[Test-Equipment] DC Breaker switches

[Ron]

--- On Sun, 7/5/09, Rasputin Novgorod <priapulus at yahoo.com> wrote:

> From: Rasputin Novgorod <priapulus at yahoo.com>
> Subject: [Test-Equipment] DC Breaker switches
> To: hp_agilent_equipment at yahoogroups.com, test-equipment at mailman.qth.net
> Date: Sunday, July 5, 2009, 4:10 PM
> 
> 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?

Depends on internal construction. If it's 
just a coil is series with the terminals,
then no. If there is a bias magnet, then 
yes. 

> 2) The breakers are rated at 80vdc and I'm using 12vdc;
> will that change the trip rating of the breaker?

Circuit breakers are designed to sence 
current, not voltage.

-- Ron


> 
> 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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