Grounding/Bonding Meter/Main

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sfav8r

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OK, I thought I knew this stuff, but for some reason this is giving me a headache.

I just installed a meter/main outside which feeds a panel inside (approx 6 feet away). The service is overhead and is feed by THHN via RMC to the meter/main. From the meter main to the panel is #2 Romex.

Isn't the panel a sub panel and therefor CANNOT have a neutral/ground bond?

I ran the #6 GEC from the rods to the water pipe to the meter/main. The EGC that is bunled in the Romex is connected to the bonded ground bus in the meter/main and is attached to the ground bus in the panel which is not bonded.

Normally I use a meter can and a main/Load center so bonding at the meter is unusal for me.

Thanks.
 
Re: Grounding/Bonding Meter/Main

It sounds like your bonding arrangement is correct. Is your #6 GEC protected from physical damage? Remember that you cant use 310.15(B)(6) with NM. Is this a 100 Amp service?
 
Re: Grounding/Bonding Meter/Main

The disconnect outside is Service Equipment and that is the only place you bond neutral and ground. The panel inside is just like a sub-panel........separate ground and neutral, no bonding jumper.
 
Re: Grounding/Bonding Meter/Main

whoa, I'm having trouble tonight - I think I should stop typing and go to bed. 310.15(B)(6) could be applied to this feeder if it carries the entire load of the service and if it is one of the wire types listed. NM is not one of the wire types in the table so as long as this is a 100 amp service you should be fine.
 
Re: Grounding/Bonding Meter/Main

Your install is correct.The disc. is considered the primary panel and all after are sub panels IE: neutral/ grnd. seperated.Personally I use #4 so as not to have to protect it but that is a personal preference I guess.
 
Re: Grounding/Bonding Meter/Main

Originally posted by electrofelon:
NM is not one of the wire types in the table so as long as this is a 100 amp service you should be fine.
Click to expand...
What wire types are listed in the table?
 
Re: Grounding/Bonding Meter/Main

The wire/cable types are listed in the heading of Table 310.15(B)(6). However, I think NM cable actually utilizes THHN conductor insulation within the cable so I believe it would be covered by this rule!
 
Re: Grounding/Bonding Meter/Main

George, the cables and conductors are as follows.

Table 310.15(B)(6) Conductor Types and Sizes for 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders. Conductor Types RHH, RHW, RHW-2, THHN, THHW, THW, THW-2, THWN, THWN-2, XHHW, XHHW-2, SE, USE, USE-2
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Ramdiesel, the conductors inside NM are a 90 deg rated conductor, but they are not marked as required by 310.11 so they can not be used as an identified single conductor would be.

We all know that there would be no danger in doing this, but the code is the code.

Roger
 
Re: Grounding/Bonding Meter/Main

Unless you inspector or juristication allows NM to be used as an applicable wire type under 310.15(B)(6), then the #2 is only good for 100A. Has anyone else gotten away with using NM under 310.15(B)(6)?
 
Re: Grounding/Bonding Meter/Main

Originally posted by roger:
George, the cables and conductors are as follows.
Table 310.15(B)(6)
Click to expand...
Click to expand...
Thanks, Roger. That was a change to the 2005. I have it in front of me now.

So, theoretically, if someone were under prior codes, NM would be acceptable. Under the 2005, table 310.15(B)(6) would no longer allow NM for the special ampacities.

[ February 22, 2006, 05:39 PM: Message edited by: georgestolz ]
 
Re: Grounding/Bonding Meter/Main

You're welcome George.

Originally posted by georgestolz:
So, theoretically, if someone were under prior codes, NM would be acceptable. Under the 2005, table 310.15(B)(6) would no longer allow NM for the special ampacities.
Click to expand...
No, not really, it was just a editing problem (omission) in the 2002 cycle that was corrected.

See This Errata

Roger
 
Re: Grounding/Bonding Meter/Main

Originally posted by m73214:
Originally posted by sfav8r:
[ From the meter main to the panel is #2 Romex.

.
Per 310.16 #2 Romex (NM-B) is only rated for 95 Amps.
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Hmmm. I have the 2002 NEC (which we're under here) and the only thing listed as 95a is TW and UF. Since Romex is made from THHN, can someone explain why it would be rated for less than 130 amps? This doesn't make any sense to me. NM isn't even listed under 310.16 in 2002.
Click to expand...
 
Re: Grounding/Bonding Meter/Main

I have never seen a reference that indicates the conductors of NM are type THHN, If you have seen this somewhere I would like to see it. I admit it is rather strange that the conductors in NM are not classified/listed as a specific wire type like every other cable i can think of. For example, MC cable does have thhn conductors, SE cable has XHHW. It is also odd that table 310.16 does not list NM with types TW and UF in the 60 degree column, but 334.80 tells us this is the applicable column. I think this is an area of the code that could be made more clear.
To get an ampacity of 130 for #2 you would have to be using the 90 degree column, which you can rarely use because most terminations on equipment are rated for only 75 degrees.
 
Re: Grounding/Bonding Meter/Main

From the UL Certifications Directory (White Book):
PWVX.GuideInfo
Nonmetallic-sheathed Cable

USE

This category covers Types NM-B and NMC-B nonmetallic-sheathed cable, rated 600 V, intended for use in accordance with Article 334 of ANSI/NFPA 70, "National Electrical Code" (NEC), and Listed in copper sizes 14 to 2 AWG inclusive and aluminum or copper-clad aluminum sizes 12 to 2 AWG inclusive.

This cable contains conductors rated 90?C; however, the ampacities of the cable are those of 60?C conductors as specified in Article 334 and Table 310.16 of the NEC.
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The sheath of the cable is limited to 60?C, so as long as the sheath is covering the conductors, that's the temp limit that is worried about.

When the sheath stops at a cable clamp, and the conductors continue into an enclosure, the temperature is allowed to rise to 90?C. . .but the heat inside the enclosure is still not from the current in the conductor, rather from things like ballasts and luminaires, etc.
 
Re: Grounding/Bonding Meter/Main

To expand on what AL said:
334.80 Ampacity.
The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The ampacity shall be in accordance with the 60?C (140?F) conductor temperature rating. The 90?C (194?F) rating shall be permitted to be used for ampacity derating purposes, provided the final derated ampacity does not exceed that for a 60?C (140?F) rated conductor. The ampacity of Types NM, NMC, and NMS cable installed in cable tray shall be determined in accordance with 392.11.
Paul
 
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