Twin Circuit Breakers?

[The Iceman]

I know I should ask one question at a time, but two things have been bothering me and I can't seem to find the article that covers them.

1. When using twin circuit breakers shouldn't you use separate nuetrals? Or when you use two single pole breakers and one twin shouldn't their be two nuetrals? Can anyone point me to an article that covers this situation?

2. Where in the NEC does it say you shouldn't exceed 80% of a branch circuit rating? I know 210.23(A)(1), is their any other articles, or does the 80% rule only apply to cord-and-plug equipment not fastened in place? I hear this 80% rule all the time but can't find the article to back it up.

Again I apologize for asking two different questions at the same time.

 

[ultramegabob]

whats a twin breaker? are you talking about a tandem or a double pole?

 

[mdshunk]

whats a twin breaker? are you talking about a tandem or a double pole?

I think "twin" might be a GE term for a tandem.

 

[ultramegabob]

deleted...........

 

[ultramegabob]

circuits on tandems should have thier own grounded conductor, double poles can share a grounded conductor...

 

[480sparky]

USUALLY 'twin' breakers are on the same bus, so each circuit needs it's own grounded.

There are some brands of twin/tandem breakers that will engage two bus bars, making the two circuits a true MWBC.

An easy way to tell is to look at the breaker and see how many bus bars it will engage when installed. If it's just one, then you need two grounded wires.

Another way to tell is to check the voltage between the two circuits. 240 volts can be a MWCB with one grounded. If it's zero volts, then you need two.

 

[The Iceman]

Sorry guys, I meant tandem. I thought you would need two neutrals but could't find an article that would cover it.

 

[480sparky]

Sorry guys, I meant tandem. I thought you would need two neutrals but could't find an article that would cover it.

Tandems are not specifically mentioned in the NEC. 110.3(B) will be the closest you'll get.

 

[Pierre C Belarge]

Question #1
Lets stir the post a little.
What if you had a tandem/twin breaker that occupies one location in a panelboard. Most think that it should generally require one grounded conductor with each phase termination.
Time to stir
Why not just up size the grounded conductor? - provided the phase conductors are installed to the same location.

 

[The Iceman]

Question #1
Lets stir the post a little.
What if you had a tandem/twin breaker that occupies one location in a panelboard. Most think that it should generally require one grounded conductor with each phase termination.
Time to stir
Why not just up size the grounded conductor? - provided the phase conductors are installed to the same location.

I think that would be a safety issue. If someone turns off only one breaker on the tandem/twin and not the other their is a possibility of current on the nuetral.

 

[ultramegabob]

Question #1
Lets stir the post a little.
What if you had a tandem/twin breaker that occupies one location in a panelboard. Most think that it should generally require one grounded conductor with each phase termination.
Time to stir
Why not just up size the grounded conductor? - provided the phase conductors are installed to the same location.

You could probley do that, but I think its flakey...

 

[Dennis Alwon]

Question #1
Lets stir the post a little.
What if you had a tandem/twin breaker that occupies one location in a panelboard. Most think that it should generally require one grounded conductor with each phase termination.
Time to stir
Why not just up size the grounded conductor? - provided the phase conductors are installed to the same location.

Usually tandems are used in residential and it would be quite difficult to upsize the grounded conductor. It is legal to do but not practical in most situations.

 

[Pierre C Belarge]

Usually tandems are used in residential and it would be quite difficult to upsize the grounded conductor. It is legal to do but not practical in most situations.

I agree, no one is buying NM cable with upsized neutrals. I was speaking theoretically as you know.


How about another angle...
What is the cause for concern using one grounded conductor with a tandem/twin breaker?

 

[480sparky]

...What is the cause for concern using one grounded conductor with a tandem/twin breaker?

You have two circuits on one neutral. If it's not a true MWBC, so you run the risk of overloading the neutral.

 

[ultramegabob]

I did a service call for a guy whos house was wired with 14-3 romex all landed on tandems on the same phase shareing a grouded conductor. with all of his christmas decorations being fed from two circuits that were both overloaded on one tandem, the grouded conductor actually burned at a wirenut connection due to having around 40 amps on it,

 

[Dennis Alwon]

You have two circuits on one neutral. If it's not a true MWBC, so you run the risk of overloading the neutral.

Pierre means with an oversized grounded conductor.

 

[ultramegabob]

backfeeding power through the grounded conductor to an unsuspecting electrician when he thought the circuit was off?

 

[Dennis Alwon]

backfeeding power through the grounded conductor to an unsuspecting electrician when he thought the circuit was off?

Is that any more dangerous than a MWBC. Of course, in 2008 that situation will be taken care of.

 

[ultramegabob]

Is that any more dangerous than a MWBC. Of course, in 2008 that situation will be taken care of.

Nope, no more dangerous, I just thought that was what he was fishing for....

 

[tonyou812]

I dont think I have ever ran a 3 wire circut to a tandem. And I dont think I ever will. And usually if I see that in someones panel Ill moved wires around to fix it. I was always taught that was a bad thing