High on c phase code change

[Raymondrestrepo@gmail.com]

2014 nec... All 3 phase systems with one phase being different (214 nominal to ground) shall terminate the varying leg to phase c at start of system(first means of disc.) I came across it in Miami at an animal hospital. When your high leg is on the c phase coming out of the meter going into a new disconnect should it stay on the c phase all the way until the load ? Or should you come out if meter c phase and then on line place on b phase and load b phase ?

 

[Raymondrestrepo@gmail.com]

Question about High leg entering first means of disconnect

Question about High leg entering first means of disconnect

I dont doubt that. 2014 nec... All 3 phase systems with one phase being different (214 nominal to ground) shall terminate the varying leg to phase c at start of system(first means of disc.) I came across it in Miami at an animal hospital.

 

[GoldDigger]

The NEC is fairly clear that the "different" phase of an asymmetric three phase source (high leg or grounded leg depending on the source) should be landed on the B phase of the service disconnect and any downstream panels.
At the same time the most common POCO standard, applying in particular to metering where the leg difference could actually affect operations, is to have the high leg on C.
The standard way to resolve the two is to use swapping or rotation of all three conductors as needed to put the different leg on B while still providing the phase rotation that the customer is expecting. (If that is an issue.)

 

[Jraef]

Yeah, really. Not sure if you were told something or thought you read something in the 2014 code that changed anything, but it looks exactly the same to me. 408.3 is the only place where it mentions the phase arrangement at all, other than that it must be marked.

(E) Bus Arrangement.
(1) AC Phase Arrangement. Alternating-current phase arrangement
on 3-phase buses shall be A, B, C from front to
back, top to bottom, or left to right, as viewed from the
front of the switchboard, switchgear, or panel board. The B
phase shall be that phase having the higher voltage to
ground on 3-phase, 4-wire, delta-connected systems.

Basically, the power utilities can do whatever the heck they want up to the service entrance, they are not bound by the NEC. We are.

 

[Raymondrestrepo@gmail.com]

Question about High leg entering first means of disconnect

Question about High leg entering first means of disconnect

Yes I agree indeed with you both. This was brought to my attention by an Electrical Inspector and I read this meter.

A1*I'm not sure of electric utility requirements, but it's my understanding that The ANSI standard for meter equipment requires the high-leg conductor to terminate on the "C" (right) phase of the meter enclosure. The NEC requirements as follows:

Identification. On a 4-wire three-phase delta-connected system, where the midpoint of one phase winding is grounded, the conductor with the higher phase voltage-to-ground must be durably and permanently marked by an outer finish that is orange in color or other effective means. Such identification must be placed at each point on the system where a connection is made if the grounded neutral conductor is present [110.15]. Figure 110-33

 

[kwired]

I'd have to do a little looking to find where it says this, but pretty certain if you had something like a meter-main and the metering required high leg to be C phase and it is not all that practical to change whatever links the meter and main together, it is still acceptable for the C phase to remain as the high leg in that situation.

I think exceptions were added sometime more recent years that also allow something existing that has high leg on C phase to remain that way. Basically if you have an entire facility that has high leg on C phase everywhere and you added more circuits - it is probably safer to maintain what is everywhere else in that facility then to start changing things.

 

[meternerd]

Three phase, four wire KWH meters require the "power leg" to be on C phase. POCO will connect the high leg to C phase on the line side of the meter and the load side of the meter will be wired with B and C swapped in the meter to disconnect wiring (pre-wired by the panel manufacturer). Linemen are taught to connect the high leg (orange marking) to C. Occasionally, though, linemen with a background in the customer side of wiring just "knew" that B phase was always the high leg. Won't work. I usually got a call that the meter was "screwed up", so come and fix it. Never did hear a good explanation as to why there was a difference between metering and Code.