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Old 08-09-2010, 02:45 PM   #1
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Wire feed to Detached shop


Shop is approximately 125' from main panel. My question is which wire type would be best suited for my need, 8/3 awg UF or 4 individual THWN wires? If THWN, what would be the size of each wire? Both would be trenched in PVC. 60 amp double pole breaker in main feeding 55 amp max in sub panel.

I was set on using the 8 awg uf until I saw another post with using THWN as an alternative.
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Old 08-09-2010, 03:05 PM   #2
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You're going to have a rough time finding UF cable in Iceland.
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Old 08-09-2010, 03:13 PM   #3
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Not really sure as to what gave the impression I was from Iceland.
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Old 08-09-2010, 03:13 PM   #4
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Not really sure as to what gave the impression I was from Iceland.
Since you didn't put a location I figured I would take a shot in the dark. Was I close?
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Old 08-09-2010, 03:19 PM   #5
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I filled in my "about me". Weren't anywhere close. I am located in the greater Memphis metro area. Which means, just on the other side of the city limits in MS.
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Old 08-09-2010, 03:37 PM   #6
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Great. That changes things since I don't know much about Icelandic electrical code. Now we know that our recommendations should be based on the NEC, but you are still responsible to check with your local inspector to see what year of the code they adopted and if there are any state or local amendments.

So let me ask you a few questions about your situation.

Are you sure 60Amps is enough for your shop? It's easy to change now, but much harder and more expensive in the future so do the load calc correctly.

What do you mean when you said "55 amp max in sub panel"? The sub panel needs to be rated for at least 60Amps if that's what you are feeding it with. Do you plan on putting a smaller breaker in or something? Mind you, this panel will need a ground rod driven in by the shop.

Where did you get the information telling you to use #8 UF for 60Amps?

As for your main question, you should run 4 individual THWN's. But there are a few more issues here that we could deal with after we get a bit more info.
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Old 08-09-2010, 11:37 PM   #7
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Quote:
Originally Posted by Jimmi View Post
Shop is approximately 125' from main panel. My question is which wire type would be best suited for my need, 8/3 awg UF or 4 individual THWN wires? If THWN, what would be the size of each wire? Both would be trenched in PVC. 60 amp double pole breaker in main feeding 55 amp max in sub panel.

I was set on using the 8 awg uf until I saw another post with using THWN as an alternative.
Let clear up few myths first.,,

The conductor size you chose is too small for that distance and load capicty

Second thing where you come up with 55 amp rated subpanel ??
I know there is no 55 amp subpanel at all.

The only time I know you got the 55 amp is reading the ampcapicity chart that is not really correct for this useage anyway due the underground conduit you have to use 75C chart not the 90C chart at all that is restricted for derating only

If you want full 60 amp going to subpanel you will need 16mm { #6 AWG } THHN/THWN conductors that will give you very reasonable voltage drop for this distance but if you going to use the UF cable you will have to bump up to 25mm { #4 AWG } and both listing is copper but if you going to use alum cable you have to bump up one size larger no question asked.

Yeah you will have to sink two ground rods down in the ground at the subpanel location and keep the netural and grounding conductor seperated at the subpanel.

And the conduit you will have to buried at 24 inch deep unless stated otherwise with your local codes.

Merci.
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Old 08-10-2010, 04:40 AM   #8
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Originally Posted by frenchelectrican View Post
.... the conduit you will have to buried at 24 inch deep unless stated otherwise with your local codes.

Merci.
Marc
What code are you working with here? I routinely bury conduit with 18" cover in these parts ....
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Old 08-10-2010, 08:10 AM   #9
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I didn't say the sub panel was rated at 55 amps. Thats all that it has in it currently. The shed was already wired by previous owner. It's just new to me. I had it moved to my house. But I was thinking of adding 2(separate) dedicated 240v 20 amp outlets for a table saw and miter saw. That would make it a total of 95 amps if all used at the same time. But seeing how I am only one person, I can't operate that many machines at the same time.

I used a wire size calculator for the #8 size wire. I already knew about adding the two grounding rods from the 2008 NEC code. My city is still on NEC 2005. But I am going to talk to the inspector when I pull my permit. I have did the same when I built my bonus room. Catch them early in the morning at city hall before they start their day.

I am just replace the panel all together cause after really looking closer at it last night, it has the neutral and grounds tied together on the same bus. I don't think the previous owner had any grounding rods and only used a two wire feed with unshielded ground.

This is just a hobby shop, not an actual woodworking shop. 4 regular outlets, 2 4' florescent lights, and a ceiling fan. Wanting to add above mentioned 240v outlets for saws and that's about it.
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Old 08-10-2010, 08:12 AM   #10
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Oh yeah, I was thinking of going in between 24" and 30" incase any ground work was to be done at a later time. I have a trencher, so that will be the easy part.
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Old 08-10-2010, 10:21 AM   #11
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I think the Op added up the equipment or breaker handle ratings to come up with the 55 amps.

To the OP, adding the breaker handle ratings has little relevance to panel capacity. Often times the panel will have 2-3 times what the panel is rated for if you were to add up the breakers.

Since you are only using one machine at a time the 60 amp feed will probably be enough. You can only run one circuit or a feeder to the shed. You cannot add additional circuits from the house out to the shed.
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Old 08-10-2010, 11:34 AM   #12
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I'd oversize the wire to be able to feed 100 amps. Who knows what you may want there someday? Window air conditioner? Beer Fridge?

Just don't combine too much beer with the miter saw
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Old 08-10-2010, 12:08 PM   #13
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Quote:
Shop is approximately 125' from main panel. My question is which wire type would be best suited for my need, 8/3 awg UF or 4 individual THWN wires? If THWN, what would be the size of each wire? Both would be trenched in PVC. 60 amp double pole breaker in main feeding 55 amp max in sub panel.

I was set on using the 8 awg uf until I saw another post with using THWN as an alternative.
8/3 G UF is only good for 40 amps. It is a cable that is restricted to the ampacity of a 60C insulated wire.

Go back to the french electricians post for your wire size to provide a 60 or 70 amp feeder to the shop.

I agree with you a 60 amp sub panel sounds good for your needs. the panel will likely be a 100 amp rated panel which you will feed something less than that.

I wouldn't give up on the existing panel in the shed unless it does'nt provide enough breaker positions for your branch circuits. The neutral and ground bonded can usually be rectified by un-bonding the panel and adding a grounding bar. If the panel is 'service equipment only' then if you run a 4 wire feeder you will have to change panels. 2005 NEC code allows you to run three wires to a bonded panel but you need to know the exceptions and local code requirements before deciding to do that. 4 wire feeder allows you to have other conductive parallel cable paths with the feeder out to the shed like tv...so if you want that it can go in the same trench with proper separation.

You have a trencher so I would definitely run pvc conduit with individual wires of thwn. You saved $ by having your own trencher so conduit is better and easier to make an upgrade in ampacity if ever needed.

If you use copper 6/3 G UF-b you can have this cable rated 55amps 60C on a 60 amp breaker in the main panel.

If you use copper thwn 6 awg in conduit you can have these wires rated 65 amps 75C on a 70 amp breaker the main panel.

If you use aluminum wire (like USE-2) for the feeder you need #4 awg rated 65 amps on a 70 amp breaker.

The breaker is allowed to be sized up to the next standard size for your application because there are no 55 or 65 amp breakers in standard sizes.

You need grounding electrode(s) at the shed.

You need a service rated disconnect at the shed nearest the point of entrance of the feeder. This can be satisfied by a main breaker panel or a backfed breaker acting as a main with hold down kit. There are a few other options as well. Some local jurisdictions allow 6 disconnect rule, .. if there are no more than 6 movements of the hand to shut of all the breakers in the panel, ... thereby removing all power to the sheds branch circuits, to serve as the required disconnect. Or remote single enclosure disconnect with mlo panel somewhere in the shed.

Neutral and ground bonded if 3 wire feeder

Neutral and ground un-bonded if 4 wire feeder
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Old 08-10-2010, 09:55 PM   #14
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Quote:
Originally Posted by kbsparky View Post
What code are you working with here? I routinely bury conduit with 18" cover in these parts ....
I used with the Wisconsin electrical code and they useally required non GFCI circuits to be buried at 24 inches down but I know some local area do allowed 18 inches.

But in France it will be min of half meter down about 18 inches or so.

Merci.
Marc
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Old 08-11-2010, 08:00 AM   #15
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Stubbie, are you sue about those ampacities?
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