A customer has a 10-2 circuit ran out to his shed.

Is there a legal way to turn this existing 10-2 circuit into a sub panel?

I thought awhile back I read a post where someone did something similar. And if I remember correctly the inspector failed it but it was legal by code.

Well, yes and yes.

First would be to make it a 120v panel, jumping the hot to both lugs. Works fine as long as you don't need 240v. Wire as a sub-panel, with ground and neutral separated.

Second would be as a 240v. feed, using the bare as a combined neutral/EGC, as in the main panel, and the neutral/ground jumper used.

This requires no other conductive pathway (water pipe, coax-cable shield, etc.) between structures, as well as a driven ground at the shed.

Better hurry on option 2. I understand that method is going to dissapear in 2008.

Gfretwell, you are correct; the code comittee has accepted such a proposal. Comments are now being accepted.

Now, to be a little fussy about the idea....

Jumpering from one lug to another; well, make sure to replace the lug with one intended for two wires!

Now... 10-2 as a feeder. Doing load calcs at 3 watts / sq ft, you have plenty of capacity for almost any residential garage that is used as a garage.
There's the rub! In my cynical view of things, sub-panel = garage being converted to somethng else.
If they're planning to make a little apartment, they'll need 100 amps, not 30.
If they're planning to make it a workshop, you'll have to do further load calcs.


The advantages of another wire are immense. Indeed, I'd rather see 14-3 than 10-2!

Now.... how is the wire geting out to the garage? If this is a detached garage, romex is out, as it's not suitable for the application. UF is possible.
I am biased in favor of pipe. If I were doing this, I would run a vastly oversized pipe- at least 1" PVC. I'd also bury it DEEP- at least 2 ft. Call me paranoid. The larger pipe makes it easy to run larger wires later, and the cost increase is minimal.

Oh, and last (but not least)... you'll want a disconnect switch on the outside of a detached garage.

Reno- I question wether or not you'd need 100a. for an apartment. Based on the definition of an apartment found in Websters. As for the disconnect, it could be a 30a if the load did not exceed 2 circuits. If it were more than 2 circuits it would need to be probably 60a. See 225.39 Also should be SUSE rated. See 225.36. As for location it could be either inside or outside the building. See 225.32

Reno, a wire-nutted pair of pigtails would also suffice, no?

Larry, I am uncomfortable with the use of wire nuts on a feeder. I tend to think of 'feeders' along the same lines as 'services,' and would prefer not to have such a splice... even if it is technically 'legal.' Mabye I'd feel better about using NSI's.
Oh, and kudos for reminding us that a panel would mean a ground rod was required!

George, I seem to recall the code specifying a minimum 100 amp service to each "residence". That would mean 100 amps per apartment.

The main point of my earlier post was to underline the need to be clear as to exactly what the intended purpose of the sub-panel was. All too often, I've seen folks try to "finesse" things, and be unhappy with the result. Might as well do it right to begin with!

[This message has been edited by renosteinke (edited 06-18-2006).]

Reno- I'm having trouble accepting your statment


I don't see where you need a 100a disconnect for an apartment and I'm looking in the code and all I find is the need for 100a disconnect for a "One-Family Dwelling".

Apartments are a different type of dwelling and are part of a multifamily building.

We are talking about a separate structure, aren't we? I cannot see how, if converted into a residence, this would be anything but a "single family" residence, or more! I don't see how it could be called 'part' of the main residence.

Perhaps that distinction would hold, were we talking about converting an attached garage into a dwelling. But, in this case, the separation is a major factor.

I will admit that my first post, describing how I would like the job done, went beyond 'code minimums.' Some of this is preference; some of it is response to my not knowing just what the shed will be used for.

We have a practical sort of "catch 22" here. Almost any use of the shed, as a shed, can be quite nicely served by a single multi-wire circuit. Almost any other use, requiring a panel with multiple circuits, is going to need more than what 10-2 can deliver.

I guess I was hung up on your use of the word "apartment" and didn't want people assuming that apartments require 100a. feeders automaticly. The examples in the back of the book kinda show that. Interestingly enough if it is a single family dwelling supplied by a "Service" it must have minumum 100a Service Disconnect and 100a. Service conductors feeding it. After the Service disconnect if you were using fuses, you could use smaller fuses and conductors if they were adaquate to supply the load. 230.79

If the single family dwelling (not an apartment) is fed with a feeder instead of a Service the Disconnect must be 100a and the conductors feeding it only need to be large enough to supply the load and be potected at their ampacity. 225 39

Larry,
What code section permits the use of the bare conductor as the grounded conductor for this application?
Don

Don, I think that the method Larry suggested is more the result of poor diting in the code, than any specific intent. Lacking any metal conduit, or other means for a 'parallel path,' some have been making the panel at the detached building a "main."

Otherwise, to play "devils' advocate,' where does it say the grounded conductor needs to be insulated? I see plenty of places where the code say "...the grounded conductor, IF insulated...."

John,
Look at this.
Where is the section that says this grounded conductor can be bare?
Don

Don, you make a very good point. I agree with you that the "Grounded" conductor needs to be insulated. There are 2 place in the code that I found that allows the "Grounded" conductor to be "covered"one is 250.140. The other instant is for Service Conductors as found in 230.41. But your correct about the "Grounded" conductor. Looks like Trick440 is stuck with a 120v. sub panel

Wow guys thanks.

And the background on this 10-2 wire is... It was used for a Jacuzzi that is long gone. It will now be turned into a 110v sub panel, to power a 110v pool pump.

Don..lest we get too far off-topic... 200.6 starts off with "An insulated grounded conductor...," leaving open the possibility that a grounded conductor might not be insulated. Indeed, nost services have bare grounded conductors.
Section 200 returns to this several times when discussing the marking of grounded conductors; it always leaves the door open for the grounded conductor to be bare.

Closer to topic, a few issues back, the IAEI presented the scenario -power to a second building- to three of it's experts, and got four answers!

Let's have a little race.... first one to find the part of the ROP that would require a separate ground in this situation will go to the 2008 forum and start a thread! :-)

I'm with the " neutral grounded only at the service " crowd.

I'd use the 10-2 strickly as a 120V branch feeder. I'd use a dinky sub-panel to permit breakout loads such as lights.

If the only load is a pump, I'd land the 10-2 on a smaller breaker (20A) and use as is. I wouldn't even set a sub-panel.

Original question was: is it OK to install a sub-panel using existing 10/2 feeder?

Section 225.39(B) allows a 30 amp feeder to a structure or building if not more than two 2-wire branch circuits are connected to the sub-panel.

Section 250.32(B)(2) allows a three wire 240/120 volt feeder without an equipment grounding conductor, provided that a grounding electrode system is installed.

Assuming the 10/2 is UF and the UF is run directly to the service panel, the uninsulated (but covered) #10 conductor will be connected to the neutral bus. This becomes the neutral (grounded conductor).

I see no requirements for the grounded conductor to be insulated in Article 200. In fact, throughout Article 200, numerous mentions of "the grounded conductor, where insulated, ...". Which leads one to assume that the grounded conductor need not always be insulated.

Sounds like it would not be a problem to use 240 and 120 volts at this shed.

250.32(B)(2) causes plenty of these type of questions. I always put it in the same category as the old dryer/range 3 wire rule. I agree with Phil Simmond's proposal that killed that one "The war is over" run 4 wires. Thanks Ryan.

earlydean,
John,
That may be true, but absent a specific provision for the use of a bare or covered grounded conductor, there would be a violation of 310.2(A).
Don

Trick440,
IMO there would be at least two violations in doing this.

1)This is not one of the wiring methods allowed in 680.25(A) for a feeder to a pool equipment panel. It doesn't sound like it meets the exception, since it is not an existing feeder, but rather an existing branch circuit, and the panel will be new.

2)Using the bare conductor as an equipment ground would violate the requirement in 680.25(B) that the equipment ground be insulated. Again, the fact that it is not an existing feeder seems to elimitate any exception to that rule.