ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat
Recent Posts
Increasing demand factors in residential
by gfretwell - 03/28/24 12:43 AM
Portable generator question
by Steve Miller - 03/19/24 08:50 PM
Do we need grounding?
by NORCAL - 03/19/24 05:11 PM
240V only in a home and NEC?
by dsk - 03/19/24 06:33 AM
Cordless Tools: The Obvious Question
by renosteinke - 03/14/24 08:05 PM
New in the Gallery:
This is a new one
This is a new one
by timmp, September 24
Few pics I found
Few pics I found
by timmp, August 15
Who's Online Now
1 members (Scott35), 277 guests, and 15 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Page 1 of 3 1 2 3
#92970 04/21/05 08:25 AM
Joined: Jun 2004
Posts: 613
S
Member
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

Stay up to Code with the Latest NEC:


>> 2023 NEC & Related Reference & Exam Prep
2023 NEC & Related Reference & Study Guides

Pass Your Exam the FIRST TIME with the Latest NEC & Exam Prep

>> 2020 NEC & Related Reference & Study Guides
 

#92971 04/21/05 08:47 AM
Joined: Jan 2004
Posts: 1,507
G
Member
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
#92972 04/21/05 05:04 PM
Joined: Jan 2003
Posts: 4,391
I
Moderator
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
#92973 04/21/05 05:19 PM
Joined: Jan 2004
Posts: 1,507
G
Member
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
#92974 04/21/05 06:23 PM
Joined: Aug 2003
Posts: 1,374
R
Moderator
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
#92975 04/21/05 06:54 PM
Joined: Jan 2003
Posts: 4,391
I
Moderator
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
#92976 04/21/05 08:24 PM
Joined: Jan 2004
Posts: 1,507
G
Member
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
#92977 04/21/05 08:32 PM
Joined: Mar 2001
Posts: 2,056
R
Member
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.

#92978 04/21/05 09:40 PM
Joined: Jun 2004
Posts: 613
S
Member
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

#92979 04/21/05 10:20 PM
Joined: Jan 2004
Posts: 1,507
G
Member
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
Page 1 of 3 1 2 3

Link Copied to Clipboard
Powered by UBB.threads™ PHP Forum Software 7.7.5