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-   -   Tandem breaker (http://www.diychatroom.com/f18/tandem-breaker-11800/)

rusty_5620 09-24-2007 11:07 AM

Tandem breaker
 
My cousin had a dead short on one of his circuits causing his breaker to trip.. He had 14/3 running upstairs supplying two circuits. The breaker was a tandem 15 amp breaker with a bar connecting the two. ( two 15 amps breakers that are connected and fit onto the bus bar together)
I disconnected the two hots from the breaker to find out which one had the short and found one of the hots in the upstairs bedroom outlet had been spliced down the middle and the ground was touching it. (strange that it would just trip the breaker just now after 15 years) repaired that and the circuit is now fine.
My question is should the tandem 15 amp breaker have the bar to trip both when one circuit trips? I noticed that when the circuit tripped it didnt always throw the switch over because they were connected.

Are they connected because the circuits share the same neutral?


Cheers,
Rusty

Andy in ATL 09-24-2007 04:24 PM

The short answer is yes...Code references to follow if requested.

jproffer 09-25-2007 01:12 AM

When I hear (or read) tandem breaker, I think of a breaker that fits into the space of one breaker (say about 1 inch), but has two connections. Is this what you have? If so, then what you have is against code.

If you have a two-pole breaker with a shared nuetral, then you're fine.

Both hots coming off of a true tandem breaker would be on the same phase of the main panel, making the nuetral carry as much as twice its rated limit instead of the difference between loads on each phase.

Andy in ATL 09-25-2007 04:13 PM

Do they make tandems with handle ties? I've never seen them, but I could be wrong. Although it doesn't make sense---Why would you need a handletie on a tandem breaker if both hots are on the same phase? I'm guessin' he has a two-pole 15A breaker correctly wired. Of course a picture is always worth a thousand words!:thumbsup:

jproffer 09-25-2007 09:04 PM

Well color me red...

I missed the handle tie part...I know, I know...big BOLD letters....It was late. You're probably right.

scorrpio 09-26-2007 12:30 PM

Looks like a former 240V circuit converted to work as two 120V ones. Someone wanted to save a buck by not buying two regular 15A breakers.

jproffer 09-26-2007 12:43 PM

Quote:

Looks like a former 240V circuit converted to work as two 120V ones. Someone wanted to save a buck by not buying two regular 15A breakers.
If it is indeed a correctly wired MWBC (and, after the second reading, I believe it is) you can't use 2 "regular" (which I assume means single pole) breakers unless they have a handle tie, which effectively makes it a double pole breaker.

NateHanson 09-26-2007 12:47 PM

Quote:

Originally Posted by scorrpio (Post 64869)
Looks like a former 240V circuit converted to work as two 120V ones. Someone wanted to save a buck by not buying two regular 15A breakers.

Actually, I think this is a legitimate way to run two circuits to the same place. Like kitchen outlets on separate circuits for each duplex plug.

Multi-Wire Branch Circuit? Something like that, right?

HouseHelper 09-26-2007 02:29 PM

Quote:

Originally Posted by jproffer (Post 64871)
If it is indeed a correctly wired MWBC (and, after the second reading, I believe it is) you can't use 2 "regular" (which I assume means single pole) breakers unless they have a handle tie, which effectively makes it a double pole breaker.

The handle tie is only required if the two circuits share the same strap, i.e., the two receptacles of a duplex receptacle split between the two hots with the neutral common.

It should be noted that this handle tie is present so that the breakers can be turned off together, and can be achieved by using a double pole breaker or two single poles with an approved handle tie. If using two single pole breakers, they may not both trip in the event of a short circuit since there is not an internal trip mechanism present.

Andy in ATL 09-26-2007 03:59 PM

[quote=HouseHelper;64907]The handle tie is only required if the two circuits share the same strap,


Thats what I meant to say:huh: . I haven't gotten my '08 book yet but isn't the handle tie gonna be required on all MWBC's?

HouseHelper 09-26-2007 04:03 PM

Quote:

Originally Posted by Andy in ATL (Post 64935)
Thats what I meant to say:huh: . I haven't gotten my '08 book yet but isn't the handle tie gonna be required on all MWBC's?

That is my understanding. Along with AFCIs being required for all general purpose receptacles or something to that effect.


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