[Test-Equipment] DC Breaker switches

[Eric Lemmon]

Rasputin,

Before accepting the advice from your friend- who may or may not know what
he's talking about- go to the source:  Heinemann Electric.  Make a list of
the complete part numbers each circuit breaker, and send an e-mail with that
list to Heinemann at
<heinemann at heinemann-electric.com >
and ask if those breakers can be back-fed.

73, Eric Lemmon WB6FLY
 

-----Original Message-----
From: test-equipment-bounces at mailman.qth.net
[mailto:test-equipment-bounces at mailman.qth.net] On Behalf Of Rasputin
Novgorod
Sent: Sunday, July 05, 2009 1:10 PM
To: hp_agilent_equipment at yahoogroups.com; test-equipment at mailman.qth.net
Subject: [Test-Equipment] DC Breaker switches


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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