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Grounding Conductor Size #92970
04/21/05 07:25 AM
04/21/05 07:25 AM
S
shortcircuit  Offline OP
Member
Joined: Jun 2004
Posts: 608
massachusetts
250.118(4) allows EMT as a means of equipment grounding.

Now, if I also install a equipment grounding conductor in that EMT, as many of us do, and I increase the ungrounded conductor size to compensate for voltage drop or for derating purposes, do I still have to increase the size of that equipment grounding conductor proportionately according to the circular mil area of the ungrounded conductors as described in 250.122(B) ?

shortcircuit

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Re: Grounding Conductor Size #92971
04/21/05 07:47 AM
04/21/05 07:47 AM
G
George Little  Offline
Member
Joined: Jan 2004
Posts: 1,489
Michigan USA
IMHO, if this were an IG circuit I'd say definitely. If it were a routine circuit I guess it would be optional. Since EMT should be an adaquate EGC for any circuit of any size permited in the raceway code, would allow it. I've seen charts that cast doubt on the raceway being a low impedance path after a certain length but that's why some of us pull in an EGC.


George Little
Re: Grounding Conductor Size #92972
04/21/05 04:04 PM
04/21/05 04:04 PM
I
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Shortcircuit In my opinion if you install it you must follow the rules.

If you want to use the EMT as the EGC thats fine.

If you install a copper EGC in the raceway it must comply with 250.122(B)

Would you install a 14 AWG EGC with 12 AWG circuit conductors on a 20 amp circuit and then say it's OK because it is in EMT?

JMO, Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Re: Grounding Conductor Size #92973
04/21/05 04:19 PM
04/21/05 04:19 PM
G
George Little  Offline
Member
Joined: Jan 2004
Posts: 1,489
Michigan USA
Bob - Your giving good design advice but as an inspector, I can't enforce it unless it's part of the construction documents submitted at plan review.


George Little
Re: Grounding Conductor Size #92974
04/21/05 05:23 PM
04/21/05 05:23 PM
R
Ryan_J  Offline
Moderator
Joined: Aug 2003
Posts: 1,374
West Jordan, Utah, USA
I don't agree that a raceway, in and of itself, is an adequate equipment ground for every purpose. It still must meet 250.4(A)(5), as indicated in the note to table 250.122. If your circuit length is such that voltage drop is an issue, than the length of the raceway and it's impedance may be an issue as well. With this said, I don't think including the raceway in the equation is valid.

EDIT for clarity: What I mean by referencing the note in table 250.122, is that following 250.118 and 250.122 doesn't automatically grant compliance with 250.4.

Just out of curiousity though, could you post the parameters of the circuit? Length, size of wire, size of pipe, size of breaker?

[This message has been edited by Ryan_J (edited 04-21-2005).]


Ryan Jackson,
Salt Lake City
Re: Grounding Conductor Size #92975
04/21/05 05:54 PM
04/21/05 05:54 PM
I
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
George

Quote
Bob - Your giving good design advice but as an inspector, I can't enforce it


Thanks, however I do believe it is enforceable.

Quote
250.122 Size of Equipment Grounding Conductors.
(A) General. Copper, aluminum, or copper-clad aluminum equipment grounding conductors of the wire type shall not be smaller than shown in Table 250.122 but shall not be required to be larger than the circuit conductors supplying the equipment. .....


And

Quote
250.122(B) Increased in Size. Where ungrounded conductors are increased in size, equipment grounding conductors, where installed, shall be increased in size proportionately according to circular mil area of the ungrounded conductors.


Personally I do not see any doubt that if you install a grounding conductor it must comply with 250.122(B). [Linked Image]

JMO, Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Re: Grounding Conductor Size #92976
04/21/05 07:24 PM
04/21/05 07:24 PM
G
George Little  Offline
Member
Joined: Jan 2004
Posts: 1,489
Michigan USA
I guess I don't know why an extra ground wire would be required unless it were a health care facility or spec'd out on the plans. If it were a required EGC I would agree with you Bob but, if it's optional I don't see any real concerns.


George Little
Re: Grounding Conductor Size #92977
04/21/05 07:32 PM
04/21/05 07:32 PM
R
Redsy  Offline
Member
Joined: Mar 2001
Posts: 2,056
Bucks County PA
shorty,

Table 11 of Soares (page 261, 7th edition) addresse the maximum length of EMT, IMC & RGC that may be used as an EGC, based on OCPD and 500% fault levels.

Re: Grounding Conductor Size #92978
04/21/05 08:40 PM
04/21/05 08:40 PM
S
shortcircuit  Offline OP
Member
Joined: Jun 2004
Posts: 608
massachusetts
This installation doesn't involve isolated grounding, it is a routine installation with multiple 3 phase 480volt circuits in one raceway about 80 feet in length.

I will increase the ungrounded conductor size for each circuit to compensate for derating due to the number of current carrying conductors in the EMT.

The maximum OCPD will be 60 amps which calls for a #10 EGC when installed. The EMT is a suitable equipment grounding means according to 250.118

I have always installed a EGC in my metalic raceways. An extra step to insure an effective ground fault path in my mind, I guess. I loose locknut, or the helper forgets to tighten a set screw on a coupling and you all know that it happens.

Iwire...I agree that the code does say to increase the size [Linked Image] So I will...

Redsy...There is nothing in the NEC that restricts the lenght of a EMT run that is used for an equipment grounding conductor.

George Little...Although the EGC I'm installing is optional, I must follow rule 250.122(B)...You see, with my reason for installing it in the first place, for a back up to a loose locknut or the forgotten tightening of the setscrew on a EMT coupling, I would want it properly sized as if the metalic pipe was not the grounding means at all [Linked Image]

shortcircuit

Re: Grounding Conductor Size #92979
04/21/05 09:20 PM
04/21/05 09:20 PM
G
George Little  Offline
Member
Joined: Jan 2004
Posts: 1,489
Michigan USA
Shortcircuit- You made a good decision. I wish more contractors would pull in EGC in raceways because the quality of materials and tolerances in fittings make a redundant grond very practical,


George Little
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