Dedicated 240 V. Sub Panel

[Mark Bosse]

This thread is scary.

Get an Electrician.

You will not save any money doing this yourself. At best, you are going to be re-doing this work (main breaker on a sub-panel, wrong wire size, wrong number of conducters, too small a panel for a work shop, incorrect ground electrode information (ya that ufer thing in the code) etc., etc.).

Who knows about the how-to details - do you know how do to this even if you finally get the rigt plan? Do you know how to connect MC, AC, NM plastic, romex ... There is something to being a trained mechanic. It is not all in the plan.

At worst, you will start a fire and, depending on your policy, go uninsured.

Get an electrician and save yourself some time and money. Not to mention legal trouble (like permits and insurance).

[Josiah Bartlett]

Ditto on this. I was going to install a 24-position panel in my shop but the electrician I hired to run the 100A service to my shop suggested a panel with 36 positions. Having that much space, I have several dedicated 220V circuits and many 110V circuits -- one per wall plus a couple of others.

Some panel types allow double pole breakers in a single pole slot. They cost more, though. You may as well get a bigger panel if it fits.

[Rob Russell]

Even though its allowed to use smaller neutral than hots, don't.

I have a 40 amp sub panel in my garage going to a 200 amp panel in my house. The sub panel had 20 amp breakers feeding four circuits. It also had a smaller neutral than hot, I think it was #10. I had some roofers working on the house and they plugged three air compressors into the garage circuits and fried the neutral. The breaker never tripped. Imagine my surprise when I went to turn on a motor and the lights got extremely bright and burnt out. The ground rod didn't seem to help. It wasn't bonded to the neutral in the subpanel.

There is nothing in the NEC that I'm aware of that allows you to run an undersize neutral. What we call the "neutral" is more properly called the "groundED" conductor (vs. the "groundING" as in Equipment Grounding Conductor) and neutral/grounded conductor is, by definition, a "current-carrying conductor". You can't undersize current-carrying conductors.

Your fried neutral/grounded conductor is a perfect example of that.

Also, you don't bond the neutral/grounded and equipment grounding conductor busses in a subpanel. The neutral/grounded is "floating" and is only bonded back at your service equipment, which will be either your main panelboard or at your meter panel - wherever your main disconnect is.

[Bill Arnold]

Some panel types allow double pole breakers in a single pole slot. They cost more, though. You may as well get a bigger panel if it fits.

The slim breakers for a single slot will give you two 110V circuits but won't work for a 220V circuit in a standard panel.