90A back feed?

[wrobotronic]

Hello,
I have a question re the use of a 90A backfed PV breaker to a 200A bus. I cant do a line side tap as the meter can is an all in one. And the bus rating doesn't allow for such a big breaker.

How can I get this system connected properly without changing the service to 225A or rebuilding said service to allow for a line side tap. As always I may be over thinking this, but my solution was to back feed one of 2 100A subs or do a "load side" tap on one of the 100A breakers? Not sure if any of these solutions are allowed.

TYIA

 

[ggunn]

Hello,
I have a question re the use of a 90A backfed PV breaker to a 200A bus. I cant do a line side tap as the meter can is an all in one. And the bus rating doesn't allow for such a big breaker.

How can I get this system connected properly without changing the service to 225A or rebuilding said service to allow for a line side tap. As always I may be over thinking this, but my solution was to back feed one of 2 100A subs or do a "load side" tap on one of the 100A breakers? Not sure if any of these solutions are allowed.

TYIA

You can't. It doesn't matter how you get that 90A onto the load side of the MDP, you still have the 120% rule to deal with in the MDP. If it's a 200A bus and a 200A main breaker, 40A is all the headroom you have on the load side. Upping the bus to 225A still won't get you there; that only gives you 70A of space. You only need to figure 125% of the inverter nameplate max current instead of the breaker rating into the equation, but that likely won't get you there, either. You'll either have to go in on the supply side or upsize the MDP bus to 225A and put in a 175A main breaker in place of the 200A one.

 

[jaggedben]

Not disagreeing with anything ggunn said, but here are your options.

1) Replace service panel.
1a) 225A bus with 175A breaker like he said
1b) 400A panel with two 200A breaker slots, one for existing loads and one for the solar.
1c) possibly there are some other configurations that would work, such as an MLO panel

2) See if a 100A main breaker is available for the panel. If yes, do a load calculation and see if the main breaker can be downsized to 100A. See if customer okay with that.

3) Cut in a new meter and tap box ahead of the existing main, put jumper bars in old meter base, but this only works if the existing main is not suitable only for use as service equipment. Probably not cheaper or better than (1).

4) Downsize the solar system (probably still in combination with a main breaker downsize to keep it closer to the goal).

 

[wrobotronic]

That's what I was afraid of. I think downgrading the overall system is gonna be the way to go. Thank you very much for your replies.

 

[pv_n00b]

3) Cut in a new meter and tap box ahead of the existing main, put jumper bars in old meter base, but this only works if the existing main is not suitable only for use as service equipment.

Not sure what you mean about the main panel proviso. Can you elaborate?

 

[GoldDigger]

Not sure what you mean about the main panel proviso. Can you elaborate?

A panel which is listed *only* for use as service equipment (possibly the existing main is) does not support separation of neutral from ground and so cannot become a subpanel.
It may be possible to convert it by adding a listed insulated neutral bar from the manufacturer.

Sent from my XT1585 using Tapatalk

 

[ggunn]

That's what I was afraid of. I think downgrading the overall system is gonna be the way to go. Thank you very much for your replies.

Cutting it back to less than half of what you planned is pretty drastic, but it may be your only cost effective option. Sorry to hear it.

 

[pv_n00b]

A panel which is listed *only* for use as service equipment (possibly the existing main is) does not support separation of neutral from ground and so cannot become a subpanel.
It may be possible to convert it by adding a listed insulated neutral bar from the manufacturer.

Sent from my XT1585 using Tapatalk

Good to know. I did not know that there were service entrance only panels where the service bond was not something that was optional.

 

[pv_n00b]

You don’t say anything about the existing loading on the panel but maybe 705.12(D)(2)(3)(c) might apply.

This is kind of a Hail Mary play, but if you can get an electrical engineer and the AHJ to agree on it you can have an engineer look at the panel loading and approve a non standard PV interconnection.

 

[GoldDigger]

Good to know. I did not know that there were service entrance only panels where the service bond was not something that was optional.

The ones that just say "Suitable for Service Equipmment" without the "Only" generally have two terminal buses, one of which is connected to the enclosure or the other bus by a removable green screw or jumper wire.

 

[electrofelon]

Good to know. I did not know that there were service entrance only panels where the service bond was not something that was optional.

Meter mains are good examples of equipment that is typically "only for use as SE". I can't think of any other examples I have seen off the top of my head.

 

[kwired]

Good to know. I did not know that there were service entrance only panels where the service bond was not something that was optional.

The typical "loadcenter" type panels may be very difficult to find one made that way. If you do it is likely 50+ years old.

 

[PWDickerson]

Do a load calc on the existing service. If it comes in at 150A or less, downsize the main breaker to 150A. This will allow up to a 90A backfeed breaker per the 120% rule.

 

[jaggedben]

Do a load calc on the existing service. If it comes in at 150A or less, downsize the main breaker to 150A. This will allow up to a 90A backfeed breaker per the 120% rule.

Oops, that's what my option (2) should have read in my first post above.

Actually this option is a lot more realistic than I made it out to be. I'd say so far only 20% or less of houses with 200A services that I've looked at actually needed more than 150A.