[c-nsp] 7609 6000W-DC PWR supply cabling Question

[Justin M. Streiner]

On Mon, 31 Mar 2008, William Jackson wrote:

> The 6000W-DC power supply takes four pairs of 4AWG PWR cables, my
> question is the following.

> Which way is this setup cabled?
>
> 1.	all 4 pairs of cables going back to a single circuit breaker of
> ( 6000/48 = 125Amp )
> 2.	each pair of cables going back to a separate circuit breaker of
> ( 6000/4 = 1500/48 = 31.25 Amp )
>
> I am not an electrical guy but I would have thought that the idea is
> that the breaker trips before the cable burns, so I would assume option
> 2?

I can't speak specifically to the needs of DC, but in the AC world, that 
same power supply takes two 208V or 240V 20A circuits to fully energize 
the unit.  Since the AC distro plant is centered around 120VAC 3-phase 
power, each one of those circuits will take up two breaker positions and 
each pair will be phased the same way.  The 6500s are fitted out with dual 
power supplies, with one being fed with a pair of circuits from one output 
panel and the other pair from another panel.

I would think in a DC environment you'd want all of the circuits for one 
power supply to come from one breaker panel, but separate breakers, then 
feed the second supply from another breaker panel.  The reason for this 
is that if you feed one supply from more than one breaker panel, the power
supply might be taken out of service if it's only partially energized. 
I'd think you would want the feed from the rest of your DC distro plant to 
the breaker panel to be sized and fused high enough to handle the 
combined draw of all of your output circuits, or whatever margins are 
dictated by your local building/electrical codes.

jms