DC circuit breaker protection

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rkrieger

rkrieger

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OK, I checked archives and didn't find anything. I am designing some HD automotive instructional "bread boards" used for students to construct sample circuits. Usually the boards are powered with several 12 volt auto batteries in parallel for lots of amps capacity. Question: Would a household 1pole breaker provide protection from OC faults in the "feeder" circuit to the boards? I don't think the "amps" are smart enough to know if they are AC or DC, but am unclear what's truly inside a CB. I think it is a mechanical trip type device.

Any help? or ideas? :smile: :)

Thanks in advance.................
 
Square D QO breakers are listed for use in DC circuits.
Voltage Rating
The circuit breaker must have a voltage rating greater than, or equal to, the system voltage. When a
circuit breaker clears an overcurrent, it is done in two steps. First, the current sensing system identifies
the overcurrent and releases the tripping mechanism. This results in a parting of the contacts. The
circuit breaker must then extinguish the voltage arc across the contacts. If the circuit breaker has the
correct voltage rating, it can efficiently extinguish this voltage arc. QO and QOB circuit breakers are
rated for use in the following voltage systems:
• 120 Vac
• 208/120 Vac
• 120/240 Vac
• 240 Vac
• 48 Vdc (10–70 A for 1 and 2 pole circuit breakers, 10–60 A for 3 pole circuit breakers)
Click to expand...
 
Thanks

Thanks

Very succinct and does indeed answers my questions.

I will use a QO 1 pole rated at 30 amps for each "buss".

Thanks so much for your reply.:D
 
Amps are indeed amps, but there is a difference when it comes to switching of DC vs AC. So unless a breaker is specifically labeled for use on DC, you cannot use it. But always check because some are, some are not. As he said Square D QO breakers are rated for 12 and 24VDC.
 
In AC the arc must be "stretched" long enough that it self extinguishes at the next zero crossing of the waveform; in DC the arc must be stretched longer. Also, the magnetic element design maybe different between AC and DC.

So, even though the current thermal element doesn't care, an AC only device (breaker or switch) should not be used on DC.
 
if you need to have the breakers out in the open, you can use the QOU variety which is wire in, wire out and can be mounted with these little mounting feet.
 
Many thanks again, to all who have posted. I am currently looking for the QOU type breaker in my little town. It would nice to have one that wires in and out instead of having to connect to the buss bar spring clips of a QO type.

RLK
 
QOUs are typically used by control panel builders. If there is one near you somewhere, call them and ask which electrical distributor carries the QOUs. Typical Construction / Residential supply houses will not have them.
 
QO and QOU style are also available with 10A trip. There are 1-pole plug-on mounting bases for QO but these maybe harder to find than QOU's
 
if you cant find QOU, you can always connect to the line side of a OQB with a ring terminal and a screw+nut, but I dont know how you would mount the breaker.
 
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