Offset Nipple between Meter and Disco

[ike5547]

• Now - the kicker - if in the event of a fault actually inside the nipple between the two enclosures - the fault may disconnect or damage grounded service conductor inside it. If only bonded downstream from the fault, this current then only has one non-qualified way to go - back to the source through the regular ol' locknut at the meter base.

I bond only one side of the nipple with a ground bushing, but I run the bonding jumper through the nipple out to the enclosure without a ground bushing and bond that enclosure also.

Three points of contact with one jumper: Both enclosures and one side of the nipple.

The alternative is two jumpers and two bushings; one for each enclosure. This method is okay as well.

 

[e57]

I bond only one side of the nipple with a ground bushing, but I run the bonding jumper through the nipple out to the enclosure without a ground bushing and bond that enclosure also.

Three points of contact with one jumper: Both enclosures and one side of the nipple.

The alternative is two jumpers and two bushings; one for each enclosure. This method is okay as well.

PG&E can often take a hissy fit if they see anything more than the hots and noodle... But one other additional option as I mentioned before is the use of grounding locknuts. Either one on the meter side, and grounding bushing on the other. Or both ends with grounding bushings - quick = cheap, and fully bonded - not half-assed... The only drawback is using full-sized/largest conduits or punched KO's - concentric/ecentric needs a jumper....

 

[ike5547]

Or both ends with grounding bushings - quick = cheap, and fully bonded - not half-assed...

Hmmm... maybe I'm not explaining this right. Picture a jumper running through the nipple bonding both cans together. Except on the way from one can to the next you hit a ground bushing on one side of the nipple.

= fully bonded.

Never heard a complaint from PGE.

But I occasionally use two bushings and two jumpers also.

 

[iwire]

FWIW - I also see this as no different as the reasoning behind bonding both ends as one would in 250.64(E)

IMO I do not have to use a 'wire' on both ends of that either.

The end at the panel is bonded via the connector.

 

[e57]

Hmmm... maybe I'm not explaining this right. Picture a jumper running through the nipple bonding both cans together. Except on the way from one can to the next you hit a ground bushing on one side of the nipple.

= fully bonded.

Never heard a complaint from PGE.

But I occasionally use two bushings and two jumpers also.

No you explianed yourself just fine - I understand what you're doing... However I did mis-type what I was trying to say ealier.... Maybe I shouldn't watch TV, read a programming manual, and post at the same time...

PG&E can often take a hissy fit if they see anything more than the hots and noodle... But one other additional option as I mentioned before is the use of grounding locknuts. Either one on the meter side, and grounding bushing on the other. Or both ends with grounding Locknuts - quick = cheap, and fully bonded - not half-assed... The only drawback is using full-sized/largest conduits or punched KO's - concentric/ecentric needs a jumper....

On the PG&E issue - I have tried your method before - shot down... Which is exactly why I switched to the locknut method... Never an aurguement.

They have a few breeds of mechanic - the 'all grounded items are a hazard' type linemen, and the 'I've never actually looked at the greenbook or any other code before type'.... Both of those freak if they see a green or bare in a sealable enclosure.

Anyway - see page 16

 

[e57]

IMO I do not have to use a 'wire' on both ends of that either.

The end at the panel is bonded via the connector.

Locally this requires a hub at the clamp end, and a bonding bushing or grounding locknut (which is what I use).... But are you reading the same code I am???? 250.64E goes so far as to say how to size said bonding jumper...

 

[iwire]

Locally this requires a hub at the clamp end, and a bonding bushing or grounding locknut (which is what I use).... But are you reading the same code I am???? 250.64E goes so far as to say how to size said bonding jumper...

There is nothing in that section that requires the use of a wire conductor to bond the end of a conduit that is already bonded to the enclosure via lock nuts.


Lets get back to the nipple between the disco and the meter.


Lets just say that the meter and disco are 25' apart and you run EMT between them.

Do put a wire bonding jumper across the couplings?

 

[ike5547]

There is nothing in that section that requires the use of a wire conductor to bond the end of a conduit that is already bonded to the enclosure via lock nuts.


Lets get back to the nipple between the disco and the meter.


Lets just say that the meter and disco are 25' apart and you run EMT between them.

Do put a wire bonding jumper across the couplings?

I can answer this one:

We're not allowed to use EMT between the meter and disconnect.

 

[ike5547]

There is nothing in that section that requires the use of a wire conductor to bond the end of a conduit that is already bonded to the enclosure via lock nuts.

This is something I've always wondered about. It seems like a connection directly from the GEC to the fitting is redundant when that connection is already made, albeit somewhat indirectly, by both the fitting's and the GEC's connection to the same metallic enclosure.

But I would expect to get tagged on this around here if I tried it.

 

[infinity]

I can answer this one:

We're not allowed to use EMT between the meter and disconnect.

Local code?

 

[ike5547]

Local code?

Local utility requirement. Has to be rigid.

 

[e57]

There is nothing in that section that requires the use of a wire conductor to bond the end of a conduit that is already bonded to the enclosure via lock nuts.


Lets get back to the nipple between the disco and the meter.


Lets just say that the meter and disco are 25' apart and you run EMT between them.

Do put a wire bonding jumper across the couplings?

A regular lock nut is not listed in 250.8...


As mentioned we are in RMC world for service conductors above grade via threaded or threadless they are mentioned in 250.92(B)2&3 - if EMT were allowed here - the couplings would be allowed under 250.92(B)3

 

[elohr46]

The electrical continuity is provided by bonding the neutral in both places. This makes using the metallic nipple for continuity unnecessary. If you had a PVC nipple you would rely on the neutral bonding for the continuity. The same rationale applies to the metallic nipple. Since it's a service raceway it requires bonding beyond standard locknuts. This can be accomplished by using a bonding bushing on one end.

I totally agree with this. My last code instructor for 2008 nec class went into this very subject at great length to explain it so everyone would understand it.

 

[e57]

I totally agree with this. My last code instructor for 2008 nec class went into this very subject at great length to explain it so everyone would understand it.

So how did he explain the two paths of current - one is an effective ground fault current path - the other is not-so-effective... Both will always exist, short of using some sort of non-existent isolating fitting.....

 

[elohr46]

So how did he explain the two paths of current - one is an effective ground fault current path - the other is not-so-effective... Both will always exist, short of using some sort of non-existent isolating fitting.....

Only one path exists, the bonded neutral. The metal nipple bonded on one side is at the same potential as the metal enclosure. No differential potential, no current flow.

 

[e57]

Only one path exists, the bonded neutral. The metal nipple bonded on one side is at the same potential as the metal enclosure. No differential potential, no current flow.

Not buying it...

If there were no metal to metal contact on the un-bonded side - I would say yeah sure.... But there is... Potential difference depends on load and distance, and the current will flow on all available paths - not the one you figure is best for it....

Take a look at the images below - schematically they are no different than a bonded meter, and bonded main enclosure with a conductive path between them.

 

[ike5547]

e57 is correct. If the nipple were PVC it wouldn't be a problem, but a metallic nipple sets up a parallel path for neutral current.

 

[e57]

e57 is correct. If the nipple were PVC it wouldn't be a problem, but a metallic nipple sets up a parallel path for neutral current.

One that by some standards could be a loosy goosy - un-bonded thingy...

 

[shepelec]

This is something I've always wondered about. It seems like a connection directly from the GEC to the fitting is redundant when that connection is already made, albeit somewhat indirectly, by both the fitting's and the GEC's connection to the same metallic enclosure.

But I would expect to get tagged on this around here if I tried it.

If you are installing the GEC in metallic conduit, you are required to bond the conduit to the GEC because the fault currents will be induced on to the conduit and will actually carry the fault current if it is not bonded.

 

[ike5547]

If you are installing the GEC in metallic conduit, you are required to bond the conduit to the GEC because the fault currents will be induced on to the conduit and will actually carry the fault current if it is not bonded.

Thanks, but...

My understanding (what I've read) is that you are required to bond the GEC to both ends of a metallic conduit it passes through because if you don't the the conduit acts as a choke on the GEC that restricts the flow of current.