Upsize EGC?

[Ponchik]

Anyone know the impedance of steel EMT versus aluminum EMT versus RMC versus GRC versus IMC versus coated versions? I can guarantee they vary. But in the NEC's eyes, they don't care about the impedance, as long as the raceways are upsized proportionally. No science behind it...

back of "Soars book on grounding & bonding" has really good charts on the conduits.

For example:

you can have maximum of 231' of 1/2" EMT that can be used as an EGC that will operate the 15A OCPD with a 75A fault current.

I will try to post the tables.

 

[Ponchik]

http://www.steelconduit.org/pdf/TechTalk_EquipmentGrounding.pdf

http://www.steelconduit.org/

the website has downloadable file. (Gemi)

 

[K8MHZ]

http://www.steelconduit.org/pdf/TechTalk_EquipmentGrounding.pdf

http://www.steelconduit.org/

the website has downloadable file. (Gemi)

From what I see there, they supposedly made field tests. If that is so, how is it that EMT and and 'steel conduit' have the exact same ratings?

Wouldn't one expect the thicker, threaded conduit to have less resistance and thus, be able to carry more fault current than EMT?

 

[mark32]

Here is a better example:

Suppose I have a 500 foot run of #6 circuit conductors, with a #10 ground wire to some pole lights.

If I put those #6 wires on a 60 Amp breaker, then it is Code-compliant.

But if I were to downsize that breaker to a 30 Amp, the Code would require me to upsize the EGC to a #6!

#10 EGC on a 60 Amp circuit is fine. But it's a violation on a 30 Amp circuit???

You just blew my mind with that one!

 

[ActionDave]

Here is a better example:

Suppose I have a 500 foot run of #6 circuit conductors, with a #10 ground wire to some pole lights.

If I put those #6 wires on a 60 Amp breaker, then it is Code-compliant.

But if I were to downsize that breaker to a 30 Amp, the Code would require me to upsize the EGC to a #6!

#10 EGC on a 60 Amp circuit is fine. But it's a violation on a 30 Amp circuit???

You just blew my mind with that one!

Crazy huh! Every time this discussion comes up the mention of voltage drop and needing enough current to trip a breaker is brought up, but then it turns out that a bigger breaker is all that is needed to make the installation safe. Crazy!

 

[david luchini]

Here is a better example:

Suppose I have a 500 foot run of #6 circuit conductors, with a #10 ground wire to some pole lights.

If I put those #6 wires on a 60 Amp breaker, then it is Code-compliant.

That'd be a violation of 210.23(D). Just sayin'.

 

[kbsparky]

That'd be a violation of 210.23(D). Just sayin'.

Not if the 60 Amp feeder went to a sub-panel first. :blink:

 

[brother]

Here is a better example:

Suppose I have a 500 foot run of #6 circuit conductors, with a #10 ground wire to some pole lights.

If I put those #6 wires on a 60 Amp breaker, then it is Code-compliant.

But if I were to downsize that breaker to a 30 Amp, the Code would require me to upsize the EGC to a #6!

#10 EGC on a 60 Amp circuit is fine. But it's a violation on a 30 Amp circuit???

Funny. but you have to remember its talking about upsizing not downsizing. One would ask, what would be the reason you had to use #6 for the 30amp breaker, (vd, etc..) . So in the real world I still see the language covering and making senses in most cases.

 

[ActionDave]

Funny. but you have to remember its talking about upsizing not downsizing. One would ask, what would be the reason you had to use #6 for the 30amp breaker, (vd, etc..) . So in the real world I still see the language covering and making senses in most cases.

So what are you saying? A #10 carries enough current to trip a 60A breaker at 500' or 600' or a thousand feet but not enough to trip a 30A? This makes sense how?

 

[kbsparky]

So what are you saying? A #10 carries enough current to trip a 60A breaker at 500' or 600' or a thousand feet but not enough to trip a 30A? This makes sense how?

This is EXACTLY what I was saying. This makes NO SENSE to me, but the Code requires it.

 

[brother]

So what are you saying? A #10 carries enough current to trip a 60A breaker at 500' or 600' or a thousand feet but not enough to trip a 30A? This makes sense how?

I never said that, nor was it implied. I just basically said that if you started out with a 30 amp breaker feed, and upsized the wire, what would be the reason for upsizing the wire. I do see you guys point about the wording of the article that needs improvement. However, I still think it would cover most cases in the real world.

Its kinda ironic, I remember asking these same questions some time ago about the upsizing of the egc and thinking that article needs some work/rewriting.

 

[ActionDave]

Its kinda ironic, I remember asking these same questions some time ago about the upsizing of the egc and thinking that article needs some work/rewriting.

I agree.

The easiest fix would be to make T250.122 work like T250.66. That is the EGC size would be based on the size of the largest circuit conductor. The size of the OCPD would not enter into the sizing of the EGC.

This seems reasonable enough. While I don't think it is perfect it is better than the current rule.

 

[brother]

I agree.
This seems reasonable enough. While I don't think it is perfect it is better than the current rule.

So who's gonna put in the proposal??

 

[charlie b]

So who's gonna put in the proposal??

No hurry. We have about 34 months before they are due (for the 2017 edition). :happyyes: