Twist Lock Plug vs. Conductor Size

[FIRERESCUE]

I have a question on temporary industrial machines that utilize 20 and 30 amp 480V 3-Phase twist lock cord and plug connections. We have multiple 30 amp receptacles located on presses within our company - properly fused at the machine for protecting the conductors supplying the receps, but the auxilliary equipment utilizes 20 Amps. I see that many of these aux. machines have (what I would call) "quick change-over" cords - or, a 30 Amp Male to a 20 Amp female short extension cord or a 30 Amp plug feeding 20 Amp flexible cord.

The department in question is not under my control but I was asked about the proper way to supply a new piece of auxilliary equipment rated at 20 Amps. So, this being the case - I had a small debate with our Master electrician this morning and we both had seemingly valid points (I am but a humble journeyman who has not been active in electrical installation for a number of years) we are both more of controls/automoation electricians who are licensed electricians and good friends - so it was a positive debate - yet still a debate.

Here were the points:

NOTE: We both agree that the best answer is to install 20 Amp receptacles on the presses.

1. Master claimed the auxilliary machine cord had to be sized for a 30 amps if using a 30 amp plug.

2. I seemed to recall (under industrial exceptions possibly?) being able to use a 30 Amp plug with 20 Amp listed flexible cord (hard-wired, not an extension cord) feeding the auxilliary unit so long as the auxilliary units supply conductors were properly protected for the load - each auxilliary unit wired in this manner has a nameplate rating of 20 Amps or less total combined load. I based my argument on the fact that other loads such as electric hand tools, fans and fluorescent lighting are done this way. Am I missing something here?

The idea being able to power the unit from provided 30 Amp receptacles yet protect the units 20 Amp conductors from SS/GF and overheating .........

Thanks for any replies

 

[FIRERESCUE]

I forgot to mention the fact that because it falls under Industrial Supervised Control - ............ where changes made to electrical components are done correctly (in theory).

 

[RICK NAPIER]

I do not beleive this would be allowed. You can find a summary of requirements in 210.24.

 

[mikeames]

I based my argument on the fact that other loads such as electric hand tools, fans and fluorescent lighting are done this way. Am I missing something here?

These would generally be UL listed and approved. You situation involves a custom made cord/ plug

 

[FIRERESCUE]

Please Help

Please Help

Thanks for the replies -

Can you give me any more clarification on this?

Would this somehow fall under a feeder tap rule?

I ask this because in reality, industrial plants often pull 20Amp 3 phase off from a fused 30 Amp receptacle with a 4 conductor 12AWG S/O cord under 10' in length - where the 20 Amp feed conductors are then properly protected at the machines disconnect and then broken down to individual protection for motors, control circuits, etc. I see this type of wiring done very frequently on temporary equipment (grinders, heaters, dryers that often get moved around) to reduce the type and number of receptacles within the industrial environment. I also have seen similar 30 Amp single phase feeds for fluorescent lighting tracks where a single flat cable feeder supplies multiple quad receptacle boxes with 15A-14AWG ballast drops (single 4' two bulb fixture). I am not saying these examples are correct - I am just looking for some direction so that I can help make sure things are being done safely and properly.

Back to my question -
For mahcine cords, I understand that this is not sized properly according to the NEC standards on flexible conductors/twist lock plugs and I can't find anything substantial within NFPA 79 covering this perticular question within machine standards. I feel this question falls into a grey area within the industrial setting and I find it most difficult to actually get a straight "defined" answer as to why this is wrong or unsafe other than the normal code references (which I agree are enough to say its wrong - so it must be wrong). But, my fuzzy logic says this is not a machine drop fed from a buss plug (which has definitions within the NEC), nor an extension cord (found within the NEC) nor permanent wiring (found within the NEC) - it is a temporary main machine feed coming from a UL listed, fused, 4 wire 30A, twist lock plug/receptacle combination which, in turn, is primarilly fed from a 70A fused disconnect on a press which is being fed from a 100A MDP breaker.

I know that under the industrial "umbrella" (if you would) electrical items such as fuses are changed by (quote) "qualified" individuals and so we find that there are many exceptions within the codes. Does this type of installation fall under any such exceptions that you know of? If not, I would like to have something concreet to show everyone how we need to correctly wire machines and how to re-wire the incorrect ones.

Thanks again for any help on this ..........