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Author Topic: This will trip a properly wired breaker, right?  (Read 6549 times)

Dennis Wiggins

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Re: This will trip a properly wired breaker, right?
« Reply #10 on: September 02, 2014, 09:54:50 am »

Thank you Mike and Ray.  How a "ganged breaker" works has been puzzling to me for a long time. 

Please emphasize that you should NEVER use 2 adjacent (single) breakers instead of a 2-pole when breaking out to two 120V circuits (using 4-wire feeder) that share common neutrals and grounds.

"The reason for requiring all poles to trip is that a 240-volt load with only a single tripped pole would back-feed current through the now non-operating 240-volt appliance through the tripped phase. That could be very dangerous for something like a sub-panel which is fed by a double-pole breaker but then breaks out into both 240-volt and 120-volt appliances. "

-Dennis
« Last Edit: September 02, 2014, 10:03:41 am by Dennis Wiggins »
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Jonathan Johnson

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Re: This will trip a properly wired breaker, right?
« Reply #11 on: September 02, 2014, 12:05:20 pm »

Thank you Mike and Ray.  How a "ganged breaker" works has been puzzling to me for a long time. 

Please emphasize that you should NEVER use 2 adjacent (single) breakers instead of a 2-pole when breaking out to two 120V circuits (using 4-wire feeder) that share common neutrals and grounds.

"The reason for requiring all poles to trip is that a 240-volt load with only a single tripped pole would back-feed current through the now non-operating 240-volt appliance through the tripped phase. That could be very dangerous for something like a sub-panel which is fed by a double-pole breaker but then breaks out into both 240-volt and 120-volt appliances. "

-Dennis

If only 120V appliances are on the shared-neutral circuits, there should be no voltage potential on the tripped hot leg if the other hot leg is not tripped. However, if there is a 240V load connected to the two legs, then certainly there WOULD be voltage potential on the tripped leg.

The hazard of a shared neutral with two 120V legs (opposite poles) would be that someone repairing the circuit could assume that it's safe to break the neutral if only one of the legs is off. When working on a 120V circuit that shares a neutral with another 120V circuit, both circuits must be disconnected (and locked/tagged).

Some inspectors may allow shared neutral without ganged breakers. That's probably not a good idea. The idea of shared neutral is to gain capacity (say, 40A total on two 20A breakers with one neutral) while saving cost (only have to run one neutral wire instead of two), for optimum safety you need a ganged breaker. This introduces an inconvenience: an overload on one circuit will cause both circuits to trip.
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Jeff Robinson

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Re: This will trip a properly wired breaker, right?
« Reply #12 on: September 02, 2014, 12:24:19 pm »

...There's only a mechanical connection in the handle so that if any single pole trips, then it mechanically trips the spring loaded latches and opens up the other pole(s)...

I want to clear up a technical error in the above. In multipole (IE: 2+ poles) circuit breakers there is an internal connection of the individual pole trip units to the other poles' trip units. A trip on any pole will trip all connected trip units (a rotating non-conductive pin, usually, only visible in 'demo' units that have a cutaway or clear side). Some DIN mount types allow access to this link, most do not.

An example you are sure to be familiar with: Square D QO (and QOB) breakers have only 1 handle, no matter how many poles they switch. They do offer handle ties for single pole units but there is no guarantee that tripping one pole will also switch the connected unit off.

HTH,
Jeff Robinson
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Ray Aberle

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Re: This will trip a properly wired breaker, right?
« Reply #13 on: September 02, 2014, 01:23:37 pm »

I want to clear up a technical error in the above. In multipole (IE: 2+ poles) circuit breakers there is an internal connection of the individual pole trip units to the other poles' trip units. A trip on any pole will trip all connected trip units (a rotating non-conductive pin, usually, only visible in 'demo' units that have a cutaway or clear side). Some DIN mount types allow access to this link, most do not.

An example you are sure to be familiar with: Square D QO (and QOB) breakers have only 1 handle, no matter how many poles they switch. They do offer handle ties for single pole units but there is no guarantee that tripping one pole will also switch the connected unit off.

HTH,
Jeff Robinson


But, a two-pole breaker is going to trip both poles if one is overloaded/triggers the circuit breaker, right?

Assuming that you are not asserting otherwise, it really doesn't matter how the second pole is tripped, just that bottom line, one leg goes, and the other does at the same time. We should be careful to not cause confusion by talking about semantics of how the internal mechanism works-- especially since with the breakers all being connected anyways, there's no chance of one leg going and the other one not.

-Ray
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Tim McCulloch

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Re: This will trip a properly wired breaker, right?
« Reply #14 on: September 02, 2014, 01:32:47 pm »


But, a two-pole breaker is going to trip both poles if one is overloaded/triggers the circuit breaker, right?

Assuming that you are not asserting otherwise, it really doesn't matter how the second pole is tripped, just that bottom line, one leg goes, and the other does at the same time. We should be careful to not cause confusion by talking about semantics of how the internal mechanism works-- especially since with the breakers all being connected anyways, there's no chance of one leg going and the other one not.

-Ray

The point Jeff is making is that INTERNALLY tied breakers will always open all legs when tripped, externally handle ties may or may not be as effective.
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Ray Aberle

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Re: This will trip a properly wired breaker, right?
« Reply #15 on: September 02, 2014, 02:43:13 pm »

The point Jeff is making is that INTERNALLY tied breakers will always open all legs when tripped, externally handle ties may or may not be as effective.
Are these external handle ties as in "they do offer external handle ties," and something that someone buys? As opposed to the example picture I posted of a three-pole breaker with all three handles molded together for one?

Or is there a chance that a breaker such as the one I posted, where the three poles are connected with one handle, could trip one leg and not actually trigger the others?

The reason I am asking is that if that's the case, where one could trip one leg and not another, that's a good thing to know-- but if it's the case of someone would have to purchase a 2 or 3 pole breaker that isn't already tied together, and then they are having to buy the handle tie- that seems to be a situation that wouldn't come up as often. And if this came about from the potential of someone buying two single breakers as opposed to a 220V 2-pole breaker, and then needing to buy the tie-- hmmm.

An example you are sure to be familiar with: Square D QO (and QOB) breakers have only 1 handle, no matter how many poles they switch. They do offer handle ties for single pole units but there is no guarantee that tripping one pole will also switch the connected unit off.
The reason I started asking what I did is that a quick internetz search shows the QO breakers to be a 220V/two pole breaker that is connected together. So are you saying that this type of breaker, with the handle molded into one piece, could trip only one leg and not the other? And this extra-purchase handle tie would be required?

I hate hate hate ever saying something that questions the Wisdom of Tim, but I am trying to be clear as to what Jeff was referring to, since the mentioned products don't appear to be what he says they are.

-Ray
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Tim McCulloch

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Re: This will trip a properly wired breaker, right?
« Reply #16 on: September 02, 2014, 03:00:35 pm »

Are these external handle ties as in "they do offer external handle ties," and something that someone buys? As opposed to the example picture I posted of a three-pole breaker with all three handles molded together for one?

Or is there a chance that a breaker such as the one I posted, where the three poles are connected with one handle, could trip one leg and not actually trigger the others?

The reason I am asking is that if that's the case, where one could trip one leg and not another, that's a good thing to know-- but if it's the case of someone would have to purchase a 2 or 3 pole breaker that isn't already tied together, and then they are having to buy the handle tie- that seems to be a situation that wouldn't come up as often. And if this came about from the potential of someone buying two single breakers as opposed to a 220V 2-pole breaker, and then needing to buy the tie-- hmmm.
The reason I started asking what I did is that a quick internetz search shows the QO breakers to be a 220V/two pole breaker that is connected together. So are you saying that this type of breaker, with the handle molded into one piece, could trip only one leg and not the other? And this extra-purchase handle tie would be required?

I hate hate hate ever saying something that questions the Wisdom of Tim, but I am trying to be clear as to what Jeff was referring to, since the mentioned products don't appear to be what he says they are.

-Ray

Question at will.  I do!

I was thinking more of the aftermarket clips or the little piece of #14 the electrician would thread through the holes in the handles.  The picture you posted uses a factory-applied metal clip which is probably much more rigid than either of the 'solutions' I was considering.

That said, the internal axle method is 100% and cannot be modified or altered by an end user.
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Ray Aberle

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Re: This will trip a properly wired breaker, right?
« Reply #17 on: September 02, 2014, 03:51:22 pm »

Question at will.  I do!

I was thinking more of the aftermarket clips or the little piece of #14 the electrician would thread through the holes in the handles.  The picture you posted uses a factory-applied metal clip which is probably much more rigid than either of the 'solutions' I was considering.

That said, the internal axle method is 100% and cannot be modified or altered by an end user.

Ah yes, so it's all a matter of shoddy electrical work being performed that opens up a potential for it not tripping properly. Hahaa. If someone uses the OEM multi-pole breaker like pictured, then they should be good. I was just worrying that it was being implied that the multi-pole breaker as shown (and others that one would use in their home, for example) could possibly only trip one leg and not the other-- I didn't think that was possible, so that's why I was questioning you, life, everything, and the lunch I just bought at Pita Pit while mystery shopping them. (Really!)

-Ray
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Jonathan Johnson

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Re: This will trip a properly wired breaker, right?
« Reply #18 on: September 02, 2014, 05:46:43 pm »

I was just worrying that it was being implied that the multi-pole breaker as shown (and others that one would use in their home, for example) could possibly only trip one leg and not the other-- I didn't think that was possible...

If the factory-installed handle tie is made of metal and securely fastened (i.e., riveted), it shouldn't be a problem. However, I have seen where the factory used a PLASTIC clip to tie the handles together, and the plastic cracks, allowing the handles to move independently so they WON'T trip in common.
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Dennis Wiggins

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Re: This will trip a properly wired breaker, right?
« Reply #19 on: September 02, 2014, 06:35:22 pm »

All,

I hope that this is the type of breaker I should be using when I have to create a 4-wire feed, for two 110V (20A each) circuits.

I use 4x12ga, not exceeding 50 feet.

Thanks,
Dennis
« Last Edit: September 02, 2014, 06:40:44 pm by Dennis Wiggins »
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Re: This will trip a properly wired breaker, right?
« Reply #19 on: September 02, 2014, 06:35:22 pm »


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