EMT as an EGC and its limitations

Status
Not open for further replies.
mbrooke

mbrooke

Batteries Included
Location
United States
Occupation
Technician
Are these bulletins valid?


https://www.nema.org/Technical/Documents/Steel Conduit and EMT-Proven to Meet the NEC Reg.pdf


https://www.google.com/url?sa=t&rct...08-20-08.ppt&usg=AOvVaw3PjNAeADwoNOWWbSRJA3l3


Basically that are saying that over 300-400 feet of conduit run you no longer have an effective fault current path. However code makes no mention of this, and some installations would automatically be in violation.


Also does the code saying anything about up sizing EMT/GRC/ect when the current carrying conductors are up-sized for voltage drop prided fill has not been exceeded?
 
Download the GEMI software from Derek's link.

Roger
 
The general belief is that the conduit is adequate for the conductors it is sized to enclose.
 
They picked a fault current of 400% of the breaker's rating. Seems very arbitrary a number. Conduit also has a pretty low resistance per 1,000' - around a 1/10th of an ohm, which is 10x less than #10 copper, with a resistance of 1ohm/1000'.

What else is coming into play to cause metal conduit to be an effective EGC to 400' or less?
 
JFletcher said:
What else is coming into play to cause metal conduit to be an effective EGC to 400' or less?
Click to expand...
If inside a normal metal frame building there is the following from NFPA 99, it is explaining the reason for 517.13(A) but could be for any building.

NFPA 99 A 4.3.3.1.3


The performance of the grounding system is made effective through the existence of the green grounding wire, the metal raceway, and all of the other building metal. Measurements have shown that it is the metal raceway and building steel that provide most of the effective grounding path of less than 10 milliohms at the receptacle, including plug to receptacle impedance. The green grounding wire becomes a backup, not a primary path performer.
Click to expand...

Roger
 
roger said:
If inside a normal metal frame building there is the following from NFPA 99, it is explaining the reason for 517.13(A) but could be for any building.



Roger
Click to expand...

This makes me want to pull a wire type EGC even less and less, more and more.

JAP>
 
jap said:
This makes me want to pull a wire type EGC even less and less, more and more.

JAP>
Click to expand...

The Cult of the Green Wire hasn't captured me yet. I never pull a green unless I'm told to. Aside from the fact that I can't see any reason to pull an extra wire in a metal conduit tied tied to metal frame that's all welded together I've done service work in plenty of old buildings that are all conduit and things there are just fine.

I know people always talk about that piece of broken emt they saw somewhere, but believe me there is just as much bad wire type egc connections.
 
ActionDave said:
The Cult of the Green Wire hasn't captured me yet. I never pull a green unless I'm told to. Aside from the fact that I can't see any reason to pull an extra wire in a metal conduit tied tied to metal frame that's all welded together I've done service work in plenty of old buildings that are all conduit and things there are just fine.

I know people always talk about that piece of broken emt they saw somewhere, but believe me there is just as much bad wire type egc connections.
Click to expand...

I agree.

JAP>
 
JFletcher said:
They picked a fault current of 400% of the breaker's rating. Seems very arbitrary a number. Conduit also has a pretty low resistance per 1,000' - around a 1/10th of an ohm, which is 10x less than #10 copper, with a resistance of 1ohm/1000'.

What else is coming into play to cause metal conduit to be an effective EGC to 400' or less?
Click to expand...

I'm guessing the minimum possible current from the POCO, but to be honest I have no idea. Anyone know?
 
ActionDave said:
The Cult of the Green Wire hasn't captured me yet. I never pull a green unless I'm told to. Aside from the fact that I can't see any reason to pull an extra wire in a metal conduit tied tied to metal frame that's all welded together I've done service work in plenty of old buildings that are all conduit and things there are just fine.

I know people always talk about that piece of broken emt they saw somewhere, but believe me there is just as much bad wire type egc connections.
Click to expand...

I don't have access anymore, but my last shop had a ton of pictures of just that condition. At a power plant. The cobbler's children...
 
Hmmm....

For the sake of debate, say i decided to run long EMT runs , and use them as the ECG

Having to also upsize conductors for VD, and having my AHJ site me on>>>

250.122 Size of Equipment Grounding Conductors.
(B) Increased in Size.
Where ungrounded conductors are
increased in size from the minimum size that has sufficient
ampacity for the intended installation, wire-type equipment
grounding conductors, where installed, shall be increased in
size proportionately, according to the circular mil area of the
ungrounded conductors.
Click to expand...

I'd be at a loss as to how to comply.....?

~RJ~
 
romex jockey said:
Hmmm....

For the sake of debate, say i decided to run long EMT runs , and use them as the ECG

Having to also upsize conductors for VD, and having my AHJ site me on>>>



I'd be at a loss as to how to comply.....?

~RJ~
Click to expand...

Nothing to comply with. The code text specifically limits its scope to wire type EGCs, when present. There is never any requirement to upsize a raceway EGC.
The simple remedy is to be sure not to pull a green wire EGC in the first place.
 
GoldDigger said:
Nothing to comply with. The code text specifically limits its scope to wire type EGCs, when present. There is never any requirement to upsize a raceway EGC.
The simple remedy is to be sure not to pull a green wire EGC in the first place.
Click to expand...

LOL! :lol:


Reminds me of a story several years ago from another member- guy has a black THHN re-identified with green tape in EMT. Inspectors calls it out. Guy has his crew pull the conductor out- inspector's look is priceless or something like that but he can't fail them.
 
romex jockey said:
Hmmm....

For the sake of debate, say i decided to run long EMT runs , and use them as the ECG

Having to also upsize conductors for VD, and having my AHJ site me on>>>



I'd be at a loss as to how to comply.....?

~RJ~
Click to expand...

As noted by Goldy above, it only refers to wire type EGCs. The words “wire type “ were added to the 2014 in part to clarify the section in a scenario such as you presented.
 
mbrooke said:
LOL! :lol:


Reminds me of a story several years ago from another member- guy has a black THHN re-identified with green tape in EMT. Inspectors calls it out. Guy has his crew pull the conductor out- inspector's look is priceless or something like that but he can't fail them.
Click to expand...

Yeah that almost happened to me once. I though it was 6 and larger, not larger than 6 ok to reidentify. Never got called on it, but was thinking I could just pull it out if I did. Was then thinking, after threatening that, the inspector would just say, well you might as well just leave it.... ;)
 
electrofelon said:
Yeah that almost happened to me once. I though it was 6 and larger, not larger than 6 ok to reidentify. Never got called on it, but was thinking I could just pull it out if I did. Was then thinking, after threatening that, the inspector would just say, well you might as well just leave it.... ;)
Click to expand...

I think that rule is silly. Good inspector would let it slide.
 
Status
Not open for further replies.
Top