UL508A: control circuit vs. power circuit

[LMAO]

My question is regarding small space heaters and fans inside a UL508A enclosure: Do you consider these fans and heaters part of "control" or "power" circuit?

I personally think they're power because they do convert electricity to mechanical power but others have different opinions. UL defines control transformers as transformers whose secondary powers control circuit devices only (excluding loads). Load is defined as a device external to the industrial control panel... so this means fans and heaters are control circuit because they are connected to control power transformer, correct?

The reason I am asking is UL508A does not allow less than 14AWG for "power" circuit conductors.

 

[petersonra]

My question is regarding small space heaters and fans inside a UL508A enclosure: Do you consider these fans and heaters part of "control" or "power" circuit?

I personally think they're power because they do convert electricity to mechanical power but others have different opinions. UL defines control transformers as transformers whose secondary powers control circuit devices only (excluding loads). Load is defined as a device external to the industrial control panel... so this means fans and heaters are control circuit because they are connected to control power transformer, correct?

The reason I am asking is UL508A does not allow less than 14AWG for "power" circuit conductors.

Take a look at the exception to 26.1.1.

 

[LMAO]

Take a look at the exception to 26.1.1.

So I guess this means I have to treat them as power circuit?

 

[Jraef]

Methinks that the time you have spent pondering this has already more than consumed any perceived savings between 14ga & 16ga wire...

I like to keep it simple; if I use black for power wiring, red and white for 120V control, I make all of my 120V red and white, that way people know what to expect. The gauge is almost irrelevant at 14ga.

 

[petersonra]

So I guess this means I have to treat them as power circuit?

Exception: A fan that complies with 26.2.1 and a heater that complies with 26.4.1 are able to be supplied
from the isolated secondary of a control transformer and comply with the requirements for control circuits.

They are control circuits if fed from a control transformer. If not fed from a control transformer they are power circuits.

Keep in mind if they are power circuits that has some SCCR considerations.

 

[petersonra]

Methinks that the time you have spent pondering this has already more than consumed any perceived savings between 14ga & 16ga wire...

I like to keep it simple; if I use black for power wiring, red and white for 120V control, I make all of my 120V red and white, that way people know what to expect. The gauge is almost irrelevant at 14ga.

The wire size does not matter much. If that is all it is about, it would be easy to wire it in #14 and call it good. However, if these are power circuits, they have to be evaluated for SCCR. Control circuits are not evaluated for SCCR of the panel.

 

[LMAO]

They are control circuits if fed from a control transformer. If not fed from a control transformer they are power circuits.

Keep in mind if they are power circuits that has some SCCR considerations.

What about 26.4.1? It requires overload, thermal or impedance protection; all I have is a little fuse for conductor short circuit protection.

And you are right, 14AWG vs 16 is not really my concern. My problem is that my control transformer will become power transformer...

 

[petersonra]

What about 26.4.1? It requires overload, thermal or impedance protection; all I have is a little fuse for conductor short circuit protection.

And you are right, 14AWG vs 16 is not really my concern. My problem is that my control transformer will become power transformer...

A control transformer can be almost any size as long as it feeds only control circuits. It only becomes a power transformer if it feeds power circuits.

26.4.1 refers to heaters. Maybe you meant 26.2.4.

If it is not marked as thermally protected or impedance protected you just have to put normal motor overload protection on it.

 

[LMAO]

A control transformer can be almost any size as long as it feeds only control circuits. It only becomes a power transformer if it feeds power circuits.

26.4.1 refers to heaters. Maybe you meant 26.2.4.

If it is not marked as thermally protected or impedance protected you just have to put normal motor overload protection on it.

Bob, I read UL508A 26 again. So if my fans comply with 26.2.1 I can just ignore 26.2.2, 26.2.3 and 26.2.4 and feed them off control transformer?

 

[petersonra]

Bob, I read UL508A 26 again. So if my fans comply with 26.2.1 I can just ignore 26.2.2, 26.2.3 and 26.2.4 and feed them off control transformer?

26.1.1 tells you fan circuits are power circuits and have to be treated that way.

26.1.1 A fan, air conditioner, or heater mounted to the industrial control panel for the purpose of
conditioning air within the control panel shall comply with the requirements for general construction and
power circuits in addition to the requirements in 26.2 – 26.6.

The exception allows you to treat it as a control circuit if the conditions of the exception are met, but does not change any other requirements.

Exception: A fan that complies with 26.2.1 and a heater that complies with 26.4.1 are able to be supplied
from the isolated secondary of a control transformer and comply with the requirements for control circuits.

[I tried to upload a pdf from Hoffman showing their fans are thermally protected, but it is too large.]

 

[LMAO]

26.1.1 tells you fan circuits are power circuits and have to be treated that way.




The exception allows you to treat it as a control circuit if the conditions of the exception are met, but does not change any other requirements.



[I tried to upload a pdf from Hoffman showing their fans are thermally protected, but it is too large.]

got it. thanks.

do you happen to have the Hoffman link?

 

[petersonra]

got it. thanks.

do you happen to have the Hoffman link?

http://www.pentairprotect.com/wcsst...nProductAttachments/SpecSheets/Spec-00036.pdf