2008 and Multiwire Branch Circuits

[cschmid]

LMAO...I wont but look at the way they are regulating them..the only spot left is...

Just for the record I normally do not promote MWBC..but since the high cost of copper I have had to have a change of heart..this is not a willing change but in some instances and situations the MWBC is a cost effective way to go..there I have admitted to it..

 

[76nemo]

Lo/to

Lo/to

This is going to put a whole new twist on LO/TO. Let's see how well our manufacturing and industrial plants, or anything besides resi for that matter, will take to this.

"Well, sorry Mrs. Production leader, you see here, I am going to have to take down this and this, so I can fix this"

Oh, this will go over REAL smooth

 

[hillbilly]

Consider yourself lucky.

The 2008 requires that a MWBC be served by a common 2-pole (or 3-pole) breaker, or with single pole breakers that have their handles tied together in some fashion.

Charlie, I don't as yet have a 08 Code, so I'm curious.

Does this mean that I can go back to making my own handle ties for use on MWBC breakers:smile: ?

steve

 

[480sparky]

This thread got me thinking....
I've never run across this situation before: Will a multi-pole breaker lock-out device fit on group of 2 or 3 single-pole breakers with handle ties when only one of them is shut off?

 

[LarryFine]

This thread got me thinking....
I've never run across this situation before: Will a multi-pole breaker lock-out device fit on group of 2 or 3 single-pole breakers with handle ties when only one of them is shut off?

How could only one be shut off?

 

[480sparky]

How could only one be shut off?

Duh. The ol' noodle isnt't working this morning. Im thinking one breaker in the tripped position.

 

[cschmid]

lets see one trips and the others do not...must be homemade handle tie..doubt that would make it through inspection..

 

[iwire]

lets see one trips and the others do not...must be homemade handle tie..doubt that would make it through inspection..

FWIW factory made handle ties are not intended to open the other poles when one pole trips, they might open the others but they are not designed for that.

They are only designed to force all poles open when a person shuts it down.

Only internal common trip breakers guarantee all poles open with a fault on one pole.

 

[Dennis Alwon]

FWIW factory made handle ties are not intended to open the other poles when one pole trips, they might open the others but they are not designed for that.

They are only designed to force all poles open when a person shuts it down.

Only internal common trip breakers guarantee all poles open with a fault on one pole.

I believe I have shut one side of a dp breaker handle. ITE make a twin dp that I am quite sure you can shut one side without the other. I have been known to be wrong (at least once in my life :smile. but if memory doesn't fail me that is the case

 

[480sparky]

I believe I have shut one side of a dp breaker handle. ITE make a twin dp that I am quite sure you can shut one side without the other. I have been known to be wrong (at least once in my life :smile. but if memory doesn't fail me that is the case

I've seen this as well, but my memory is so poor I don't remember what brand it was.

 

[iwire]

I believe I have shut one side of a dp breaker handle. ITE make a twin dp that I am quite sure you can shut one side without the other.

Are you telling me that some stuff does not work as designed? I am shocked. :grin:

The entire point of a handle tie is to open all poles when one pole is manually shut down. That is a handle ties only reason for getting up in the morning. :wink:

 

[LarryFine]

I think many people don't realize that multi-pole breakers have a link between poles other than the handle-tie. If you remove the handle-tie and overload one pole, they all will still trip simultaneously.

There is a mechanical link between them that you can see if you drill out the long rivets and separate the cases. It's typically just a little metal rectangle that joins rotating parts in each breaker.

Each pole's mechanism rotates that piece when it trips, and the metal rectangle joins them so they rotate together. Simply adding a handle-tie does not make a multi-pole breaker for line-to-line loads.

Usually the singtle-pole units have the holes covered, but some breakers have one end of the rotating part visible even in single-pole units. If you twist it with a screwdriver, the breaker will trip.

 

[roger]

Larry, there is a term for your explanation it's called "common trip" which handles ties tyeing single pole breakers together do not accomplish.

Roger

 

[cschmid]

FWIW factory made handle ties are not intended to open the other poles when one pole trips, they might open the others but they are not designed for that.

They are only designed to force all poles open when a person shuts it down.

Only internal common trip breakers guarantee all poles open with a fault on one pole.

The ones I have installed are tight enough I thought they would trip both breakers..But As I recall only one pole trips on a handle tied breaker while the 2 or 3 pole breaker might not trip at all..You can tell I have encountered allot of tripped MWBC OCPD's in the 25 years I have been doing this..

most installers use the 2 or 3 pole breakers..I hate it when they use 2 or 3 pole breakers as they are not the same after 10 years or longer installed..normally don't quite work the same as they were designed to..seen some severe equipment damage..I even welded with the wires attached to a receptacle one day just to see how long it took to trip..It did not trip the OCPD and it was in a commercial kitchen..OCPD was 2 pole Square D 20 amp...

 

[iwire]

The ones I have installed are tight enough I thought they would trip both breakers

They might, it's just not definite either way. :smile:

The reason even a tight handle tie may not trip the other breakers is because breakers must be able to trip even if the breaker handle is held in the on position.

So if you have three breakers handle tied together and the center pole trips the handle is not likely to move, the tripping breaker will not push hard enough to open the other two.

 

[LarryFine]

Larry, there is a term for your explanation it's called "common trip" which handles ties tyeing single pole breakers together do not accomplish.

I had hoped my explanation made it clear that I was aware of this. In fact, I said the last part.

It's possible there are those who have never drilled a multi-pole breaker apart. It is for these people my explanation was intended.

 

[cschmid]

I had hoped my explanation made it clear that I was aware of this. In fact, I said the last part.

It's possible there are those who have never drilled a multi-pole breaker apart. It is for these people my explanation was intended.

Here I thought I was the only who did that..

 

[iwire]

It's possible there are those who have never drilled a multi-pole breaker apart.

Been there, done that. :smile:

What I think Roger was trying to point out is the the words "Common Trip" have important and definable meaning.

 

[roger]

I had hoped my explanation made it clear that I was aware of this. In fact, I said the last part.

Well, since you didn't use term, I didn't know if you knew it or not.

Roger

 

[iwire]

I went to add circuits to a recently completed office building.

What I found in many of the panels where groups of four single pole 20 amp breakers handle tied together.

The modular office furniture was of the '3 +1' circuit type.

One network with 3 hots and a neutral then an additional two wire circuit. Typically the network will come from a 'dirty power' panel and the two wire circuit comes from a 'clean power' panel.

In this case they all came from the same panel and where handle tied together. I would love to know why as that is not required by code. My guess is a misinformed inspector as I know the company that did the work and they would not have provide the extra handle tie for no reason.