in 240.6.

feeder-overcurrent-protection-blog-2-options-revised-2

Conductors must be protected against overcurrent in accordance with 240.4.


 

For example, the allowable ampacity of a 500 kcmil THWN aluminum conductor in Table 310.15(B)(16) is 310 amps. The ampacity of the conductor falls in between the standard overcurrent device ratings of 300 amps and 350 amps in section 240.6. Section 240.4(B) allows the next higher standard overcurrent device rating to be used as long as the standard rating does not exceed 800 amps. So, a 350-amp overcurrent device can be used to protect the conductor provided the noncontinuous load plus 125% of the continuous load does not exceed the conductor ampacity of 310 amps.

With large feeders where conductors are often connected in parallel, selecting the rating for the feeder overcurrent device is not as simple. Assuming there are not more than 3 current-carrying conductors in a raceway and the ambient temperature is 86oF (30oC), the allowable ampacity of three 500 kcmil THWN aluminum conductors connected in parallel is, 310 amps X 3 = 930 amps. The ampacity of the feeder conductors falls between the standard overcurrent device ratings of 800 amps and 1000 amps in 240.6. The next higher rating (1000 amps) cannot be used to protect the conductors because it is over the 800-amp limit set in 240.4(B), but an 800-amp rated overcurrent device may not be large enough for the load served.

For example, if the feeder supplies 400 amperes of continuous load and 400 amperes of noncontinuous load, the feeder overcurrent device must be rated not less than the 400 amps of noncontinuous load plus 125% of the 400 amps of continuous load.

400 amps of continuous load X 125% = 500 amps

500 amps + 400 amps noncontinuous load = 900 amps

A minimum overcurrent device rating of 900 amps is required, but 900 amps is not one of the standard ratings listed in 240.6.

What are the options?

1.One option is to change to a conductor with an allowable ampacity of at least 1000 amps and use a standard 1000-amp overcurrent device.  The allowable ampacity of a 600 kcmil THWN aluminum conductor in Table 310.15(B)(16) is 340 amps. The ampacity of three 600 kcmil conductors in parallel is 340 amps X 3 = 1020 amps. A 1000-amp rated overcurrent device can now be used to protect the feeder.

2. A second option is to use a nonstandard rated fuse or inverse time circuit breaker rated not less than the 900 amps required for the overcurrent device and not more than the 930 amps allowed by the conductor ampacity. Section 240.6 specifically permits the use of fuses or inverse time circuit breakers with nonstandard ampere ratings, but fuses or circuit breakers with non-standard ratings may not be readily available.

non-standard-rated-overcurrent-devices

900 amps is not a standard rating for an overcurrent device.


3. Exception No.1 to 215.3 offers a third option that would allow an 800-amp overcurrent device to be used at 100% of its rating, but only if the entire assembly including the overcurrent device(s) protecting the feeder(s) is listed for operation at 100% of its rating. Standard overcurrent devices, panelboards and switchgear are not listed for operation at 100% of their nameplate rating so this would likely require special ordering the equipment.

Any one of the three options above provide an acceptable level of overcurrent protection for general applications. Selecting an overcurrent protective device for specific conductor applications, such as a motor feeder, is a topic for another day. Power your career by learning more about overcurrent protection and the electrical code at JadeLearning.com.

Posted in 2014 NEC, Ampacity, Calculations, Conductors, Electrical Exam Prep, Feeders, Wiring Tagged with: , , , , ,

Feeders Part 1: What is a Feeder?

Author: Dennis Bordeaux

Illustration: Ivan Torres

In order to understand what a feeder is, it is best to start with what a feeder is not.

The conductors between the utility service point and the service disconnecting means are service conductors, not feeder conductors. Special service conductor rules apply because these conductors do not have short-circuit or ground-fault protection other than what is provided on the primary side of the utility transformer. Service conductors are not feeders.

Branch circuits are not feeders. A branch circuit is defined as, the circuit conductors between the final overcurrent device protecting the circuit and the outlet(s). Even the conductors for a circuit rated at 1000-amps is a branch circuit if the conductors are on the load side of the final branch circuit overcurrent device. The conductors on the load side of the final branch circuit overcurrent device are branch circuit conductors, not feeder conductors, no matter how large the circuit rating.

So, feeder conductors are conductors that are not service conductors and not branch circuit conductors. All circuit conductors between the load side of the service equipment and the line side of the final branch circuit overcurrent device are feeder conductors. The definition of a feeder also includes the conductors from the source of a separately derived system or other non-utility power supply source and the final branch circuit overcurrent device.

A Type SER cable between a 200-amp residential service disconnect and a subpanel is a feeder. The conductors between an 800-amp circuit breaker and a fused branch circuit disconnect supplying a single motor are also feeder conductors. So are the conductors between a standby generator and an emergency transfer switch. Although the overcurrent protection rules  for these different feeders vary depending on the load(s) supplied, overcurrent protection is typically provided at the supply end of the feeder.

The conductors between the secondary side of a 480-volt/208-volt transformer and the secondary-side overcurrent device are feeder conductors as well, but are not considered to be protected by the transformer circuit primary overcurrent device.

feeders-part1

Circuit conductors between the service point and the final branch-circuit overcurrent device.

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Prior to the installation of feeder conductors, the authority having jurisdiction may require a feeder diagram. A feeder diagram should include the total calculated load on the feeder and any demand factors used in sizing the feeder conductors. The size and type of feeder conductors, as well as the rating of the feeder overcurrent protective devices, should also be included with the feeder diagram.

A typical electrical system may have many types of feeders supplying many different types of loads. Feeders supplying a combination of continuous and noncontinuous loads, motor feeders, outside feeders or feeders to separate buildings are often included on a feeder diagram. In many cases there may be feeders from more than one voltage system on the same premises. DC system feeders may also be present.

riser-diagram-feeders-part-1

   A typical feeder diagram.

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Where feeders supplied from different voltage systems are present, each ungrounded conductor must be identified by phase or line and system at all termination, connection, and splice points. Identification of ungrounded AC system conductors may be by color coding, marking tape, tagging, or other approved means. Ungrounded feeder conductors supplied by a DC system must be identified by one of the methods listed in 215.12(C)(2). The color red is permitted to be used to identify an ungrounded positive polarity conductor and the color black is permitted to identify an ungrounded negative polarity conductor.

feeders-part-1-dc-identification

215.12(C)(2) Direct-Current Feeder Identification Methods.

With the exception of high-leg systems and isolated power systems, the NEC does not require specific colors to identify ungrounded AC conductors. The NEC mandates the use of the color orange to identify the high-leg of a 4-wire delta-connected system where the mid-point of one phase winding is grounded (110.15). If a high-leg system is present on the same premises with a 480-volt system, the common practice of identifying 480-volt feeder conductors using the colors brown, orange, and yellow may need to be adjusted. Marking tape, tagging or other approved means of feeder identification may be required to distinguish the different feeder voltages.

js-12

Typical 480-Volt AC Feeder Identification

Grounded feeder conductors if present, including grounded DC system conductors, must be identified in accordance with 200.6. Where grounded conductors of different voltage systems are installed in the same enclosure or raceway, each grounded conductor must be identified by system.

The feeder identification method used is required to be posted at each feeder panelboard or documented and readily available to those who will service the electrical system. Using a standard feeder identification method throughout the premises wiring system allows a qualified person to quickly identify the phase and voltage of the feeder conductors at all termination or splice points after the installation is completed.

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Posted in 2014 NEC, Conductor Identification, Conductors, Equipment, Feeders, Marking and Labeling Tagged with: , , , , , , , ,
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