Equipment power cable

S

SCovert

Member
Location
VA
Occupation
Engineer
I work for a laboratory. We have many in-house custom-made pieces of equipment. We are doing an inspection of this equipment to be sure that it’s safe. A question came up about power cords supplying the equipment. For example, we have a wall outlet rated at 220V 30A, and have a piece of equipment plugged into it that is rated for only 5 A. We use a 14 gauge wire into a metal rack mount box. The cable enters the box through a standard compression cable clamp.

The issue at hand is trying to find the NEC codes that allow a smaller gauge wire to plug into the 30 wall outlet. Consider a lamp zip wire plugged into a 20 amp 120V outlet. Certainly doesn’t require anCertainly doesn’t require a 20 amp cable. Our local authority won’t let us use the equipment. Until we show the proper code that allows the smaller gauge wire supplying a smaller load.

any help appreciated.
Steve
 
I’m allowing this because it is not asking about DIY work.

The NEC is generally about building structure wiring, not wiring in a piece of plug-in equipment. The equipment wiring is covered under whatever listing agency (if any) approves and lists the equipment as safe, which generally includes instructions as to how it is to be connected and protected. So to that end, the NEC simply says that you are REQUIRED to use listed equipment in the manner it was intended and connect it per the manufacturer instructions. So if the device came either a 39A 249V plug on it from the factory, and it is listed by UL, CSA, ETL or such, then it’s likely that it was tested and listed with that plug and the implied circuit protection for it.

But if someone cut the factory plug off and installed a larger one, that may be a violation. Do you have the instruction manual for this and does it say anything?
 
While not strictly applicable by the NEC, you might be able to argue it based on the logic of the tap rules of 240.21, and the fixture wire rules of 402.
 
As usual with inspectors, they really should cite a code why there's a problem. Now if the inspectors say that all lab equipment must be listed, that's a fight probably above all of our pay grades :).

Custom-built equipment isn't that likely to be listed (is this stuff?). If each machine has supplementary over-current protection internally, should suffice for protecting a power cord. Start with 400.16, which leads to 240.5, which then includes 240.10 Supplementary Overcurrent Protection (see Overcurrent Protective Device, Supplementary in Art 100).
 
Welcome to the forum.

In my opinion, it's not an issue. I have never heard of any code that requires a power cord to be sized for the circuit it plugs into.

Just like the lamp cord you mentioned.
 
SCovert said:
For example, we have a wall outlet rated at 220V 30A, and have a piece of equipment plugged into it that is rated for only 5 A. We use a 14 gauge wire into a metal rack mount box. The cable enters the box through a standard compression cable clamp.
Click to expand...
Hold on now. Sounds like you have a piece of equipment connected via fabricated rack wiring that in turn plugs into a 30A receptacle. If the equipment connected to the receptacle directly that's one thing. But through some field fabricated wiring is another.

-Hal
 
zbang said:
As usual with inspectors, they really should cite a code why there's a problem. Now if the inspectors say that all lab equipment must be listed, that's a fight probably above all of our pay grades :).

Custom-built equipment isn't that likely to be listed (is this stuff?). If each machine has supplementary over-current protection internally, should suffice for protecting a power cord. Start with 400.16, which leads to 240.5, which then includes 240.10 Supplementary Overcurrent Protection (see Overcurrent Protective Device, Supplementary in Art 100).
Click to expand...
Thanks for the info! This equipment is just a 240V temperate controller mounted in a small metal portable box. The box has both legs fused at 3 amps. The heater load is 300W. The power cable going to the wall outlet currently is a 12awg overkill. But the inspector is complaining the the wall outlet is rated 30 amps and want a 10awg cable!! We all know a smaller awg is fine but the has to be a code somewhere. I found NEC 210? Code that describes this well, but uses the word “branch “. The definition of branch seems to apply to in wall wiring. The code talks about cabling that meets the load requirement at 125% , seems legit. I’ll go through what you posted and see if it covers power cables! Thanks!
 
SCovert said:
Thanks for the info! This equipment is just a 240V temperate controller mounted in a small metal portable box. The box has both legs fused at 3 amps. The heater load is 300W. The power cable going to the wall outlet currently is a 12awg overkill. But the inspector is complaining the the wall outlet is rated 30 amps and want a 10awg cable!! We all know a smaller awg is fine but the has to be a code somewhere. I found NEC 210? Code that describes this well, but uses the word “branch “. The definition of branch seems to apply to in wall wiring. The code talks about cabling that meets the load requirement at 125% , seems legit. I’ll go through what you posted and see if it covers power cables! Thanks!
Click to expand...
Just to reiterate, this process is to say home built equipment (non NRTL) goes through a basic safety inspection by the local authority!
 
SCovert said:
Just to reiterate, this process is to say home built equipment (non NRTL) goes through a basic safety inspection by the local authority!
Click to expand...
Being an electron accelerator facility, we have tons of in house designed equipment, this is a new requirement having the equipment safety inspected, they get a sticker with a QR code that traces back to a wiring and schematic, tech notes, etc.
 
SCovert said:
For example, we have a wall outlet rated at 220V 30A, and have a piece of equipment plugged into it that is rated for only 5 A. We use a 14 gauge wire into a metal rack mount box.
Click to expand...
Is the 30a plug temporary, for testing? What plug will each equipment be fitted with for the customer?

Why not have either an array of receptacles to match the final-product plugs, or an array of adapters?

Either way, I still think it's none of his business unless he can show you a code requirement.
 
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