Adding new service and sub pannel to a detached Garrage


Old 05-11-07, 10:43 PM
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Adding new service and sub pannel to a detached Garrage

I am changing out a 2 #12 awg circuit underground run to my detached garrage with a single 3 wire, #4 copper, run in new 2"conduit to a new subpannel. I have put in two 8 foot ground stakes at the detached garrage and connected them and run them into the building.

Do I need to run a fourth wire for ground or should I run this new ground, from the two rods, into the nutral bus on the new sub pannel?

Are there service length and insulation trim back requiremennts for junction boxes?

Do I install all the parts and call for inpection before conecting wires or fully complete the work leaving the boxes openand and call for inspection before switching on the main supply?

Do I need a main disconect in the 6 place sub-pannel or will the disconect in the main pannel in the house be enough?
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Old 05-12-07, 01:05 AM
Join Date: Aug 2005
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I highly recommend pulling in a 4th wire for ground. There are special conditions which must be met for a 3-wire service and it keeps you from adding metal water pipes or other metallic paths at any time.

There should be an inspection schedule with your permit. Do you have a permit?

Do you mean jacket length of Romex showing when you said "insulation trim back"? I'm usually at a half-inch. If there's a specific length needed, I'll have to look it up. Others here will know.

If by "service length" you are referring to the overall length of the wires in each box, they must be long enough for 6" to be able to stick out of the box, but that is a minimum; you'd be better off shooting for 8" as your minimum, even if you wind up cutting two inches off later.
Old 05-12-07, 08:03 AM
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Yes I have a permit but I'm in Washington State and I got the permit 'on line'.
There is one inspection (I additionally paid for a second) which I must call in for.

I will run a #8 ground from the main pannel in the house.

Sounds like I will need an independant ground bus within the sub pannel for the ground line from the main pannel.

What do I do with the wire from the two new ground stakes?
Old 05-12-07, 10:31 AM
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the new ground stakes get attached to the ground bus.

re; the ground wire size

it is based on the overcurrent device for the circuit it is for. with #4, you could be could be up to a 85 though.

the ground also has to be upsized if the power conductors are upsized for voltage drop.

So, in either case, regrdless what breaker/circuit size you are actually running, because of that, you need to run a #6 ground.

length of conductors; actually you need a minimum of 6 inches from where they enter the box. If the opening of an outlet, junction, or switch point is less than 8 inches in any dimension, each conductor shall be long enough to extend at least 3 inches outside the opening.

re; trim back of insulation

if you speak of Romex (NM), (I don't do much but i believe the rules are) the outer insulation is to extend into the box around 1/4 to 1/2 inch but no more (it takes up a lot of space).

If you speak of the insulation areound the metal conductor, this would be determined by the requirement of the device you are inserting it into. generlly most devices require 1/2 to 3/4 inch of exposed insulation abd in the case of wirenuts or such, you do not want to have exposed bare metal when you are done.
Old 05-12-07, 10:36 AM
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forgot a few things

disconnect; yes, you need one at the subpanel but since it is only a 6 space panel, it would itself suffice as such. You are allowed to have a max of 6 disconnects grouped together that will be allowed as the disconect.

inspections; unless you are required to have a rough in before you close up a wall or such, you should install everything before the inspect.

DO NOT power anything up until the inspector gives you the ok. Leave things open to aid in the inspection.
Old 05-16-07, 03:06 AM
Join Date: Feb 2007
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I also live in Washington State and just completed a sub panel using existing 4-2 (with ground) AL wire. I got my permit online, and passed my inspection on Monday.

If you're splicing your #4 wire in a metal J box, you must ground that box as well.

Yes, you should run a 4th wire for ground. I didn't have that luxury, so I got to pound 2 8' ground rods outside the house. I also had to ground the panel to the copper plumbing so the main panel would know if there was a short. Do not run the ground and neutral together at the feeder (sub panel). The ground and neutral are together at the main panel, but they must be separate at the feeder.

Absolutely use #6 for the ground.

Have a "Main" breaker at your sub panel that matches the one at the main panel. Make sure you get a retainer clip for that breaker in the sub panel so it cannot be inadvertently pulled out.

As stated, hook everything up, leave all breakers in the "off" position, and leave it all open so the inspector can, well, inspect.

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