Carultch
Senior Member
- Location
- Massachusetts
Consider this example.
You have a 100A circuit, which would ordinarily require #3 Cu wire with a #8 Cu EGC. You then upsize it to a #3/0 Cu circuit for voltage drop, which would require a #3 Cu egc. (KCMIL 3/0)/(KCMIL 3) * (KCMIL 8) = 51.6 kcmil = #3.
If you plan on using MC cable, the combination of #3/0 with #3 doesn't exist. Because the #3/0 Cu cable was built with a 200A circuit in mind, which would usually require #6 Cu EGC. This manufacturer planned a #4 Cu EGC to allow room for error.
https://www.encorewire.com/wp-content/uploads/EncoreWire-MC_SL-THHN.pdf
What course of action would you recommend, to work through this situation?
1. Have the AHJ make an exception to approve the #4 EGC and call it day, noting that the metal cladding and cable tray also carry the ground.
2. Change the breaker to 150A, so that 3/0 & #4 is now compliant. Note that equipment manufacturers may limit the maximum ocpd, and thus not allow this.
3. Run a #3 EGC externally, grouped with the cable, in the same cable tray if applicable, and bonded at every opportunity. Note that this will leave an "insufficinetly sized" EGC inside the cable.
You have a 100A circuit, which would ordinarily require #3 Cu wire with a #8 Cu EGC. You then upsize it to a #3/0 Cu circuit for voltage drop, which would require a #3 Cu egc. (KCMIL 3/0)/(KCMIL 3) * (KCMIL 8) = 51.6 kcmil = #3.
If you plan on using MC cable, the combination of #3/0 with #3 doesn't exist. Because the #3/0 Cu cable was built with a 200A circuit in mind, which would usually require #6 Cu EGC. This manufacturer planned a #4 Cu EGC to allow room for error.
https://www.encorewire.com/wp-content/uploads/EncoreWire-MC_SL-THHN.pdf
What course of action would you recommend, to work through this situation?
1. Have the AHJ make an exception to approve the #4 EGC and call it day, noting that the metal cladding and cable tray also carry the ground.
2. Change the breaker to 150A, so that 3/0 & #4 is now compliant. Note that equipment manufacturers may limit the maximum ocpd, and thus not allow this.
3. Run a #3 EGC externally, grouped with the cable, in the same cable tray if applicable, and bonded at every opportunity. Note that this will leave an "insufficinetly sized" EGC inside the cable.