277 3 phase grounding

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jerryb52

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Lake Worth, Florida
I'm in the process of running some new feeds for some A/C units that will be on the roof of a large industrial building.
I've always pulled a ground in all my conduits over the years as just a loose set screw will cause a poor ground.
These units are three phase @ 60 Amps, #4 copper will be run.
Isn't it always , a good practice to run a ground wire with this type of installation?
I was told not to.
 
The NEC does not require that you pull a 'ground wire'.

A properly run conduit can provide a better fault path than the EGC pulled inside it.

However the conduit and an EGC combined provide redundancy and a lower impedance fault path than either alone.

In the end IMO it is up to the person paying the bill.

If your boss says don't pull an EGC than the correct answer is don't pull an EGC.
 
277 3-phase grounding

277 3-phase grounding

i always use the steel compression connectors instead of the set screw type when useing the conduit for the ground conductor.
 
sparky59 said:
i always use the steel compression connectors instead of the set screw type when useing the conduit for the ground conductor.
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Doesn't 250.97 "Bonding for Over 250 Volts", and 250.92(B) prohibit set-screw fittings?
 
ramsy said:
Doesn't 250.97 "Bonding for Over 250 Volts", and 250.92(B) prohibit set-screw fittings?
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No, it doesn't.

250.97 Bonding for Over 250 Volts
For circuits of over 250 volts to ground, the electrical continuity of metal raceways and cables with metal sheaths that contain any conductor other than service conductors shall be ensured by one or more of the methods specified for services in 250.92(B), except for (B)(1).
Exception: Where oversized, concentric, or eccentric knockouts are not encountered, or where a box or enclosure with concentric or eccentric knockouts is listed to provide a permanent, reliable electrical bond, the following methods shall be permitted:

(1) Threadless couplings and connectors for cables with metal sheaths

(2) Two locknuts, on rigid metal conduit or intermediate metal conduit, one inside and one outside of boxes and cabinets

(3) Fittings with shoulders that seat firmly against the box or cabinet, such as electrical metallic tubing connectors, flexible metal conduit connectors, and cable connectors, with one locknut on the inside of boxes and cabinets

(4) Listed fittings
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A listed set screw fitting is fine.

Roger
 
a properly installed raceway doesn't always "stay" properly installed or intact. for what it cost i would suggest discussing it with your customer -- the labor is basically the same. with everything being computerized it is important to be properly grounded---and your inflorida. lots of water to rust away the raceway and the lightning capital of the world!
 
iwire said:
......
A properly run conduit can provide a better fault path than the EGC pulled inside it.

However the conduit and an EGC combined provide redundancy and a lower impedance fault path than either alone.

.......

If your boss says don't pull an EGC than the correct answer is don't pull an EGC.
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Keyword in the first sentence: PROPERLY. Remember the path has to be permanent per the Code. You need to look at what can happen to it. As per C.T.'s comment.

Second sentence comment: I agree 100+ %. I would add to do a good job, bond your EGC to the conduit at both ends.

Third sentence: Good old rule #1: The boss is always right.

My own comment. Make sure you bond around any concentric/eccentric KO's.
 
sandsnow said:
My own comment. Make sure you bond around any concentric/eccentric KO's.
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Larry, I agree, but it is not neccessarily required.

Roger
 
roger said:
Larry, I agree, but it is not neccessarily required.

Roger
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Right

aside from the Raco boxes, I don't know of any concentric/eccentric that are listed for grounding.

Use conduit as ground path: bond around concentric/eccentric at both ends

Pull ground wire and only bond conduit at one.

Is that what you're thinking??
 
sandsnow said:
Right

aside from the Raco boxes, I don't know of any concentric/eccentric that are listed for grounding.

Use conduit as ground path: bond around concentric/eccentric at both ends

Pull ground wire and only bond conduit at one.

Is that what you're thinking??
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Steel City boxes with eccentric KO's are also listed for bonding over 250 volts.
 
I agree the conduits are OK for your ground but remember that these runs are up on a rooftop for A/C units of a build and like these conduit runs will be exposed to the outside. Also as we all see when other people are on the roof and they trip over the conduits by accident? A good chance some fitting will weaken or come loose. That's why I like to run the extra ground wire but again by the book you don't.
Jim
 
The allowed types of equip grounding conductors (EGC)include metallic conduit. If you are pulling an wire type EGC that suggests poor workmanship on the metallic conduit installation. At least that is what the Steel Tube Institute and CMP states for the many proposals to include a wire type EGC in a metallic conduit.
Personally I always pull a wire type EGC.
 
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