Need help with multiwire branch circuit serving both 120V and 240V loads

[tom kanzler]

I have a question about multiwire branch circuits that I can?t find any specific information on, here or elsewhere.

For a single-phase, 120/240V MWBC serving both 120V and 240V loads, does the OCPD have to automatically and simultaneously open both ungrounded conductors?

From 2002 NEC:

210.4 Multiwire Branch Circuits.

(C) Line-to-Neutral Loads Multiwire branch circuits shall supply only line-to-neutral loads.

Exception No. 2: Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch-circuit overcurrent device.

From a later NEC, lifted from a thread on this forum, originally posted by Charlie Eldridge (my apologies if it violates protocol)

http://www.mikeholt.com/code_forum/showthread.php?t=62569&page=2&highlight=multiwire

240.20(B) Circuit Breaker as Overcurrent Device. Circuit breakers shall open all ungrounded conductors of the circuit both manually and automatically unless otherwise permitted in 240.20(B)(1), (B)(2), and (B)(3).

(2) Grounded Single-Phase and 3-Wire dc Circuits. In grounded systems, individual single-pole circuit breakers with identified handle ties shall be permitted as the protection for each ungrounded conductor for line-to-line connected loads for single-phase circuits or 3-wire, direct-current circuits

The confusion comes in where, while it seems 240.20(B)(2) allows approved (or identified) handle ties for single-pole breakers serving 240V loads, 210.4(C) exception 2 seems to require that, for MWBC's specifically, the OCPD automatically open both ungrounded conductors. That sounds like automatic, as well as manual, though it doesn't say that. Does 210.4(C) ex 2 supercede 240.20(B)(2), or am I reading it wrong? Handle ties won't necessarily open the other breaker, especially with free-trip mechanisms.

The problem, as I see it, with not opening both ungrounded conductors when both line-to-neutral and line-to-line loads are being served is that the 240V load(s) could backfeed into the 120V loads that were supposedly disconnected when the OP for those line-to-neutral loads opened.

Can anyone shed any light on this. I?m trying to clarify exactly when handle ties are allowed, and when they are not.

p.s. I know, it's time to upgrade my Code books.

 

[paul32]

The 240.20(B)(2) as you have posted, says line to line loads but not multiwire branch circuits. The 210 section is specifically for multiwire branch circuits, so it handle ties are not sufficient.

The problem, as I see it, with not opening both ungrounded conductors when both line-to-neutral and line-to-line loads are being served is that the 240V load(s) could backfeed into the 120V loads that were supposedly disconnected when the OP for those line-to-neutral loads opened.

Yup.

 

[charlie b]

Before I looked at the book, my view was that you would not want the OCPD to open the current path to only one ungrounded conductor. After I looked at the book, I still think that. Here is my interpretation of 210.4(C):
? First, I don?t need to read article 240, in order to say that you must open all ungrounded conductors, in the situation you have described.
? Please take note that in Exception 2 to 210.4(C), the final word is singular. It is ?device,? and not ?devices.?
? That tells me that you cannot use two single-pole breakers to protect a MWBC that serves line-to-line loads. You have to use a two-pole breaker, in your 120/240 MWBC.
? So the question of handle ties becomes irrelevant.

 

[allenwayne]

Charlie this is a subject that has intrigued me for awhile.I feel that if there is a MWBC that ALL ungrounded conductors need to be disconnected together,as in a 2 pole breaker not just a handle tie.If there is a fault that trips out an OCPD it needs to open all ungrounded conductors associated with that circuit.

I`ve seen all to many open neutrals that have reeked havoc on 120 volt circuits.I went to Oklahoma to wire a church in the Cherrokee nation for my church 2 years ago and when I came back I found one leg of what I thought was a 2 pole breaker tripped due to lightning and the 2nd leg held.All my electronics were fried.120 on one leg a common neutral and a dead phase.3 tv`s 3 dvd`s and 2 computers as well as a microwave and my #8 dale earnhart alarm clock fried !!!!!!

 

[steve66]

Not the #8 alarm clock!!!

 

[tom kanzler]

Thanks for confirming my suspicions (or prejudices).

 

[charlie b]

Thanks for the story Allen (or is it Wayne? I?m not sure which, if either, is your first name). That experience gives a far stronger basis for failing an installation that uses two single pole breakers in this manner, handle or no handle.

My argument is based on nothing stronger than the absence of the letter ?s,? at the end of a key word. But I am willing to give the code authors credit for doing that on purpose, for intending to limit the use of a single device for protection of a MWBC that serves line-to-line loads.

 

[tom kanzler]

mea culpa

I just noticed 240.20(B)(1) Multiwire Branch Circuit., which was sitting in front of me all along -

"Except where limited by 210.4(B), individual single-pole circuit breakers, with or without approved handle ties, shall be permitted as the protection for each ungrounded conductor of multiwire branch circuits that serve only single-phase line-to-neutral loads." [emphasis mine]

I guess that, coupled with 240.20(B)(2) and 210.4(C) exeption no. 2 (using the singular "overcurrent device"), puts a stake in the heart of using two breakers with handle ties for both line-to-line and line-to-neutral loads on a multiwire branch circuit.

So does that mean that a MWBC serving a single utilization equipment, such as a clothes dryer or range, also cannot have single-pole breakers with handle ties. It would seem so, to me at least.

 

[charlie b]

No problem, Tom; we?ve all had our ?culpas.? Welcome to the Forum.

I agree that a MWBC serving a dryer or range would require a single breaker (2-pole or 3-pole, as needed). But it has nothing to do with whether there is only one utilization equipment. It has to do with line-to-line loads.

 

[milwaukeesteve]

Hello, and let me introduce myself. I was part of that last thread that you referenced, and this was one of the 2 issues that discouraged me for a long while from this forum. (the other is Small Appliance recepts, but that's another story). On this one, and a similar topic, more closely related to your question than the thread you referenced, I ended up admitting I was wrong in the end, according to the NEC, but I still don't think I was wrong.

The other topic I am referring to was a thread about a 120V load that was associated with a 220V Well Pump. Since they were related equipment, the postee thought they could be on the same MWBC and fed with a 2pole breaker.

I argued that MWBC are for only Line to Neutral loads, unless it falls under the exceptions. However, it is in the wording of those 2 exceptions that lies the problem.

210.4 (C) exception 1 states that it is for only ONE load
210.4 (C) exception 2 states that all ungrounded conductors must be opened simultaneously.

exception 2 does not limit you on how many loads, like exception 1 does. Nor does it say anything about combined loads or combining types of loads.

I have a problem with the 240V AND 120V loads sharing one breaker, regardless of the double pole, single pole, handle tie issues. But that is my opinion, I don't have a code rule for my opinion.

As for Handle Ties, I believe they can only be used where a code rule states that 'a means shall be provided for simultaneous' as stated in the other thread, or if your local AHJ allows handletied breakers to act as one. As for your 240V load, that should be treated as a single load, and should be OCPD'ed as such, and not treat this as a MWBC, because you need to focus first on the 240V load. - NOTE: like CharlieB states, 240.20(B) does not allow you to call a 240V load a MWBC.

Again, this is why I left this forum for a while, because this is how I see it, but not as others will see it, yet I feel I lean towards safety and electrically sound installations, where as others might lean towards what the code says (or more importantly, what it doesn't say). This issue hits and involves several code rules, but also dances between them. Unfortunately, too many people in this forum just want to dance.

Sorry to confuse you more,

 

[allenwayne]

Thanks for the story Allen (or is it Wayne? I?m not sure which, if either, is your first name). That experience gives a far stronger basis for failing an installation that uses two single pole breakers in this manner, handle or no handle.

My argument is based on nothing stronger than the absence of the letter ?s,? at the end of a key word. But I am willing to give the code authors credit for doing that on purpose, for intending to limit the use of a single device for protection of a MWBC that serves line-to-line loads.

It`s Allen charlie.... just have 3 first names lol allen john wayne.... I also feel the when you have a MWBC a handle tie is not sufficient.They should trip out together to prevent the experience I had to endure.An open neutral or a secondary line to load fault will fry what ever is on the circuit.

I`m no E.E. but from experience if there is an available current that is connected to a common neutral then there is an available 120 volt force or if you lose the neutral then it turns into 240 volts and that means sizzle for electronics.

Just a by the seat of my pants electrician,I bow down to the more educated ones.....

 

[roger]

Steve, here are a couple of graphics and associated commentary that may help.

Notice where "common Trip" verses "Opening All Ungrounded Conductors" comes into play.

Part I. General Provisions

New FPN alerts the Code user to ensure that the continuity of the grounded neutral conductor of a multiwire circuit isn’t interrupted (open), because doing so can result in a fire and/or destruction of electrical equipment because of under- or over-voltage.

(C) Line-to-Neutral Loads. Multiwire branch circuits must supply only line-to-neutral loads.​

Ex 1: A multiwire branch circuit is permitted to supply line-to-line utilization equipment, such as a range or dryer.

Ex 2: A multiwire branch circuit is permitted to supply both line-to-line and line-to-neutral loads if the circuit protection device opens all ungrounded conductors of the multiwire branch circuit simultaneously under a fault condition (multipole circuit breaker with common internal trip). Figure 210-1

FPN: See 300.13(B) for the requirements relating to the continuity of grounded neutral conductor on multiwire circuits.

CAUTION: If the continuity of the grounded neutral conductor of a multiwire circuit is interrupted (open), the resultant over- or undervoltage could cause a fire and/or destruction to electrical equipment. Figure 210-2



And

Part II. Location

The word “approved” was replaced with “identified for the purpose.” The result… nails, screws, or wire are no longer permitted to be used for circuit breaker handle ties. Handle ties must be identified for the purpose, which means designed by the manufacturer to perform this function.

(B) Circuit Breaker as Overcurrent Device. Circuit breakers must open all ungrounded conductors of the circuit, unless otherwise permitted in 240.20(B)(1), (B)(2), and (B)(3).

(1) Multiwire Branch Circuit. Except where limited by 210.4(B), individual single-pole breakers are permitted on each ungrounded conductor of a multiwire branch circuit that supplies line-to-neutral loads. Figure 240-1

(2) Single-Phase, Line-to-Line Loads. Individual single-pole circuit breakers with handle ties identified for the purpose are permitted on each ungrounded conductor of a branch circuit that supplies single-phase, line-to-line loads. Figure 240-2

(3) Three-Phase, Line-to-Line Loads. Individual single-pole breakers with handle ties identified for the purpose are permitted on each ungrounded conductor of a branch circuit that serves three-phase, line-to-line loads. Figure 240-3

Author’s Comment: Handle ties made from nails, screws, wires, or other nonconforming methods are not permitted. Figure 240-4

Hope this helps you.

Roger


​

 

[milwaukeesteve]

Thank you Roger for the graphic.
I do need clarification though.

In your first graphic, the caption at the bottom states...
--A Multiwire Branch Circuit can supply both Line-to-Line and Line-to-Neutral Loads providing that a common trip circuit breaker is used to protect the circuit--

Where in 210.4(C) Exception 2 does it say that?

It is a nice graphic, and I understand what the graphic is saying, but is that someone's interpretation of the rule, or is that the rule?

I also have a problem with the words following that caption. You have written Ex 1: and then some type in both bold and not bold, and same thing with Ex 2:. Are these quotes from something, or is that yours or someone elses interpretation? Those aren't the words I find in my 05 NEC.



What I see in Exception 1 and Exception 2 is that the first exception LIMITS me, but the second exception does NOT limit me, rather it tells me what I need to do.

That is where I think people make the leap and say that Exception 2 ALLOWS them to use Line to Neutral AND Line to Line on the same circuit, ONLY because it doesn't tell them they CAN'T.

 

[milwaukeesteve]

Allen John Wayne,
I found one of your statements troubling about the Handleties. That a Handletie is not sufficient.

First, the Code states "Approved" HandleTies. If the approved handle tie does not work, that is a manufacturer problem, and should be brought up with the manufacturer, not the NEC. Approved HandleTies do work if installed properly. If you are not using the correct handle tie, then you are going against manufacturers instruction, and that is a code violation.

Second, there is a difference in the code when it states "Common Trip" and "a Means shall be provided".
Common trip is very specific in what it needs: a multipole breaker with and internal common trip.
A Means shall be provided is also specific that you should provide a means for simultaneous opening, and that a Internal Common Trip is NOT allowed, because it is not "provided". How can something be "provided" if it would already exist?


On a MWBC we don't want to open a neutral while energized with loads on the Circuits, or have a voltage potential on that neutral. That is why the code tells us to use Common Trip or Means Shall Be Provided, and that the code also tells us that the integrity of the Neutral must be maintained. 300.13(B)

 

[Rockyd]

The graphic Roger brought over is from Mike Holt. In addition to the graphic being available online here in the Graphics section when you click on the main webpage, it is also in Mike's "Changes to the NEC 2005" fifth edition page 15. Comes with all the warnings in regard to 300.13(B) included. It seems that it is only done this way as it is code.

The NEC Handbook points out that 2005 was the first year that this moved out of the residential application only, and to all applications now. Be interesting to see if 2008 approaches the issue.

It may be a hack installation to have 120 and 240 coved by both breakers, but it's legal, at least that was the implication I read. I don't do it, however, that doesn't make it the law. It just means I strive for a safe installation.

 

[milwaukeesteve]

I know where the picture came from.

What I am asking Roger and you, is where does the content in it come from? Is that someone's interpretation, or is that a rule.
The hand book, also, is just an interpretation. Yes, it is from those that wrote the Code, but it is still an interpretation.
Just because Mike Holt says it is so, does it make it so? I am looking for the link that gets me from what the Code says in Exception 1 and 2, to what that picture shows. So far I havent seen it.
If I don't see the 'link' then I assume its a 'leap'.

Look closely at Mike Holts description of this. Roger posted it in his reply.
What is written below the illustration is all his interpretation. He even paraphrases Exception 2 in his own words, but does not support that with anything. Where does it say anything about a common trip breaker in the code book? Yes it does say 'opened simutaneously by the BCOP device" but again he paraphrased AND interpreted. More importantly, where does exception as written in the NEC state anything about "permitted to supply both Line to Line and Line to Neutral loads if...." I don't see that in my code book.

I am not trying to say that Mike is wrong. He may or may not be. What I am saying is that something is missing in his illustration that supports the statements made in it.

 

[roger]

Steve, the commentary is Mikes, but let it be known I agree with it as does many others.

Don't take this wrong or as an insult, we all have opinions, but yours seems to be in the minority.

I will continue to do installations this way if it is convenient, and IMO there is no violation.

Roger

 

[milwaukeesteve]

Ok, next step

Say you have a 10 AMP Well Pump 240V
Along with that, you have a filter system that is attached to the incoming water. Since you have justified in your mind that this is legal, you put the 5 AMP 120Volt filter onto the same MWBC.

Now what size breaker do you put in?
- A 15 Amp 2Pole Breaker - won't handle it if both kick on at the same time
- A 20 Amp 2pole Breaker - Now the pump could run up to almost twice its rating before the breaker would trip. Not so good if a pump bearing starts going. You'll burn out the motor before the breaker trips.
- I know, you'll put in a single pole 15A and a single pole 20A, and handletie the breakers together. That sounds like it will work. Why not, the NEC never told you that you couldn't.

Would you wire it this way Roger? If the answer is no, which I hope, then realize that there is someone out there that will, and will be satisfied with the great job they did, because they didn't do anything illegal.

 

[roger]

Well, I'd probably put a small panel (six circuit) at the unit for the required "with in site disconnect" and fuse the pump and the filter separately.

That was not a very good hypothetical situation.


Roger

 

[milwaukeesteve]

Then your MWBC is no longer a Branch circuit but a Feeder.

That was not a very good hypothetical answer.