Matt Donovan
Member
- Location
- United States
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?
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?