Load shifting to fake breaker out

[Cletis]

I have a friend who was asking me if having say 200 amps per phase would trip a 200 amp main the same as loading it 195/205 ?
I didnt have an answer. Are there 1 or 2 bi metal strips in a 2 pole and are they cumlitive or can you trick them a bit?


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[GoldDigger]

I have a friend who was asking me if having say 200 amps per phase would trip a 200 amp main the same as loading it 195/205 ?
I didnt have an answer. Are there 1 or 2 bi metal strips in a 2 pole and are they cumlitive or can you trick them a bit?


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There are independent bimetal strips, not even very close to each other, but they share a larger thermal environment, just as adjacent breakers can have a cumulative effect.
Instead of 195/205 you might see 195/201.
Not that the thermal trip is that precise and could hold up to over 120%.
But there will be an effect, just not necessarily measureable.
Motor overloads, OTOH, are designed to be cumulative across all poles. But some have an intentional differential effect to try to catch single phasing more sensitively.

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[JFletcher]

Overall heat is the issue there, and 200/200 will generate nearly the same as 195/205. Not that I would recommend running a 200A breaker at 200A for any amount of time, but if it's unavoidable, a decent sized fan aimed at the panel will help.

Unless you have all resistive loads, running the breaker at max is going to cause trips when inductive loads are powered up.

(just fmoi, are 200A residential mains breakers rated for 200A continuous, or 160, or something else?)

 

[mopowr steve]

I don't believe they are continuous rated.
Anybody else agree?

 

[big john]

I don't believe they are continuous rated.
Anybody else agree?

They aren't, but at ambient temperature I would expect the breaker to hold indefinitely. The only requirement for a UL489 200 amp breaker is that it trip within 2 hours when loaded at 135%.

I agree with the other posters that eventually the net heat would begin to impact both poles: When we test multipole thermal mag breakers we have to let the breaker frame completely cool between each test or else you will get a faster trip time on the remaining poles, even though they hadn't been carrying current.

 

[Fnewman]

I assume the numbers used were just examples, with the actual question being whether both poles of a 2 pole breaker are somewhat common. While all the discussion about common heating is valid and does occur between any adjacent breakers, if we assume the case where the loads on each pole are farther apart, say 150 and 250 for example, the overloaded pole will trip fairly quickly taking the other pole out with it due to the handle tie.

 

[GoldDigger]

That is due to the internal tie between the trip mechanisms, not the handle tie.
A handle tie alone does not cause a common trip!
And the poles trip essentially at the same time.
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[mbrooke]

I have a friend who was asking me if having say 200 amps per phase would trip a 200 amp main the same as loading it 195/205 ?
I didnt have an answer. Are there 1 or 2 bi metal strips in a 2 pole and are they cumlitive or can you trick them a bit?


Sent from my iPhone using Tapatalk

My understanding is that GE quad breakers are made of one breaker with a current sense strip (100amps) and the other only have open/close contacts per phase.

 

[mbrooke]

Overall heat is the issue there, and 200/200 will generate nearly the same as 195/205. Not that I would recommend running a 200A breaker at 200A for any amount of time, but if it's unavoidable, a decent sized fan aimed at the panel will help.

Unless you have all resistive loads, running the breaker at max is going to cause trips when inductive loads are powered up.

(just fmoi, are 200A residential mains breakers rated for 200A continuous, or 160, or something else?)

Technically speaking your terminals are not rated 90*C, which is basically where the dwelling ampacity table resides.

 

[dmxtothemax]

QUOTE [ I have a friend who was asking me if having say 200 amps per phase would trip a 200 amp main the same as loading it 195/205 ? ] END QUOTE.

If you are asking weather a 200A breaker would trip out at 200A ?

I would say no !
Even at 205A no !
it would have to be 25% to 50% over to have any effect.
the trip curve plays a part in it.

 

[GoldDigger]

My understanding is that GE quad breakers are made of one breaker with a current sense strip (100amps) and the other only have open/close contacts per phase.

I rather doubt that unless that one bimetal is equally heated by an insulated shunt in each of the four poles.
Auxiliary contacts could be without current sensors, but not current carrying poles.
You can never assume that fault current will flow in more than one pole.

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[mbrooke]

I rather doubt that unless that one bimetal is equally heated by an insulated shunt in each of the four poles.

Why so?

Auxiliary contacts could be without current sensors, but not current carrying poles.
You can never assume that fault current will flow in more than one pole.

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Of course it won't. Current takes all paths and that is actually the point in using 4 breakers.

 

[GoldDigger]

So when you say "quad breaker" you are referring specifically to one where all four poles are internally connected in parallel?
If that is what you meant it was not clear to me from your post.

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[mbrooke]

So when you say "quad breaker" you are referring specifically to one where all four poles are internally connected in parallel?
If that is what you meant it was not clear to me from your post.

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Yup, one of these:

 

[GoldDigger]

Yup, one of these:

I still do not believe that one of those uses only one bimetal strip, since a small variation in contact resistance could cause uneven current distribution and the failure of one contact could then leave the other three totally unprotected.
Also, FWIW, I do not see one of those breakers matching the conditions of the original posts talking about current one the other phases, not just other poles.

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[mbrooke]

I still do not believe that one of those uses only one bimetal strip, since a small variation in contact resistance could cause uneven current distribution and the failure of one contact could then leave the other three totally unprotected.
Also, FWIW, I do not see one of those breakers matching the conditions of the original posts talking about current one the other phases, not just other poles.

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2 bimetals, one per leg.

 

[kwired]

2 bimetals, one per leg.

Whatever they did, they got it listed for use as a two pole unit.

 

[mbrooke]

Whatever they did, they got it listed for use as a two pole unit.

:thumbsup:

 

[NAMAHDDUB]

Stop it!

Stop it!

I have a friend who was asking me if having say 200 amps per phase would trip a 200 amp main the same as loading it 195/205 ?
I didnt have an answer. Are there 1 or 2 bi metal strips in a 2 pole and are they cumlitive or can you trick them a bit?


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You should not be loading a breaker more than 80% to begin with!

 

[ron]

You should not be loading a breaker more than 80% to begin with!

I disagree. It is fine to load a regular molded case 200A breaker to 200A all day long if the loads are non-continuous. At least as long as code allows.

Likely not a good design idea, but sometimes we have to push the minimums.