600 VDC switches [RE-wrenches]

Brad Bassett bsbassett at earthlink.net
Wed Sep 18 13:32:24 PDT 2002


Matt,

I believe that Sq D does not put the necessary jumper in at the factory 
between the two poles to get the 600vDC rating. The lebelling on various 
disconnects has sometimes been lacking also. Although GE has supplied 
the jumper for many years, their labeling was confusing. It now appears 
that they got the message and the labelling is clear and they call out 
the difference between the single pole 250v DC rating and the two pole 
break 600vDC rating. I don't know what the other mfg's do. 

Back almost a decade ago, we had someone in the field installing our 
first 600vDC array and used a single pole, which when opened sustained 
an arc until they literally blew it out. In our subsequent conversations 
with various disconnect engineers we learned that a single pole will 
come close to breaking 600v and sometimes will depending on current etc. 
But to be reliable and meet UL testing, breaking two poles is needed at 
these voltages.

Brad


matthew tritt wrote:
> William,
> 
> Your questions bring up some very interesting points. I did an install
> yesterday using a Sq D 3 pole breaker which has no jumper and no mention
> anywhere of a decreased rating. > > manufacturers achieve the 600 volt 
> rating:  They use a 3 pole disconnectI'm going to check with the 
> distributor and
> see if I can get an answer on the need to add a 3rd breaker to the 
> system,
> or if these switches are actually rated @ 600 volts per contact.
> Also, I regularly used to switch both DC inputs until I was admonished 
> by an
> electrician who insisted it was illegal to break the negative lead. I
> believe that he said this because of his assumption that the neutral in 
> AC
> is grounded and it would be somehow interrupting the ground to break the
> neutral on the DC circuit as well. Why not switch both?
> 
> Matt



Brad Bassett
Schott Applied Power 
Tumwater, WA office
bsbassett at earthlink.net

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