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Old 05-30-2012, 07:59 PM   #1
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Using both PVC and RMC/IMC Conduit Path


I am considering using a combination of PVC and RMC/IMC to complete a conduit path for SE cable (individual 4/0-4/0-2/0 conductors) from my dual-lug meter enclosure to a new main breaker panel.

The meter box is surface mounted on the outside wall of the garage and the new main breaker panel is recessed into a wall cavity on the inside of the garage in the next wall cavity over from the existing main breaker panel that the meter box will be mounted behind.

I plan to come out of the side of the meter box via a PVC male adapter, into a short piece of PVC into a PVC LB and then transition to a piece of threaded RMC or IMC to come out of the LB through the siding/sheathing and into a knockout in the back of the new main breaker panel. I plan to secure the RMC/IMC to the main breaker panel with a lock ring on both sides of the knockout.

My concern is regarding bonding requirements. The meter box will be bonded to two ground rods (at least 6 feet apart). Do I need to be concerned with bonding of the RMC/IMC piece of conduit that is secured to the main breaker panel? If so, I was thinking of using a bonding bushing (it has a lug on it to connect wire and has a plastic insert to protect wires from chafing as the exit the conduit into the main breaker panel.

If bonding is required, must I run a separate bare copper wire from the bonding bushing in the breaker panel to both ground rods just like the meter box is connected? Would it be acceptable to have one continuous ground conductor from both ground rods, running through the ground lug in the meter box, exiting the meter box, running along side the conduit over to the back of the new main breaker panel and then into it, terminating at the lug on the bonding bushing?

Thanks in advance for all assistance.

Best Regards,

Ted

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Old 05-30-2012, 08:05 PM   #2
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Using both PVC and RMC/IMC Conduit Path


You may want to check with your power company to see if the allow grounding connections in their meter socket. Some do not.

I would advise you not to try and run SE cable in conduit. Individual conductors will be easier to work with.

Is there a reason you cannot do PVC the whole way or just use the SE without the conduit?

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Old 05-30-2012, 11:31 PM   #3
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Using both PVC and RMC/IMC Conduit Path


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Originally Posted by Jim Port View Post
You may want to check with your power company to see if the allow grounding connections in their meter socket. Some do not.

I would advise you not to try and run SE cable in conduit. Individual conductors will be easier to work with.

Is there a reason you cannot do PVC the whole way or just use the SE without the conduit?
Hi Jim,

The existing grounding connection terminates in the power companies meter box. There is a small hole drilled in the bottom of the meter box where the wire from the ground rod enters it.

I may have used the incorrect acronym (SE) for the service entrance cable. I am indeed using individual conductors running from the meter box in the conduit to the new breaker panel, two hots and a bare stranded neutral.

The reason for switching from PVC to RMC/IMC is to try to find a solution to secure the conduit to the new main breaker panel. The siding, sheathing, and air gap behind the breaker panel is approximately 1 5/8" thick. The neck of the 2" PVC LB is only 1 1/16" long. This leaves a 9/16" gap between the LB neck and the back of the main breaker panel knockout. If I try to use a PVC male adapter, the female receiver portion of the male adapter is approximately 1 3/8" deep. Even if I use a short enough piece of PVC to connect it to the LB that the LB neck and male adapter butt against each other, this makes the LB sit approximately 13/16" away from the siding of the house. I was trying to avoid this because I wasn't sure what the AHJ would think of it and I didn't know how easy it would be to find a clamp to stabilize it and or the PVC running from it into the side of the meter box with this big of a gap from the siding surface.

I hope this makes some sense. Thanks again for the response.

Best Regards,

Ted
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Old 05-31-2012, 07:17 AM   #4
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Using both PVC and RMC/IMC Conduit Path


With individual conductors would would have all insulated conductors.

The conduit nipple would not need a clamp between the panel and meter socket.

If you have vinyl siiding you may want to look at something like the Arlington MM18 to mount the socket on.
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Old 05-31-2012, 01:25 PM   #5
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Using both PVC and RMC/IMC Conduit Path


If you use a PVC LB, which is not threaded, you will have to use a threaded female fitting between the LB and the RMC/IMC. Spacewise, that's the same as using a male adapter and all PVC.
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Old 05-31-2012, 02:25 PM   #6
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Using both PVC and RMC/IMC Conduit Path


I would use a metal LB with a short nipple and locknuts, to come out the back of the panel. You can adjust the length of the nipple infinitely if you get all-thread by simply cutting it with a hacksaw. You can get all-thread up to 36".

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Old 05-31-2012, 05:30 PM   #7
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Originally Posted by JulieMor View Post
I would use a metal LB with a short nipple and locknuts, to come out the back of the panel. You can adjust the length of the nipple infinitely if you get all-thread by simply cutting it with a hacksaw. You can get all-thread up to 36".

+
If I were to go with all metal conduit out the side of the meter box via a male adapter, a short piece of pipe, a metal LB, and then threaded pipe in through the siding/sheathing into the back of the breaker panel and secure it with a locknut, what is the bonding requirement and what would be the recommended way to do it given that the meter box is already going to be bonded to two ground rods? Do I need a separate #4 AWG bare copper wire clamped to the metal conduit to bond it to the ground rods as well or since it will be all metal from the meter box (which is metal and bonded) through to the breaker panel (which has neutral bonded to ground) is there a need to provide a separate bonding for the metallic conduit?

Best Regards,

Ted
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Old 05-31-2012, 06:21 PM   #8
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Using both PVC and RMC/IMC Conduit Path


Grounding for a service is only done once, at the service entrance point and that means either at the meter or the main panel, depending on local codes. You already have a service ground at your meter.

From that point you need to make sure every load that comes off the panel has some sort of ground to go with it. If you use metallic conduit and fittings, that is your ground. If not, you need to include a ground wire with whatever means you are feeding those loads.

If you install PVC, you need to pull in a ground wire with the other conductors and make sure all loads and devices downstream are bonded to ground. If you install metallic conduit, boxes and fittings no ground wire is needed.

In your case, you are coming off a dual meter that has a ground. If that meterbank is metallic and you run metallic conduit from it, the new panel is grounded, unless you come into the panel using the concentric knockouts (KOs). In that case you would need a grounding bushing on the metallic fitting and you'd have to run a ground wire from the lug on the bushing to either the ground bus in the panel or to some lug bonded to the case (panel cabinet).

This is what a concentric knockout looks like:

If the conduit you bring into or take out of a cabinet requires the removal of ALL the KOs, no grounding bushing is required. If not, you must use a grounding bushing wherever there are KOs left.

One question, are you pulling in a 2/0 neutral with the 4/0?
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Old 05-31-2012, 09:58 PM   #9
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Using both PVC and RMC/IMC Conduit Path


Quote:
Originally Posted by JulieMor View Post
Grounding for a service is only done once, at the service entrance point and that means either at the meter or the main panel, depending on local codes. You already have a service ground at your meter.

From that point you need to make sure every load that comes off the panel has some sort of ground to go with it. If you use metallic conduit and fittings, that is your ground. If not, you need to include a ground wire with whatever means you are feeding those loads.

If you install PVC, you need to pull in a ground wire with the other conductors and make sure all loads and devices downstream are bonded to ground. If you install metallic conduit, boxes and fittings no ground wire is needed.

In your case, you are coming off a dual meter that has a ground. If that meterbank is metallic and you run metallic conduit from it, the new panel is grounded, unless you come into the panel using the concentric knockouts (KOs). In that case you would need a grounding bushing on the metallic fitting and you'd have to run a ground wire from the lug on the bushing to either the ground bus in the panel or to some lug bonded to the case (panel cabinet).

This is what a concentric knockout looks like:

If the conduit you bring into or take out of a cabinet requires the removal of ALL the KOs, no grounding bushing is required. If not, you must use a grounding bushing wherever there are KOs left.

One question, are you pulling in a 2/0 neutral with the 4/0?
Yes, a 2/0 neutral is coming in from the dual-lug meter box to the new breaker panel along with the two 4/0 lines. The knockout that I have elected to use coming into the breaker panel is a concentric knockout. I am not at home right now and can't look to confirm, but I believe I removed all of the concentric rings in that particular knockout location in the back of the new main breaker panel.
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Old 06-01-2012, 09:13 PM   #10
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Using both PVC and RMC/IMC Conduit Path


Quote:
Originally Posted by JulieMor View Post
If the conduit you bring into or take out of a cabinet requires the removal of ALL the KOs, no grounding bushing is required. If not, you must use a grounding bushing wherever there are KOs left.
I verified that all concentric rings of the knockout location I plan to use to enter the breaker panel with service were removed. If that negates the need for a grounding bushing, would I be OK using RMC/IMC to bring the individual service from the side of the meter box in through the siding/sheathing and into the back of the breaker panel without any bonding bushing on either end of the conduit and anytype of additional bonding? Would the answer differ depending on whether there are remaining concentric rings present in the knockout in the side of the meter box where the conduit is exiting?

Best Regards,

Ted
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Old 06-02-2012, 07:37 AM   #11
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Using both PVC and RMC/IMC Conduit Path


If you use a metallic raceway between your meter and panel you would not need any additional grounding bond unless local codes require it.

If EITHER of the KOs you use to install conduit from one to the other has any concentric rings left, you must use grounding bushings or install an appropriately sized ground wire.
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Old 06-04-2012, 07:19 AM   #12
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I just verified that the knockout I plan to use in the new meter box would still have concentric rings left in it. If I use RMC/IMC to connect the meter box to the new (second) main breaker panel coming of the dual lugs, how do I need to ground it? There will be two insulated hots (4/0 each) and a bare aluminum (2/0) braid being carried within the conduit. The meter box has a #4 bare copper ground wire attached to two 5/8" x 8' ground rods spaced approximately 7' apart.

Do I need to use a grounding bushing on the conduit end in the new breaker panel? If so, do I need to use another piece of #4 bare copper wire and run it all the way from the grounding bushing to both ground rods? If not, where do I need to ground the grounding bushing to and with what type/size of wire?

Thanks,

Ted
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Old 06-04-2012, 07:38 AM   #13
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The neutral should be insulated. Are you planning on stripping it out of a piece of SE cable?
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Old 06-04-2012, 07:39 PM   #14
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Quote:
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The neutral should be insulated. Are you planning on stripping it out of a piece of SE cable?
That is what I thought about doing. I have a piece of SE cable in the sheath that has a braided neutral (uninsulated within it). My existing meter box connection to my existing breaker panel has a braided uninsulated neutral and I was planning to mimic the same configuration. I believe that that short conduit connection going from the back of the meter box directly into the back of the existing breaker panel is all PVC if this makes a difference as to whether the neutral is shielded or not.

Thanks,

Ted

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