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#50474 - 04/04/05 12:09 PM Question about mixing RNC & RMC...
DougW Offline
Member

Registered: 06/08/03
Posts: 1083
Loc: North Chicago, IL
specifically as physical protection for a service lateral.

Still working on the new service for the parsonage garage - getting yanked between the PoCo and AHJ. Business as usual I suppose!

The latest development: I had contacted ComEd and they had said that they could trench & place the run from the pole to the garage, but at a significant expense... mostly the trenching time. I JULIE's the site, and got the AHJ OK to trench. I called ComEd back to see if they could just drop the URD in the trench.

They responded that they had reviewed the site, and, since the majority of the property was commercial, I, as the contractor, would be responsible for placing the lateral, and that the AHJ would have the say-so on the conductors.

I priced out URD, and got a fair price from my local house.

Back to the AHJ - they said that the only folks who could bury a lateral (even 24"+) was ComEd, due to liability concerns. If the homeowner or contractor did it, it needed to be in conduit, either RMC/IMC (required for grade penetration & above) buried 18", or RNC at 24", with Cu conductors throughout. (bye bye affordable Al)

With 1 1/2" RMC @ $520/100', and 1 1/2" RNC @ $52/100', my thought was to combine the two - use metal for the risers and elbows at either end, and PVC for the horizontal run - the long and expensive part. I'm renting a trencher, so depth = extra labor isn't an issue.

My question is this - is an additional bonding means between the RMC elbow and riser at the pole and the RMC elbow and riser at the structure required? Should I sink grounding electrodes at each end to be safe? I can't find anything in the AHJ's electrical ordinance or the ComEd installation handbook, and I want to make sure I'm doing this run the right way. I've got calls in to ComEd and the AHJ, but I figured I'd troll for info here while I'm waiting.

Thanks for the help,

Doug

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#50475 - 04/04/05 01:01 PM Re: Question about mixing RNC & RMC...
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
If you maintain the metal raceway all the way to the cabinet at the load end and use bonding bushings it would seem you are bonded. You should be able to bond to the POCOs ground at the pole.
_________________________
Greg Fretwell

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#50476 - 04/04/05 01:14 PM Re: Question about mixing RNC & RMC...
earlydean Offline
Member

Registered: 12/22/03
Posts: 749
Loc: Griswold, CT, USA
Bonding to a ground rod is called grounding and does no good. 250.86 of the NECode requires isolated 90s above 18 inches of cover to be bonded to the grounding or grounded conductor to minimize shock hazards in the event of a fault. This can be accomplished most easily by extending the RMC from the 90 up to the metal enclosure at the building, and up the pole at the utility end. Grounding bushings and jumpers sized from 250.66 at both ends will complete the job.

It is far less expensive to install PVC 90s.
_________________________
Earl

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#50477 - 04/04/05 04:07 PM Re: Question about mixing RNC & RMC...
Active 1 Offline
Member

Registered: 02/22/03
Posts: 684
Loc: Grayslake IL, USA
Hey Doug,

I know some EC do the underground but I could never make it work dollar wise.

Like you said when the utility does the underground they just burry the AL sometimes undersized and they are done. For the EC to do it all different rules apply. It needs to be copper and in pipe. Conductores sized per NEC and inspected.

Last one I priced was something like this:
$2,200 ComEd does all underground work
$1,900 If we trench it 60' around trees
$1,600 If we trench, pipe, and back fill; they pull their AL wires
$1,000 If we trench, pipe, pull CU, back fill; they will run the wires up the pole and do final connections

Maby the numbers are off a bit but the point is if I bought the material, permits, rented trencher there was not enough left for the labor and proffit.

A subcontractor for ComEd told us when they do work for the utility they only have to meet the utility standards. When they do customer work they have to do what we spoke about above.

Yes, sometimes the utility yanks you around. When a job is proposed like this I believe it is assigned to a utility salesperson. They look at the job and try to get as much as they can. They don't seem to give you all your options or an honest answer.

The good news is when the utility does the work it is billed right to the customer on his electric bill. I just tell the customer what they charge is between you and the utillity.

Don't forget to figure going underground with the phone or cable if desired.

I know you can get 2" RMC for $50-55 or AL 2" RMC for $30. I want to say 1 1/2 should be in the $30 range.

What size service / conductors are you doing 100 amp?

If you need to use a ridgid or PVC bender or threader let me know.

Tom

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#50478 - 04/04/05 04:45 PM Re: Question about mixing RNC & RMC...
Roger Offline
Member

Registered: 05/18/02
Posts: 1779
Loc: N.C.
Doug, as stated, you can stay with metal after the 90's if you want too and use bond bushings or what ever it takes to assure a grounded conduit to the enclosures, or you can change back to PVC.

You won't need to bond the metallic 90's if the shallowest part of the 90 is below 18" from the surface, see 250.86 Exception No.3

I would definitely stay with a metal 90 at the end you are going to pull from to prevent burn through.

Roger

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#50479 - 04/04/05 05:52 PM Re: Question about mixing RNC & RMC...
Dave55 Offline
Member

Registered: 05/08/04
Posts: 666
Loc: Crystal Lake, Illinois, USA
I haven't checked lately, but my past experience is that ComEd can do it for less than I would want to. Especially nice is the fact that they will also be responsible for the installation. You wouldn't want to do this one over on warranty.

If you decide to do it, you might be able to glue the PVC together at grade, pull the wires through, then glue the PVC elbows on & slide it in the trench. That way there is no burn through & no bonding issue.

Dave

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#50480 - 04/04/05 06:46 PM Re: Question about mixing RNC & RMC...
Roger Offline
Member

Registered: 05/18/02
Posts: 1779
Loc: N.C.
Dave,
 Quote:
If you decide to do it, you might be able to glue the PVC together at grade, pull the wires through, then glue the PVC elbows on & slide it in the trench. That way there is no burn through & no bonding issue
unfortunately that is a violation of 300.18(A).

Roger

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#50481 - 04/04/05 07:15 PM Re: Question about mixing RNC & RMC...
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
Roger, that is why it is better to let the POCO do it. They don't care about the NEC.
We see 4/0 THHN in 2" here all the time, from the FPL sub. They do exactly what Dave said. They pull in the long straight part. cut it to length, then glue on the elbows and knock it in the trench with the Mini Kabota. Set the risers and backfill.
_________________________
Greg Fretwell

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#50482 - 04/04/05 09:11 PM Re: Question about mixing RNC & RMC...
DougW Offline
Member

Registered: 06/08/03
Posts: 1083
Loc: North Chicago, IL
Great responses, but I fear that I didn't illustrate my idea completely...

At Pole: 10' Above grade RMC
Additional RMC to get to 24" depth
Metal 90
Transition to PVC Sched 80 RNC
(40', 1 bend, (probably metal,
unbonded per 250.86 Exception No.3
and then another 18')
Transition to RMC 90
RMC riser to
Meter enclosure (or to bushed entrance that is bonded to service cabinet.

I know that attaching a chunk of the raceway to a ground rod is grounding - the question I had was if anybody thought it neccessary to run an additional bare 6 AWG Cu with the conductors that was attached to bonding bushings (or soldered per ComEd) at the metal riser at the pole and at the meter enclosure.

ComEd originally told me they'd do the work, and that's what I told my customer - apparantly someone's mind got changed. Good thing I told them to expect an additional charge for the service drop/lateral installation. My bid's just for tearout, the panel and interior conduit so far.

I was told because it's classed as "commercial", the contractor is responsible for running the lateral.

As folks here (and the AHJ) have said - the PoCos follow their own rules, because it's on them, liability-wise.

[This message has been edited by DougW (edited 04-05-2005).]

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#50483 - 04/05/05 07:16 AM Re: Question about mixing RNC & RMC...
Active 1 Offline
Member

Registered: 02/22/03
Posts: 684
Loc: Grayslake IL, USA
I would still think you would have the option of Com Ed doing the underground. They would charge you for this. Underground upgrades are not free. Maybe the problem is the customer wanted the lateral upgraded/replaced/repaired for free by the utility. The sales person tired of saying no gave an excuse of "we don't do comercial laterials".

Dave has a point about warranty. If the utility does the lateral they are responcable for maintaining it. It the EC does it then the customer is allways responcable for it.

If you want a utility sub to price it out try Trench-it in Lakemore, Il.

As far a RMC up the pole it's been done that way but is that what the utility wants you to do? They told me to end near the pole underground with no 90 and they will go up the pole with a wire guard. I see the wire guard most often.

As for on the merer side you did not say what the set up was. Make sure you don't pipe right into the bottom of the meter without a way for expansion. The old undergrounds were done this way. Some had an expansion pipe. Things move in the ground the wires become too short and things break. The whole idea of the underground meter raceway was to allow an "s" shape of slack for ground movement. So be sure to leave litle extra slack at the meter.

Tom

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