Clarification Please???

[Strahan]

I seem to keep running into some confusion each time this topic comes up regarding feeder conductors and grounding. I'm mostly an industrial guy but do get involved in residential from time to time.
First question: When running feeders to a subpanel (example detached garage) what are the guidlines? Do I run a 4-wire feed keeping ground and neutral separate at garage panel? Do I run a 3-wire feed and install a ground rod at garage panel? Or do I run a 4-wire feed and also install a ground rod at garage?
2nd Question: 480/277 3phase feeder to an MCC. I'm not going to use the neutral so can I run a 4-wire feed with the 4th conductor being the grounding (bonding) conductor? Or do I still need to run the neutral causing this to be a 5-wire feed? Can I eliminate the grounding conductor by running RMC with bonding bushings and simply make this a 3-wire feed?

Right when I think I have this all figured out some time passes and I find myself confused again; so I would like if you guys can help. I will concrete this into my head this time. Thanks!!!

 

[mcclary's electrical]

I seem to keep running into some confusion each time this topic comes up regarding feeder conductors and grounding. I'm mostly an industrial guy but do get involved in residential from time to time.
First question: When running feeders to a subpanel (example detached garage) what are the guidlines? Do I run a 4-wire feed keeping ground and neutral separate at garage panel? Do I run a 3-wire feed and install a ground rod at garage panel? Or do I run a 4-wire feed and also install a ground rod at garage?
2nd Question: 480/277 3phase feeder to an MCC. I'm not going to use the neutral so can I run a 4-wire feed with the 4th conductor being the grounding (bonding) conductor? Or do I still need to run the neutral causing this to be a 5-wire feed? Can I eliminate the grounding conductor by running RMC with bonding bushings and simply make this a 3-wire feed?

Right when I think I have this all figured out some time passes and I find myself confused again; so I would like if you guys can help. I will concrete this into my head this time. Thanks!!!

Your first question depends on what code cycle you're on. 05' with no other metallic paths, you can run 3 wire. 08' 4 wire.

Second question, you only run the neutral to a mcc if you need it. Yes, the pipe can be the ground, and the wire can be your neutral, but again, it's not required unless you need it for the MCC.

 

[Strahan]

Your first question depends on what code cycle you're on. 05' with no other metallic paths, you can run 3 wire. 08' 4 wire.

Second question, you only run the neutral to a mcc if you need it. Yes, the pipe can be the ground, and the wire can be your neutral, but again, it's not required unless you need it for the MCC.

Ok what if there is a water line run from house to detached garage 05'?
So in the next question the neutral is not needed so I don't install it and use my rmc as ground so I can get away with a 3-wire feed just 3-phase conductors?

 

[iwire]

First question: When running feeders to a subpanel (example detached garage) what are the guidelines?

As mcclary's pointed out this depends on the code cycle your on.

Do I run a 4-wire feed keeping ground and neutral separate at garage panel?

This has always been, and still is acceptable but requires a grounding electrode system of some type tied into the EGC at the separate structure.

Do I run a 3-wire feed and install a ground rod at garage panel?

Under the 2005 or older codes this can also be acceptable under certain conditions but also requires a grounding electrode system.

Or do I run a 4-wire feed and also install a ground rod at garage?

Feeders to separate buildings or structures always require a grounding electrode system.

2nd Question: 480/277 3phase feeder to an MCC. I'm not going to use the neutral so can I run a 4-wire feed with the 4th conductor being the grounding (bonding) conductor?

If you don't need a neutral you do not have to run one.

Can I eliminate the grounding conductor by running RMC with bonding bushings and simply make this a 3-wire feed?

Yes and you do not necessarily need bonding bushings unless your entering into concentric knock outs.

 

[iwire]

Ok what if there is a water line run from house to detached garage 05'?

Then you would have run both grounded and grounding conductors.

By the way, all of what we have been discussing applies equally to dwellings and non-dwellings, single phase or 3 phase.

So in the next question the neutral is not needed so I don't install it and use my rmc as ground so I can get away with a 3-wire feed just 3-phase conductors?

Yes you can, and assuming the RMC is made up properly it will provided a lower impedance fault path than the EGC you would have installed inside it.

 

[Strahan]

As mcclary's pointed out this depends on the code cycle your on.



This has always been, and still is acceptable but requires a grounding electrode system of some type tied into the EGC at the separate structure.



Under the 2005 or older codes this can also be acceptable under certain conditions but also requires a grounding electrode system.




Feeders to separate buildings or structures always requires a grounding electrode system.




If you don't need a neutral you do not have to run one.





Yes and you do not necessarily need bonding bushings unless your entering into concentric knock outs.

Thanks very clear! I understand the bonding bushing part it has just always been my stance to install them and avoid the confusion.

 

[iwire]

Relevant code sections

250.32(A) Grounding electrodes at separate buildings or structures

250.32(B)(1) and (2) using the grounded conductor as the grounding means or not.

250.97 Bonding over 250 volts / bonding bushings required or not.

 

[iwire]

I understand the bonding bushing part it has just always been my stance to install them and avoid the confusion.

Yeah I hear you.

They don't cost much but adding one after all is done is a real pain.

 

[Strahan]

Relevant code sections

250.32(A) Grounding electrodes at separate buildings or structures

250.32(B)(1) and (2) using the grounded conductor as the grounding means or not.

250.97 Bonding over 250 volts / bonding bushings required or not.

Thanks!

 

[Strahan]

Yeah I hear you.

They don't cost much but adding one after all is done is a real pain.

Yes been there done that! That is why I always include them in the installation plans. Guys always ask what are these never used them before and I try to explain.

 

[iwire]

Thanks!

No problem and if your looking at the sections that apply to 'separate buildings or structures' it is really worth taking a look at the Article 100 definition of structure.

Pretty much anything that humans have built or constructed is a structure to the NEC.

 

[Pierre C Belarge]

Bonding around concentrics is treated differently for 'enclosures' and 'boxes'. Yes, I know boxes are a form of enclosures.
By boxes I mean less than 100sqin and enclosures are large boxes and back boxes, large disconnect enclosures, etc...

Article 312 enclosures
and
Article 314 boxes are an example of what I mean.

Although there are exceptions even to this generalization.

See (QCIT) and (BGUZ), in the White Book

 

[iwire]

Bonding around concentrics is treated differently for 'enclosures' and 'boxes'. Yes, I know boxes are a form of enclosures.
By boxes I mean less than 100sqin and enclosures are large boxes and back boxes, large disconnect enclosures, etc...

Article 312 enclosures
and
Article 314 boxes are an example of what I mean.

Although there are exceptions even to this generalization.

See (QCIT) and (BGUZ), in the White Book

Pierre, I am not trying to be rude here but I have no clue what you are getting at.

 

[mcclary's electrical]

Bonding around concentrics is treated differently for 'enclosures' and 'boxes'. Yes, I know boxes are a form of enclosures.
By boxes I mean less than 100sqin and enclosures are large boxes and back boxes, large disconnect enclosures, etc...

Article 312 enclosures
and
Article 314 boxes are an example of what I mean.

Although there are exceptions even to this generalization.

See (QCIT) and (BGUZ), in the White Book

Please explain further. I'm not quite getting what you mean

 

[rwreuter]

As mcclary's pointed out this depends on the code cycle your on.



This has always been, and still is acceptable but requires a grounding electrode system of some type tied into the EGC at the separate structure.



Under the 2005 or older codes this can also be acceptable under certain conditions but also requires a grounding electrode system.




Feeders to separate buildings or structures always require a grounding electrode system.




If you don't need a neutral you do not have to run one.





Yes and you do not necessarily need bonding bushings unless your entering into concentric knock outs.

ok, let me throw you a curve ball here. what if the county you lived in has NO code requirements at all. NONE, ZERO, ZIP. you know that the NEC (2008) requires the 4th wire, the cost is over $2.00 a foot for for that 4/0-4/0-2/0-4. what would you do?

i am in that very situation, i am going to wire my house (not a trailer or manufactured home) but it will have a remote meter and 200 amp main disconnect sitting on a pole and the 200 amp service will be in the basement. there are no rules here, no inspections, no permits.

i wired houses for about 10 years in washington state and the only time you were required to run that grounding conductor was with trailers or temp buildings like job shacks. i have never heard of any problems running standard urd triplex to a separate building when there was no metal connecting them.

i don't want to spend waste the money (about $4.00) a foot but i don't want to do something stupid either just because of money.

opinion please.

 

[rwreuter]

As mcclary's pointed out this depends on the code cycle your on.



This has always been, and still is acceptable but requires a grounding electrode system of some type tied into the EGC at the separate structure.



Under the 2005 or older codes this can also be acceptable under certain conditions but also requires a grounding electrode system.




Feeders to separate buildings or structures always require a grounding electrode system.




If you don't need a neutral you do not have to run one.





Yes and you do not necessarily need bonding bushings unless your entering into concentric knock outs.

ok, let me throw you a curve ball here. what if the county you lived in has NO code requirements at all. NONE, ZERO, ZIP. you know that the NEC (2008) requires the 4th wire, the cost is over $2.00 a foot for for that 4/0-4/0-2/0-4. what would you do?

i am in that very situation, i am going to wire my house (not a trailer or manufactured home) but it will have a remote meter and 200 amp main disconnect sitting on a pole and the 200 amp service will be in the basement. there are no rules here, no inspections, no permits.

i wired houses for about 10 years in washington state and the only time you were required to run that grounding conductor was with trailers or temp buildings like job shacks. i have never heard of any problems running standard urd triplex to a separate building when there was no metal connecting them.

i don't want to spend waste the money (about $4.00) a foot but i don't want to do something stupid either just because of money.

opinion please.

 

[Jim W in Tampa]

Permit ,inspections or not should not change how we wire anything. Lives are at risk either way.

 

[dcspector]

Bonding around concentrics is treated differently for 'enclosures' and 'boxes'.

Pierre were you trying to say that concentric knock outs are listed for over 250v without having to provide a bonding jumper?