Feeder in same trench as SE?

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jeff43222

Senior Member
I did a service upgrade a couple months ago (overhead to underground), and the HO recently contacted me and said the PoCo will be out tomorrow to run the new service wires to the meter. HO has asked the PoCo to leave their trench open so I can use it to put in a UF feeder cable for the detached garage. I don't know of anything in the code that prohibits doing this, but I've never been asked to do this before, so I'm not sure.

I'm hesitant at this point, mainly because the PoCo wires will be coming in from one corner of the property next to the alley, but the garage abuts the other corner of the property. Even if I did this, the UF feeder would only make it about halfway to the garage, and another trench would have to be dug from the PoCo trench to the garage to get the feeder to it. I really don't want to do any digging/trenching near the PoCo's live wires.

Suggestions?
 

jeff43222

Senior Member
Theoretically, the PoCo lines will be 36" deep, but in this case the alley/garage/pole are about a half a story above where the house is situated. Given that, and the fact that I've seen some less-than-stellar work done by the PoCo in cases like this, I wouldn't count on the lines being that deep.

Either way, I'm going to have to arrange for some trenching, and I don't see how using the PoCo's trench really helps much. We're talking about a city lot, so the distances are relatively small.

And I'm pretty sure UF cable needs to be 24" down. :D
 

dnem

Senior Member
Location
Ohio
The only code issue I can think of is bundling. I saw some slides in a continuing ed class that was showing over 3 direct burial wires needing to have a small amount of space between conductors so as not to have to derate.

If the UF isn't in direct contact with the USE then there's no derating issue and no other issue. I'm assuming that your USE is on the load side of the last transformer and is energized at house voltage.

The only other burial issue you might find is a gas company restriction on the spacing between their nat gas lines and any electrical.

David
 

jeff43222

Senior Member
Around these parts, the PoCo puts in the wire from the pole to the meter, and I have no idea what kind of wire they use. The last time I looked, the markings didn't match any of the wire types in the NEC. I'm assuming their stuff is listed in the NESC, of which I know absolutely nothing.

I hadn't considered the bundling/derating issue. The PoCo wires would be on the load side of their last transformer and energized to around 120-125V/phase.

To avoid gas-electrical conflicts, gas comes in from the front of the house, while electric comes in from the back or side. I've never seen a case where gas and electric came in from the same direction, but I'm sure it happens every now and then.
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
Hey Jeff,

Working in the same area as you a couple thoughts come to mind.

There's the real possibility that the service lateral installers will use a pnuema-gopher instead of cutting a trench. Unless pre-arranged in the Overhead to Underground Conversion Contract, the installation technic and tools used will be up to the PoCo crew that is assigned the job. . .it may even be subcontracted to a non-PoCo entity.

Back when I was in St. Paul I did what your client is asking for, on my own place. I ran PVC at 18" over their lateral. The timing of the Open-Trench-Inspection is a likely source of delay, as well as a liability concern on the part of the PoCo (liability for them, having cut the trench then leaving it as a potential ankle breaker).

If there is no trench (in the case of the pneuma-gopher) then the installation has to be worked out to the satisfaction of the AHJ without an "Open-Trench-Inspection". . .I've not tried that one yet, so I don't have any idea how that would work out.

Also, in my experience, the PoCo around here rarely gets their line down below 24". The PoCo pulls in, at no additional cost, Telco and Cable conductors if they are provided at the job site by others before their work begins. The PoCo installs these additional utilities with, and against the service lateral. I am not surprised that they will pull in the UF also.

But, they are not the one who has to get the inspection completed by the AHJ.
 

hillbilly

Senior Member
I'm with you jeff...I would let the POCO do their thing and I would do mine, on my own schedule.
If hitting their line is a concern, you can use RMC or IMC and bury it 6" deep (18" under the the driveway). Surely the POCO will bury deeper than that. Be sure to call first before you dig.
steve
 

jeff43222

Senior Member
I'm not sure how they are planning on running the lateral, but it will be interesting. The alley is about 4-5' above the grade where the house sits, and the homeowner has installed a large concrete pad next to the garage, so almost the entire back of the lot is taken up by the garage and the pad. the only place the PoCo can go underground is in a narrow path next to the pad.

I don't know that they would pull UF through a bored hole. This is speculation based on the homeowner's suggestion. I've had inspectors let a previous underground installation (HO did it before I was called in) pass without a trench inspection if I dug a hole and verified the depth, but I don't want to try to get them to approve a covered cable I installed since they know that I know better.

Since the garage doesn't need anything beyond basic power, the plan was to run a single 20A circuit with UF. The depth issue is a problem, though, if the PoCo doesn't go deeper than 24". Cost would be an issue if I put the whole thing in conduit.

My gut tells me that I should just do the garage without regard for what the PoCo guys are doing. I think that route would involve the least hassle and lowest cost.
 

pete m.

Senior Member
Location
Ohio
It's interesting that the commentary to section 230.7 in the '05 handbook states that:

"All feeder and branch-circuit conductors must be separated from service conductors. Service conductors are not provided with overcurrent protection where they receive their supply; they are protected against overload conditions at their load end by the service disconnect fuses or circuit breakers. The amount of current that could be imposed on feeder or branch-circuit conductors, should they be in the same raceway and a fault occur, would be much higher than the ampacity of the feeder or branch-circuit conductors."

Of course 230.7 deals with raceways and cables, not direct burial installations, but if the concern as shown in the commentary is the reason to keep branch circuit conductors and feeders separate from service conductors why couldn't this same condition exist in an underground installation where the service conductors and the branch circuit or feeder conductors are in contact with each other?

Anyone care to weigh-in?

Pete
 

jeff43222

Senior Member
In theory, it sounds like good rationale for keeping them separate, but the wording of 230.7 is fairly clear and doesn't list trenches. Also, since the trench in question is being filled with PoCo cable, all bets are off since the PoCo is under the NESC.

This time around, though, it doesn't matter. I advised the homeowner to tell the PoCo crew to do their normal thing and not leave the trench open for me.

As for only having to go down 12" with GFCI protection at the source, that would work great, except that the HO told me in the same e-mail that she thinks her husband wants 240V in the garage. So much for 12".
 
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