I have a 600A 120/240V Delta service which has an undersized high leg; A and C are 350KCmil parallel; B is 2/0 parallel (all copper). This is an existing installation. We had to move the meter to another wall. We re-used the existing can and risers, hooked it back up, and called it for inspection. Inspector says we have to upgrade the B phase to 350 -- Yet the loads on A and C are about 500A, and B is 100A. I have personally never undersized the B leg, but why can't this work?
Undersized High Leg
- Thread starter Horst1
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chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
roger said:
Come on Roger, no NEC reference?
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
What about 240.4? 
What size overcurrent protective device is protecting this conductor?
What size overcurrent protective device is protecting this conductor?
georgestolz said:What about 240.4?
What size overcurrent protective device is protecting this conductor?
George, you would protect this conductor at it's ampacity, this could be with a properly sized fuse in the Main.
Roger
Last edited:
chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
roger said:
Fuses in the main yes. Smaller breaker downstream?
Main
Main
This is fused with a 600A breaker. The riser has the undersized fed to the line side of meter, then the undersized goes from load to line of 600A breaker, the load on the 600A breaker is also undersized with the 350's feeding all the single phase panels and the 2/0 feeding the only 3 phase panel, the wires tie into a 200A main breaker feeding the 3 phase loads.
Main
This is fused with a 600A breaker. The riser has the undersized fed to the line side of meter, then the undersized goes from load to line of 600A breaker, the load on the 600A breaker is also undersized with the 350's feeding all the single phase panels and the 2/0 feeding the only 3 phase panel, the wires tie into a 200A main breaker feeding the 3 phase loads.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
For the record, I didn't mean to make that out like it was directed at you, Roger. I was trying to say, "Maybe that's a possibility...?"
Edit: By Horst's last post, I'd say that's the problem. The conductor isn't protected to it's ampacity, it's protected by a 600A breaker.
chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
roger said:I was watching a movie and trying to post at the same time.
Roger
I'm watching Saturday Night Live reruns.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Horst, I'm doing a new service with the same setup. We're about to watch Ghost Rider on the big screen, so I'll be back in a while.
high leg
high leg
these situations are rare in this area but are usually addressed by a fusible main with fuse reducers (gagggg) on "B" phase.
I've seen industrial machinery with circuit breakers with different amperages per pole, and I one inquired as to the avaialbity of such for these type installlations, but the mfg. I checked with said nada.
high leg
these situations are rare in this area but are usually addressed by a fusible main with fuse reducers (gagggg) on "B" phase.
I've seen industrial machinery with circuit breakers with different amperages per pole, and I one inquired as to the avaialbity of such for these type installlations, but the mfg. I checked with said nada.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Okay, it's tomorrow, but Ghost Rider was great!
Yes, it is okay to use a smaller conductor on the high-leg, as long as it is protected at its ampacity. We're doing a new service in an older gutted brick building, being made into two apartments updtairs and a retail space down.
The upstairs service is a typical 2-meter base, fed from A and C phases and the neutral only, with a pair of 200a disco's feeding 4/0 al SER to the two 200a main-lug panels.
The downstairs service is a 200a 3-ph, high-leg open Delta, with a single 200a 3-ph meter. I used two 3/0 cu conductors for A and C phases, a 4 cu for the B phase, and a 1/0 cu for the neutral.
I used #4 for the high-leg for a combination of reasons: first, that is the POCO's minimum conductor size in a 200a meter base, and in case another 3-ph load is ever added to the smaller panel.
I'm using the 6-max-disco allowance as the service disconnecting means, with a 125a 3-ph main-lug panel with a single 3-pole 30a breaker for an existing A/C unit, and a 200a 1-ph main-breaker load-center for the rest of the service.
I tapped A and C phases in a J-box below the meter, and used two separate conduits to feed the two panels. The B phase runs unbroken from the meter lug, through the box, to the smaller panel.
I used a bare #4 cu from a meter neutral lug, through the J-box, where it passes through a lug to bond the box, and on to the smaller panel, which has no line-to-neutral loads, as its neutral-bonding conductor.
The 1/0 cu neutral passes through the J-box unbroken into the larger panel. I could have used a smaller neutral conductor according to the neutral load calc, but since the only electrode is a pair of rods, I went bigger.
Yes, it is okay to use a smaller conductor on the high-leg, as long as it is protected at its ampacity. We're doing a new service in an older gutted brick building, being made into two apartments updtairs and a retail space down.
The upstairs service is a typical 2-meter base, fed from A and C phases and the neutral only, with a pair of 200a disco's feeding 4/0 al SER to the two 200a main-lug panels.
The downstairs service is a 200a 3-ph, high-leg open Delta, with a single 200a 3-ph meter. I used two 3/0 cu conductors for A and C phases, a 4 cu for the B phase, and a 1/0 cu for the neutral.
I used #4 for the high-leg for a combination of reasons: first, that is the POCO's minimum conductor size in a 200a meter base, and in case another 3-ph load is ever added to the smaller panel.
I'm using the 6-max-disco allowance as the service disconnecting means, with a 125a 3-ph main-lug panel with a single 3-pole 30a breaker for an existing A/C unit, and a 200a 1-ph main-breaker load-center for the rest of the service.
I tapped A and C phases in a J-box below the meter, and used two separate conduits to feed the two panels. The B phase runs unbroken from the meter lug, through the box, to the smaller panel.
I used a bare #4 cu from a meter neutral lug, through the J-box, where it passes through a lug to bond the box, and on to the smaller panel, which has no line-to-neutral loads, as its neutral-bonding conductor.
The 1/0 cu neutral passes through the J-box unbroken into the larger panel. I could have used a smaller neutral conductor according to the neutral load calc, but since the only electrode is a pair of rods, I went bigger.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I see nothing wrong with well-made reducers properly installed on a fuse. If that's what it takes to protect a reduced conductor, so be it.augie47 said:
fuse
fuse
I can't argue, but every time I've used them, they always just seemed so "mickey mouse". I always feel like I;m installing the weak link in the chain, but for the problem noted, they are viable solution..
fuse
I can't argue, but every time I've used them, they always just seemed so "mickey mouse". I always feel like I;m installing the weak link in the chain, but for the problem noted, they are viable solution..
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