Question about an underground splice

12 years ago

Folks,

We're replacing a 600 square foot shed/barn. The old one had 220 supplied to it, from the house, via a 150 foot-long three-wire underground 4 gauge cable in a PVC tube. The old feed went into the building in a PVC tube that runs about 5' up the side of the building. The wire is aluminum. The new building will be located about 6' away from the old one. This means I need to do something to "stretch" the wiring. I'd like to (somehow) bury a splice from the old Al wire to a run of new Cu, and run the new Cu in PVC to the new building. We only need 30 amp 220 service so the 4 gauge should be fine. We will have a building permit and inspections.

Questions:
- How can I do the Al to Cu splice in a manner that's code compliant and underground?
- Should the splice be in a box of some sort? What sort?
- The feed to the building will be in a PVC pipe running vertically up the side of the building. My amateur reading of the code seems to suggest this needs to be 8' high before entering the building. That seems odd. How high must it be before the pipe enters the building?
- My on-line reading suggests that we should have a 4-wire run from the house to the barn (hot-hot-neutral-ground). Is this a code requirement? I'd hate to have to re-run the entire cable.

Thanks so much, in advance, for your insight.

Jack

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Comments (4)

Ron Natalie
12 years ago
You'll need to put it in a box and use a connector that is approved for both aluminum and copper (these are typically terminal blocks with a bolt for each conductor). I've seen direct bury splices otherwise, but only for copper-to-copper connections.

There's no requirement conduit run up the building 8' (at least not in the electrical code). There's no requirement at all.

How many conductors that are run to the barn depends what the load is out there. If you have a subpanel, you do need four. There used to be an exemption to permit you to run only three if you had no other metalic connections (pipes, phone wires, etc...) between the buildings but that has been removed from the code.

If you have more than one circuit (to include both sides of a single MWBC) then you MUST have a grounding system at the other structure as well.
weedmeister
12 years ago
Just a learning question: If the load(s) in the barn are 220v only, is a neutral required? Or would that be penny-wise and pound foolish?
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bus_driver
12 years ago
Ron, time does not permit immediate research of the conduit height question. 300.50(c) does require protection from the burial depth to where the conductors enter the building.
I recall years ago that we used Sunlight Resistant UF on the exterior surface of residences with conduit protection on the portion that was within 8 feet of the ground, the remainder of the cable was exposed. It was a quick cheap way to add circuits in existing houses. Looked like crap but some customers wanted the lowest price possible. 300.5(D)(1). I think that 300.5(D) (2) was added later.
Ron Natalie
12 years ago
If there are only 220 loads, you might get away without a neutral, but practically I don't know of any 220 ONLY panels available and I would not trust that someone won't stick in a single pole breaker to their detriment.

Cable (like UF) coming up out of the ground needs to be protected where exposed up to 18", but that's NOT what he was talking about, he was talking about conduit emerging from the ground and entering the building. THere's NO, ZIPPO, NADA, NOTHING that says it can't be an inch or twelve feet.