Another 25 ft Tap rule

[kec]

I'm proposing to install a metered 200A 3 phase panel from a existing 1200A 120/208 SVC
Existing MB is 1200A
Feeder length is more than 10 FT but less than 25
Question [1] Tapping off load side of MB, 1200A divided by 3 = 400A
Conductor size should be rated for 400A

Question [2] Does the feeder tap need to first land in a OCPD, then Meter
Or can it be Meter, than OCPD

Estimated load on this panel is 150A
Feeder will be installed in conduit

 

[infinity]

So this tap is after the 1200 amp OCPD?

 

[Elect117]

For question 1: conductor rated 400A or more. no rounding up from a conductor rating lower than 400A.

For question 2: OCPD then meter. Also, you might also need a disconnect before the meter. Like a fused disconnect would work. Most likely at 400A you will need CT rated meter. I know you said 200A, but they don't typically have the space to land 400A of conductor. Maybe you will though.

Estimate load is 150A but since the wire will be large, you might want a larger board just to avoid landing issues, wire spacing, etc. inside the board. Especially if you do parallel runs of 3/0 or 600kcmil copper.

 

[kec]

So this tap is after the 1200 amp OCPD?

yes

 

[kec]

For question 2: OCPD then meter. Also, you might also need a disconnect before the meter. Like a fused disconnect would work. Most likely at 400A you will need CT rated meter. I know you said 200A, but they don't typically have the space to land 400A of conductor. Maybe you will though.

How about a 320A meter to avoid CT

 

[Elect117]

How about a 320A meter to avoid CT

It should be fine.

As long as the meter is good for the wire size and such. The OCPD won't protect it, but you aren't technically installing 400A of load. So the meter will be accurate and won't error out.

 

[KevinKos]

Question 1: Conductor Size for a 400A Feeder Tap​

For a feeder tap, the conductor size must be rated to carry the current. In this case, if you are tapping off the load side of a 1200A main breaker, and dividing it by three (1200A / 3 = 400A), the conductors must be sized to handle 400A.

According to NEC 2020, section 240.21(B)(2), the ampacity of the tap conductors more than 10 feet but not greater than 25 feet in length must be at least one-third of the rating of the overcurrent device protecting the feeder conductors. This implies the conductors should be rated for at least 400A in this scenario.

Question 2: Feeder Tap Landing Sequence​

The sequence of connecting the feeder tap to the overcurrent protection device (OCPD) and meter is crucial.

According to NEC 2020, Article 240.21(B)(2):

1. The tap conductors must terminate in a single circuit breaker or a single set of fuses that limit the load to the ampacity of the tap conductors.
2. The conductors must be protected from physical damage by being enclosed in a raceway or by other approved means.

Thus, the feeder tap conductors should first land in an OCPD before proceeding to the meter to comply with the requirement that tap conductors must terminate in a protective device that limits the load to the ampacity of the tap conductors.

However, local service provider guidelines, like those from CenterPoint Energy and Oncor, may have additional or different requirements about meter mounting and sequencing. These guidelines indicate that typically, the meter should be installed before the service equipment (including OCPD).

Summary​

1. Conductor Size: The conductors for a 400A tap should be rated for 400A.
2. Sequence: The feeder tap should first land in an OCPD before the meter to comply with NEC 2020.