Electrical Wiring in the Home/Wiring Shed



I am running power to a shed in the Seattle, WA area.  Have permit but haven't been able to get questions answered by inspector before doing the work.  For reference, the enforce the 2008 NEC in my area.

I intend to run a 20 amp multi-wire circuit to the shed and split it off into two: 1 for lights/receptacles and 1 for a 1500w heater.

There is existing #4 wire running under the house that used to power a spa.  The spa is gone, but I would like to use the existing conduit and wire to save time and money.

Since a 20 amp breaker won't accommodate #4 wire, I want to splice short runs of #10 to the #4 in the panel box to make the final connection, but am not sure if that may be a problem.

On the other end, I want to connect #10 UF to the 60 amp spa disconnect and run it underground to the shed.  Here I'm not sure if using the spa disconnect is a problem.  I don't need it for over current or ground fault protection, but it sure is a convenient connection point.  Also, I believe a 20 amp circuit in this situation only needs to be buried 12" but I can't find a definitive answer.

In the shed I will install a 30 amp toggle switch to act as main disconnect and split the lines.  I will protect the receptacles with a GFCI outlet but don't think the heater requires GFCI.      

So my main questions are:
1)  Any problems with splicing #4 to #10 to connect to my breaker?
2)  Any problems with using a 60 amp disconnect as a connection point?
3)  Can I bury UF cable only 12" in the circumstances described?

Any thoughts or suggestions (on my specific concerns or other) would be appreciated.

Thanks,  CD


1) yes

2) yes

3) no

Let me know how far the shed will be from the old Spa disconnect and I'll address your other issues then.

BTW you will need a "trench inspection" when you do the UF in additon to a "final" inspection.

In other words the inspector is going to want to see how deep your trench is and what you have in it.


---------- FOLLOW-UP ----------

QUESTION: Thanks Bob,

The shed will be about 15' from the spa disconnect.  Straight forward enough to dig to 24" but the ground is all clay and rock and I thought (hoped) there was a single 20 amp circuit residential exemption if it was GFCI protected.

Do your yes answers to 1) and 2) mean "Yes, there are problems"?  If so, can you elaborate?  My plan B is to remove the #4 and spa disconnect and pull #10 through the existing conduit.

Thanks again for your help.



There is an exemption of 12" but the cable or wire has to be in pipe and it can only be for lighting.

Yes there are problems with those two questions. I will elaborate on that but first I need to know how many wires feed the 60 amp switch for the spa ? 3 or 4  In other words if its cable how many wires including the ground wire are there in the cable. Like wise if its conduit how many wires are in the conduit and is the conduit steel or PVC.


---------- FOLLOW-UP ----------


Thanks for responding so quickly.

There are four #4 wires running through 1.25" PVC conduit from service panel to spa disconnect(wire ends are color coded with tape: red, white, black, green).



Suffice it to say the first two options you mentioned you can't do and its not practical either. You don't want to terminate #10 gauge wire's on 20 or 15 amp devices that are designed for #12 or #14. You can't just tap a #4 wire with 10 and go from there. It has to be properly fused or in this case the right size circuit breaker needs to be use when going from one size wire to another. There are exceptions to this rule but they don't work here.

OK here's what you need to do:

Remove the spa 60 amp disconnect. Replace it with a 100 amp 20 circuit "main lug" panel. No need for a main unless you want one. HD or Lowes will have Square D QO or Home Line panels. The 20 circuit panel I mentioned is common, cheap and readily available there. If your spa disconnect is not protected from the rain you will have to use a "rain tight" (NEMA 3R) panel. A little more money but still inexpensive. You will need an accessory grounding block (strip) also readily available at HD or Lowes. This will screw into predrilled holes inside the panel in two locations. Pick the one thats best for the #4 green ground wire to reach it. You will also need the adapter lug that screws on the ground bar so you can terminate the #4. The rest of the wiring is simple. The white #4 goes to the "neutral block" where all the small white wires from the branch circuits will go. The black and red # 4 wires will terminate on the main power lugs near the top of the panel above the where the breakers will sit. You must also drive an 8' ground rod and run a # 6 black ground wire from it to the grounding bar inside the panel. Now you are ready to run your individual circuits to the shed. Run a 2" PVC conduit from the panel to the shed so you can pull in cables directly from the panel, through the pipe and go right to the things in the shed you want to power up. Instead of messing with #10 which is too big and clumsy you will be working with #12 or 14 gauge Romex cables.

You can do this another way if it suits you better. Locate the new panel in the shed and make a splice box where the 60 amp spa disconnect is. Still run a 1-1/4" PVC pipe to the shed and  splice out the #4's at the spa switch with matching #4's to reach the new panel in the shed. This is actually the simplest and most direct way to do it. But which way is better for you, thats for you to decide.  
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Licensed Master Electrician (32 years) 6165B Contractor in Closter New Jersey with 40 years total experience in Residential - Commercial - Industrial work. Emergency Service - General trouble shooting and repair work - ONAN & GENERAC generator installation - Paddle fans - Kitchen & Bath exhaust fans - AC lines - Smoke detectors - Telephone lines - Cable TV lines - Computer network cabling - Exterior lighting - Recessed lighting - Security lighting - (200 - 150 - 100 amp service up grades) - Electric Heat - New circuits - New appliance hook ups - and more ! FREE ESTIMATES 201-358-1552 Fully Insured


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"The Frank Williams School of Electrical Construction". My dear old boss is 100 ! and still going God Bless him. I started working for "Tenafly Electric" right out of high school at 19. He was tough but I learned more working for him in 8 and half years than most guys. We did mostly industrial work while doing some commercial and residential so I was fortunate to be exposed to all 3 areas of electrical construction. The guys I worked with were all good guys and I stay in touch with some of them still. Most of us went into our own buisness's which says something about the caliber of the guys I worked with. We had some interesting clients : Wella Corp. of shampoo fame, Farah Fawcett etc, I didn't buy shampoo for 10 years. It was a great place to work. Pan Am the former airline just before they went under, another great place to work, nice clean environment. C&C Metals, the largest button manufacturer in the US at that time, a not so clean environment but a very interesting place to work, lots of machine's cranking out buttons of all kinds but you had to be on your toes, it was a potentially dangerous place to be . All kinds of action going on around you.

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