EMT as EGC for large feeders

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What do people think of using EMT as the only EGC on large feeders for 480V systems? It's permitted by code, but when are people comfortable that it will be sufficient? Especially considering long and oversized feeders.

For example, a 1600A feeder with 8 sets AL 500MCM run 850ft in 3" EMT on a rooftop (oversized to keep voltage drop below 2%). If using a wire-type EGC, 250.122 requires a #4/0 CU in each conduit, but we'd actually need to oversize to 350MCM CU per 250.122(B) since the wires are oversized. That's getting expensive. (This is a solar PV application.)

Here's an idea... What if I call the EMT the "primary EGC", but install an "auxiliary EGC" to satisfy anyone who doesn't trust a long run of EMT to maintain a low impedance ground? I'm thinking that in my example, this auxiliary ground could be as small as #1/0 CU (1 per each conduit), or a single 350MCM CU (installed in a separate conduit). Dubious?
 

iwire

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Location
Massachusetts
I am much more comfortable using the EMT as the EGC for large feeders vs branch circuits. The chance for damage to the conduit is much less.

The steel of the EMT is lower impedance than the wire EGC you would install inside it.

When it has been my choice I have used EMT as the EGC for 1,200 amp 480 feeders.

Also keep in mind at this level the feeder is required to have ground fault protection.
 

electricalist

Senior Member
Location
dallas tx
I second Mr. iwire s comment, an auxiliary ground won't work. I use the raceway as the egc when it's my choice and it's my belief it's a better conductor, on long runs the conduit will increase as the wire size increases.
Imo there are more wire type grounds done poorly than any amount of loose connections or lack of bonding with any metallic raceway egc s .
 

electricalist

Senior Member
Location
dallas tx
Now let me help the opposition.
My supervisor has never had a poor connection with anything he is involved in except maybe other employees, that aside he insists on a wire type and he is firm believer that when it's there and it's landed and you can check for what it should be by code, then he is content that the free world is safe and so he can rest his robot like mind.
 

iwire

Moderator
Staff member
Location
Massachusetts
Sign me up for iwire's team too.

:cool:


Cool, but be warned before every game we all sing White Wedding with our best sneers on.


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