Method For Sizing A Branch Circuit

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PillarOfAutumn

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Electrician
I have a customer that owns a commercial vehicle with a 50 amp receptacle. They have requested a retractable cord reel be installed in their shop to plug in their vehicle while not in use, in order to charge/maintain some battery powered electronic equipment. This load is 10 amps max. However if they were to turn on all of the equipment in their vehicle it could require up to the full 50 amp service. They have assured me this won't happen because they don't use all their equipment when the vehicle is parked in the shop. This makes sense to me but the potential for it to be turned on is still there.

My question is, do I need to size the branch circuit to include all of the potential loads (all of the equipment in the vehicle) or is it permissible to size the circuit (and the cord reel) to the loads they are saying they will use?
 
Code aside, size the receptacle in the building for the circuit. It is possible to plug anything else into that outlet (e.g. an EV charger, welder or spider box), causing an overload if the wire is undersized and tripped circuit breaker. If he uses a NEMA 5-15P or 6-15P cord to connect the load, so be it. Perhaps that is a better way to accomplish this.
 
I intend to size the wire and cord reel to match the size breaker that I put in. The issue is that a 50 amp cord reel is over $4,000 so I need to know if a 50 amp circuit is mandatory by code in this application.
 
PillarOfAutumn said:
I intend to size the wire and cord reel to match the size breaker that I put in. The issue is that a 50 amp cord reel is over $4,000 so I need to know if a 50 amp circuit is mandatory by code in this application.
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What kind of plug are you using? You can run a 20 amp individual branch circuit with a 50 amp single receptacle.
 
Its single phase 240 volt. The truck has a flanged twist lock 50 amp inlet. But I need to provide a complete solution. I was planning to put a 50 amp cord end on whatever size cord reel/circuit I install. I don't think its prohibited to put a larger amperage cord end on because it is a single outlet.
 
PillarOfAutumn said:
Its single phase 240 volt. The truck has a flanged twist lock 50 amp inlet. But I need to provide a complete solution. I was planning to put a 50 amp cord end on whatever size cord reel/circuit I install. I don't think its prohibited to put a larger amperage cord end on because it is a single outlet.
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Since their target is 10 amps and they're looking to save money I would provide them with a 20 amp circuit.
 
I would put a label "20 AMP circuit," so if someone uses it for something else down the road and at least has the faintest clue, they won't unexpectedly trip the circuit. EV charging specifically comes to mind, if this is in a vehicular area. With most EVs, you can set a current limit (e.g. 16 A in this case).
 
If you run a 15 or 20 amp circuit and they plug in more than 15 or 20 amps the CB will trip to protect the wiring just like if you do the same thing inside your house and someone plugs in too many things on the same circuit
 
My biggest concern is the fact that cord reels are only capable of carrying their full rating if fully extended. It’s not a problem when used for power tools, etc. due to the intermittent use, but this application sounds like it may be loaded continuously.
 
retirede said:
My biggest concern is the fact that cord reels are only capable of carrying their full rating if fully extended. It’s not a problem when used for power tools, etc. due to the intermittent use, but this application sounds like it may be loaded continuously.
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Not an issue for the guy wiring a branch circuit to a receptacle.
 
If he only wants a 20A receptacle and a 20A OCPD, you can do that, and then he can get an RV adapter to go from the 20A to the 50A.

It’s done quite often with RVs. The bigger ones have a 50A inlet, but sometimes you’ll only have a 20 available. It’s up to the RV owner/user to limit their use to what the circuit can handle.
 
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