Vendor Equipment Wire Sizing

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EmagSamurai

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Is there a standard that governs wire sizing for vendor equipment? I see equipment regularly where the "internal" wiring does not appear to be protected. E.g., control wiring (14, 16, 18 AWG) that is fed from the secondary side of the main breaker/fuse (80, 100, 125 A) feeding the major equipment loads. I understand NEC doesn't govern in this case, but I'm not sure if there is some other standard that would govern and provide guidance on what is safe.

I know switchgear manufacturers will routinely use a 30 A fuse to "protect" the breaker trip circuit that uses 14 AWG panel wiring. Their reasoning is usually that it is more important to ensure power to trip circuit if at all possible. Though I have yet to find a manufacturer that will explain why they don't use larger conductors in the trip circuit as well. I haven't looked at the auto-ignition curves, but perhaps there is an argument to be made there. I have generally accepted this configuration because it seems to be standard across manufacturers, but what about cases with much larger protective devices supplying the same size control wiring in other applications?
 
If that equipment is built to a listing standard then that standard applies.

If it is not listed then NEC sort of applies by default in many cases and the EI can certainly investigate how that equipment was put together as well.

Pump panels with 200 amp overcurrent devices will have 14 AWG control wiring tapped from the 200 amp supply with no additional overcurrent protection factory installed. They are listed as is though. Any field installed control wiring however usually is going to need proper overcurrent protection, especially if it leaves the enclosure.
 
I wish I knew the reasoning behind how that is considered safe. Maybe it's just considered such a low probability of a short/failure that it's accepted?
 
I occasionally see stuff that has UL 508A stickers on it that do not meet the requirements. I would imagine a pump panel would be listed to UL 508A and UL 508A would not allow a 14 gauge wire of any kind to be protected by a 200 amp overcurrent protection device.

Now if it was a fire pump controller that would be a different story. That might be acceptable to a fire pump controller listing.
 
EmagSamurai said:
Is there a standard that governs wire sizing for vendor equipment? I see equipment regularly where the "internal" wiring does not appear to be protected. E.g., control wiring (14, 16, 18 AWG) that is fed from the secondary side of the main breaker/fuse (80, 100, 125 A) feeding the major equipment loads. I understand NEC doesn't govern in this case, but I'm not sure if there is some other standard that would govern and provide guidance on what is safe.

I know switchgear manufacturers will routinely use a 30 A fuse to "protect" the breaker trip circuit that uses 14 AWG panel wiring. Their reasoning is usually that it is more important to ensure power to trip circuit if at all possible. Though I have yet to find a manufacturer that will explain why they don't use larger conductors in the trip circuit as well. I haven't looked at the auto-ignition curves, but perhaps there is an argument to be made there. I have generally accepted this configuration because it seems to be standard across manufacturers, but what about cases with much larger protective devices supplying the same size control wiring in other applications?
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IEEE/ANSI/NEMA/UL/NFPA
 
EmagSamurai said:
But do any of those allow for a 14 awg to be protected by a 200 A OPD?
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Yes it’s possible. For products, much of the way things are done are at the manufacturers discretion and industry recommended standards, so its not necessary the same approach as the NEC. For example, IEEE Std C37.20.1 (Metal-Enclosed Low-Voltage Switchgear) provides guidelines for wire sizes and overcurrent protection of control circuits. For currents up to 40-amperes, the standard has its own minimum sizes; but above 40-amperes, it refers you to the NEC. For overcurrent protection the standard also refers you to the NEC, but allows you to omit overcurrent protection if interruption of the circuit may create a hazard.

What you need to do is find the applicable standard for what you are trying to do and reference that.

For situations where the NEC applies, check Article 409. Also, 240.4(E),(G) and 240.12.
 
petersonra said:
I occasionally see stuff that has UL 508A stickers on it that do not meet the requirements. I would imagine a pump panel would be listed to UL 508A and UL 508A would not allow a 14 gauge wire of any kind to be protected by a 200 amp overcurrent protection device.

Now if it was a fire pump controller that would be a different story. That might be acceptable to a fire pump controller listing.
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I don't know for certain what standards apply but that is what is what is out there with pump panels with NEMA size 4 contactors in them in most manufacturer's products. They come with no provisions for overcurrent protection installed on the control circuit if it is same control volts as input power.
 
kwired said:
I don't know for certain what standards apply but that is what is what is out there with pump panels with NEMA size 4 contactors in them in most manufacturer's products. They come with no provisions for overcurrent protection installed on the control circuit if it is same control volts as input power.
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Maybe they are not listed to UL508a. I don't know what other standard would cover them though.

It is also possible they got some kind of special dispensation for UL.

It is like MCC manufacturers using red wire for neutrals in control circuits.
 
kwired said:
I don't know for certain what standards apply but that is what is what is out there with pump panels with NEMA size 4 contactors in them in most manufacturer's products. They come with no provisions for overcurrent protection installed on the control circuit if it is same control volts as input power.
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Really all sizes don't have overcurrent protection that I have seen - when motor and control voltage are the same. The size 4 I mentioned just happens to normally have a 200 amp fuse holder for the motor circuit, which was brought up in earlier posts.

Get a 10 HP 480 volt pump panel and you get to where there are NEC allowances on overcurrent protection of the control circuit that are easily met because the fuse holder (for motor circuit) is only 30 amp, and on top of that you possibly only have a 20 amp fuse installed, or even smaller if motor is less than 10 HP.
 
kwired said:
Pump panels with 200 amp overcurrent devices will have 14 AWG control wiring tapped from the 200 amp supply with no additional overcurrent protection factory installed. They are listed as is though. Any field installed control wiring however usually is going to need proper overcurrent protection, especially if it leaves the enclosure.
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In a UL panel panel (like a Pump Panel), you can tap off of the Main OCPD device and feed a Control Power Transformer and they consider the Primary fuses of the CPT as protection for those conductors, because nothing else is going to cause a short or overload on that circuit so long as the wires of that circuit never leave the panel. As soon as a wire leaves the panel, it falls under NEC rules.

If it is Full Voltage Control however, (i.e. no CPT with primary fusing), UL would require the control circuit to be fused.
Related discussion: https://forums.mikeholt.com/threads/480v-control-circuit-wiring.133310/

Even under the NEC, you can apply the Feeder Tap Rules (240.21(B)(1)) to do stuff like this, although the tap has to be rated for 10% of the Feeder OCPD, so on a 200A it would have to be 12ga, not 14.
 
Jraef said:
In a UL panel panel (like a Pump Panel), you can tap off of the Main OCPD device and feed a Control Power Transformer and they consider the Primary fuses of the CPT as protection for those conductors, because nothing else is going to cause a short or overload on that circuit so long as the wires of that circuit never leave the panel. As soon as a wire leaves the panel, it falls under NEC rules.

If it is Full Voltage Control however, (i.e. no CPT with primary fusing), UL would require the control circuit to be fused.
Related discussion: https://forums.mikeholt.com/threads/480v-control-circuit-wiring.133310/

Even under the NEC, you can apply the Feeder Tap Rules (240.21(B)(1)) to do stuff like this, although the tap has to be rated for 10% of the Feeder OCPD, so on a 200A it would have to be 12ga, not 14.
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To use the feeder tap rules you still need to have an overcurrent device at the end of the tap.

These things come with a H O A switch and a Start button that starts it in "hand" and are ready to operate with no OCPD in the control circuit. The Auto side of the HOA switch is field installed wiring. If it leaves the enclosure some maybe do put fuses in it, some don't. Others never leave enclosure with the 480 volt control circuit but rather put in a control relay with coil powered by center pivot (usually 120 volt control circuit in those, though there is some with 24 VAC control circuit) and use that as the primary control when in auto, often with no additional OCPD.

POCO's often install load management control devices that they tap from the 480 controls and they install fuses for those, often they use 12 AWG conductors don't know what their reasoning is, though technically it is correct thing NEC wise for the tap conductors, but they normally put 5 amp fuses in and in reality could use 18 AWG conductors after that but they still use 12 AWG. Since they basically have a fuse on the L1 side of the control power coming back from the load management device I often move the L2 lead off the starter so it is fused as well, and sometimes have other aux controls that really need OCP anyway.

Inspectors have never asked for additional OCPD other than if something leaves the enclose. I kind of presume it is because they also presume it is listed as is, I have seen Square D, Allen Bradley, Siemens, GE, and Cutler Hammer pump panels that are all like this, maybe another name or two on some old installs.
 
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