Wiring a shed

Windows

I am working on wiring my newly constructed shed for interior and exterior lights and a few outlets. I am permitted and spoke with the inspector today briefly but still have a few questions.

I am doing UF-B cable and was planning on running a single circuit because I did not want to mess around with a sub panel in the shed. THe inspector told me I would be allowed to run 2 circuits without needing a sub panel providing that each circuit first ran to a switch once it reached the shed. The idea I gather then is to have a switch on the 20 amp circuit inside the shed that will control all of the outlets downstream, and then do I need a similar switch before the 2 light switches (one for interior lights and one for exterior) or do the switches for the lights themselves perform that function? Sorry if this is an idiotic question. Thanks for the help.

andrew79

strange, i've never heard of requiring a switch, might be best to ask the inspector.

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ryan50hrl

I would assume the one switch would be sufficent as its a way to turn off power to the fixtures......but ya, i'd ask the inspector....

rjniles

Inspector is wrong or you misunderstood. Only 1 circuit to an outbuilding. That 1 circuit can be a 15 or 20 amp MWBC ( multi-wire branch circuit). This will give you effectively 2 circuits. It must start at a 2 pole breaker in the house. If you use UF cable it must be 14/3 or 12/3.
The switches are provided as a means of disconnect at the shed.

Do you really need 2 circuits?

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Location:
Coastal South Carolina

stickboy1375

You need a disconnect at the structure...

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Windows

I think this is what the inspector must have meant. He seemed pretty with it but I could tell that explaining things was not his strong suit. THanks for clearing that up and to the others for confirming the disconnect. It would be easier if I just could run a single 20 amp circuit. I am going to run six 75 watt (max) potlights, a 200 watt low voltage lighting transformer and three outlets that should see very occasional light duty work. In terms of load one circuit would be sufficient but I was not sure if it was kosher to have lights and outlets on the same circuit.

rjniles

Your total load is under a 1000 watts, a single 20 amp circuit is plenty. Lights and receptacles can be on the same circuit. Another advantage is that if you provide the required GFCI protection at the house, you only need to dig your trench (burial depth) to 12".

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Location:
Coastal South Carolina

AllanJ

For a single 20 amp 120 volt circuit, the disconnect at the shed can be an ordinary light switch (heavy duty 20 amp model).

For a double 20 amp circuit (multiwire branch circuit) a double pole heavy duty but otherwise ordinary light switch can be used.

For a shed that is large enough to be made into a workshop at a later date, it is suggested that a heavier multiwire branch circuit (10-3 or even 8-3 cable) be run. For starters it can still be wired to a 20 amp breaker set at the house panel in which case no subpanel is needed in the shed (yet).

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Jim Port

If you run the xx-3 cable you can have a single circuit while retaining room for expansion later without needing to dig again,

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Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.

Windows

I ended up with 100' of 12/3 UF-B this afternoon - more by circumstance than anything else, but I feel good about how it worked out - it's already in the ground and buried. I am pretty familiar with many of the electrical basics, but I only recently heard the phrase 'multi wire branch circuit' for the first time, so now I have some reading to do. Thanks again for the help. I am sure I will be back with a few more questions.

AllanJ

Multiwire branch circuit -- Two hot wires share a neutral (using 12-3, 10-3, 6-3, etc. cable) and can be used as if they were two independent circuits (some limitations apply). Those two hot wires (typically red and black) must be connected to a double wide double breaker with handles tied together and positioned in the panel so as to fit onto two fins (stabs) that measure 240 volts between them.

If you only need one circuit you can leave the red wire taped off at both ends and connect up black and white as an ordinary 120 volt circuit on a single breaker for the time being.

Usually a MWBC that needs ground fault circuit interrupter protection is equipped with a (double; 240 volt) GFCI breaker at the panel. You can feed any number of GFCI receptacles with a MWBC but separate 2 conductor cable is needed to continue GFCI protection to additional outlet boxes without their own GFCI receptacle units.

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The disadvantages of crab apple trees. In summer, the apples are too sour to pick and eat. In winter the birds come and leave dropping all over the place.

rjniles

Although you can use cables larger than #12 to reduce voyage drop, a MWBC feeding general purpose receptacles and lights is limited by code to 20 amps.

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Location:
Coastal South Carolina

Windows

I have a quick followup question -- If I have one circuit running to my shed for both outlets and lights, do I need to protect the lights portion of the circuit as well with a GFCI outlet upstream, or just the receptacle portion? THanks

electures

Lights do not have to be GFI. Only receptacles. If you GFI protect the entire branch circuit from the house out to the shed, it only has to be 12" deep.

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All responses based on the 2011 NEC.
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Windows

Last question... I hope. ALmost done - inspector coming tomorrow. I capped the red wire in the first j box in the shed, and the other end of the red wire gets capped inside the breaker box itself. That's correct? Thanks again for the help. It's been a great project.