passed final inspection

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  #1  
Old 06-18-01, 09:13 PM
Able Sashweight
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Last Friday the city electrical inspector gave final approval my handywork to upgrade and relocate the service entrance. Hurray! He asked me if I was an electrician by trade, which I took as a compliment.

Here are the details. This is an overhead entrance, 200 amp, dropping to a meter base and cutoff panel, with 2 inch conduit extending down the wall to an SLB and nipple that pierced the brick wall into the crawl space. Entering the crawlspace through that nipple are a 4 wire (3 x 3/0 plus 4AWG ground) feed to a 200 amp bottom fed GE subpanel in the utility room, and the two ends of a 4AW bare copper round electrode conductor loop. The GEC loop is Cadwelded to two ground rods on opposite sides of the house, and clamped to the cold water pipes.

Whether or not the GEC could share the conduit between the service entrance and the crawlspace with the 200A feed to the subpanel was the subject of a thread here. The view of the AHJ was yes, providing certain bonding requirements were met and providing that the place where the feeder and the GEC part ways be in a junction box.

Its kind of a trip to have done this, having had no practical electrical experience before. And it would have been immeasurably more difficult without the help of those who post here.

My humble thanks,
Able Sashweight
 
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Old 06-19-01, 08:31 AM
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Please accept a question. You state: "entering the crawl space thru the nipple are a 4-wire (3X3/0 + 4AWG ground) AND 2 ends of a loop---". Do this mean 5 cables in the nipple? What is the wiring method between the OD service disconnect and the interior load center? You mention 2" conduit on the exterior wall-does the conduit extend thru the crawl space to the load center? I don't understand the grounding connections. My undersanding is that the service grounding conductor is connected between the line side of the service disconnect and the main grounding electrode as an un-broken (no splices,joints) conductor. I have the impression you'r doing expert work-congrats!!!
 
  #3  
Old 06-19-01, 10:07 AM
Able Sashweight
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switchman:

Passing through the 2" conduit, 2" SLB and 2" x 12" nipple are 6 cables or wires:
2 hots of the feeder (3/0 THHN/THWN)
1 neutral of the feeder (3/0 THHN/THWN)
1 ground of the feeder (bare solid 4 AWG)
2 ends of the Ground Electrode Conductor GEC (bare solid 4 AWG) (I count that as 2 wires)

The nipple ends at a small junction box. The 4 wires/cables of the feeder pass straight through that box into a 2" flexible aluminum conduit, which snakes to the interior load center. The flexible conduit enters a hole in the floor/subfloor directly under the flush mounted load center. The conduit is inside the wall between the floor and the panel.

In the service panel (meter base with main breaker and no branch circuits) the neutral from the service drop is fastened to the lug at one end of the neutral/ground bar. The neutral and the ground wire for the feeder connect at the load end of that panel's neutral/ground bar , as does the two ends of the GEC.

The GEC must travel between the service entrance to the grounding electrodes in either
a. a continuous strand, or
b. in multiple segments that are exothermically welded, or
c. in multiple segments that are spliced with irreversible splices.
I used method "b", welding the conductors to the ground rods. Welding is overkill, though it means I don't have to worry about neighboring youngsters practicing their screwdriver skills on an acorn clamp on my ground rod. And using multiple segments made it much easier to manipulate the wire.

Leading both ends of the GEC into the service panel is also overkill, however the redundancy means that the conductor would have to be broken or cut in two places to sever the panel from ground.

Where the GEC shares metal conduit with the feeder, I had to bond that segment of conduit with the GEC. On the end of the conduit where it enter the service panel, I put a grounding bushing and ran a short #4 bare copper wire from the bushing to the neutral/ground bar of the panel. On the end of the nipple in the junction box, I put a grounding bushing, clamped a #4 bare copper wire to the bushing, and used a copper split bolt to clamp the other end to one of the GEC segments within the junction box.

I hope I caught all of your Q's.

AS
 
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Old 06-19-01, 11:11 AM
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Thanks for the explanantion-allow me to submit a different connection that may reveal if I understand the installation. In the juction box the grounding conductor for the interior CB panel could have jumped between the bonding bushings and then been bolted(or double-bolted) to the 2 cables that connect to the grounding electrodes.This eliminate a wire in the 2" conduit.In the service disconnect 1 of the grounding conductors could have been lugged to the bonding bushing,eliminating a jumper.If my understanding is correct you have 4 #4 wires connected to the neutral.You'r double-ended connection for the ground is a spendid idea.
 
  #5  
Old 06-19-01, 11:27 PM
Able Sashweight
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switchman:

Sounds like you're understanding the wiring.

> In the juction box the grounding conductor for the interior CB panel could have jumped between the bonding bushings and then been bolted(or double-bolted) to the 2 cables that connect to the grounding electrodes.This eliminate a wire in the 2" conduit.

If you mean to terminate the grounding conductor for the interior panel within the junction box, bolting it there to one or both of the GECs: I don't know if that's code correct. If it was, then that would have been simpler by eliminating a wire in the conduit between the junction box and the service entrance. If that grounding conductor terminates (as it does), it might have been better to split bolt it to one of the GEC's in the juntion box just to make sure all of the conductors parallel to the conduit were bonded to one another. I don't know.



>In the service disconnect 1 of the grounding conductors could have been lugged to the bonding bushing,eliminating a jumper.

That's correct, and that was the original plan. I opted for the jumper when I realized the shape the bend would have to take. Up out of the conduit, down through the bushing, up to the lug; All of this very close to the bottom of the SE panel and close to the face plate of that panel. Maybe I could have gotten it right, but I didn't want to chance screwing it up.

>If my understanding is correct you have 4 #4 wires connected to the neutral.

That's right. 2 under each of two large lugs.

Able
 
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