One (1) duplex receptacle for disposal and dish washer?

[George Stolz]

I thought the rating of the branch circuit would be determined by the 20 amp Over- current protection.

You're right, it is indeed a 240V 20A circuit, which is what the calculation would be based upon.

 

[david]

You're right, it is indeed a 240V 20A circuit, which is what the calculation would be based upon.

Ok
I thought when we looked at the 20 amp rating of a circuit and we would consider the ampacity of the equipment being utilized. I though we would add the amps of all utilization equipment together to compare a percentage to the rating of the branch circuit which is in amps

I never heard it explained that way before.

 

[George Stolz]

Since the branch circuit MWBC resembles a feeder MWBC, the calc would be the same format.

L1 / L2 / N

 

[david]

Since the branch circuit MWBC resembles a feeder MWBC, the calc would be the same format.

L1 / L2 / N

I know how the calculation would work out but the rule says the rating of the utilization equipments (witch is in amps) compares in percentage to the rating of the branch circuit witch is 20 amps in this discussion.

It is clear that the code allows a multiwire circuit it be consider two circuits and the only way I can see in what me and you have been discussing here is that the multiwire circuit in this case would have to be two 20 amp rated circuits. I do not see how you could apply 210.21 (a) (2) correctly any other way even if your math works out that’s not what the rule says to compare.


just my thoughts though

 

[hurk27]

Way back we once discussed that a 15 amp rated duplex receptacle outlet was rated per each individual contact device on the outlet, and that the NEC allows that duplex outlet to be used on a 20 amp circuit because of the fact that it was the rating of each contact device would be allowed because of the 20 amp pass through current rating given by UL, when we remove the tab between the contact devices on the duplex, it no longer meets the 20 amp pass through rating given by UL, it now becomes two individual 15 amp rated receptacles on one yoke, allowing a individual circuit to feed each side of this device is now not in compliance with the UL listing for said device.

Second: 210.21(B)(1) does not say "a single" branch circuit it says "Individual"

from article 100:

Branch Circuit, Individual. A branch circuit that supplies only one utilization equipment.

so:

Branch Circuit. The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).

Means that the circuit conductors from the OCPD to the outlet is a "Individual" branch circuit serving the single receptacle of a duplex receptacle which will be required to meet 210.21(B)(1)) I can not see this knowing the intent of UL and NFPA to mean otherwise:?

Third: 210.21(B)(3) do we agree there are two "outlets" on a duplex receptacle?

(3) Receptacle Ratings. Where connected to a branch circuit
supplying two or more receptacles or outlets, receptacle
ratings shall conform to the values listed in Table
210.21(B)(3), or where larger than 50 amperes, the receptacle
rating shall not be less than the branch-circuit rating.

have we forgot how to read? it says receptacles "OR" outlets? when we break the tap it is no longer two receptacles, it is two individual receptacles that are served by two individual circuits that 210.21(B)(1) will require that they shall have an ampere rating not less than that of the branch
circuit.

Wow if this can't clear this up I don't know what will.:happysad:

 

[cmreschke]

Smart ass side of the arguement here. How would you charge for billing with a mwbc? Would you charge them for one circuit or multiple circuits? Would you pay for one circuit or multiple circuits on your permit?

 

[david]

Smart ass side of the arguement here. How would you charge for billing with a mwbc? Would you charge them for one circuit or multiple circuits? Would you pay for one circuit or multiple circuits on your permit?

Well here the electrical fee would be based on the number of rec. sw. and so forth the type of branch circuit would not enter into the calculation

 

[cmreschke]

Here we pay for ckts.

 

[dwellselectric]

When wiring a kitchen I do the same thing. I find it alot easier to run a single 12/3 as opposed to two 12/2's. Also will bring a 12/3 to a kitchen outlet and branch off for the micro

 

[Dennis Alwon]

Okay, I lied. So if I run two 20 amp circuits of 12/2 to two single receptacles I need a 20 amp receptacle on each. If I run 12/3 to a single receptacle and then 12/2 to the second single receptacle, then by your theory the first one should not need a 20 amp receptacle but the second one does? At least that is how it sounds.

Now a 12/3 run to a duplex that has been split does not need to be 20 amps simply because of the way you interpret the code- whether correct or not. Now I ask you does this make sense or are you all just trying to prove a point. I get the point but in terms of the reasoning behind 210.21(B) seems to be ignored and it makes no sense to not apply it.

A 20 amp duplex recep is capable of 20 amps on each section of the duplex-- obviously not at the same time unless the tabs are separated.
Of course in the op's case there will never be an issue and quite frankly I don't understand the reason for the section anyway. Since a 20 amp appliance would need a 20 amp receptacle why is it necessary if a 15 amp single receptacle is installed and the appliance that is installed has a 15 amp cord cap. That's a different issue.

 

[George Stolz]

I have moved Sahib's portion of this discussion to it's own thread, here:
http://forums.mikeholt.com/showthread.php?t=141887

 

[George Stolz]

It is clear that the code allows a multiwire circuit it be consider two circuits and the only way I can see in what me and you have been discussing here is that the multiwire circuit in this case would have to be two 20 amp rated circuits. I do not see how you could apply 210.21 (a) (2) correctly any other way even if your math works out that?s not what the rule says to compare.

Using that reasoning (I have to observe the amps without adjusting for voltage), it doesn't matter what rating duplex receptacle you install - you lose credit for half of wattage of the multiwire circuit, and therefore can't use the second leg anyway. :happyno:

I get the point but in terms of the reasoning behind 210.21(B) seems to be ignored and it makes no sense to not apply it.

What is the reasoning of 210.21(B)?

A 15A receptacle is listed for use on a 20 ampere circuit. The 15A receptacle is further limited to the 12A level through the attachment cap that is placed on the product.

 

[renosteinke]

I had never thought much about this issue....

Code semantics aside, it seems to me that if you have a 20 amp breaker supplying only one load, everything up to that load needs to be rated for 20 amps. In this case, that would mean a 20 amp receptacle pattern.

Is there a safety issue? I can answer that with an absolute 'no.' I say this because the very code provision that allows multiple 15a devices to be on a 20a circuit has the result of making UL write its' standards so that 15a and 20a receptacles are tested to exactly the same criteria. The only difference is the plug pattern.

While we're at it, there is no requirement that the switches be rated to the full ampacity of the circuit. You're likely to find the switch for the disposal is rated for only 8 or 10 amps.

 

[david]

Using that reasoning (I have to observe the amps without adjusting for voltage), it doesn't matter what rating duplex receptacle you install - you lose credit for half of wattage of the multiwire circuit, and therefore can't use the second leg anyway. :happyno:

George I understand what you’re saying but i cannot agree that this a 240 Volt multiwire branch circuit.

Does the math work when you consider it two 120 volt 20 amp branch circuits or not. What do we do with,
• 110.4 Voltages. Throughout this Code, the voltage considered shall be that at which the circuit operates. The voltage rating of electrical equipment shall not be less than the nominal voltage of a circuit to which it is connected.
• 210.6 Branch-Circuit Voltage Limitations.
• The nominal voltage of branch circuits shall not exceed the values permitted by 210.6(A) through 210.6(E).
• (A) Occupancy Limitation. In dwelling units and guest rooms or guest suites of hotels, motels, and similar occupancies, the voltage shall not exceed 120 volts, nominal, between conductors that supply the terminals of the following:
• (1) Luminaires (lighting fixtures)
• (2) Cord-and-plug-connected loads 1440 volt-amperes, nominal, or less or less than ? hp
• (B) 120 Volts Between Conductors. Circuits not exceeding 120 volts, nominal, between conductors shall be permitted to supply the following:
• (1) The terminals of lampholders applied within their voltage ratings

 

[iwire]

George I understand what you’re saying but i cannot agree that this a 240 Volt multiwire branch circuit.

If it supplied from a 120/240 supply it has to be 120/240 or it is not a MWBC per the definition in 100.

 

[david]

If it supplied from a 120/240 supply it has to be 120/240 or it is not a MWBC per the definition in 100.

I agree, But the issue is not how the circuit is configured but when is it a single branch circuit or when to consider it two branch circuits.
It has to be a 120volt circuit to be connected to the dish washer in a dwelling, or can you connect a 120 volt rated dish washer to a 240 volt circuit

 

[kwired]

I agree, But the issue is not how the circuit is configured but when is it a single branch circuit or when to consider it two branch circuits.
It has to be a 120volt circuit to be connected to the dish washer in a dwelling, or can you connect a 120 volt rated dish washer to a 240 volt circuit

But it is not a 240 volt circuit. it is a 120/240 volt circuit.

 

[George Stolz]

I guess I'll have to burn my book, it has omissions in it.

 

[cadpoint]

Paraphrased

I feel I am getting caught up in the vortex of this MHF discussion.

I wish the NEC would come out and define MWBC as a circuit that can have a split phase property that is part of a single circuit. Once and for all.... a split phase is only part of an MWBC. Does that seem to make sense?

Why what happens when one run's a 12/6 w G or a 12/7?

Getting back to terminology, isn't it reasonable that a split-wired duplex is not the same as a multi-wired duplex that has a 240v potential on the same yolk?

It's clearly been defined why and how one uses this device. The rating of the equipment is now stamped for corect usuage. It's usage is allowed for by various NEC applications and even clarified on a per event basis, take the useage and enjoy the entertainment that comes out of that receptacle.

I've always looked at as a point of usage situation, if it's a problem of not the correct service at this point, then yes one has a problem!

 

[david]

I guess I'll have to burn my book, it has omissions in it.

I don't evem know what that means

But it is not a 240 volt circuit. it is a 120/240 volt circuit.

So under the 2005 NEC before I was required to tie the handle ties to gather i run potential multi wire circuit to two rec. in a two gang box I close the breaker for line one but I leave the breaker for line to open. My garbage disposal is tied to line one but I don?t own a dishwasher. So I have a 20 amp 120 volt circuit. After working on my disposal I plug it into the rec. that is feed from line two this breaker is in the open position , so my disposal doesn?t work. Am I plug in to a branch circuit or not.

Line one meets the definition of a branch circuit with the breaker in the closed position
Line two meets the definition of a branch circuit with the breaker in the open position
Neither one of these circuits meets the definition of a multiwite branch circuit until I close both line one and line two breakers.
Line one and line two are two 20 amp branch circuits working independent of each other