# Conduit as EGC Size?



## Shockdoc (Mar 4, 2010)

1000 mcm


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## Cletis (Aug 20, 2010)

*1000*

Sure 1000 or whatever. I"m guessing that the increase in diameter to hold the larger wires will always exceed the fault current for ungrounded conductors but just checking...


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## mbednarik (Oct 10, 2011)

I think the only metallic conduit systems with an amperage limitation are FMC, LFMC and FMT. FMC is limited to 20 amp, LFMC is 20 amp for 3/8 and 1/2 - 60 amp 3/4 to 1 1/4, FMT is 20 amp. Cable trays are limited per table 392.60 A with a steel limitation of 600 amps and an aluminum of 2000 amp providing there is ground fault protection. I would assume equipment ground fault protection not class A. Also any of the flex conduit has to have an egc if it will be moving around.


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## Cletis (Aug 20, 2010)

*2000mcm*

Let's say you ran 3-2000 MCM through an EMT conduit 12 ft to a sub-panel and used the emt as the egc. Would that suffice for equiptment ground???


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## 480sparky (Sep 20, 2007)

Metal conduit always has the capacity to properly ground the conductors contained within.


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## Cletis (Aug 20, 2010)

*?*



480sparky said:


> Metal conduit always has the capacity to properly ground the conductors contained within.


Coriolis effect right?

Oops. I meant the Amperian loop


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## Cletis (Aug 20, 2010)

*this and dat*

like this


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## 480sparky (Sep 20, 2007)

Cletis said:


> Coriolis effect right?
> 
> Oops. I meant the Amperian loop



Not really. Just physical size (CSA). I recall Soares saying ½" EMT can carry something like 180amps continuously.


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## acrwc10 (Jan 28, 2007)

480sparky said:


> Not really. Just physical size (CSA). I recall Soares saying ½" EMT can carry something like 180amps continuously.


What about surge? I would bet its in the thousands of amps for a fault condition to trip an OCPD.


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## 480sparky (Sep 20, 2007)

acrwc10 said:


> What about surge? I would bet its in the thousands of amps for a fault condition to trip an OCPD.


I dunno. I can't put my paws on my Soares book at the moment.


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## mbednarik (Oct 10, 2011)

acrwc10 said:


> What about surge? I would bet its in the thousands of amps for a fault condition to trip an OCPD.


and a #14 can only carry 15, but we can still use it. I suppose your circuit impedance on the circuit conductors would help to limit the amount on the EGC. I think the conduit would be fine in a pinch, but for new installations i usally pull a EGC.


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## Cletis (Aug 20, 2010)

*par*

Wouldn't an EGC in Addition to the conduit as an EGC create a dangerous and deadly parallel path and choking effect ???


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## mbednarik (Oct 10, 2011)

Cletis said:


> Wouldn't an EGC in Addition to the conduit as an EGC create a dangerous and deadly parallel path and choking effect ???


Can't be too deadly as it is required in health care patient care areas.


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## JohnR (Apr 12, 2010)

If you use the conduit as an EGC, you will have to upsize the conduit just as you upsize the awg for distance. So, if you have a 3" conduit, and you had to increase the AWG for distance, then you would have to increase the conduit size respectively. An AWG step per 1/2" of conduit size.:whistling2:


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## mbednarik (Oct 10, 2011)

JohnR said:


> If you use the conduit as an EGC, you will have to upsize the conduit just as you upsize the awg for distance. So, if you have a 3" conduit, and you had to increase the AWG for distance, then you would have to increase the conduit size respectively. An AWG step per 1/2" of conduit size.:whistling2:


where do you get the 1/2" size = one step of AWG? What if you had a circuit with a required ampacity of 66 amps, but you run #3 instead of number #4. In a typical circuit they both would have a #8 EGC.


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## Big John (May 23, 2010)

acrwc10 said:


> What about surge? I would bet its in the thousands of amps for a fault condition to trip an OCPD.


 It is, but during a short-circuit that can be true even for a the 15A circuit breaker on the 14AWG in your house. The two problems to consider are: 
A) Does the EGC permit enough current flow to clear the fault in a reasonable amount of time? 
B) Does the EGC allow that current flow without getting dangerously hot?
I'd bet most conduit systems would meet those marks.

_Soares _does have a whole study of the ability of conduit to carry fault currents, and the effectiveness of different types of EGCs. It makes for interesting reading.

I seem to recall that during a high-current bolted fault, they found that threaded conduit used as the EGC had a tendency to spray sparks from all the couplings. :icon_eek:

-John


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## ptcrtn (Mar 14, 2011)

STEEL CONDUIT AND EMT: PROVEN TO MEET
THE NEC® REQUIREMENTS FOR EQUIPMENT
GROUNDING
http://www.steelconduit.org/pdf/TechTalk_EquipmentGrounding.pdf


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## RIVETER (Sep 26, 2009)

Cletis said:


> Yo. You know how you increase the egc along with the largest conductor size?, well, what if you had a really large conductor and using the conduit as egc. Are conduits ALWAYS big enough to be used with any conductor (no matter the size) for the EGC ??
> 
> Say, for 1000MCM feeders using the EMT as EGC ??? Is there a limit?


Yes it is.


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## RIVETER (Sep 26, 2009)

480sparky said:


> Metal conduit always has the capacity to properly ground the conductors contained within.


I agree.


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## Cletis (Aug 20, 2010)

*?*



ptcrtn said:


> STEEL CONDUIT AND EMT: PROVEN TO MEET
> THE NEC® REQUIREMENTS FOR EQUIPMENT
> GROUNDING
> http://www.steelconduit.org/pdf/TechTalk_EquipmentGrounding.pdf


Hummm, well, as long as some knucklehead decides not to tighten down some couplings 25 ft up on a friday ?? possible ?


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## ampman (Apr 2, 2009)

when you increace wire size for VD you have to increace conduit size anyway


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