Can an AC breaker be used to for DC application? I need a 30a 48v breaker for dc equipment. I can put an inline fuse but customer wants a switch or breaker for servicing the equipment. I wanted to find a feed thru breaker I can put on a DIN rail. I can find a ac breaker just not a dc so i was wondering it i can use the AC breaker. Thanks for any help
DC/AC
- Thread starter mannyb
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- Location
- New Jersey
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- Journeyman Electrician
Not as a rule. AC has zero crossing points. DC doesn't so breaking the current is a more arduous duty.
Andy Delle
Senior Member
- Location
- Los Angeles CA
One example is the battery disconnect breakers on large 100kva+ UPS systems. AFAIK, they are standard 3phase beakers. But what is done is the + side comes into the A phase breaker, then loops back through the B phase breaker, then out. The - side just goes through the C phase breaker. So the DC + side has two breakers in series.
I think it's done to provide a greater gap length to help quench arcing? I have seen this on several UPS brands, Liebert, APC, MGE, so it must be a common design or even a listing requirement.
I think it's done to provide a greater gap length to help quench arcing? I have seen this on several UPS brands, Liebert, APC, MGE, so it must be a common design or even a listing requirement.
I like this application. Thanks
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- Placerville, CA, USA
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- Retired PV System Designer
The breakers that infinity posted are IEC rated for AC only, but are UL rated (for use in US) at 240 or 277V AC (depending on the current range) and 48VDC for one pole or 96VDC for two poles in series.
The use of two poles in series gives twice the air gap when open to extinguish the arc.
The use of two poles in series gives twice the air gap when open to extinguish the arc.
Adamjamma
Senior Member
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- Jamaica and london
Yep... used them some..
LarryFine
Master Electrician Electric Contractor Richmond VA
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- Henrico County, VA
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- Electrical Contractor
Two contacts in series have the same effect as contacts separating twice as fast. It works with relays and contactors, too.
- Location
- Placerville, CA, USA
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- Retired PV System Designer
Since the current is flowing through the entire circuit, the + side contacts and the - side contacts are in series (just not next to each other in the schematic.) That means that in the case you describe you have exactly the same effect for a current overload as if you had three contacts in series on the + side.
However, in the event of a ground fault, if the negative side of the battery is grounded separately on the battery side of the breaker connection, you would have only two contacts in series.
So you have to look carefully at the grounding scheme to determine the exact effect of using multiple poles.
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
The thing is, 48VDC is usually the limit of what most Molded Case Circuit Breakers are rated for. So in this case you can likely use any of those DIN rail mounted breakers.
Where it gets hairy is if you want to use them at the same voltage they are rated st for AC, ie 500VDC on a 600VAC rated Breaker. They have to be specifically listed for that and many are not, those that are will usually involve 2 or 3 poles in series.
Where it gets hairy is if you want to use them at the same voltage they are rated st for AC, ie 500VDC on a 600VAC rated Breaker. They have to be specifically listed for that and many are not, those that are will usually involve 2 or 3 poles in series.
Andy Delle
Senior Member
- Location
- Los Angeles CA
On APC Silcon units the battery is floating, not gounded. Not sure about Liebert but both use the triple pole battery breaker arrangement.
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- Illinois
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- retired electrician
Standard Square D QO breakers are listed for use at 48 volts DC.
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