LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Hey, all. I'm back.
I'm looking at a 400a 3ph existing service to feed a new panel in the ground floor of a gutted building. There are four 750mcm conductors in a 4" EMT that run from an outside disconnect, through the wall, and feed a 3ph panel. The customer wants the panel relocated several feet farther away, and to have the new ceiling hug the existing ceiling closer than the 4" EMT would allow.
I'm suggesting using MC cable above the new ceiling to feed the panel, transitioning from the EMT at the wall penetration by stripping the MC and pulling the conductors through the outside existing EMT. My understanding is there are two possible objections: the conductors must be individually marked, and an approved transition device must be used where the MC sheath meets the EMT.
The other question is how small can I go with the conductors and still comply with the requirements that they be protected from over-current.
'
1. I'm looking at a Bridgeport 290-XS to join the MC to the EMT. Am I okay here as long as the conductors are labeled?
2. Can I use 600mcm aluminum at its 385-amp rating in the 90-degree column (presuming the right insulation type) in Table 310-16, on 400-amp fuses, or must I use 750mcm aluminum at the same 385 amps as in the 75-degree column? Or must the conductors be sized at the full 400-amp rating?
I'm looking at a 400a 3ph existing service to feed a new panel in the ground floor of a gutted building. There are four 750mcm conductors in a 4" EMT that run from an outside disconnect, through the wall, and feed a 3ph panel. The customer wants the panel relocated several feet farther away, and to have the new ceiling hug the existing ceiling closer than the 4" EMT would allow.
I'm suggesting using MC cable above the new ceiling to feed the panel, transitioning from the EMT at the wall penetration by stripping the MC and pulling the conductors through the outside existing EMT. My understanding is there are two possible objections: the conductors must be individually marked, and an approved transition device must be used where the MC sheath meets the EMT.
The other question is how small can I go with the conductors and still comply with the requirements that they be protected from over-current.
'
1. I'm looking at a Bridgeport 290-XS to join the MC to the EMT. Am I okay here as long as the conductors are labeled?
2. Can I use 600mcm aluminum at its 385-amp rating in the 90-degree column (presuming the right insulation type) in Table 310-16, on 400-amp fuses, or must I use 750mcm aluminum at the same 385 amps as in the 75-degree column? Or must the conductors be sized at the full 400-amp rating?
