15A Duplex on 20A Multiwire Branch Circuit?

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Tyson Brown

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I think it is well established that the Code permits a single 15A duplex receptacle to be installed on an individual branch circuit (say, one run of 12/2 Romex). Article 210.21(B)(3) is the section that permits this - see "Is it legal to install a 15A receptacle on a 20A circuit?" in this forum for more info.

My question is this: does the Code permit a single 15A duplex receptacle to be installed on a 20A multiwire branch circuit (say, one run of 12/3 Romex - in this case, you would break the tab on the hot side of the duplex but not on the neutral side.)

*My feeling* is that the answer rests on whether you define a multiwire branch circuit to be one (1) circuit or two (2) circuits. Article 210.4(A) "Multiwire Branch Circuits" > "General" states that a MWBC is "...permitted to be considered as multiple circuits." Additional Code language refers to a MWBC as a singular "branch circuit" (i.e. 210.4(B)). This indicates by inference that normally a MWBC would be considered a single circuit. If this is true, then 210.21(B)(3) would allow the 15A duplex to be installed on this circuit.

The background info is below, but I'd rather just answer the question based on pure Code alone for the simple case posed above.

The MWBC and duplex receptacle are for cord & plug connected dishwasher and garbage disposal. The hot leg for the disposal's portion of the duplex receptacle is also switched. Inspectors from certain municipalities are not allowing the 15A duplex for this type of installation, requiring a 20A duplex instead. I believe their rationale is that the MWBC is two circuits and therefore the 15A duplex is split into 2 receptacles with only one installed on each circuit.
 
I will side with the inspectors on this one. My rationale, however, is not related to whether a MWBC is one or two circuits.

We all know that the disposal will be turned off over 99.9% of the time. For the rest of the time, whenever the dishwasher is running, you will have a single 15 amp receptacle being supplied by a 20 amp breaker. Ungood. This is essentially the same situation that 210.21(B)(1) tells us to avoid.

Whether or not this is actually a violation of 210.21(B)(1) may be the subject of some debate. But to me it is clearly a violation of that article's intent.

Welcome to the Forum.
 
Tyson Brown said:
My question is this: does the Code permit a single 15A duplex receptacle to be installed on a 20A multiwire branch circuit (say, one run of 12/3 Romex - in this case, you would break the tab on the hot side of the duplex but not on the neutral side.)
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Can't see why not...
Tyson Brown said:
*My feeling* is that the answer rests on whether you define a multiwire branch circuit to be one (1) circuit or two (2) circuits. Article 210.4(A) "Multiwire Branch Circuits" > "General" states that a MWBC is "...permitted to be considered as multiple circuits." Additional Code language refers to a MWBC as a singular "branch circuit" (i.e. 210.4(B)). This indicates by inference that normally a MWBC would be considered a single circuit.
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I don't think so... It's just grammatically correct that any given MWBC taken as a unit is one (1), and so it is referred to in the singular. That does not mean of course that we can't think of the two or more ungrounded conductors with a common grounded conductor as circuits (plural).
Tyson Brown said:
If this is true, then 210.21(B)(3) would allow the 15A duplex to be installed on this circuit.
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Wouldn't it be true regardless? The only thing that would not make it true would be if it was the only duplex on the circuit(s), which would mean each would have to comply with 210.21(B)(1).
Tyson Brown said:
The background info is below, but I'd rather just answer the question based on pure Code alone for the simple case posed above.

The MWBC and duplex receptacle are for cord & plug connected dishwasher and garbage disposal. The hot leg for the disposal's portion of the duplex receptacle is also switched. Inspectors from certain municipalities are not allowing the 15A duplex for this type of installation, requiring a 20A duplex instead. I believe their rationale is that the MWBC is two circuits and therefore the 15A duplex is split into 2 receptacles with only one installed on each circuit.
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210.21(B)(1) -- you can play around with what you call an MWBC all you want, but if you only have a single receptacle on each ungrounded conductor, it's an "Individual Branch Circuit" as per Article 100.
 
Charlie B:
But the same could be said of a 15A duplex on an individual branch circuit - when only one piece of equipment is plugged in, you have a 20A branch circuit supplying a single "15A" receptacle. So, I counter your assertion with another: this is the situation that 210.21(B)(2) was designed to allow. We're always assuming that no overload condition will exist for the receptacle, hence the 12A max draw through each receptacle. And as Mike Holt has presented, 15A receptacles really have 20A guts, so the "15A" receptacle would clearly handle short-ckt / ground fault current.

Tallguy:
But my branch circuit (of the multiwire variety) supplies two pieces of utilization equipment. What Code article defines each ungrounded conductor of a MWBC as a separate circuit? Plus, see the definition of "Branch Circuit, Multiwire" in Article 100: "A branch circuit that consists of two or more ungrounded conductors that have a voltage between them, ..."

And just to be clear, yes I am talking about the case where the MWBC serves no other outlets besides the duplex receptacle in question.
 
Tyson Brown said:
15A duplex on an individual branch circuit - when only one piece of equipment is plugged in, you have a 20A branch circuit supplying a single "15A" receptacle.
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No you don't, you have two 15 amp receptacles on a 20 amp circuit. A single 15 amp receptacle is not permitted on a 20 amp circuit.
 
infinity: Yes, I understand that & totally agree with you; however I was responding to charlie_b's post. Please refer to that post & interpret my response in that regard only.
 
Once you break a tab on the duplex recptacle, it is no longer a duplex and is 2 seperate receptacles. You can't use a 20A breaker for a single receptacle rated for 15A
 
I understand everything you're saying (which is more than can be said for a lot of what I try to read :rolleyes:), but you're trying to make a loophole where there isn't one. Here's a simple answer if you tried this line of reasoning with the inspector: "Yep, I see your point -- you got me. As a result, I will forthwith exercise my right to consider an MWBC as multiple circuits. Here's your red tag." :smile:
 
Better make sure your receptacle is listed for 250V before you hook it up to a MWBC. Some are, and some aren't. For example Hubbell's CR115 is not listed for that purpose, whereas a HBL5252 is.
 
paul said:
Better make sure your receptacle is listed for 250V before you hook it up to a MWBC. Some are, and some aren't. For example Hubbell's CR115 is not listed for that purpose, whereas a HBL5252 is.
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Why would a 125v receptacle need to be rated at 250v?
 
Tyson Brown said:
infinity: Yes, I understand that & totally agree with you; however I was responding to charlie_b's post. Please refer to that post & interpret my response in that regard only.
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OK sorry I missed that part. A duplex with the tab broken and supplied by two circuits IMO is two single receptacles.
 
stickboy1375 said:
Why would a 125v receptacle need to be rated at 250v?
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Because you are supplying it with 240 volts. (It's a multi wire branch circuit)

It's all just listing CYA type stuff.

Like a double pole switches have not been listed to control separate circuits.
 
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