Series circuit breakers might work if you have a common trip type, like a

two pole or three pole circuit breaker, so all the poles will trip at the

same time.

With single breakers that are tie together with a tie handle, there is too

much movement between the two. Normally if a circuit goes into a over

current fault, than one breaker will open which then pull the next one with

a little lag time.

If this is the case, then one breaker is opening while the other one may be

close and you will have the same air gap.

There is also the frame size of the circuit breaker to be consider, not just

the gap between the contact pads. A 600 volt frame mechanism must also have

more spacing than a 120 volt frame or the increase voltage could take out or

shunt out the magnetic trips.

In our electrical work, we use industrial I-Line circuit breakers, which

plug in to a buss line. We can use these on AC or DC circuits. A circuit

breaker design for 3 hp load on AC is only good for 1 hp on DC. So it about

a 3 to 1 factor.

Roland

----- Original Message -----

From: "Dave Cover" <[email protected]>

To: <[email protected]>

Sent: Wednesday, September 12, 2007 5:49 PM

Subject: [EVDL] Clearing the air (gap), breaker theory question

> I have a simple question about air gap and DC breakers. AC breakers don't

> need a lot of help

> extinguishing an arc because the voltage crosses zero many times a second.

> But DC voltage is

> constant and an arc might be sustained if the air gap is not large enough.

> And I assume that

> higher voltage needs a larger air gap. And for the purposes of this

> question, let's ignore

> magnetic blowouts, etc.

>

> Suppose we have a breaker with gap X and we needed to increase it's

> voltage rating. 2 of these

> breakers in series (mechanically tied so they trip together) would in

> theory give twice the air

> gap, or 2X. But neither air gap is larger than the original air gap X.

>

> My question is, does putting breakers in series increase the air gap (and

> voltage rating) by

> adding them together? Or is the voltage rating about the same as the

> original since the individual

> gaps are the same as the original? Don't forget, I'm asking so I can

> understand if putting

> breakers in series increases their voltage rating. Or not.

>

> Thanks

>

> Dave Cover

>

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