Just a little help please. A customer wants to use the existing wire that fed a irrigation pump to install a sub panel to supply 110 and 220 to new boat dock.
Question. How do I make this code? Do I drive a ground rod at new sub-panel and seperate nutral or do I add a transformer to create new neutral?
any suggestions?

how do you get 120/240 from a 2 wire cable

The irrigation pump is currently runing on 240. He wants to add receptacles. Thats my question? Do I need to install a transformer so the neutral will be correct. I dont want to use the bare ground as the neutral from the 10/2.

Just checking, does anyone have an answer for this. The inspector says that he will let me know if this is ok. he also says that the ground wire has to be an insulated conductor all the way from the source if used around water. The wire if 10/2 UF.

I just don't know of any legal way that you can do this. If you had three insulated conductors and there was no other metallic connection (water pipes, etc.) between the feed location and the structure where the sub panel is located, there could be some exceptions. A grounding conductor in a piece of 10/2 would not be considered to be an insulated conductor.

I don't even see how you could do this with a transformer while still maintaining the original circuit to the irrigation pump.

Sorry for the bad news, but it looks like the original UF is going to have to be replaced.

This is one of those classic "but it works" death traps that the untrained handyman types come up with. The short version:

There is NO substitute for good design, especially near water!

I run into this sort of thing all the time ... guy wants to cheap out, run as little wire as possible ... 'all I need is 220' they swear. Then. before the sod takes root, they wnat to 'make' 120 for 'just alight,' etc.

NO. NO. And again- NO. What part of 'NO'can they not understand?

Your 'service' is where your meter is. Period. Let the PoCo bring in just three wires.

YOU, on the other hand, get to run FOUR wires. A sub is a sub is a sub. Period. Plus, since you're adding a panel, you ALSO get to bang in a ground rod.

Which brings us to issue #2: Just what size panel? I can't say I've ever seen a 20 amp panel before. 20 amps is all you'll get, over any distance, with #10. Maybe even less.

Chances are, that UF isn't buried 2ft down either. So - do it right, or pass it by. Dig deep, run big pipe, and four wires. Expensive? Well, you get what you pay for. Had the guy designed well in the beginning, he would not be crying today.

What does he want to supply there? If this is just a lift and some lights, do it with 240. A am sure you can get a 240v GFCI and that is the only way I could sleep at night.
My guess is it could all be on 120v, small pumps can usually be switched, but you probably run out of amps.

Pardon if I misunderstand, but the problem is not that this UF lacks a ground, but that it lacks a neutral. I don't see any issue with feeding an isolation transformer from the existing cable, and using the isolation transformer to feed a new 30A panel.

The tricky question is not whether to drive a new ground rod, but whether it's safer to bond the neutral or leave it floating, which would reduce shock hazard. In this case, I don't think code gives us an option; the neutral must be bonded. As it's a separately derived system, there is no issue with bonding the new neutral and existing #10/2 UF ground wire to the new ground rod.

Edit: oops, missed the statement that the inspector wants the ground wire to be insulated the entire way back to the source if used by water. Unbroken is a good point, that's a safety issue... but why insulated? What code requires the ground wire to be insulated, and why would UF (in which, the ground IS insulated) not be considered insulated? Driving a new ground rod and installing an isolation transformer seems to make both these objections rather moot.

Steve I would disagree with you on the point that the bare wire in 10/2wg UF cable is considered an insulated conductor. Article 200 makes it quite clear that a wire of this gauge used as a neutral must be colored white or grey the entire length and the bare conductor don't get it. As for the xformer approach that could work. Under the '05 NEC you can still run a feeder to a "Structure" and not include a neutral and an EGC but under the '08 that would be an issue. So depending on your definition of a "Structure" his only choice is a xformer.

Isolation transformer? I might go along with that for the control circuit for the motor controls, but that's it.

If nothing else, he simply doesn't have the power available.

True, we're not on-site, and cannot know all the details. Yet, as my earlier post suggests, I've seen this scenario all too many times. I suspect that many borderline compromises were necessary for the OP to get painted into this corner - and there's a world of difference between 'code compliant' and 'good design.' Those poor choices have finally caught up, and are no longer adequate.

If he does anything - panel, transformer, whatever - to make the location have more than one circuit, he has a separate structure that requires a 4-wire feed. Especially with the revisions in the 2008 NEC, that's what he needs. He also needs a ground rod.

Off on a tangent ..... one of my 'wish list' items is a nice, little, very quite generator. Just enough for a tool and a light. Premium models sell for about $800. If this guy's needs are truly that little, such a generator will solve his problem, and for a lot less than installing a transformer, replacing his feed, etc.

George,
I was not intending for him to use the ground as a neutral, only as a ground. You don't need a neutral to an isolation transformer; a new neutral is derived on the transformer secondary.

Also... you can't do it with Romex, but isn't the ground in UF encased in gray insulator? Looks to me like it meets the letter of the law! (j/k!)

Reno,
If the existing run were 480V 1-phase, and he wanted to step it down to install a 240/120V panel, would any of us have any issues at all feeding a panel off off this circuit? An isolation transformer is no different. Shoot, carolina_elect might have to step this up at the house to 480V anyhow just for voltage drop. A 480V feeder would let him feed a 60A 240V panel from this #10 wire, too.

I see this as an economic/design choice, not a code issue. An isolation transformer is safe and acceptable to feed a panel if it's uneconomical to replace the feeder cable.

A 5 KW isolation (not an auto transformer) transformer 240 volt primary and 120/240 secondary center tapped and ground the centerpoint should be compliant. The supply bare wire is a bonding conductor not a ground wire. A new ground at the second service. The new neutral has a bonding jumper installed so the service and new system are bonded together. I don't know why the inspector would need the bond wire to be insulated.

Caveat My answer is based on the CEC but the NEC requirements should pretty much match. Technically this works and is safe.

Steve I guess I was thinking of the options and got them mixed up. Hey- It happens. Thanks for making that neutral/ground thingee clear.

I'm reading in the NEC at 340.108 and 340.112 and 340.116 of the '05 edition and I get the impression that the bare conductor is not considered as insulated but only as contained in the sheath which doesn't qualify as an insulated as described in 340.112. IMHO I know there is something in the UL white book about the insulation on NM cable conductors and the sheath but I can't really find anything along those lines for UF cable.

As for approaching this as a xformer application, with a 240v. supply to the primary and a 120/240v. secondary he could use a 7.2KVA xformer if they made such a thing and it may or may not be adequate. He would need a grounding electrode (probably a rod or two) and sub panel with a main in it.

Thanks Guys for the input. This was my first post. I know there are sub panels every where that only have a three wire feed (two insulated conductors and a bare ground).
I also know that code now requires a forth wire or seperate ground. I was asked for the most economical way to use this existing conductor. The transformer idea was the only way I could think of to create a neutral and still have the seperate grounding conductor. Just wanted to see how this post thing works.
Reno: Not all people are handymen tring for the cheap way out. Some are people trying to think out of the box, keep the price down, make money and do it safe.
The inspector also called back and said he had no problem using the transformer as long as article 682 guidelines where followed. I am still concerned that the feeder grounding wire is bare and not insulated and by this wire being in uf cable does this make it insulated?

I think I found the answer to my last question about the 10/2 w/ground. look at article 250.32 2008 code and then 250:118. Am I correct that this bare wire can be used to feed another structure. or transformer.

Was an interesting question for a first post
I believe the "insulated wire" requirement is for a grounded conductor, AKA neutral. In this case, it will not be used for a neutral, and will be used only to bond the two grounding systems together. I can see no reason why it would matter if this conductor is grounded or not.

I know I made a tongue-in-cheek comment about it, but I would not consider the bare copper wire in UF to be insulated.