On 3/16/2010 7:12 AM, Mike Marlow wrote:
Bill wrote:


Some of what I've learned since I read Lew's post the first time:

Evidentally, a load center is "Main Lug Only" when it doesn't have
it's own main breaker like the primary load center would probably
have.
Load Units, such as made by Eator Cutler-Hammer use descriptions such
as "12 spaces, 24 circuits".
If I learned part of my lesson yesterday, the only way you'd get 24
circuits would be to use 1 Hot
and a 1 Common for every circuit.

In 120v circuits you would always use one Hot and one Neutral, plus a ground
for every circuit, so if what you are trying to say is that you can only get
24 circuits by wiring only for 120v, then you would be correct. You get 24
branch circuits by using mini breakers instead of full size breakers.
Mini's will give you two breakers in the space of one. Each half of a mini
gets wired the same way as a full sized breaker - a hot wire to the breaker
and the neutral and ground to the respective buss bar(s).

Mike is spot on as usual.

There is one gotcha to watch for when using a 220 c'bkr in a load center
which, by design, can be used with both full size and mini breakers:

When using these load centers it is possible to insert the full size
220/240v c'bkr into two adjacent slots that are both fed by one hot leg
.... the result being that you will get no voltage to the tool whatsoever.

Nothing dangerous will result, but you'll be left scratching your head.

Basically, just be careful when you install a 220/240v c'bkr that you
put it in two adjacent slots where each draws from a different bus. You
can do this visually.

On new houses I've even had licensed electricians do this (hopefully
accidentally) on more than one occasion. It is a PITA to be called on a
Thanksgiving morning when everything but the oven on a dual fuel stove
works. DAMHIKT

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Last update: 10/22/08
KarlC@ (the obvious)