Fuse/Breaker voltage rataing

[LMAO]

You can use two over-current protection devices in parallel to double the trip rating (conductor lengths must be equal).
Here is my question: what about voltage rating? Can you wire a two-pole breaker/fuse in series to double its voltage rating? I know that some manufacturers specify so in their datasheet, but is this a general rule?
Thanks

 

[rcwilson]

I didn't know it was per code to parallel overcurrent devices to double the rating. Cables yes, overcurrent protection, no.

It may be acceptable if the product is a listed/tested product from a manufacturer like the large 5 kV fuses that have two fuses in the same package. Or GE's 6,000 A circuit breaker which was two 3-pole breakers paralleled into a 6-pole. (Still available from PACs Industries).

I've only seen connecting devices in series to achieve a voltage rating on circuit breakers for DC circuits. Manufacturer?s instructions required using two poles of the same breaker to achieve the 250V interrupting rating.

If you did series two fuses or breakers, how would you guarantee that both opened simultaneously on overload or a fault. If the two breakers?/fuses? tripping was off by milliseconds, they would not share the arc voltage as well.

 

[LMAO]

I didn't know it was per code to parallel overcurrent devices to double the rating. Cables yes, overcurrent protection, no.

It may be acceptable if the product is a listed/tested product from a manufacturer like the large 5 kV fuses that have two fuses in the same package. Or GE's 6,000 A circuit breaker which was two 3-pole breakers paralleled into a 6-pole. (Still available from PACs Industries).

I've only seen connecting devices in series to achieve a voltage rating on circuit breakers for DC circuits. Manufacturer?s instructions required using two poles of the same breaker to achieve the 250V interrupting rating.

If you did series two fuses or breakers, how would you guarantee that both opened simultaneously on overload or a fault. If the two breakers?/fuses? tripping was off by milliseconds, they would not share the arc voltage as well.

my application is DC too; up to 1200VDC. 600VAC bridge rectifiers feeding inverters; DC voltage is typically 850VDC but can rise up to 1200VDC during regeneration.

You have a good point about "simultaneous operation". What if the poles are mchanically interlocked, like normal two-pole breakers? Does that guarantee simultaneous operation?

 

[hurk27]

I have seen two and three pole breakers on DC circuits with a common trip that was wired in series also.
I think they were DC drives

 

[Jraef]

A Manufacturer can test and list a SINGLE device with multiple parallel operating poles wired in series to get a higher DC voltage rating on it, because with DC, the voltage rating has a lot to do with the total air gap that is created by the arc when the contacts close. So the theory is, multiple arcs in series increase the circuit resistance, which divides the voltage, effectively lowering it across each gap to a manageable level.

I have seen this used to get to 600VDC on breakers and disconnect switches that otherwise were rated for 300VDC, but never higher than that. But there are not rules that allow this to be done in the field with separate devices, they must ALL open simultaneously.

UL, by the way, will not list anything higher than 600V anyway as "low voltage" and once you get to higher levels, it becomes "medium voltage" and subject to a whole new set of rules. So hopefully UL is not an issue for you.

The other aspect that you have to contend with is creapage distance between current carrying components. Something designed for 600V is very different from something designed for 1000V and up.

 

[weressl]

You can use two over-current protection devices in parallel to double the trip rating (conductor lengths must be equal).
Here is my question: what about voltage rating? Can you wire a two-pole breaker/fuse in series to double its voltage rating? I know that some manufacturers specify so in their datasheet, but is this a general rule?
Thanks

I doubt that there are fuses or breakers that are listed for parallel operation. I give you the technical reasoning why. Fuses and circuit breakers have manufacturing tolerances and that result in operational tolerances. This results in that two identical devices will not open at the same exact current/time. That would result in one fuse or circuit breaker exposed to double of its rated voltage that it may not be able to interrupt. Mechanically linked breakers are a good idea, but questionable if it can be done satisfying all the potential problems. Zone interlocked and series rated breakers is the closest to the question but they are provided for a different reason. Electronic trip is certainly the best avenue to explore, to investigate.

 

[hurk27]

I doubt that there are fuses or breakers that are listed for parallel operation. I give you the technical reasoning why. Fuses and circuit breakers have manufacturing tolerances and that result in operational tolerances. This results in that two identical devices will not open at the same exact current/time. That would result in one fuse or circuit breaker exposed to double of its rated voltage that it may not be able to interrupt. Mechanically linked breakers are a good idea, but questionable if it can be done satisfying all the potential problems. Zone interlocked and series rated breakers is the closest to the question but they are provided for a different reason. Electronic trip is certainly the best avenue to explore, to investigate.

Actually ITE did this very thing with 200 amp mains where they had 4 breakers riveted together, two for one leg and two for the other leg, of course they were all common trip, but look at any 200 amp MB ITE panel late "80's" or early "90's" and you will see 4 breakers put together.

And yes each breaker stabbed on a buss that was extended from the top of the buss bars.

 

[weressl]

Actually ITE did this very thing with 200 amp mains where they had 4 breakers riveted together, two for one leg and two for the other leg, of course they were all common trip, but look at any 200 amp MB ITE panel late "80's" or early "90's" and you will see 4 breakers put together.

And yes each breaker stabbed on a buss that was extended from the top of the buss bars.

The issue is SERIES connection of breakers. I believe you are talking about parallel connection for each phase.

 

[hurk27]

I doubt that there are fuses or breakers that are listed for parallel operation. I give you the technical reasoning why. Fuses and circuit breakers have manufacturing tolerances and that result in operational tolerances. This results in that two identical devices will not open at the same exact current/time. That would result in one fuse or circuit breaker exposed to double of its rated voltage that it may not be able to interrupt. Mechanically linked breakers are a good idea, but questionable if it can be done satisfying all the potential problems. Zone interlocked and series rated breakers is the closest to the question but they are provided for a different reason. Electronic trip is certainly the best avenue to explore, to investigate.

The issue is SERIES connection of breakers. I believe you are talking about parallel connection for each phase.

I know the thread was about series, but look at your post above???

 

[weressl]

I know the thread was about series, but look at your post above???

Yep. Your right is my left.....:happysad:

 

[weressl]

I doubt that there are fuses or breakers that are listed for parallel operation. I give you the technical reasoning why. Fuses and circuit breakers have manufacturing tolerances and that result in operational tolerances. This results in that two identical devices will not open at the same exact current/time. That would result in one fuse or circuit breaker exposed to double of its rated voltage that it may not be able to interrupt. Mechanically linked breakers are a good idea, but questionable if it can be done satisfying all the potential problems. Zone interlocked and series rated breakers is the closest to the question but they are provided for a different reason. Electronic trip is certainly the best avenue to explore, to investigate.

Let me rephrase that (thanks hurk): "I doubt that there are fuses or breakers that are listed for SERIES operation."

I think though that the mistake became clear from the explanation I've given, parallel halfs current, series halfs voltage, approximately anyways, in proportionate to their resistance difference.