When homeowners receive quotes from HVAC contractors, they typically are given two duct replacement options, sheet metal or fiberglass duct board. There is a third option, phenolic duct, that is made of plastic foam with a foil liner on the inside and exterior. It hasn’t been on the market long enough to weigh in on its merits and shortcomings and will not be included in this comparison. Homeowners usually go for the product their HVAC contractor recommends; however, all systems have their strengths and weaknesses. Here are the advantages and disadvantages of two of these materials when installed in the typical residence.

By: David Herres – Variable Frequency Drives (VFD’s), also referred to as Adjustable Speed Drives, are prominent in today’s workplace. They are used in elevator, water pump, high-volume air compressor applications and material-handling systems wherever speed and torque characteristics of AC motors are regulated. In Thomas Edison’s time, the DC […]

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 […]

Let’s start out with the first basic requirement in 705.12(D)(2): 125% of the inverter output circuit current must be used for the ampacity calculations for most of the interconnection methods used. Whether interconnecting the Inverter Output Circuit through a breaker at the service panel or directly to a feeder, it is important to first know the inverter output circuit current.