wiring a sub-panel

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Old 02-07-10, 11:01 AM
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wiring a sub-panel

Hi, I am considering replacing my "old style" sub-panel box in my garage and updating it to a modern breaker box. I'm not really interested on bringing more amps to the garage at this point, but just want to update it to something better. It currently has 40 amps brought in from the main panel via a 240 line that has 2 hots, a common, and a ground. I have some electrical experience and know how to use a multi-meter for troubleshooting, etc. Is something that would be easy to do? There are currently 4 circuits out there, each on a 30 amp fuse (seems odd). I would try to keep the four circuits if possible, or just make 2 20 amps circuits (which seems to make more sense in my mind). Any suggestions would be greatly appreciated. Thanks,
Chris
 
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Old 02-07-10, 11:10 AM
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The existing circuits are over-fused if they are general lighting and 120v receptacles. What size wire to the garage and distance?
 
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Old 02-07-10, 01:05 PM
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the distance to the garage from the main panel is probably 30 feet. I'm guessing it is 8 or 10 gauge, but no markings on the casing. Casing is dark grey.
 
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Old 02-07-10, 01:14 PM
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Here is a picture of the existing box. I know, it's pretty scary.
http://www.flickr.com/photos/boedeke...es/4338827398/
 

Last edited by boecycle; 02-07-10 at 01:15 PM. Reason: picture didn't load
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Old 02-07-10, 09:21 PM
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Originally Posted by boecycle View Post
Here is a picture of the existing box. I know, it's pretty scary.
DSC02438 on Flickr - Photo Sharing!
It looks like by the wires on the top this panel is also being double fused.... we have a few of these older panels in buildings and that the lugs on the top side of the range fuses are meant to go to a range not meant to have power fed into them....therefor if there are fuses in the main side and in the range side the panel is double fuses....of course if the correct size breaker is in the main panel that part might not matter

looks like you have 8 gauge wire.. should be simple to change your panel if you have a 4 wire feed from the main and you will need to isolate your neutral and ground....also you will most likely need to add a new ground rod... and last a few cables on the bottom look like they the insulation on the conductors is fryed....make sure its not brittle good luck
 
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Old 02-08-10, 06:19 AM
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Thanks for the feedback. Would you just recommend 2- 20 amp circuits? I think I understand what it means to "double fuse" in my current box. It seems like a weird practice. The reason that all this started was when I blew a fuse the other day and replaced it with one I found in the garage. A day later, it blew again and kind of melted the 60 amp "shotgun" style fuse above it. Other than being a pain, it seemed a little unsafe, so I think it will be worth it to update it. Thanks again for the help.
 
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Old 02-08-10, 06:55 AM
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I suggest splitting up the circuits so that each have their own breaker. Also buy a panel that will allow you to have some open spaces for future.
 
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Old 02-08-10, 08:48 AM
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So, can I keep the four circuits that are existing and put each on its own circuit? For some reason, that doesn't seem to make sense to me if there are only 40 amps going to the box. I guess if you are not running all circuits at the same time, it would work. My mind is telling me 2 20 amp circuits with a main 40 amp breaker.
 
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Old 02-08-10, 09:23 AM
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The four circuits will give you greater flexibility. They will not use any more power that being combined into two circuits.
 
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Old 02-08-10, 03:23 PM
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does what i told him sound correct guys? Im ad Hvac guy and a farmer and follow code and try to give the best advise
 
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Old 02-08-10, 03:31 PM
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Originally Posted by braether3 View Post
does what i told him sound correct guys? Im ad Hvac guy and a farmer and follow code and try to give the best advise
Hard to tell from his picture what is fused and how, but like you said, I doesn't matter much since it is getting replaced.

Your other info is pretty much spot on.
 
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Old 02-08-10, 04:27 PM
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Thanks for all the help. I plan to rewire it some time this week.
Chris
 
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Old 02-08-10, 05:03 PM
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Just to sum up for you use a panel large enough to give room for future breakers. A 100 amp panel with 100a main breaker is very common and may be a good choice. The 100a main breaker only acts as a disconnect so size is OK. You need a 40a breaker at the main (service) panel and three #8 wires and at least #10 for ground.

No general purpose 120v breaker may be greater then 20 amps. Because this was a fuse panel I suspect the garage may have been wired with #14. If that is true it must be replaced with #12 for receptacles and 20 amp breakers used. A GFCI receptacle or breaker must be at the beginning of the run. Lighting if on #14 must use a 15 amp breaker.
 
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Old 02-08-10, 07:43 PM
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Ray, thanks for the summary. I checked a book out from the library today, and it also helped explain some of the theorys that I was not grasping. It looks easy enough. Good advice for the GFCI outlet first in the series. I think it is #12 wire in the garage. It will all get replaced soon enough, but for now I think the box is a priority. I hope I can get a grounding rod into the ground. I live in Montana. Thanks again.
 
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Old 02-08-10, 07:56 PM
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If you can't get it in the ground now, it can wait till spring.
 
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Old 02-09-10, 08:48 PM
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Originally Posted by Tolyn Ironhand View Post
If you can't get it in the ground now, it can wait till spring.

just dont put it off till next winter after spring comes and goes...
 
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Old 02-09-10, 09:57 PM
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If you can get a warm enough day to get down a few inches for eight feet you can bury it horizontally till spring.
 
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Old 02-11-10, 01:45 PM
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We all forgot to mention that when you install your breakers weather you get a 6 space or 8 or whatever size panel make sure you balance your load so you get an even MWBC multi-wire branch circuit. a 20 on the red .. put the other 20 on the black... 15 on red other 15 on black... they don't have to match identically but that will help you from blowing the breaker in the house if you have a high load.. with your set up you could pull 80 amps 120 (40 amps 220) if it was totally balanced because the power flows hot to hot....the neutral connects the loads and carries any unbalanced load back to the other panel or and the transformer

Anyways... just try to balance it out best you can based on what you know gets plugged in where and how much its used. You can always go back and move a breaker later
good luck
 
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