Running smaller than #12 on a 480-volt feed

[dcheser]

Can anyone tell me what the reasoning is for not running anything smaller than #12AWG on a 480-volt feed? Industry Standard or something in the NEC?

 

[infinity]

I would say neither. In some locales #12 AWG is the minimum permitted. The NEC would permit #14 AWG conductors for branch circuits.

 

[jumper]

AFAIK not in the NEC. Seems to be a common spec that commercial and industrial will call for a minimum of #12 and 20A general purpose circuits, but I do not remember a spec that says any 480V circuit has to #12.

 

[dcheser]

Thanks, been doing this for years now and that has always been in the clients standard specification at the facilities where we work. I've never questioned it but was questioned about it today. I could not find anything in the NEC that states it and the only answer I could give was its an industry standard. Was curious if anyone else had any specifics.

Thanks again for the input.

 

[Fnewman]

It has been used as the standard in many industrial plants for at least 50 years, I know. Most things in industrial environments tend to be oversized, often to allow for possible future upgrading of a load without having to pull new cable. The other reason given is that 3/c #12 w/gnd is a bit more rugged than #14 in physically challenging environments.

 

[gadfly56]

It has been used as the standard in many industrial plants for at least 50 years, I know. Most things in industrial environments tend to be oversized, often to allow for possible future upgrading of a load without having to pull new cable. The other reason given is that 3/c #12 w/gnd is a bit more rugged than #14 in physically challenging environments.

I would also guess that as commercial/industrial properties are far larger than residential, spec'ing #12 gives you a little cushion for voltage drop.

 

[Fnewman]

I would also guess that as commercial/industrial properties are far larger than residential, spec'ing #12 gives you a little cushion for voltage drop.

Well possibly, but distances are not as far as you might think given that power is usually distributed at a medium voltage such as 13.8 kV to each area where local substations step it down to 4.16 2.4 kV and 480 for use mostly by motors.

 

[kwired]

I would also guess that as commercial/industrial properties are far larger than residential, spec'ing #12 gives you a little cushion for voltage drop.

480 volts gives you a pretty good cushion for voltage drop compared to 208-240 and even bigger yet cushion then 120 volts.

Say you have a 1000 foot run to a 1/2 hp motor, for cost of conductor/raceway/cable sake, would you prefer to use a 120 volt motor or a 480 volt motor for this application? Both can easily get by with 14 AWG if it were only a short run.