Electrical Calculations

Preparing for an Electrical Exam

Not every electrical license exam is the same, so here are some important steps that you can take to improve your chance of passing this difficult exam.

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Most Recent

Ground Resistance Testing

How do we know if our single ground rod has the proper earth resistance? We don’t know unless we have a ground resistance tester and know how to use it. So let’s look at how we perform this test.

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Derating Current-Carrying Conductors for Conditions of Use

If you ask a seasoned electrician how many No. 12 AWG conductors will fit into a 3/4″ EMT conduit system, you may get a response such as “one more!” While this is amusing (and typically true), there are precautions that must be taken according to the NEC whenever conductors are bundled together in a raceway, cable, or even in a ditch in the earth.

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Conduit and Cables Exposed to Sunlight on Rooftops

Anyone who has been on top of a roof on a hot summer day knows what it’s like to stand in the middle of an oven. Extreme temperatures from the sun can bake everything in sight, from shingles to appliances, and even electrical conductors and conduit.
Conductor insulation is meant to provide long lasting protection from expected heat due to the flow of electricity and normal environmental factors. However, excessive heat from solar radiation can damage conductors and cause premature failures.

Read Article
Sizing RV-Park Electrical Services Using NEC Table

The Electrical Service supplying an entire RV park must be sized to accommodate the electrical demands of multiple modern recreational vehicles drawing power simultaneously from the individual park sites.

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Recently in Electrical Calculations

Preparing for an Electrical Exam

Not every electrical license exam is the same, so here are some important steps that you can take to improve your chance of passing this difficult exam.

Read Article

Ground Resistance Testing

How do we know if our single ground rod has the proper earth resistance? We don’t know unless we have a ground resistance tester and know how to use it. So let’s look at how we perform this test.

Read Article

Derating Current-Carrying Conductors for Conditions of Use

If you ask a seasoned electrician how many No. 12 AWG conductors will fit into a 3/4″ EMT conduit system, you may get a response such as “one more!” While this is amusing (and typically true), there are precautions that must be taken according to the NEC whenever conductors are bundled together in a raceway, cable, or even in a ditch in the earth.

Read Article

Conduit and Cables Exposed to Sunlight on Rooftops

Anyone who has been on top of a roof on a hot summer day knows what it’s like to stand in the middle of an oven. Extreme temperatures from the sun can bake everything in sight, from shingles to appliances, and even electrical conductors and conduit.
Conductor insulation is meant to provide long lasting protection from expected heat due to the flow of electricity and normal environmental factors. However, excessive heat from solar radiation can damage conductors and cause premature failures.

Read Article

Sizing RV-Park Electrical Services Using NEC Table

The Electrical Service supplying an entire RV park must be sized to accommodate the electrical demands of multiple modern recreational vehicles drawing power simultaneously from the individual park sites.

Read Article

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 […]

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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 […]

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210.23(A)(1)&(2) Permissible Loads, Multiple-Outlet Branch Circuits.

A multiple-outlet branch circuit is a branch circuit that supplies two or more outlets. With the exception of the required small appliance, laundry, and bathroom receptacle circuits in dwelling units, those outlets may be a combination of lighting outlets for luminaires, receptacle outlets for cord and plug connected utilization equipment […]

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Single Family Dwelling Calculation, Optional Method.

If you are preparing to take an electrical licensing exam, you will need to know how to calculate the feeder or service load for a single family dwelling. Refer to section 220.82(A)&(B) in the 2014 National Electrical Code (NEC). Here is a sample problem. Use the optional calculation to find […]

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Applying NEC 310.15(B)(7)

The fact that the table was removed is neither here nor there. More importantly is how to apply the 83% and when the Code section allows us to use it. Applying 310.15(B)(7) to one-family dwellings or the individual dwelling units of two-family and multi-family dwellings, has always been dependent on a few important factors:

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