Conductor adjustments

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Jeremiah Jenison

New User
Location
Chesapeake Virginia
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Electrician
I am wanting to install multiple conductors in a single raceway inside a cold storage freezer that has a constant temperature of -5 degrees. I have already increased the wire size for voltage drop. Do I need to still adjust the conductors based on the quantity of conductors installed in the single raceway?
 
Jeremiah Jenison said:
I am wanting to install multiple conductors in a single raceway inside a cold storage freezer that has a constant temperature of -5 degrees. I have already increased the wire size for voltage drop. Do I need to still adjust the conductors based on the quantity of conductors installed in the single raceway?
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Depends on what you mean by "still". If you think of starting at the "standard" size, it's not like you compute two different penalties, one for adjustment and one for voltage drop, and then stack the two penalties on top of each other.

Any conductor size increase from ampacity adjustment/correction will contribute to decreasing voltage drop. So typically you'd first figure out the minimum conductor size based on ampacity with adjustment and correction, then check the voltage drop and increase if necessary to reduce voltage drop. In other words ampacity and voltage drop are two separate considerations, and you use the larger of the two sizes from each of those two considerations.

And if you are using a wire-type EGC, because of 250.122(B) you need to know both of those sizes when voltage drop controls, to determine how much you need to upsize the EGC.

Cheers, Wayne
 
Voltage drop and ampacity adjustments/corrections are two independent calculations. The ampacity derates are compounded calculations, but voltage drop is an independent issue. Find the minimum local size as if distance were insignificant enough for voltage drop not to matter, and then increase it as needed to meet voltage drop criteria.

I'd also advise against relying on any artificially-maintained cold environment temperature for conductor ampacity, unless the circuit in question is guaranteed only to operate when its environment is colder than the natural ambient temperature. Account for manmade hot environments when applicable (e.g. for circuits in a boiler room), but otherwise default to the natural ambient temperature that it would be, if all equipment fails. I have a similar concern with taking credit for heated buildings for structural snow loads; many of us can relate to a failed heater or fuel outage during a snow storm, and the last thing you want is a collapsing roof to add insult to injury.
 
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