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Puzzling~1950 QO Split bus

7469 Views 14 Replies 8 Participants Last post by  brodgers
I just came across a 100A single-phase 120/240 Sq D residential panel (still in use) whose MAIN section has not eight spaces for four 2-pole CBs including the lighting main, not 12 spaces for six 2-pole CBs, but TEN spaces. Anybody familiar with these and know why? I double-checked the schematic; I didn't miscount.
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Discussion Starter · #5 ·
they rarely fail if ever.
What failure modes are you talking about, pard?

The reason I'm asking is that I'm going over some material about Stabloks, and about how they may not stop conducting even when they should. Though it seems kind of unfair to mention SqD and FPE in the same breath.
 

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I see lots of old split buss panels but, this answers a question about one I saw a few months back.
It appeared that the panel had the six two pole breakers that I expected to see and then it had two 60s feeding double split lower sections.
I now speculate that they limited the amount of amperage on each buss stab to a max of 60 amps.

Does this make sense?

Check this out:

http://www.nachi.org/forum/attachments/f19/88597d1428750511-split-bus-panel-splitbuss.jpg

Why are there 4 wires going into the bottom from two separate breakers.
I theorized this just due to the fact that they wouldn't parallel breakers like that.
 

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Not really sure from your description but could it be an old 2-phase system? I still see them in use all the time in the Old City area of Philadelphia.

NVM....Ignore above....saw the picture....Now I understand what you are talking about. And No...I never say one with 10 spaces either
 

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I grabbed that pic off of a Google image search. I think they have it wrong.
I would like someone here that knows for sure, why we have two sets of conductors heading for the lighting section.
Its from this:

http://www.nachi.org/forum/f19/split-bus-panel-100328/#post1321572

Double split buss, they exist for some odd reason. I think it has something to do with being lower cost when using two 60 amp lighting section breakers then one 125 or 150 amp lighting breaker.

I have some pics of a CH, let me see if I find them.
 

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Discussion Starter · #14 ·

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Seeing Roger's pictures reminds me of something that I wonder every time I work in an older QO panel...why were the old style 2-pole 100-amp breakers so wide that they blanked off the 2 slots across from the breaker? Today's 2-pole 100-amp QO breakers are standard size like any other 2-pole breaker.
 
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