How do you wire an existing 240V circuit line as the feed to a new subpanel with 120V circuit breakers?

Answer 1

== == == == Warning that must be heeded Firstly, you MUST have 4 wires run to your sub-panel. If the existing feed was 3 wire (two hots and ground) you cannot get 110 Volts off it safely. If this is in an outbuilding, you may be able to get away with it. There are many ifs to that (more than I can go into, or even know), so you must talk to a licensed electrician first. No matter what, if your existing circuit only has 3 wires STOP! You must pull new wire or at least talk with someone licensed. Also, this is a big job. You are adding a whole new breaker panel to your property. Are you comfortable doing this? If not, hire someone. If you botch neutral you can burn up anything plugged into it. If you botch ground you can zap yourself. Planning, planning, planning Now, first things first. What do you plan to power with this? What will you power with this in the future? You must sit down and answer these questions as they determine the size of box and current rating of the feed. Remember the golden rule, you want your expected load to be 80% of the breaker size. So if you plan to draw 24A or less you want a 30A feed. 32A or less on 40A, 40A or less on 50A, etc... Is the existing circuit big enough? If not, you need to run new wire. Also try to determine how many breakers you want to put in this. That will determine the physical size of the breaker box you buy. Installing something oversized now is easy. Upgrading an undersized sub-panel 5 years from now is not. How to install For the scope of this how-to you only need to buy a new breaker box and a clamp. I strongly recommend going with the same brand as your existing panel (if still available) so the breakers will be interchangeable. For a sub-panel you shouldn't run into current limitations, but check just to be safe. Home Depot and Lowes carry a line of 6 position Square D panels that are inexpensive and good for sub-panels. Also buy a clamp to secure the feed wire to your new panel. If this is in an outbuilding that does not have its own panel already, you will need a ground rod. Beyond that, it is all downhill from here. Steps to follow * Shut the outlet off. (If you needed me to tell you this, hire an electrician. :) ) * Remove the old outlet and box. * Mount the new panel and secure the wire to the box * Remove any bonds or screws that connect the neutral to ground. Neutral can only be bonded to ground in the main panel. * Connect the hot wires to the hot busses of your panel * Connect the neutral wire to the neutral bus. * Connect the ground wire to the ground bus. If this panel is not in the same building as the panel feeding it, drive in the ground rod and connect that to the ground bus as well. * Recheck the torque on the screws connecting the wires you just connected. They must be tight. That's it! Your panel is installed. Now it's just a matter of installing branch circuits, which is not within the scope of this how-to. Website How-tohttp://www.electrical-online.com/howtoarticles/subpanel.htm BCLEAR. Note BCLEAR's link seems to be gone. You can still find it in the way-back machine over at archive.org. I found it after 11/6/2005 in their archive. Take a look, it's a good article.

<><><>

As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.

If you do this work yourself, always turn off the power

at the breaker box/fuse panel BEFORE you attempt to do any work AND

always use an electrician's test meter having metal-tipped probes

(not a simple proximity voltage indicator)

to insure the circuit is, in fact, de-energized.

IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB

SAFELY AND COMPETENTLY

REFER THIS WORK TO QUALIFIED PROFESSIONALS.