50A Receptacle on 40A 240V Circuit?

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  #1  
Old 09-03-06, 07:54 PM
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50A Receptacle on 40A 240V Circuit?

I'm wiring up a kitchen in my house. I'm planning to have a gas cooktop and a built in electric oven below it, which I haven't yet bought. I'm guessing that 40A will be sufficient for the oven - is this reasonable? Or should I go for 50A to be safe?

If I do go for 40A, I'll be using 8/3 cable. If 50A then 6/3. Is this right?

Now for the bit I'm less sure about. I couldn't find any 40A 240V receptacles at the store. Should I just use a 50A receptacle, whether the circuit is 40A or 50A? This is a dedicated circuit.

Are there any issues with putting in a receptacle for a built in oven, or should I be using a hardwire anyway. As I say, I haven't really looked into oven units yet, so I thought I'd just put in the receptacle for flexibility... Cash flow issues might mean I hold off on on buying the oven unit for a bit...

Cheers,

Sy
 
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  #2  
Old 09-03-06, 08:09 PM
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A 50 amp receptacle is legal and acceptable on a 40 amp circuit.
As you said, there are no 40 amp receptacles.
 
  #3  
Old 09-05-06, 06:32 AM
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Originally Posted by Speedy Petey
A 50 amp receptacle is legal and acceptable on a 40 amp circuit.
As you said, there are no 40 amp receptacles.
Are you sure the code allows this? It does not seem safe to me. Somewhere down the road someone could plug a 50A appliance into that plug, but only have 40A worth of breaker & wire on it. Wouldn't it be the same as putting a 20A receptacle on a 15A circuit. Code does not allow that, so why would it allow a 50A on a 40A circuit. I would just wire it for 50A with a 50A breaker.
 
  #4  
Old 09-05-06, 07:11 AM
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This is not a general use circuit and dedicated to the oven, why would someone just "come along" and plug something in? Not only that the breaker is a limiting factor, on the outside chance they would overload it would just trip.
 
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Old 09-05-06, 07:21 AM
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Originally Posted by sberry27
This is not a general use circuit and dedicated to the oven, why would someone just "come along" and plug something in? Not only that the breaker is a limiting factor, on the outside chance they would overload it would just trip.
Well, someone, as in the next homeowner, could "come along" & plug in a new stove. I do see your point on the 40A breaker though, but why can you not put a 20A recepticle on a 15A circuit? It would seem like the same philosophy to me.
 
  #6  
Old 09-05-06, 07:34 AM
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Originally Posted by Danno6102
Are you sure the code allows this? It does not seem safe to me. Somewhere down the road someone could plug a 50A appliance into that plug, but only have 40A worth of breaker & wire on it. Wouldn't it be the same as putting a 20A receptacle on a 15A circuit. Code does not allow that, so why would it allow a 50A on a 40A circuit. I would just wire it for 50A with a 50A breaker.
Heh... actually the NEC does allow 15A receptacles on a 20A circuit. NEC 210.21.

In your example cited, putting a 50A receptacle on a 40A circuit presents no safety problem, because the wire and breaker are correctly matched. The wire is rated for 40A, and so is the breaker. If the appliance starts drawing more than 40A, the breaker kills the circuit. The receptacle is overkill, since you could be fine with a 40A rating.

The dangerous situation is presented by the reverse, say putting a 30A receptacle on 6-3 wire and a 50A breaker. The wire and breaker can handle 50A, but the receptacle is rated only for 30A, and may be pulling more current than it can safely handle.
 
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Old 09-05-06, 07:56 AM
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arnie,

Nobody is talking about putting a 15 amp receptacle on a 20 amp circuit.
 
  #8  
Old 09-05-06, 08:17 AM
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Though I do not differ with the responses for the most part but IMO the correct answer here is... wait till you get the oven. I doubt a built in will be cord and plug anyway. And you are speculating what the branch circuit requirements will be. This implies to me that you are thinking about installing the branch circuit before you know what the requirements are going to be for the new oven. I would agree that a 40 amp branch circuit will handle most single built ins and then some but I dont agree with the method your using for determining the branch circuit rating.

Most of the single convection built ins I have experience with never take more than a 30 amp branch circuit many are 20 amps. The double ovens are the ones that need 40 amps. From your design it sounds like the oven is going in under the cook-top so wont be much chance of any doubles going in there in the future. Its just going to depend on the oven and type of oven. But 40 amps could be unnecessary overkill with no possibility of ever needing it.

Roger
 
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Old 09-05-06, 09:16 AM
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Originally Posted by racraft
arnie,

Nobody is talking about putting a 15 amp receptacle on a 20 amp circuit.
Danno6102 mentioned it (and said it wasn't code compliant), so I corrected him. I know the original poster wasn't asking about that, hence the rest of my post...
 
  #10  
Old 09-05-06, 09:33 AM
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Danno6102 was talking about putting a 20 amp receptacle on a 15 amp circuit, not the other way around.
 
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Old 09-05-06, 09:40 AM
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Originally Posted by arniebuteft
Danno6102 mentioned it (and said it wasn't code compliant), so I corrected him. I know the original poster wasn't asking about that, hence the rest of my post...
Actually I beleive that Danno6102 was talking about putting a 20A receptacle on a 15A circuit.

And I agree with him that it seems a little odd that 50A receptacles are allowed on 40A circuits, when 20A receptacles are not allowed on 15A circuits. But I accept the arguments about the wire and breaker being the important things.

Is this difference related to the fact that the circuit only has one outlet at all?

Cheers,

Simon
 
  #12  
Old 09-05-06, 09:46 AM
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Thanks for the various responses on this. In answer to Roger's comment, I wanted to install the oven circuit now while I have all the sheetrock off, rather than later when everything is sealed up. Running a 6/3 wire (or even 8/3) through finished walls didn't sound like much fun...

Having said all that, I think I'm now going to switch to a gas oven anyway! I already have the gas connection in place for the cooktop, and given the uncertainty about the electrical needs, I'm thinking I might just go for a all in one slide in gas range instead....

Cheers,

Sy
 
  #13  
Old 09-05-06, 09:49 AM
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Sy,

You can ALWAYS install larger cable than needed. If you want to allow for whatever the needs may be then go ahead and install a 50 amp circuit using 6-3 NM cable. You can wait until later to install the circuit breaker and the receptacle (if needed).
 
  #14  
Old 09-05-06, 11:01 AM
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210.21(B) Receptacles
(1) Single Receptacle on an Individual Branch Circuit-
A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.

A 50a receptacle on a 40 amp circuit is fine.
A 30a on a 40 amp circuit is not fine.
 
  #15  
Old 09-05-06, 11:06 AM
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Yea what Petey said, and table 210.24

Sorry it will not copy and paste

The colum for 40 amps lists 40 or 50 amp recs.
 
  #16  
Old 09-05-06, 11:20 AM
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Originally Posted by Speedy Petey
210.21(B) Receptacles
(1) Single Receptacle on an Individual Branch Circuit-
A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.

A 50a receptacle on a 40 amp circuit is fine.
A 30a on a 40 amp circuit is not fine.
OK, fair enough. But it certainly seems confusing that things seem to be the opposite for 15A and 20 A circuits.

i.e. A 20A circuit can have 20A or 15A receptacles installe don it, and a 15A circuit cannot have 20A receptacles on it.

Anybody have a nice simple explanation for this discrepancy?

Cheers,

Sy
 
  #17  
Old 09-05-06, 11:38 AM
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The main difference is that one circuit is dedicated, the other is not.

A 20 amp circuit can have multiple 15 amp receptacles on it. However, it cannot have a single 15 amp receptacle on it.
 
  #18  
Old 09-05-06, 11:47 AM
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Originally Posted by syperk
A 20A circuit can have 20A or 15A receptacles installed on it, and a 15A circuit cannot have 20A receptacles on it.

Anybody have a nice simple explanation for this discrepancy?
Sy

1. A fifteen amp outlet is required to be rated for 20 amp feed through. The configuration on the face prevents you from plugging a 20 amp appliance into it.

2. Because people will just keep reseting the breaker on this type of cord connected appliance instead of finding out what the problem really is. The "well the cord fits" mentality usually ends when the devices are of a higher amperage.
 
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