Can I use 400 amp AC breaker instead of class T 400 amp fuse

[centrix29]

I was reading in the Xantrex manual that you must use a fuse and disconnet between the positive leg of the batteries and the inverter.  I was thinking of using a Class T 400 amp fuse and a 400 amp rotary type switch.  I was wondering though if I can use a 400 amp AC breaker instead.  Some are going cheap on E.

Thanks for the help!

Pat 

[Kristinsgrandpa]

Only if it's DC rated.

Ed

[grantgoold]

I would be very careful. You may void any warranty you might have with your inverter by not using the exact recommended set up.


Grant

[belfert]

I used a 225 amp breaker from a UPS that was being dismantled.  The breaker actually breaks both the positive and neutral.  The breaker almost looks like it was originally three phase as it has three connections with one connection connected across to one of the other lugs.

I figured if it worked on the DC side of a large UPS it should work for me.  I have a 24 volt inverter which is why 225 amps.

[DrivingMissLazy]

It is common practice when using AC breakers for DC applications to connect two sets of the contacts in series which significantly increases the voltage breaking capacity of the breaker.

The bottom terminal of one set of contacts is connected to the top terminal of the second set of contacts to accomplish this. In much of the equipment that I manufactured I typically did this for the 600 volt DC battery source that fed the equipment.

I do not recall for sure, but I believe that all AC breakers are rated for at least 50 volts DC.

Richard

[Ncbob]

I certainly wouldn't challenge anything that Richard would offer as far as this situation is concerned because he has the experience and testing behind his recommendations....but (and isn't there always a 'but?) while the more learned among us might know well that it will work...how would the Underwriters for the Insurance Company feel about it should the be an 'incident' wherein there was an injury or even a total loss?

We all have Liability Coverage on our buses and probably most have coverage for a total loss.  Should the Inspectors find something which would allow the Underwriters 'off the hook' and we didn't have the expertise to explain something which was installed 'not to code', therein lies the rub.

I don't wish to be a wet blanket on ideas...but the conservative side of me always keeps an eye on where I stand from a Liability standpoint inasmuch as I am 'the builder'.

FWIW.

NCbob

[DrivingMissLazy]

Everything I manufactured was either UL, ABYS or Lloyds listed. And if it is below 50 volts DC, UL is not even interested in how it is done. They feel there is no personal safety hazard at that level.
Richard

[Ncbob]

Richard, I'd be the last person in this world to challenge you or your knowledge. I don't know first hand of an AC breaker (by Brand name) which would do the job....perhaps you might.

Sometimes I play the 'Devil's Advocate' only to remind our friends that 'balls to the wall' or 'let it all hang out' won't do the job.

No offense meant or intended.

NCbob

[Nusa]

In series, Richard? I would have thought that in parallel would be more effective by doubling the contact area.

[DrivingMissLazy]

In series, Richard? I would have thought that in parallel would be more effective by doubling the contact area.

Yes, in series. Then you have two sets of contacts breaking the DC voltage at the same time, significantly increasing the voltage breaking capability of the contacts, whether in a breaker or a contactor or relay.

If I were doing it I would probably use a three phase breaker and series all three sets of contacts. There is absolutely no reason, in my opinion, to break both the positive and the negative leads.

Richard

[Len Silva]

While I couldn't tell you off hand where to find one, there are 400 amp, DC rated breakers available.  They are used in telephone company power plants all over.  A search for telco surplus might find something.

Len

[DrivingMissLazy]

DC rated breakers are available and they are very expensive. I have had to buy 800 amp units rated at 600 volts DC and they cost a small fortune.
I reiterate however, that for DC voltages below 50 volts, UL does not require a DC rating. The voltage is so low that it can not sustain an arc when the contacts open.
Richard

[belfert]

The only reason I switched both positive and negative is the breaker was wired up that way from the UPS.  I guess I could have bypassed the breaker with the negative wire.  I wonder if breaking both postive and negative at the same time is hard on the inverter?

[NJT5047]

While I have no opinion on AC circuit breakers....I can tell ya'll where to find 400 A DC circuit breakers.   Electric vehicle builders use them. 
www.EV-America.com is one source.  Electro Automotive is another. 
They are used as a sort of emergency shutdown devices.  Often located within the drivers compartment (not the best of ideas), or remoted with a Bowden cable.  The EV companies also have very large contactors for DC loads.  Like big enough to handle bus starters.  However, they are expensive. 
Another idea is ANL fuses....not a recommendation...just something that isn't expensive and will protect DC circuits. 
i'm in the process of converting a Nissan 200SX into an electric vehicle.  Just bought some of the above components.  For what they cost, I thought that they would be gold plated...they ain't. 
Anyway, the EV folk sell large amp DC load components with 12V DC control voltage. 
JR

[HB of CJ]

I think one reason the manufacture wants a fuse and not a breaker is that if and when the fuze blows, they do NOT want the circuit reestablished quickly or easily.  Particularily not an automatic-resetting breaker.  Perhaps the requirement just comes from their legal department and has no real engineering reason.  These things happen.