50A receptacle on a 30A Circuit

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Bo Stauffer

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Location
Lancaster, PA
I recently started a new job and noticed two Single Phase 240V 50A Receptacles on 30A Circuits. The welder normally used on this circuit draws 27 amps. It has a cable with #10-2 w/g cable. There is another receptacle in the main plant they use for the welder that has a 240V 50A Recept. with a 50A Breaker. Now I know we have some problems but they have been working this way for years and I'm the new guy. I told my boss we need to change things but I'm hoping that I can be more specific. I know the 30A circuits are protected properly but a 50A Recp? For sure the 50A Circuit should not be used for the welder but again, I'm the new guy and they have have done it for years. These folks are all mechanics.
 

augie47

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Location
Tennessee
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State Electrical Inspector (Retired)
IMO, no violation. 210.21 states a single receptacle shall have a rating not less than the branch circuit. It does not prohibit one larger. Often times industrial facilities will use oversize receptacles as they withstand the fatigue of plugging and unplugging better than ones rated per the circuit.
 

Carultch

Senior Member
Location
Massachusetts
IMO, no violation. 210.21 states a single receptacle shall have a rating not less than the branch circuit. It does not prohibit one larger. Often times industrial facilities will use oversize receptacles as they withstand the fatigue of plugging and unplugging better than ones rated per the circuit.

Except in the special case of a 15A receptacle on a 20A circuit. Other than "because the code says so", is there a reason why this particular counter-intuitive example would be permitted?
 

ActionDave

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Durango, CO, 10 h 20 min from the winged horses.
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Licensed Electrician
Except in the special case of a 15A receptacle on a 20A circuit. Other than "because the code says so", is there a reason why this particular counter-intuitive example would be permitted?
15A recpts on a 20A breaker applies to duplex receptacles and their guts are are rated for 20A feed through. For a single receptacles devices the rules are the same.

The code says it's okay because the wiring and equipment are protected by the breaker. You don't want to go the other way and put a 30A receptacle on a 50A breaker, even if you had 50A conductors because the equipment would not be protected.

There are also exception in the code for welders because the peak load is intermittent.
 

augie47

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Tennessee
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State Electrical Inspector (Retired)
Except in the special case of a 15A receptacle on a 20A circuit. Other than "because the code says so", is there a reason why this particular counter-intuitive example would be permitted?
sorry,, i'm wearing my stupid hat this morning,..I don't understand your question.
 

Carultch

Senior Member
Location
Massachusetts
sorry,, i'm wearing my stupid hat this morning,..I don't understand your question.

What I mean, is that the NEC allows a 15A receptacle on a 20A circuit, and this is counterintuitive. Action Dave successfully answered what I asked. The inner workings of the 15A duplex receptacle are rated to pass through 20A to the next receptacle, but only supply 15A to its own loads.
 

don_resqcapt19

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Location
Illinois
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retired electrician
What I mean, is that the NEC allows a 15A receptacle on a 20A circuit, and this is counterintuitive. Action Dave successfully answered what I asked. The inner workings of the 15A duplex receptacle are rated to pass through 20A to the next receptacle, but only supply 15A to its own loads.
The code does not permit a single 15 amp receptacle on a circuit that has a 20 amp OCPD.
 

FionaZuppa

Senior Member
Location
AZ
Occupation
Part Time Electrician (semi retired, old) - EE retired.
What I mean, is that the NEC allows a 15A receptacle on a 20A circuit, and this is counterintuitive. Action Dave successfully answered what I asked. The inner workings of the 15A duplex receptacle are rated to pass through 20A to the next receptacle, but only supply 15A to its own loads.

one dual receptacle device mold is two receptacles. the rule applies to a single receptacle, etc.
 

templdl

Senior Member
Location
Wisconsin
A 30at OCPD will certainly protect a 50a circuit down stream. The only caviot is when you have a 50a receptacle that provides the opportunity to plug in loads that have a 50a plug. This translates to the opportunity to overload the 30a circuit which would result in relying on the 30a OCPD to protect the 30a wire for which you never intentionally rely on an OCPD to protect a circuit from intentionally being overloaded. I would consider this issue as a coordination concern by providing an opportunity to overload the 30a circuit with a 50s receptacle and a 40a load.
In my own woodshop I do have oversized 30a twist locks on a 20a circuit but I am the sole user of the shop with machines that draw less current such.as 15a. Since twistlocks are not cheap and that's what I had and didn't find it logical to spend money of a lower rated twist lock..
I would not have the problem of someone plugging in a machine that would have a 25a load since I am the only user.
 

Strathead

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Location
Ocala, Florida, USA
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Electrician/Estimator/Project Manager/Superintendent
I was going to say one thing. It would have been wrong, but I wisely looked at the code FIRST this time. 21.21(B)(3) technically doesn't allow this. Is states that a 30 Amp circuit shall have receptacles rated 30 amps. Given the additional wording about a branch circuit higher than 50 amps, I contend this is probably in error, but the table nor the wording says, "shall not be less than" it says "shall conform" .
 

Smart $

Esteemed Member
Location
Ohio
I was going to say one thing. It would have been wrong, but I wisely looked at the code FIRST this time. 21.21(B)(3) technically doesn't allow this. Is states that a 30 Amp circuit shall have receptacles rated 30 amps. Given the additional wording about a branch circuit higher than 50 amps, I contend this is probably in error, but the table nor the wording says, "shall not be less than" it says "shall conform" .
See 210.21(B)(3) Exception No. 1.
 

curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
A 30at OCPD will certainly protect a 50a circuit down stream. The only caviot is when you have a 50a receptacle that provides the opportunity to plug in loads that have a 50a plug. This translates to the opportunity to overload the 30a circuit which would result in relying on the 30a OCPD to protect the 30a wire for which you never intentionally rely on an OCPD to protect a circuit from intentionally being overloaded. I would consider this issue as a coordination concern by providing an opportunity to overload the 30a circuit with a 50s receptacle and a 40a load.

How is this any different than having multiple 15 or 20 amp receptacles on a general use branch circuit? Are you suggesting that the NEC should only allow 1 receptacle per circuit?

You are not supposed to rely on on the branch circuit OCPD to protect the circuit? If so what is the purpose of the branch circuit OCPD?
 

templdl

Senior Member
Location
Wisconsin
How is this any different than having multiple 15 or 20 amp receptacles on a general use branch circuit? Are you suggesting that the NEC should only allow 1 receptacle per circuit?

You are not supposed to rely on on the branch circuit OCPD to protect the circuit? If so what is the purpose of the branch circuit OCPD?
It is a matter of knowingly overloading a circuit with the expectation that the OCPD will protect your backside, is this good practice? Or inadvertantly overloading (unintentionally), a circuit such as with holidays when the women plug in a bunch of roasters, frying pans, hot plate, etc for dinner. They don't intentionally do it and we wonder why the the food isn't being kept warm or cooking when a breaker trips.
Also, shouid a circuit be extended on existing circuit trusting that the OCPD will provide over current protection for the unknown addition load?
 

iwire

Moderator
Staff member
Location
Massachusetts
It is a matter of knowingly overloading a circuit with the expectation that the OCPD will protect your backside, is this good practice?

That is how every general use branch circuit operates.

The expectation is that the OCPD will open when the circuit gets overloaded.
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
See 210.21(B)(3) Exception No. 1.


I had read that, and I was directing my comment at the general thread where they were not speaking specifically of welding receptacles. But there wasn't any one in particular that I wanted to quote.
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
How is this any different than having multiple 15 or 20 amp receptacles on a general use branch circuit? Are you suggesting that the NEC should only allow 1 receptacle per circuit?

You are not supposed to rely on on the branch circuit OCPD to protect the circuit? If so what is the purpose of the branch circuit OCPD?

On top of what tempdl said, it doesn't matter. The code says what the code says. Sometimes it doesn't make sense. Why do you have to upsize the ground if you upsize the current carrying conductors for voltage drop, but you could pull the ground out of the conduit altogether and use only the conduit as the grounding conductor? In the words of every parent in the universe, "Because I said so."
 

Smart $

Esteemed Member
Location
Ohio
I had read that, and I was directing my comment at the general thread where they were not speaking specifically of welding receptacles. But there wasn't any one in particular that I wanted to quote.
Well in the general, non-excepted case, a 50A receptacle is not permitted on a multi-receptacle 30A circuit... according to the words.

That should be wrong. It should allow any receptacle with a rating not less than the circuit.
 

templdl

Senior Member
Location
Wisconsin
That is how every general use branch circuit operates.

The expectation is that the OCPD will open when the circuit gets overloaded.

Should it be an inadvertent overload or knowing overloading a circuit with the expectation that the OCPD will provide protection? I have always been of the school that one should never "intentionally" overload or short circuit a circuit.
 
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