Two dedicated 20 AMP Circuits...

[milwaukeesteve]

Re: Two dedicated 20 AMP Circuits...

Bob,
I don't like to argue things I don't like without basis for the argument. 'Not liking' an installation is my opinion, but I do try to keep my arguements based in NEC. Sometimes that may not work.
For this one, yes I am throwing in some opinion, but that opinion is based in experience. I don't like protecting 2 individual circuits with a double pole breaker, when not needed. For one, I like to keep a circuit a circuit. I am allowed to share a neutral with another circuit, but on the control and protection of that circuit, I would rather see it have its own breaker for each circuit. Now that is my opinion. Yet, when I look at the code rules, they don't tell me that I CAN use a 2 pole breaker for this installation (yes, it also doesn't say I can't), yet it tells me that I CAN use individual breakers, and handle ties if needed. This helps solidify my opinion, and back my argument.
As far as the handle tie, I believe that they are designed for and do work automatically. That is if they are installed correctly, and are the correct handle tie. Again, that is more a manufacturer problem, rather than a NEC item. The NEC is asking for automatic, not handle ties that actually do the job their supposed to.

 

[JohnE]

Re: Two dedicated 20 AMP Circuits...

Steve,

I guess I'm agreeing with everyone else. I can not see where the nec prohibits use of a common trip 2 pole breaker for this installation.

John

 

[rattus]

Re: Two dedicated 20 AMP Circuits...

Originally posted by j_erickson:
Steve,

I guess I'm agreeing with everyone else. I can not see where the nec prohibits use of a common trip 2 pole breaker for this installation.

John

In fact it is required if the two outlets are on a common yoke, but don't ask me to quote chapter and verse. I am just repeating what someone else said.

[ August 08, 2005, 11:50 PM: Message edited by: rattus ]

 

[LarryFine]

Re: Two dedicated 20 AMP Circuits...

If I may throw in my two-cent's (i.e., my opinion) worth...

The only reason to not use a multi-pole breaker when not specifically required is nuisance tripping of the second circuit when the first one trips. To make this "illegal" would be like making accidentally bumping a breaker off illegal.

Nuisance, yes; crime, no.


I believe that the large single neutral with multiple circuits originated in string lighting like you used to see over used car lots and county fairs. It was more economical to run a large single conductor down the length of the lot.

In other words, outdoors.

 

[don_resqcapt19]

Re: Two dedicated 20 AMP Circuits...

Steve,

As far as the handle tie, I believe that they are designed for and do work automatically.

Handle ties are "common disconnect", not "common trip". As others have told you, all currently available breakers are of the "trip free" design. This means that the contacts will open on a fault even when the exterior handle is held in place. Very little force is transferred to the exterior operating handle. In many cases this force is not enough to operate the other breaker when a handle tie is used. In may, but that is not the intended function of a handle tie used with multiple single pole breakers.
Don

 

[mvannevel]

Re: Two dedicated 20 AMP Circuits...

First of all, let me say that I haven't delved into the 2005 code, as we're still using the '02 code here. The new language may be different but 240.20(B)(2) in the '02 permits the use of single pole circuit breakers with approved handle ties as protection for line-to-line loads on single phase circuits of grounded systems. Keep in mind this is not a circuit which supplies line-to-line and line-to-neutral loads. That would require a 2-pole breaker. Good idea? Probably not, but permitted all the same.

As far as the use of a handle tie or 2-pole breaker on a multiwire branch circuit the code certainly permits it, and absent any consideration for nuisance if both circuits trip at the same time, I think it's a good idea. In other than dwelling units, you're not required to open both poles even if it supplies more than one device on the same yoke. Now THAT sounds wrong to me. But, the code allows it. A multiwire branch circuit is a wonderful and useful circuit IF installed correctly. Unfortunately they often times aren't. Both legs installed on the same phase, grounded conductors which rely on devices for continuity. In these situations they cease to be useful, and instead become dangerous.

 

[milwaukeesteve]

Re: Two dedicated 20 AMP Circuits...

Rattus,
You are just a bit off on your 'just repeating what someone else said'.
I was that 'someone else'.
210.7(B) Multiple Branch Circuits. Where two or more branch circuits supply devices or equipment on the same yoke, a means to simultaniously disconnect the ungrounded conductors supplying those devices shall be provided at the point at which the branch circuits originate.

'A means to simultaneously disconnect' does not mean automatic or common trip, nor does it mandate the use of a 2 pole breaker. (these may be two different size circuits on the same yoke, you can't do that with a 2 pole breaker)

 

[rattus]

Re: Two dedicated 20 AMP Circuits...

MWSteve,

Thanks for the clarification. A handle tie should provide simultaneous disconnect, but don't you think it would be unusual to mix 15A and 20A circuits on the same multiwire even if it is allowed?

Rattus

[ August 10, 2005, 09:50 AM: Message edited by: rattus ]

 

[mvannevel]

Re: Two dedicated 20 AMP Circuits...

Originally posted by milwaukeesteve:

'A means to simultaneously disconnect' does not mean automatic or common trip, nor does it mandate the use of a 2 pole breaker.

You're right about that Steve, but it also doesn't preclude the use of a 2-pole breaker. Look at the full wording in 240.20(B)(1) that you cited part of earlier.

240.20(B)(1)individual breakers with or without handle ties....that serve only line to neutral loads.

It says those individual breakers shall be permitted as the protection for each ungrounded conductor. Now, if you look at 240.20(B)(2) it says that individual single-pole circuit breakers with approved handle ties shall be permitted as the protection for each ungrounded conductor for line-to line connected loads for single phase circuits. Does this mean (since it doesn't specifically give us permission to do so) that we can't use a 2-pole breaker on these line to line loads? Of course not. It merely gives us permission to use the single-pole with handle tie option. Just as it does in 240.20(B)(1) and 210.4(B).

Your example of the mixing of 15 and 20 ampere overcurrent protection for devices on the same yoke is an excellent reason not to use a 2-pole breaker, but only for that instance. If both are protected at the same amperage you could use individual breakers with handle ties or a 2-pole. Either way would be correct. It's a matter of personal preference of the electrician, the designer, or the end user.

 

[JohnE]

Re: Two dedicated 20 AMP Circuits...

Originally posted by rattus:

Originally posted by j_erickson:
Steve,

I guess I'm agreeing with everyone else. I can not see where the nec prohibits use of a common trip 2 pole breaker for this installation.

John

In fact it is required if the two outlets are on a common yoke, but don't ask me to quote chapter and verse. I am just repeating what someone else said.

Rattus,

I thought that it was obvious that if on a single strap or yoke that handle tie is required. I guess that what I was not clear in is that I am agreeing that I believe a double pole circuit breaker with internal trip is legal for mw branch circuit.

John

 

[milwaukeesteve]

Re: Two dedicated 20 AMP Circuits...

This whole thing with Multi wire branch circuits is funny.
First, MWBC contain 2 or more phase conductors sharing a neutral. Typical installations would be a 3wire or a 4 wire network, but as IWIRE pointed out, a MWBC could be multiple hots with an appropriately sized neutral.
Second, the NEC refers in the descriptions to this being a Multi wire branch circuit... singular. Yet it is made up of 2 or more individual circuits. In this post we have been talking about 2pole breakers protecting the MWBC (and all have stated their cases well), yet as in IWIRE's example, we could not come up with a 6pole breaker, yet we are trying to protect a "circuit" as defined by art 100.
Third, it doesn't say we can't use a 2pole, and it doesn't say we can. Yet as MVANNEVEL just pointed out, the use of the phrase "shall be permitted" does not exclude or limit anything, just states what could be used if desired.
Fourth, the wording used throughout all applicable codes makes things worse. One code uses manual and automatic, and another uses common trip. Circuit vs. cicuits.

When looking at this topic again, are we looking at protecting the circuit (MWBC) or the individual circuits? Is there a need for the simultaneous trip or not?

I believe Don, in a previous post, mentioned that 2pole breakers are rated for an individual circuit. (that should be the manufacturer and UL that have made that determination). But are 2pole breakers rated for 2 individual circuits and 2 different loads? Does the overcurrent protection work with the dual currents? I am curious about that, and if anyone has some documentation, that would be great. I know how breakers work, I am more interested in whether or not they are rated for such.

Again, it has been wonderful out on this Island. I am starting to feel a bit lonely

 

[milwaukeesteve]

Re: Two dedicated 20 AMP Circuits...

Sorry for the delay in my replies. I am sure most have now moved on, but I am unable to check the forum regularly sometimes.

 

[physis]

Re: Two dedicated 20 AMP Circuits...

By Rattus:

but don't you think it would be unusual to mix 15A and 20A circuits on the same multiwire even if it is allowed?

Yeah, it is unusual. But it's also allowed. It only seems weird because it is unusual.

You're a theory expert, What happens?

 

[charlie b]

Re: Two dedicated 20 AMP Circuits...

Here's what happens:

In a single 20 amp circuit, current leaves the breaker, travels out the ungrounded (phase) conductor, passes through the load, and returns to the source via the neutral conductor.

In a perfectly balanced, 3-wire, 20 amp, multi-wire branch circuit, current will leave one breaker, travel out one of the ungrounded (phase) conductors, pass through the load, then pass through the other load, travel through the other phase conductor, and return to the source via the second breaker. The neutral conductor carries no current in this circumstance.

If one of the breakers is 15 amps, and the other is 20 amps, and the loads are perfectly balanced (let us say at 12 amps for each circuit), then the current path is exactly as I describe above, and the neutral carries no current. If one of the breakers is 15 amps, and the other is 20 amps, but the loads are not balanced, then some of the current will flow through the path I describe above, and there will be some neutral current.

 

[physis]

Re: Two dedicated 20 AMP Circuits...

You do realize of course Charlie, the question was retorical.

 

[charlie b]

Re: Two dedicated 20 AMP Circuits...

I do. But some of the younger members of the Forum might not have known the answer. I had some time on my hands, so I thought I'd fill in that blank for them. The bit about current leaving one breaker and returning via the other breaker is not something a person just starting in this business is likely to expect.

 

[physis]

Re: Two dedicated 20 AMP Circuits...

Of course you're right. Sometimes I forget other people are watching.

 

[allenwayne]

Re: Two dedicated 20 AMP Circuits...

Hey I just wanted to share a part of my history,sometimes we do stupid things and if lucky enough to be here to post.Maybe just maybe some green help will take heed I am sure there is nobody here who has done something dumb and after say WHY IN THE H _ _ L DID I DO THAT.

 

[allenwayne]

Re: Two dedicated 20 AMP Circuits...

HOW DID THIS POST IN THIS THREAD

 

[roger]

Re: Two dedicated 20 AMP Circuits...

Allen, what are you talking about? It's to early to be doing 12 ounce curls.

On another note; you may want to invest in some grounding and bonding educational material, see this thread.


Roger

[ August 16, 2005, 07:57 AM: Message edited by: roger ]