[Test-Equipment] DC Breaker switches

[J. Forster]

Some DC breakers DO CARE about polarity. They have magnets to "blow out"
the arc that DC makes.

OTOH, at 12 VDC, unless your load is very highly inductive, it should not
matter much. At 48 VDC it would certainly matter.

FWIW,
-John

==============

> Gentlemen:
>
> Besides test gear, I'm also a Ham (radio amateur) so have
> a bunch of 12 dc powered radios. I recently got a bunch of
> (Telco surplus) DC breaker switches.
>
> I mounted two 75-amp and twenty 30-amp breakers in a
> 19 inch rack panel. I ganged all the breaker line (inputs)
> to a common copper buss bar.
>
> The load(!) side of the two 75-amp breakers go to a 75 amp
> 12vdc power supply, and battery (for backup), respectively.
> The load side of the 30-amp breakers go to various loads.
>
> By reversing the line and load connections on the two 75-amp
> breakers, the breakers could all use a common buss, making a
> tidy, elegant installation.
>
> ~BUT~ a fiend (sic) of mine saw what I'd done and had a fit.
> He said that you cannot reverse the load and line connections
> on a DC breaker switch; terrible things will happen. When I
> look inside a DC breaker, there is just a coil in series with
> a spst switch. If enough current flows thru the coil, it
> magnetically trips the switch.
>
> I can't see why polarity or line/load could make a difference.
> So I query the group:
>
> 1) Does it matter if I reverse the load and line connections?
>
> 2) The breakers are rated at 80vdc and I'm using 12vdc;
> will that change the trip rating of the breaker?
>
> The breakers are Heinemann 30 amp, trip 37.5, volt: 80vdc.
>
> Actually, the protection is redundant, as the power supply,
> battery and loads are all fused. I'm using the breakers as
> switches (because I had them, cheap) to control various loads.
> The breaker protection is a nice bonus protection/isolation
> of a dead short in a load line.
>
> Sincerely
> /blair
>
>
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