Delta High Leg

[Electricalhelp]

The electrical inspector is requiring the “C phase High Leg” to be connected to phase B in the 600amp 3 phase panel. He said everything is installed correctly to the service disconnect with the high leg on Phase C because that is what utility company requires. But when we pull our wire from our main disconnect to the 600amp panel, we need to swap the phases B and C in the panel making B phase the high leg.

In which section or reference of the NEC Code does it specify that Phase B must be designated as the high leg, as informed by the electrical inspector?

 

[zbang]

The inspector ought to provide their citation, but from the 2017 code index-
Identifying high-leg, 3-phase supply, 4-wire, 110.15, 230.56, 408.3(E)(1), 408.3(F), 409.102


It's in 408.3(E)(1).

 

[Filthy]

110.15, 408.3

 

[jap]

The electrical inspector is requiring the “C phase High Leg” to be connected to phase B in the 600amp 3 phase panel. He said everything is installed correctly to the service disconnect with the high leg on Phase C because that is what utility company requires. But when we pull our wire from our main disconnect to the 600amp panel, we need to swap the phases B and C in the panel making B phase the high leg.

In which section or reference of the NEC Code does it specify that Phase B must be designated as the high leg, as informed by the electrical inspector?

Most around here swap the wild leg to B phase as soon as it leaves the meter so even the Service disconnect would have the wild leg landed on B phase.

Jap>

 

[jap]

I'm also surprised you're having to run a 600 amp service through a self contained meterbase and it's not CT'd although we've had to do that in the past also.

Jap>

 

[texie]

Jap pointed out some of the leg requirements but I might add a few things. Back when dirt was invented, the POCOs standardized on the C leg to be used for the high leg for the correct operation of their meters Never saw one that does not require that, even today. As a result it was very common to put the high leg on the C phase thru out a building in decades past. In the 1975 NEC it became a requirement for the high leg to be on the B phase in panelboards. As the code cycles progressed over the years we now have a number of location and marking requirements.
As noted by Jap, the standard practice today is to put the high leg on C at the meter and then swap it to the B leg at the service equipment and thru out the premises. If you have to change rotation then just swap the A and C legs so the high leg will always be on B.
One needs to never assume where the B leg on an existing installation is as this is wildly violated, especially in older buildings.

 

[Hv&Lv]

9S meter doesn’t “require” it.
we require the high leg on the far right just for uniformity now. helps us when the service gets torn down in a storm for example.

The old mechanical meters had two CTs in them. The one for the single phase parts (A & B phase) was like a 3S with the currents passing through the CT in opposite directions. The CT for the far right(C phase) had only one CT for that phase. Thats why it was required on the far right In the meter base.

 

[Carultch]

9S meter doesn’t “require” it.
we require the high leg on the far right just for uniformity now. helps us when the service gets torn down in a storm for example.

The old mechanical meters had two CTs in them. The one for the single phase parts (A & B phase) was like a 3S with the currents passing through the CT in opposite directions. The CT for the far right(C phase) had only one CT for that phase. Thats why it was required on the far right In the meter base.

If modern meters do the proper vector math anyway, and don't require a C-phase high leg anymore, why not just allow the customers' electricians land it on the phase that the NEC requires throughout the rest of the system, as long as they provide clear labeling?

 

[Hv&Lv]

If modern meters do the proper vector math anyway, and don't require a C-phase high leg anymore, why not just allow the customers' electricians land it on the phase that the NEC requires throughout the rest of the system, as long as they provide clear labeling?

Uniformity across the system.

Most linemen aren't electricians, and understand very little about electrical theory or any NEC codes.

say a storm comes, tree falls and tears the service down. We go to put it back up in the middle of the night..

 

[herding_cats]

2020 NEC code requires high leg at B phase.

 

[Tulsa Electrician]

Here in Tulsa it's required to be on C or far right and is marked power leg. It's an AEP requirement.

Here is few pics I used to share with the guys as to why.
As noted above for the power company guys.

These pics are from an AEP metering guide lines and other sources.