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MEC 02-08-2009 09:52 PM

How to install sub panel in detached garage 70' away
 
I think I am learning the right things needed to add a Sub Panel in my garage. My house panel is currently full (200 Amp service) so I would have to put in some half breakers to open up two positions. I have to go 40' inside my house before I go out and underground. Would it be cost effective to run indoor wire to a junction box then splice to the direct bury kind? Being that I am going 70' outside, should I not run ground wire but instead put a ground rod in at the garage service entrance? With this distance in mind, what guage and type wire should be used for a 60 amp service? What if I decide to go 100 Amp service. With a full house panel and a 200 main, I have two central AC units, electric stove and many houshold circuits. Is the addition of the 60 or 100 amp sub panel pushing the limit?
Thanks for any advice someone can provide to me.

jamiedolan 02-09-2009 12:19 AM

Quote:

Originally Posted by MEC (Post 227437)
I think I am learning the right things needed to add a Sub Panel in my garage. My house panel is currently full (200 Amp service) so I would have to put in some half breakers to open up two positions. I have to go 40' inside my house before I go out and underground. Would it be cost effective to run indoor wire to a junction box then splice to the direct bury kind? Being that I am going 70' outside, should I not run ground wire but instead put a ground rod in at the garage service entrance? With this distance in mind, what guage and type wire should be used for a 60 amp service? What if I decide to go 100 Amp service. With a full house panel and a 200 main, I have two central AC units, electric stove and many houshold circuits. Is the addition of the 60 or 100 amp sub panel pushing the limit?
Thanks for any advice someone can provide to me.



Use pvc conduit for the full run. You must use rods and run a ground wire to the service equiptment per nec 08.
There is no way anyone can give you a serious answer about your capicity with out much more detailed information about your appliances.
Jamie

ACB Electric 02-09-2009 04:30 AM

what kind of run do you have from your exit point to your panel? that will make sence of the use of conduit or to use romex and a large JB at the exit point, a #6 or bigger wire is not really something that should be joined with a marrette, crimps or splitbolts are a much more secure conection if you are going to make a joint.
there is really no reason not to go 100 amp other than cost, it can only be benificial, if you ever need it, personally I would include a ground wire in the pipe as well as drive a ground rod. If your going to use direct burial wire go the full distance with it, one less joint in the line is one less point for potential problems in the future.
based on your mesurements you have 110 feet is that the exact total? including droping underground and coming up into sub and into main? based on 120 feet (adding 10) you will need to use a #4 wire for 60 amp or a #1 for 100 amp (copper) to stay within the limits of allowable voltage drop.

MEC 02-09-2009 08:56 AM

ABC - in response to your questions -

based on your mesurements you have 110 feet is that the exact total? Total to the box woulds be more like 140'.

Can you put direct bury cable in conduit?

I will be using conduit at the points of entry to each building.

220/221 02-09-2009 09:30 AM

Quote:

Being that I am going 70' outside, should I not run ground wire but instead put a ground rod in at the garage service entrance?
You need both. They serve different purposes.




Quote:

Is the addition of the 60 or 100 amp sub panel pushing the limit?

It depends on what you plug in :laughing: The panel draws nothing.



I always advise against direct burial as it's vulnerable to damage from digging, backfill and rodents. If you want to use it, use 6/3 for 60A.

What we generally do is run NM cable thru the house and switch at a j box to conduit and individual wires (three 6's and a 10 ground) in a 1" PVC conduit.

ACB Electric 02-09-2009 05:31 PM

Quote:

Originally Posted by MEC (Post 227618)
ABC - in response to your questions -

based on your mesurements you have 110 feet is that the exact total? Total to the box woulds be more like 140'.

Can you put direct bury cable in conduit?

I will be using conduit at the points of entry to each building.


if your using direct burial wire where it emerges from the ground it should have mechanical protection so yes you can slip it through a conduit, make sure that it fits loosely in the pipe and use a bell end underground so as it is not copresed against a sharp edge. and be sure wire is set so that settling or ground movement wont put a strain on it in the pipe. as 220/221 mentioned direct burial wire is easily suseptable to damage , if you have rocky soild or any debris you may want to consider conduit all the way, or you can run the direct burial in some pvc duct or the flexable corigated pipe (we call it "big O), go oversize for ease of pull like 3 inch. but be sure thats allowed in your area, it is something we do up here and its well accepted. as for the pipe emerging from the ground I personaly would go with a 2 inch as the LB will have enough space to make the turn with direct burial wire so as not to overbend or kink it. by time you do all that you could be just as well off to run pvc all the way and pull in the size wires you need in individual wires and either pipe directly to the main panel if its an easy run or JB and splice in a romex to the main panel. I have personally done it both ways, all depends on the situation.


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