Sub panel question


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Old 12-19-13, 05:46 PM
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Sub panel question

Recently bought a home in foreclosure. Been checking everything out and have a question. It has a detached garage with a 100 amp sub panel, fed from the 200 amp main panel in the house. Wire appears to be 2 gauge aluminum, but there is only 3 feeds. Now if I understand it correctly this was allowed before 2008, but didnt it still require a ground rod? The garage shares no other attachment with the house, not even metal conduit. There is nothing but 2 hots and a neutral. Is this safe as is or do I need to install a ground rod?
 
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Old 12-19-13, 05:51 PM
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A ground rod should be installed. Make sure the bond screw is installed.
 
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Old 12-19-13, 06:24 PM
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A ground rod should be installed. Make sure the bond screw is installed.
OK, so the bond screw forms a connection between the neutral bus and the panel case... correct?

After that it will be ok to run my welder (220v 30a)? Didnt want to hook anything up yet and run the risk of frying equipment or myself. It looks like the previous owner used it successfully for some time just like it is. Glad I asked first, THANKS!
 
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Old 12-19-13, 06:33 PM
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OK, so the bond screw forms a connection between the neutral bus and the panel case... correct?
Yes

After that it will be ok to run my welder (220v 30a)?
Yes ...................
 
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Old 12-19-13, 07:48 PM
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Thanks for all the help guys, couple of things I want to add.

Of the 3 wires feeding the subpanel, only the 2 hots are insulated, the neutral/ground is uninsulated. It looks like a mobile home feeder cable, with the uninsulated neutral woven around the 2 insulated hots, all encased in plastic sheathing.

The subpanel is bolted to a metal girder, and the garage is all metal.

Does this change anything?
 
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Old 12-19-13, 07:51 PM
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If that is SE cable used underground you have issues. SE cable cannot be used underground. Can you post a pic?
 
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Old 12-19-13, 08:19 PM
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I hope to get back to the house next week and will take pictures. Yes it is SE, and it is in PVC conduit. Looks like im screwed...

So until I can pull a new 4 wire feed to bring up to code is it safe to use with a ground rod as is, less than 1 year?
 

Last edited by BobJ72; 12-19-13 at 08:46 PM.
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Old 12-20-13, 06:28 AM
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Yes it is SE, and it is in PVC conduit.
That must have been a fun pull!
 
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Old 12-20-13, 08:45 AM
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I don't know of any way to say if it will be safe to use for another year. I will leave it as it was never correct and should be changed.
 
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Old 12-20-13, 07:18 PM
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I understand and have decided to fix it immediately. What kind of wire would you recommend?

Running 100', underground in conduit or direct burial, feeding 100 amp subpanel. Although could drop back to 50 amp for significant savings. I probably won't use much more than 30 amps at one time.

Was looking at some at Menards, it's 2-2-2-4 aluminum feeder, all wires insulated and rated for direct burial. Its about $1.50 foot. Know of a cheaper or better option?
 

Last edited by BobJ72; 12-20-13 at 08:35 PM.
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Old 12-20-13, 09:34 PM
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The smallest of those is rated for 100A. I would pull individual THWN inductors in PVC, #6 with a #8 ground on a 60A breaker, to allow for a future upgrade.
 
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Old 12-21-13, 05:09 AM
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What size is the PVC conduit? That will make a difference on what size wire will fit.
 
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Old 12-21-13, 07:11 AM
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I believe it's 2", but will replace if neccesary.
 
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Old 12-21-13, 07:33 AM
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2" will be plenty big to run any 100 amp wire out there.

For 100 amps I would suggest using either #3 THWN (CU) (#8 ground) or #1 XHHW (AL) (#6 ground)

You could drop it down to 90 amps and use #4 THWN / #2 XHHW ,or 70 amps for #6 THWN /#4 XHHW.

To use these wires the conduit needs to be continuous between panels.
 
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Old 12-24-13, 07:45 PM
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Thanks for info, with 4 wire feed do I still need ground rods?
 
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Old 12-24-13, 08:08 PM
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Ground rods are needed even with the four wire feeder.
 
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Old 12-25-13, 11:53 AM
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with 4 wire feed do I still need ground rods?
Yes. In your subpanel, the grounds need to be tied together and bonded to the enclosure. The neutrals need to be tied together and isolated from all paths to ground, including the panel enclosure.

See Sub Panel Diagrams.
 
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Old 12-27-13, 09:56 PM
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Thanks for the help so far. I went ahead and ran 90 feet of 2/2/2/4 Al (listed as direct burial) in 2" conduit buried 18" to the 100 amp sub panel in garage. Neutral bus separated, ground bus grounded to box and going out to ground rods.

Now my next step is:
Run 10 120v outlets off a 20 amp breaker, first outlet being a ground fault, with 10/2 copper romex. Total run 70 feet.
Run 11 48" fluorescent shop lights with 10/2 copper romex on a 20 amp breaker. Total run less than 70 feet.
Run 3 240v outlets off a 50 amp breaker with 8/3 copper, total run 60 feet.

Does this sound OK?
 
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Old 12-28-13, 06:46 AM
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I would use 12-2 NM-B cable for the 20 amp 120 volt circuits rather than 10-2. 8-3 NM-B cable is limited to 40 amps, use 6-3 if you want a 50 amp circuit.
 
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Old 12-28-13, 06:48 AM
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20 amp circuits do not need #10 wire/cable. 12/2 is just fine and you will find solid #10 difficult to work with and terminate onto the devices.

The 50 amp circuit will require 6/3 for a NM-b wiring method. Why do you have 3 240 volt receptacles on the same circuit? Most cases these would need to be dedicated.
 
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Old 12-28-13, 08:22 AM
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No need or real benefit to using the #10 and harder to work with.
 
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Old 12-28-13, 05:35 PM
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Thanks once again guys for setting me straight. I used one of those online calculators where you put in the length and amps and it tells you the wire gauge. Only having to run 12 instead of 10 for the 120 outlets will save me some cash... that I will have to spend to upgrade from 8 to 6 for the 240 outlets. Maybe I will just drop back to 30 amps instead of 50, then I could use the 8 correct? Dont think I will ever need anything that actually requires 50 amps. And I will run separate breakers for every outlet as suggested.

Now to find a use for the 100' of 2/2/2 SE that I have now inherited from the previous install...
 
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Old 12-28-13, 06:27 PM
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Maybe I will just drop back to 30 amps instead of 50, then I could use the 8 correct?
If the #8 is NM cable (aka romex) it can be protected at 40 amps.
 
 

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