120% Rule and Feed-through Lugs

[PWDickerson]

Does the 120% rule in the 2014 NEC prevent you from installing a backfeed breaker in a panel with feedthrough lugs?

Example: Residential 120/240 service, 200 amp rated Meter-main at a detached garage, main breaker at meter-main supplies a distribution bus bar with 8 spaces and feed-through lugs at the bottom of the bus bars, 4/0 AL conductors from the feed-through lugs to a 200 amp rated distribution panel in the home where the majority of the loads are.

A strict reading of 705.12(D)(2)(3)(b) appears to allow the installation of a 40 amp backfeed breaker (32 amps of backfeed current) at the bottom of the meter-main bus bar, but this seems to me to be a clear violation of the intent of this code section. The feeders and the busbar in the panel in the home are fed from the combined current of the 200 amp main breaker and the 40 amp backfeed breaker.

Is this a violation of some other code section?

 

[Smart $]

Not a violation of any other Code section that I'm aware of.

As to whether the installation qualifies for and is compliant with (b) is subjective. Suggest verifying with the AHJ before committing.

 

[ggunn]

Does the 120% rule in the 2014 NEC prevent you from installing a backfeed breaker in a panel with feedthrough lugs?

Example: Residential 120/240 service, 200 amp rated Meter-main at a detached garage, main breaker at meter-main supplies a distribution bus bar with 8 spaces and feed-through lugs at the bottom of the bus bars, 4/0 AL conductors from the feed-through lugs to a 200 amp rated distribution panel in the home where the majority of the loads are.

A strict reading of 705.12(D)(2)(3)(b) appears to allow the installation of a 40 amp backfeed breaker (32 amps of backfeed current) at the bottom of the meter-main bus bar, but this seems to me to be a clear violation of the intent of this code section. The feeders and the busbar in the panel in the home are fed from the combined current of the 200 amp main breaker and the 40 amp backfeed breaker.

Is this a violation of some other code section?

I wouldn't do it. Whether it's a violation of the NEC or just something that wasn't considered notwithstanding, if there are feedthrough lugs below the end of the bus, I do not see how the PV could be connected at the end of the bus, electrically speaking. If the feedthrough lugs feed an MLO panel, as they frequently do, then it's a no-brainer; you cannot do it.

 

[jaggedben]

I think it's a violation of 705.12(D)(2)(1). You have an inverter output that's connected to a feeder other than at the opposite end from the primary source, you have feeder conductors that aren't rated for the combined output of both sources, and you haven't mentioned a downstream overcurrent device. If it were stipulated that the downstream panel has a main breaker, then in my opinion it would be okay. Option 2: put the inverter output at the opposite end of the down stream panel instead of the main.

 

[Smart $]

I think it's a violation of 705.12(D)(2)(1). You have an inverter output that's connected to a feeder other than at the opposite end from the primary source, you have feeder conductors that aren't rated for the combined output of both sources, and you haven't mentioned a downstream overcurrent device. If it were stipulated that the downstream panel has a main breaker, then in my opinion it would be okay. ...

The point in your premise that I question is whether or not the inverter output is connected to a feeder. In many cases, we must tender bus as a feeder simply because no account is given by the requirement in debate for the bus being a circuit conductor. In this case, however, the requirement does account for bus [705.12(D)(2)(3)]... and the PV system disconnecting means (breaker) is connected to the panel bus, not the feed-through conductors (feeder).

That said, when I evaluate your premise on the basis of what I believe to be the intent of the section as a whole, I agree. :happyno::happyyes::happysad::lol:

 

[MJRobinson]

The Tap should be before the Busing

The Tap should be before the Busing

The tap need to happen before the main bus, its the bus rating that you are measuring against.. We use Burndy connectors.