50A outlet, 40A breaker. Do I use my 50A Distro or my 30A dostro?

[StratGuy22]

Im doing our local prom this year. The power available is a 40A circuit (the rating on the breaker) with a 50A range style outlet. Should I use my 50A peavey Distro or my 30A Distro. The 50A has the proper plug to fit the range style plug. There's a pigtail that goes from the range plug to a 4 pole 30A twist lock style.

 

My 30A Distro has 4 - 20A breakers

My peavey 50A Distro has 6 - 20A breakers

 

Which would be better to use. I haven't metresd the power yet, that's the plan tonight. The gig is this sat. Basically I only need 2 of the outlets from either Distro. There's 4 outlets on stage, but they are all on the same 20A circuit and that's not going to work for my full setup, but I can run my lights off the Distro (2 circuits) and the rest from the stage.

 

Thanks.

[dboomer]

My first question would be ... why is there a 50A outlet connected to at 40A breaker upstream?

 

That said I can't imagine an advantage using a distro with a lower current capability when there is one available with a higher capacity.

[StratGuy22]

I'm not sure. Local arena. Nema 14-50 outlet, labelled as 40A and the breaker is 40A. I'm not an electrician so I wasn't sure if my 50A Distro would work on that.

[BillESC]

Your distro will work but only to the level of the circuit breakers capacity.

[StratGuy22]

Perfect. I really only need two of the 20a circuits for lights. Everything else I can run from the stages power which is separate.

[Craig Vecchione]

My first question would be ... why is there a 50A outlet connected to at 40A breaker upstream?

 

 

Good question.

 

Several possibilities exist, but one common reason is that someone goofed on the wire size, this was discovered upon inspection and the circuit had to be de-rated to the next smaller common breaker size. While there are 75C and 90C versions of 8AWG copper cable that will handle 50 and 55 amps respectively, some folks misread the charts and assume any type of #6 cable will do the same, and use aluminum or NM-B copper with 60C insulation that are only rated for 40 amps.

 

Another error discovered on inspection is using the right size cable, but then bundling it with other circuits, or running it through a 'hot' space such as an attic. Both circumstances require the circuit capacity be de-rated.

 

There isn't a common 40a receptacle so it's possible the intended capacity was 40 amps, perhaps due to limitations in the available power. A persnickety inspector could force this issue.

[agedhorse]

It is (generally) legal to supply a receptacle with less than its rated maximum, most authorities will require that it's labeled as such too. It is illegal to supply a receptacle with greater than it's rated maximum current however. With that in mind, you will need to use your 50A distro with a 50 amp connector because you can't use a 50 amp plug on a 30 amp distro because (assuming the feeder is 10 gauge and/or there is a 30 amp connector) the ampacity of the cable would be exceeded at 40 amps as would the maximum connector current rating.

[RoadRanger]

^ Isn't there one exception where you can supply "normal" 15A outlets with a 20A circuit?

[agedhorse]

^ Isn't there one exception where you can supply "normal" 15A outlets with a 20A circuit?

 

 

Only for duplex. A 15 amp single (1 receptacle on a yoke) must be protected by no more than a 15 amp breaker/fuse.

[RoadRanger]

Only for duplex. A 15 amp single (1 receptacle on a yoke) must be protected by no more than a 15 amp breaker/fuse.

That makes sense, thanks!