need some help with a 100 amp sub panel

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  #1  
Old 03-05-16, 11:27 AM
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need some help with a 100 amp sub panel

I want to install a sub panel to my shop, the sub panel will be about 200 feet away from the main panel the main panel is a 200 amp service, would a 100 amp service be enough I will have a welder running off if it that draws less than 30 amps ad 240v I have a compressor running off of it not sure of the amps over head lights and probly about 5 110v outlets in the shop. What size and type of wire wpuld I need to go from the sub panel to the main panel and if ypu could think of anything else that I would need Thanks
 
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Old 03-05-16, 01:00 PM
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You can run a whole house on 100 amps so a shop should be fine. Your receptacles will be 120 not 110. If this is detached you will need to run conduit with four individual wires buried 18" or cable direct buried at 24". Best practice is to not run cable in conduit.

If detached shop at the shop you will need a 100 amp main breaker panel and a ground rod. Most panels do not come with a ground bar so you will need to buy and add a ground bar. The panel neutral bar will not be bonded to the panel so the bonding strap or screw will not be used.

At the main panel you will install a 100 amp breaker. Wire size depends on type used and whether copper or aluminum but it will be #2 or larger except for the ground wire.
 
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Old 03-05-16, 02:13 PM
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For a 100A feed to your shop I highly recommend 2/0-2/0-2/0-1 aluminum Mobile Home Feeder (MHF). I also highly recommend you use PVC conduit where buried even though MHF is direct bury rated. It does have to be in conduit where inside the structure. 200ft is a long run and this size feeder is needed to prevent any possible large voltage drop. You could go with 2-2-2-4 MHF but the max you should go is about 70A at that distance.
 
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Old 03-05-16, 02:29 PM
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Note mobile home feeder can not be run into buildings unless it is dual rated. Basically that means if the individual wires are not marked as a type of wire that can be used in building it can't enter a building.
 
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Old 03-05-16, 03:03 PM
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Mobile Home Feeder is rated as RHH/RHW-2/USE_2 and can be installed inside the structure, but does need to be in conduit. Do not confuse MHF with URD. URD is just USE-2 and is not rated for inside and must be terminated outside of the structure.
 
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Old 03-05-16, 04:07 PM
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Thanks for the clarification.
 
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Old 03-05-16, 04:33 PM
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Is a screw needed to secure the 100 amp breaker to the main box? I'm not clear when a screw is needed and when is not.
 
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Old 03-05-16, 04:59 PM
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No. Example is if a main lug panel is used as a subpanel and you install a back fed breaker to be used as a main breaker then that breaker needs a retainer clip. The breaker back in the primary panel feeding the subpanel is not considered as being a main breaker and does not need a retainer clip.
 
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Old 03-05-16, 05:25 PM
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More detail. A retainer is used if the breaker would have electrically live metal parts if it came loose from the breaker box as would be the case with a back fed breaker.
 
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Old 03-05-16, 05:33 PM
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OK, NOW it makes sense ...thanks guys.
 
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Old 03-06-16, 01:55 PM
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Thanks for the info the panel I have is a square d home line 125 amp panel with 100 amp breaker is that good or should I get something else also I'm still a little confused on how I make my connection at the main panel in the house
 
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Old 03-06-16, 02:16 PM
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I have is a square d home line 125 amp panel with 100 amp breaker is that good
If it has an enough spaces and you mean a 100 amp main breaker.
I'm still a little confused on how I make my connection at the main panel in the house
You install a 90 or 100 amp breaker in the main panel.
 
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Old 03-06-16, 03:19 PM
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the panel I have is a square d home line 125 amp panel with 100 amp breaker
That's good if you're talking about 125A panel with a 100A main breaker already installed in the panel for the subpanel.

I'm still a little confused on how I make my connection at the main panel in the house
The feeding double pole breaker in the main panel is installed just as any other branch circuit breaker. The two hots go to the breaker and the neutral and ground connect to the neutral/ground bar. You will most likely need to buy large lugs to connect the ground and neutral to the bar in the main panel if using wire large enough for 100A. Just remember that the neutral is to be isolated from the ground in the subpanel.
 
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