EGC Smaller than Line

[Cletis]

I'm bidding on a job where the old RTU was a 3 phase 125amp rated unit. The new unit is 90 amp max fuse size. Because of length of run and old #1 Cu wires jammed in pipe its easier to leave old phase conductors. Unfortunately, the conduit was the egc but had to be removed below the gutter and some 1" Sealtight ran to make it to new disconnect area. I have a 2 part question.

Can I run old pipe into a 12x12 metal enclosure then out with sealtight to RTU ? (right above acoustical ceiling grid) provided I bond the enclosure ? Thinking yes

Can I run a # 4 Cu THWN (for the new egc) from a bonding lug in enclosure through sealtight to the new disconnect based on max 90 amp breaker? I know a # 4 Cu doesn't match the #1 cu in size but I was hoping the new load would trump this ?? The old 125 amp breaker would be replaced to a 90 amp as well at the disconnect on the roof.

 

[petersonra]

I'm bidding on a job where the old RTU was a 3 phase 125amp rated unit. The new unit is 90 amp max fuse size. Because of length of run and old #1 Cu wires jammed in pipe its easier to leave old phase conductors. Unfortunately, the conduit was the egc but had to be removed below the gutter and some 1" Sealtight ran to make it to new disconnect area. I have a 2 part question.

Can I run old pipe into a 12x12 metal enclosure then out with sealtight to RTU ? (right above acoustical ceiling grid) provided I bond the enclosure ? Thinking yes

What do you mean by "bond the enclosure"? The incoming conduit will bond the metal box so nothing else needs doing to the box.

Can I run a # 4 Cu THWN (for the new egc) from a bonding lug in enclosure through sealtight to the new disconnect based on max 90 amp breaker? I know a # 4 Cu doesn't match the #1 cu in size but I was hoping the new load would trump this ?? The old 125 amp breaker would be replaced to a 90 amp as well at the disconnect on the roof.

IMO, it depends entirely on what size circuit conductors are in the sealtight. You could run a #8 EGC if you can run #4 circuit conductors.

 

[Cletis]

What do you mean by "bond the enclosure"? The incoming conduit will bond the metal box so nothing else needs doing to the box.

Just meant gonna install a bonding lug in enclosure to run new egc from



IMO, it depends entirely on what size circuit conductors are in the sealtight. You could run a #8 EGC if you can run #4 circuit conductors.

Was going to butt splice the old #1 Cu to new # 4 Cu conductors (lines) and # 4 EGC

Similar to parking lot lighting scenarios (large conductor than smaller and smaller)

I'm surfing 250.122 but can't come up with anything as of yet

 

[petersonra]

Was going to butt splice the old #1 Cu to new # 4 Cu conductors (lines) and # 4 EGC

Similar to parking lot lighting scenarios (large conductor than smaller and smaller)

I'm surfing 250.122 but can't come up with anything as of yet

I see nothing wrong with this.

 

[kwired]

Was going to butt splice the old #1 Cu to new # 4 Cu conductors (lines) and # 4 EGC

Similar to parking lot lighting scenarios (large conductor than smaller and smaller)

I'm surfing 250.122 but can't come up with anything as of yet

You have 90 amp overcurrent device, you don't have increased ungrounded conductor size, end result comes straight from the table.