Ask Me Help Desk - 100 amp sub panel

Hey guys,

I would like to add a 100-200 amp /230-240 volt sub panel in my garage to power my welder <230v/50 amp> lathe<230volt/50 amp> as well as for general purpose 115-120volt 20 amp boxes. I also need 220/30 for a window AC unit.
Can I safely get 100 amps or even 200 into my garage with buried cable. Ill need about 60 feet of cable to get from the house box to the area Ive set aside for the box in the garage.
Also, can power be pulled from my house supply WITHOUT using a breaker at the main box. I was thinking of power out of the main box to a disconnect box, then from that disconnect to a new distribution box inside the garage. Am I way out for this idea? Id like very much not to interfere with my homes power supply if possible.

If this is feasible... what sort of wire would I need to feed to the garage?

BTW, I have NO plan of doing this myself; I just want to know some basic info before I get contractors out to bid on it. I like to be an informed consumer.

Best bet is to have a few different electrical contractors out to give bids and have them explain the way they would do it with your current set up. This way you will be an informed consumer. Good luck on your project.

Dak,

You really need to get the project sized properly.

Since the sub panel is intended for a remote building (Garage) there are many things to be concerned with. Here are some very important questions you have to answer.

You are more than likely to need an Electricial Permit and final inspection.

What is the amperage of the Main Service Panel? You don't want to pull 200 amps off a 200 amp panel.

Is there electricial service to the garage already?

If you are planing to do a straight 240 drop you are also in trouble. You really need to do a 120/240 run to the garage and you can use THHN/THWN or THHW (# 2 AWG copper @ 75(C) or #1 AWG Aluminium) insulated wire from the main panel to the sub panel. The run needs to be four wire and inside conduit. <Use T. 310.16 of the NEC Code to select the correct amperage sized wire.>

You can also use "USE" < # 2 AWG copper @ 75 (C) or #1 AWG Aluminum> or "UF" < # 1 AWG copper @ 60 (C) or #1/0 Aluminum > insulated cable for direct burial without using conduit.

Since it is only sixty feet I believe the # 3 AWG Copper or #1 AWG Al. would meet your needs.

Your sub panel needs to have 6 or less switches or a main cut off switch (to kill the sub-panel or a 100 Amp breaker for the sub panel.

If you plan to pull 200 Amp. Then the cable sizes will be larger as well as the conduit requirement.

Your electrician and size the bare ground wire if you place the conductors into conduit. If you use a cable, the ground wire is already there for you.

The sub-panel will need a EGC and at least one grounding rod. At the sub-panel you must make absoultely certain that Ground and Neutral are isolated from each other. The only place where ground and neutral are allowed to be in joined together (Bonded) is the Main Service Panel. (Editorial correction)

You should use a Black (Hot), RED (Hot), White (Neutral) and Green (Ground cable).

Inside the garage you will need to use either GFCI protected breakers or GFCI protected outlets. I believe that you run electricity to a garage, you must put in an outside light.

I'll have to verify that.

As stated in the previous post, I strongly suggest that you get bids for the work and that you require the electrician to pull the permit. If you gert the permit and the electrical inspector find problems or reason to red tag the project, you get to fix the problems.

If the electrician pulled the permit, the corections are his to make at his costs.

This one statement needs correction:

Quote:

Originally Posted by donf

The only place where ground and neutral are allowed to be in the same box in the Main Service Panel.

Statement is confusing and misleading.

Neutral and ground can be in the same "box", but must be separated, in other words, cannot be connected.

The neutral wire must be insulated and connected to the neutral bar, which is insulated from the panel metal box by insulating mounting feet.

The neutral bar shall not get "bonded" to the metal panel box, with the green screw or bare strap that comes with the panel.

The equipment grounding bar is bolted directly to the metal box, and only is for green or bare equipment grounding conductors.

One question that seemed to get missed, is, yes, the feeder to the garage must have a circuit breaker at the Main panel.