Will the 120% rule apply to this meter panel if the PV will be tapped into the conductor that is going to the MSP inside the house which is rated for 200A with a 200A main breaker? I was thinking it would not be the case since it seems the meter main bus would not see 200A since the PV would be supplying the panel inside the house.
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Question about 120% rule and load side tap on meter main.
- Thread starter vertx93
- Start date
Carultch
Senior Member
- Location
- Massachusetts
The 120% rule applies to busbars, rather than to feeders. Feeder interconnections have their own section in 705.12. 705.12 rules continue to upstream panelboards, all the way to the service point, so you want to anticipate the complete path to the service point when determining how to tie-in.
Ultimately, to tie-in to a feeder, you need it protected on both ends, to prevent overload on the feeder. E.g. given a meter/main and a feeder to an MLO panel, a tie-in on the feeder would create a possibility of overloading the main panelboard in the blindspot of the meter/main. Therefore, you'd want to place your feeder tap between OCPD's on both sides, in some form or another.
Ultimately, to tie-in to a feeder, you need it protected on both ends, to prevent overload on the feeder. E.g. given a meter/main and a feeder to an MLO panel, a tie-in on the feeder would create a possibility of overloading the main panelboard in the blindspot of the meter/main. Therefore, you'd want to place your feeder tap between OCPD's on both sides, in some form or another.
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
Yeah that's a good one, a panel with feed through lugs that aren't at the same ends of the busbar, and that's also effectively center-fed.Will the 120% rule apply to this meter panel if the PV will be tapped into the conductor that is going to the MSP inside the house which is rated for 200A with a 200A main breaker? I was thinking it would not be the case since it seems the meter main bus would not see 200A since the PV would be supplying the panel inside the house.
For residential you could get to use 705.12(B)(4), for centerfed panels. [2023 NEC reference]
You can also use one of the other rules like 705.2(B)(3) or PCS (705.13).
As noted if you do a feeder tap you have additional rules to comply with.
PWDickerson
Senior Member
- Location
- Clinton, WA
- Occupation
- Solar Contractor
I believe the OP stated that the distribution panel in the home has a 200A bus and a 200A main breaker. If so, there should be no issue doing a feeder tap in the meter-main. A 705.13 (PCS) solution will likely involve CT's at the service conductors, which are bussing in this case, and not really accessible.