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Old 06-23-2010, 06:03 PM   #1
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240 volt circuit and 120 volt circuit to shed


My neighbor wants to wire one 240 volt circuit and one 110 volt circuit to his small shed, about 30 feet from his house. I suggested 1" PVC conduit 18" underground, with 3 each #8 THWN wires (red, white, black - very old style ungrounded 240 volt equipment, so no provision for ground) for the 40 amp rated 240 line, and 3 each #12 THWN (red, white, green) for the 110 volt 20 amp rated outlet. Three questions:
1) Does this sound like the correct conduit size, wire size, and conduit depth?
2) Does the shed need a separate disconnect panel inside the shed, or are the cords from the appliances inside the shed sufficient "disconnect" ?
3) Does this installation require "derating" (i.e. larger wire size required) due to underground location? This is in southern Arizona?
Thanks.

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Old 06-23-2010, 06:13 PM   #2
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240 volt circuit and 120 volt circuit to shed


You can't run 2 seperate circuits to a detached structure
As far as I can tell with the power needed he would need to run a sub panel
Best bet is probably a 60a sub

Derating (voltage drop) depends upon the distance

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Old 06-23-2010, 06:18 PM   #3
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240 volt circuit and 120 volt circuit to shed


I thought this might have to do with sharing a neutral, which is why I recommended separate neutrals for separate circuits.
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Old 06-23-2010, 06:25 PM   #4
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240 volt circuit and 120 volt circuit to shed


To have both 120 and 240 volts at the shed or other separate building you must run one combination 120/240 volt circuit aka multiwire branch circuit. (It has two hots, one shared neutral, and one ground).

To have more than 20 amps of 240 volts or more than two 20 amp subcircuits of 120 volts you must have a subpanel out in the shed.

Thirty feet to the shed would not need de-rating; use #6 gauge wires (copper) for 60 amps.
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Old 06-23-2010, 06:33 PM   #5
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240 volt circuit and 120 volt circuit to shed


So, any thoughts on how to wire this? 60 amp 240 volt panel in shed? What size wire/conduit, etc.? Can the 60 amps be supplied by a 60 amp breaker in the house circuit panel?
I am not clear on the multiwire branch circuit, if both circuits have separate conductors supplied by separate circuit breakers (separate branches) in the main house panel. For example, what if two separate runs of conduit provided power to the two separate circuits?
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Old 06-23-2010, 06:41 PM   #6
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240 volt circuit and 120 volt circuit to shed


You need to run a feeder out to a subpanel nounted in the shed, not two circuits. The circuits will be split in the subpanel.

Check this sticky for a better idea of the process.

Stubbies Diagrams and other stuff
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Old 06-23-2010, 07:47 PM   #7
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240 volt circuit and 120 volt circuit to shed


So, one circuit (240V or 120V) can be supplied to the shed with the only disconnect being the circuit breaker in the main service panel, and no sub panel or ground rod needed in the shed - correct?
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Old 06-23-2010, 07:52 PM   #8
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240 volt circuit and 120 volt circuit to shed


One circuit

OR a MWBC
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Old 06-23-2010, 07:57 PM   #9
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240 volt circuit and 120 volt circuit to shed


Under 2008 code you need the fourth wire for ground.
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Old 06-23-2010, 08:29 PM   #10
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240 volt circuit and 120 volt circuit to shed


I would use the green wire for ground, to ground the 110 volt (GFCI) circuit. The old 240 volt equipment has no provision for equipment ground.
So, if the shed were physically attached to the house - just run conduit for all conductors to the outlets in the shed - correct?
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Old 06-23-2010, 08:48 PM   #11
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240 volt circuit and 120 volt circuit to shed


Suddenly the shed 30' away is connected to the house?
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Old 06-23-2010, 10:07 PM   #12
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240 volt circuit and 120 volt circuit to shed


Not saying the shed will be connected to the house, just asking the question - looking for the answer, exploring options: virtual "duplicate service entrance" sub panel in the yard shed, with double ground rods, etc., vs. running cable in conduit on the wall of the existing building. I have never had a high powered shed myself - couple of high powered cars though
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Old 06-24-2010, 12:31 AM   #13
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240 volt circuit and 120 volt circuit to shed


Fortop.,

To make it simple ., Nope you must have one circuit which it will be MWBC going to the shed and you can have big as 60 amp with 16mm˛{ #6 AWG } THHN/THWN conductors in the conduit and by the way it must run full 4 conductors { Black , Red , White and Green } and with subpanel keep the netural and ground seperated on subpanel and install the main breaker in there that is your main disconnection for your subpanel.

For conduit depth it will need at least 18 inches { most area will ask for 24 inches anyway }

and for 120 volt recepetals it must have RCD { GFCI } protection and I am pretty sure that will included the luminaries as well { the 2008 NEC code stated all 120 volt circuits}

240 volts no it not need RCD unless you are dealing with pool pump { that will be diffrent ball park of game to deal with it }

But really I will recomend that you do the load demand to make sure it will handle the addtional load without issue.

No., you do not need to derated the conductor size due you are very short distance from the load centre.

Merci.
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Old 06-24-2010, 06:07 AM   #14
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240 volt circuit and 120 volt circuit to shed


Quote:
Originally Posted by fortop View Post
So, one circuit (240V or 120V) can be supplied to the shed with the only disconnect being the circuit breaker in the main service panel, and no sub panel or ground rod needed in the shed - correct?

Quote:
Originally Posted by fortop View Post
I would use the green wire for ground, to ground the 110 volt (GFCI) circuit. The old 240 volt equipment has no provision for equipment ground.
So, if the shed were physically attached to the house - just run conduit for all conductors to the outlets in the shed - correct?
Absolutely not. You cannot combine the 40A 240v circuit with the 20A 120v circuit.

You MUST install a sub-panel in the shed to do what you want.
You need a 50 or 60 amp feeder (60 will be better).
You need a sub-panel with a main disconnect.
You need a ground rod (or two) at the shed.

The 240v circuit does not have, require or need a neutral. Just two hots and a ground. If the equipment does not have a ground, I'd find a way to get one on it.
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Old 06-24-2010, 08:29 AM   #15
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240 volt circuit and 120 volt circuit to shed


Thanks everyone for the responses.
I was not suggesting combining a 240 volt and 120 volt on one circuit - I was asking about either one 240 volt OR one 120 volt circuit as an option to avoid the separate sub panel with disconnect in the shed. I was asking what would one 240 volt circuit or one 120 volt circuit require at the shed.
So, I see 3 options:
1) 1" PVC underground conduit 18" minimum deep, with #6 wire (4 insulated conductors - red, black, white, green) supplied from a 60 amp breaker in the main house service, with 2 ground rods driven in at the shed, with 60 amp sub panel in shed, containing one 60 amp main breaker, one 40 amp breaker for the 240 volt equipment, and one 20 amp breaker for the 120 volt GFCI outlet. The manufacturer of the 240 volt equipment specifies red, black, white (neutral) with no ground - but rig up another ground to the equipment frame anyway.
2) Eliminate one circuit at the shed. Have only one 240 volt or one 120 volt circuit at the shed. Supply the one circuit from a breaker in the main house service (240 volt 40 amp, or 120 volt 20 amp) with separate insulated conductors in 1" PVC conduit 18" deep (4 conductors for 240 volt,or 3 conductors for 120 volt. No sub panel or separate disconnect or ground rods needed at the shed.
3) Forget the detached shed. Attach the shed to the side of the house. Run 1" PVC conduit with 4 #8 conductors for the 240 volt circuit and 3 #12 conductors for the 120 volt circuit. Attach conductors to appropriate 240 volt outlet and 120 volt outlet in the shed.
Do I have this right? Thanks.

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