Grounding Conductor
- Thread starter mrq
- Start date
- Status
- Location
- Illinois
- Occupation
- retired electrician
Re: Grounding Conductor
Note: the topic title and question do not match. The conduit can never be used as the grounded conductor.
Don
Note: the topic title and question do not match. The conduit can never be used as the grounded conductor.
Don
- Location
- Massachusetts
Re: Grounding Conductor
It's certainly not a bad thing to pull an EGC, but I have read a properly installed conduit has a lower impedance than the conductor pulled inside it many times.
I would ask the person paying the bill.
It's certainly not a bad thing to pull an EGC, but I have read a properly installed conduit has a lower impedance than the conductor pulled inside it many times.
You are not required to.
jwelectric
Senior Member
- Location
- North Carolina
Re: Grounding Conductor
I am not so sure that we are talking about the same thing here. This could be a classic case of confusion of ground and bond.
A metal raceway can never be used for the grounded (neutral) conductor but is great for the grounding (bonding) conductor.
I am not so sure that we are talking about the same thing here. This could be a classic case of confusion of ground and bond.
A metal raceway can never be used for the grounded (neutral) conductor but is great for the grounding (bonding) conductor.
Re: Grounding Conductor
just 2 cents
If you check the tables in the IAEI adaptation of Soares book on grounding. Tables 11 and 13 suggest that the size of the OCPD and the length and diameter of the raceways; Conduit , and EMT are terminal when employed as an EGC.
For example a run with conductors 12AWG protected at 20A in 1/2 EMT. The maximum length of raceway is indicated as 265 feet.
Yes yes I know rare to exceed that length, but these test were most likely conducted with 26 and 1 /2, lengths of emt. No boxes and maybe set screw connectors.
I'm not an engineer but I do think about this stuff at times.
"Edited for my usual poor grammer"
Charlie
[ February 17, 2005, 07:35 PM: Message edited by: cpal ]
just 2 cents
If you check the tables in the IAEI adaptation of Soares book on grounding. Tables 11 and 13 suggest that the size of the OCPD and the length and diameter of the raceways; Conduit , and EMT are terminal when employed as an EGC.
For example a run with conductors 12AWG protected at 20A in 1/2 EMT. The maximum length of raceway is indicated as 265 feet.
Yes yes I know rare to exceed that length, but these test were most likely conducted with 26 and 1 /2, lengths of emt. No boxes and maybe set screw connectors.
I'm not an engineer but I do think about this stuff at times.
"Edited for my usual poor grammer"
Charlie
[ February 17, 2005, 07:35 PM: Message edited by: cpal ]
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: Grounding Conductor
I'm going to start a thread called "ungrounded conductor" and see how convuluted it gets.
I'm going to start a thread called "ungrounded conductor" and see how convuluted it gets.
- Location
- Illinois
- Occupation
- retired electrician
Re: Grounding Conductor
Charlie,
Don
Charlie,
If I use the GEMI software from the Steel Tube Institute, it shows that for a circuit with #12 wires and a 120 amp fault (6x20A breaker) that the maximum length using nonmetallic pipe and an EGC is 200', but when using 1/2" EMT without an EGC the maximum length is 269', and when I pull a #12 EGC into the EMT the maximum length is 282'.
Don
Re: Grounding Conductor
Is it over kill?
Not IMO, but some will think it is over kill. If you are bidding a job that does not specify it and you include it, chances are your competitor will beat you. I consider it good practice. However it doesn't lower the fault path impedance as much as you might think. It does provide a redundant path in the event couplings fail or become loose.
[ February 18, 2005, 10:14 AM: Message edited by: dereckbc ]
Just because you do not like it, does not mean it is not permitted and used.
Is it over kill?
Not IMO, but some will think it is over kill. If you are bidding a job that does not specify it and you include it, chances are your competitor will beat you. I consider it good practice. However it doesn't lower the fault path impedance as much as you might think. It does provide a redundant path in the event couplings fail or become loose.
[ February 18, 2005, 10:14 AM: Message edited by: dereckbc ]
Re: Grounding Conductor
Not much difference is there!
I had the same discussion during the 96 - 99 Code cycle with Richard Loyd,he was working with a university at the time to developed software to fend off the RNC industry. It may very well be the one you refer to.
Also if you can obtain a copy of a Factor Mutual Research TR #FMRC J.I. OP2R3. RU of 1987 the first 4-6 pages make for interesting reading. The conclusion appears to be that the average conduit installation is deficient against high fault currents resulting from poor connections at the discontinuities (couplings and locknuts). Also the report indicates that a ground fault tends to restrict it's flow to the inner wall, increasing the resistance of the return path.
Don't get me wrong!!! I have used raceway and continue to use it as a EGC, but after some of my reading I am aware that at some point the inclusion of an EGC (to the disgression of the installer) may be warranted.
The major impact of the IAs book and this other report I've read is that incidental connections at enclosures , coupling and fittings may contribute to an increased impedance of the raceway at fault level currents.
Just a thought. From an enforcement point of view 250.118 establishes the use of these wiring methods for this purpose. It's allowed and I do not have a blanket problem with it.
Charlie
Not much difference is there!
I had the same discussion during the 96 - 99 Code cycle with Richard Loyd,he was working with a university at the time to developed software to fend off the RNC industry. It may very well be the one you refer to.
Also if you can obtain a copy of a Factor Mutual Research TR #FMRC J.I. OP2R3. RU of 1987 the first 4-6 pages make for interesting reading. The conclusion appears to be that the average conduit installation is deficient against high fault currents resulting from poor connections at the discontinuities (couplings and locknuts). Also the report indicates that a ground fault tends to restrict it's flow to the inner wall, increasing the resistance of the return path.
Don't get me wrong!!! I have used raceway and continue to use it as a EGC, but after some of my reading I am aware that at some point the inclusion of an EGC (to the disgression of the installer) may be warranted.
The major impact of the IAs book and this other report I've read is that incidental connections at enclosures , coupling and fittings may contribute to an increased impedance of the raceway at fault level currents.
Just a thought. From an enforcement point of view 250.118 establishes the use of these wiring methods for this purpose. It's allowed and I do not have a blanket problem with it.
Charlie
- Location
- Illinois
- Occupation
- retired electrician
Re: Grounding Conductor
Charlie,
The GEMI Software was developed by Georgia Tech base on research funded by the Steel Tube Institute. It is a free download if anyone wants to use it.
Don
Charlie,
The GEMI Software was developed by Georgia Tech base on research funded by the Steel Tube Institute. It is a free download if anyone wants to use it.
Don
karl riley
Senior Member
Re: Grounding Conductor
Here's another angle on this question. I was working with an electrician to find the cause of high magnetic fields in some classrooms in an elementary school. We found that it was due to neutral/ground bonding in a second floor sub panel. He disconnected the bond and the field disappeared.
Then the electricians who had made the bond came in (one was the town inspector) and re-established the bond. They said they didn't trust the conduits. I said why not test them. They said they didn't have a megger.
My electrician appealed to the State (MA) licensing bureaucrat (who happened to live in the same town and was the ex-inspector) and he denied the appeal, thus re-establishing the Code violation and the magnetic field.
Anyhow, this situation could have been prevented if they had originally run an EGC with the feed.
Karl
Here's another angle on this question. I was working with an electrician to find the cause of high magnetic fields in some classrooms in an elementary school. We found that it was due to neutral/ground bonding in a second floor sub panel. He disconnected the bond and the field disappeared.
Then the electricians who had made the bond came in (one was the town inspector) and re-established the bond. They said they didn't trust the conduits. I said why not test them. They said they didn't have a megger.
My electrician appealed to the State (MA) licensing bureaucrat (who happened to live in the same town and was the ex-inspector) and he denied the appeal, thus re-establishing the Code violation and the magnetic field.
Anyhow, this situation could have been prevented if they had originally run an EGC with the feed.
Karl
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