Inverter in Garage

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I have a client that wants to put his solar inverter in his garage, and interconnect into the subpanel located in this garage. Is this allowed? If so, will the 2014 NEC require a directory, or an extra AC disconnect, or some other type of special requirements?

Regards,
Andy
 
Thanks for your reply, GoldDigger.

In the garage, there's a new Murray 150 amp subpanel. On the panel sticker, it says "Back-Fed Breaker Requires Hold-Down Kit MBR2M". Is it safe to assume since I'm putting in a back-fed PV breaker, the installer would need this kit? Or am I misunderstanding something? (I'm a designer, but this a piece of information I'd like to know nonetheless)

The main panel is an MLO being fed by 1/0 copper service entrance conductors. It lacks a sticker that tells me the busbar rating of the panel, but there's a single 125 amp subpanel breaker on the bus (which feeds the subpanel in the garage). For the sake of this conversation, I will assume the busbar rating of the main panel is 125 amps.

From a 120% Rule point-of-view, would this be the correct way to think of the calculations:

Subpanel: (150A * 120%) - 125A = 55A of available PV amperage

Main Panel: Since it's a MLO panel, I can have PV amperage up to the limit of the service entrance conductors

Is my way of reasoning correct?

Thanks in advance.

Kind Regards,
Andy
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
There's nothing wrong with what you propose. You don't need the hold down on the breaker, that's for a main breaker. I think it's 705.12 (D)(5) that says you don't need it for an interactive inverter.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Thanks for your reply, GoldDigger.

In the garage, there's a new Murray 150 amp subpanel. On the panel sticker, it says "Back-Fed Breaker Requires Hold-Down Kit MBR2M". Is it safe to assume since I'm putting in a back-fed PV breaker, the installer would need this kit? Or am I misunderstanding something? (I'm a designer, but this a piece of information I'd like to know nonetheless)

The main panel is an MLO being fed by 1/0 copper service entrance conductors. It lacks a sticker that tells me the busbar rating of the panel, but there's a single 125 amp subpanel breaker on the bus (which feeds the subpanel in the garage). For the sake of this conversation, I will assume the busbar rating of the main panel is 125 amps.

From a 120% Rule point-of-view, would this be the correct way to think of the calculations:

Subpanel: (150A * 120%) - 125A = 55A of available PV amperage

Main Panel: Since it's a MLO panel, I can have PV amperage up to the limit of the service entrance conductors

Is my way of reasoning correct?

Thanks in advance.

Kind Regards,
Andy

A couple of the AHJ's I deal with will not allow me to backfeed an MLO main panel.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
A couple of the AHJ's I deal with will not allow me to backfeed an MLO main panel.
If there is no upstream service disconnect (with OCPD), then backfeeding an MLO main would seem to be a line side (supply side) connection, which some jurisdictions and POCOs do not allow.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
If there is no upstream service disconnect (with OCPD), then backfeeding an MLO main would seem to be a line side (supply side) connection, which some jurisdictions and POCOs do not allow.

True, but that isn't what's happening here. We can interconnect on the line side via IPCs but we still have to install a main breaker in the MDP.
 

Ctay005

Member
Location
Orem, Utah, USA
A couple of the AHJ's I deal with will not allow me to backfeed an MLO main panel.

After talking to many AHJ's about this, all but one have allowed us to backfeed a MLO panel after talking to them and explaining the reasoning behind why it works.

We've had a few AHJ's that don't like inverters installed in garages and make us install an additional AC disco adjacent to the MSP when we do this. It's not common but I can't remember when we were actually rejected for it, just frowned upon!
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I'm not clear on this part? Is it as long as the sum of the load breakers doesn't surpass the buss rating, assuming you find it.

Oddly enough, if you look at 230.90 Exception 3, it is the calculated load on the service that determines what the busbar must be rated, not the sum of the load breakers. But that's more or less irrelevant to how much solar you can put on under 705.12(A). That section says 'rating of the 'service', which I take to be whatever is the weakest link between the solar breaker and the service point: busbar, conductors, meter socket...whatever. And the solar isn't a load so has nothing to do with complying with 230.90.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I'm not clear on this part? Is it as long as the sum of the load breakers doesn't surpass the buss rating, assuming you find it.
Unless you are dealing with 705.12(D)(2)(3)(c), the sum of the load breaker ratings when you are qualifying a bus is irrelevant. Is that article pertinent to an MLO service entrance panel?
 
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