emt used as equipment ground

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slc410

Electrician
Location
Madison wi
Occupation
Electrician
When using emt as the equipment ground is there a size limitation on the ungrounded wire that would require you to run a supplemental egc? In other words no matter what size ungrounded wire, can the emt can still be used? Code article if possible?
 

ADub

Senior Member
Location
Midwest
Occupation
Estimator/Project Manager
When using emt as the equipment ground is there a size limitation on the ungrounded wire that would require you to run a supplemental egc? In other words no matter what size ungrounded wire, can the emt can still be used? Code article if possible?

358.60

What more do you need?


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infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
When using emt as the equipment ground is there a size limitation on the ungrounded wire that would require you to run a supplemental egc? In other words no matter what size ungrounded wire, can the emt can still be used? Code article if possible?

No, but there may be a length limitation.
 

macmikeman

Senior Member
You walk into an older factory on the East Coast or along the Detroit River and you see miles of conduit run all without an equipment ground. So the part about limiting length is more or less a theoretical conversation, not a reality. Conduit used as ground has been shown in testing to be a superior way to deal with returning fault current to it's source than using a copper conductor run inside the conduit.
 

Dennis Alwon

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Staff member
Location
Chapel Hill, NC
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Retired Electrical Contractor
I always thought that the emt was a better equipment grounding conductor than the conductor sized for the situation. I cannot imagine at what point a conductor would be better. Eventually the conductor would have to be so large that the emt would also have to be increased.
 

macmikeman

Senior Member
A better way to state this is to say that if the conduit run is so long the conduit itself is not able to handle enough current to create an effective ground fault return path, than by that same length the circuit wiring contained within has suffered enough voltage drop from extended length to be virtually worthless. So in conclusion----


Length limitation for metal conduit systems is determined by voltage drop on conductors rather than by the fault ability of the conduit itself.
 

big john

Senior Member
Location
Portland, ME
I always thought that the emt was a better equipment grounding conductor than the conductor sized for the situation. I cannot imagine at what point a conductor would be better. Eventually the conductor would have to be so large that the emt would also have to be increased.
Exactly.It's an interesting hypothetical to bear in mind, but practically speaking the odds of this being a problem are very low.

Based on the paper Infinity posted, any equipment ground would become ineffective after 400 feet, conduit or cable, if not upsized for voltage drop.

It seems uncommon that someone would be powering a load at such long distances with zero VD consideration.
 

peter d

Senior Member
Location
New England
You walk into an older factory on the East Coast or along the Detroit River and you see miles of conduit run all without an equipment ground. So the part about limiting length is more or less a theoretical conversation, not a reality. Conduit used as ground has been shown in testing to be a superior way to deal with returning fault current to it's source than using a copper conductor run inside the conduit.

Yes, I've observed the same thing. Once upon a time, it was standard practice not to run an EGC in metal raceway just about nationwide. I'm not sure what turned the corner on that issue, but maybe electricians took their time back then and did better work. Either that, copper.org's marketing campaign was very effective.
 

peter d

Senior Member
Location
New England
Exactly.It's an interesting hypothetical to bear in mind, but practically speaking the odds of this being a problem are very low.Based on the paper Infinity posted, any equipment ground would become ineffective after 400 feet, conduit or cable, if not upsized for voltage drop.It seems uncommon that someone would be powering a load at such long distances with zero VD consideration.

There's also the high probability that in a commercial or industrial setting, the raceway is mounted to metal (rack, building structure, steel frame, etc) about a jillion times back to the source, thus vastly increasing its current carrying capability.
 

big john

Senior Member
Location
Portland, ME
There's also the high probability that in a commercial or industrial setting, the raceway is mounted to metal (rack, building structure, steel frame, etc) about a jillion times back to the source, thus vastly increasing its current carrying capability.
Absolutely, there will almost always be parallel paths.

But I will concede that when designing a circuit the electrician can't depend on that, so it should be wired for a worst-case scenario.
 

kwired

Electron manager
Location
NE Nebraska
Absolutely, there will almost always be parallel paths.

But I will concede that when designing a circuit the electrician can't depend on that, so it should be wired for a worst-case scenario.

As a general rule no you can't depend on that.

Some applications however you have steel everywhere, no matter how hard you try to increase resistance to ground - you will have a hard time if that is your intent. Worst case still generally means if the ungrounded conductors fit inside the raceway - it has lower resistance then the wire type EGC you otherwise would pull in that raceway. If you have to upsize conductors for VD, there is a good chance you also need to upsize raceway.
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
For anybody interested you can download the GEMI software HERE



Roger
 

MasterTheNEC

CEO and President of Electrical Code Academy, Inc.
Location
McKinney, Texas
Occupation
CEO
I always thought that the emt was a better equipment grounding conductor than the conductor sized for the situation. I cannot imagine at what point a conductor would be better. Eventually the conductor would have to be so large that the emt would also have to be increased.
SHHH........
 

Carultch

Senior Member
Location
Massachusetts
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kwired

Electron manager
Location
NE Nebraska
I'm surprised to see that EMT has a longer length limit than RMC for a given trade size/OCPD combination. Intuitively I would think that RMC with threaded couplings would have the best grounding performance of any steel raceway.
What blows my mind is the thousands of irrigation services around here with runs of 1300-1500 feet or even more that are usually aluminum conductor in PVC conduit.
The tables there only say aluminum conductors are effective (per the standards stated) up to maybe 100-150 feet in the sizes most commonly encountered:eek:

But I can agree from some personal experiences that not enough fault current flows to blow fuses in a lot of these applications - quite often you just find a lot of arc damage at the fault location but fuse never blows.
 
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