"Separate Building" Ground Question

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#1

Originally Posted By: jpope
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Okay, we’ve determined through previous topics that the neutral is not to be “regrounded” after the service with the exception of separate buildings that do not have a parallel metal path to the first building.


Does this "parallel metal path" refer to the conduit and/or the EGC? And does this mean that the presence of the "pmp" requires an isolated neutral even in a separate building?

--
Jeff Pope
JPI Home Inspection Service
"At JPI, we'll help you look better"
(661) 212-0738

#2

Originally Posted By: Greg Fretwell
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It especially refers to a metalic wiring method. The only way to legally run a 3 wire feeder is 3 wires in a cable or in PVC.


I am a little more ambivilent when this “metalic path” is a buried water pipe but I would still enforce it. … If anyone actually used metal pipe around here.


As far as I am concerned I am not sure what the difference is between the metal pipe that serves all of your neighbors and carries neutral current and a metal pipe that is totally on your property. If it is buried for 10 feet it is still a ground electrode.
These are the kind of arguments that keep IAEI meetings from being dull.

As for those other "metalic paths" like phone, LAN etc, you would have to be a moron to do it. Your electronics would end up being the path for surge current and ground shift.

#3

Originally Posted By: jpope
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sense?

–
Jeff Pope


JPI Home Inspection Service


“At JPI, we’ll help you look better”


(661) 212-0738

#4

Originally Posted By: Greg Fretwell
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Yes you reground a 3 wire and you float a 4 wire.


I though you were getting into other parallel paths.

#5

Originally Posted By: bbadger
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jpope wrote:
Does this "parallel metal path" refer to the conduit and/or the EGC? And does this mean that the presence of the "pmp" requires an isolated neutral even in a separate building?


Here is part of the section in the NEC that allows a 3 wire feeder to a separate structure.

If you want to run a 3 wire feeder you must meet this requirement along with some others

Quote:
there are no continuous metallic paths bonded to the grounding system in both buildings or structures involved,




I take this to mean absolutely any metallic paths, an EGC, a metal conduit, a metal water, gas, steam, compressed air line, cable TV, phone, security etc.

Not that you will run into this at a dwelling but the metallic path could be a chain link fence between two metal buildings. This is very common at warehouse buildings.

A separate out building at a dwelling unit that has no utilities at all except for electricity is a candidate for a 3 wire feeder H, H, N then bond the outbuildings panel just like a service panel.

Most times it is just simpler to run a 4 wire feeder H, H, N, G and 'float' the neutral. Done this way if someone adds a metallic path later they will not create an NEC violation.

Bob

--
Bob Badger
Electrical Construction & Maintenance
Moderator at ECN
#6

Originally Posted By: Brian A. Goodman
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Quote:
there are no continuous metallic paths bonded to the grounding system in both buildings or structures involved,


I take this to mean absolutely any metallic paths, an EGC, a metal conduit, a metal water, gas, steam, compressed air line, cable TV, phone, security etc.

I agree, that's the way I take too.

Not that you will run into this at a dwelling but the metallic path could be a chain link fence between two metal buildings. This is very common at warehouse buildings.

Also watch out for connecting sidewalks that may have rebar in them.

Most times it is just simpler to run a 4 wire feeder H, H, N, G and 'float' the neutral. Done this way if someone adds a metallic path later they will not create an NEC violation.

And don't forget that a seperate building still needs its own grounding electrode either way, if it has more than one circuit.
#7

Originally Posted By: cbuell
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Quote:
this way if someone adds a metallic path later they will not create an NEC violation.

In all of this great discussion I think this is perhaps one of the most important things to consider.
The defects in the "rules" are usually easier to pick out than the "exceptions-to-the-rules".

--
It is easier to change direction than it is to forget where one has been.
#8

Originally Posted By: Mike Parks
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“And does this mean that the presence of the “pmp” requires an isolated neutral even in a separate building?”


Yes.

Mike P.