NEC 705.12(D) - Does this apply to main panel if subpanel used?

[reader2580]

I am planning to hook up my inverter to a subpanel in my garage. Does NEC 705.12(D) apply in any way to the main load center in the house since the main load center feeds the garage subpanel? I would ask the local electrical inspector, but I can't get in touch with him.

I will probably just put in a 175 amp main breaker in if I need to meet 705.12(D), but I might replace the load center with one with a 225 amp bus.

[adoublee]

It applies - you have to protect all bus downstream of the utility service disconnect (probably your main breaker in your house).

[reader2580]

This is just silly. I can run 60 amps of power to my garage subpanel without upgrading my main panel, but if I add in solar then suddenly my bus bar is too small even though I still can't run more than 60 amps on the same circuit to the garage subpanel?

This basically means I am going to be without power for an entire weekend plus Monday so I can replace the main load center. The electric company has to send someone out to pull the meter and then send someone out again to enable the power after the electrical inspector signs off. I have a whole house generator with a separate sub panel, but I don't think the neighbors will like me running it at night.

[adoublee]

This is just silly. I can run 60 amps of power to my garage subpanel without upgrading my main panel, but if I add in solar then suddenly my bus bar is too small even though I still can't run more than 60 amps on the same circuit to the garage subpanel?

There are some silly things in the NEC but this has some merit. The bus in your main panel has an amp rating. In a situation where you are only feeding loads, a main breaker prevents more amps from entering the bus than it is rated for. If you now turn a load breaker into a source of amps, that bus can get more amps than it is rated for unless something is done to limit it. Count up the ampacity of all the other breakers in your main panel and you will probably find they they total more than the value of your main breaker, so there needs to be another limit on how much current can feed backwards into that bus.

[reader2580]

I suppose what they are worried about is pulling 35 amps from solar and then another 200 amps from the main breaker thus overloading the bus bars.

I'm really close to just abandoning my solar plans because the costs and work involved keep going up and up. It will cost me $300 plus a full weekend to replace my main panel and I have no power for three days. I will most likely have to replace the power feed to my detached garage as part of this and it will cost me several thousand for that. I have to remove a slab, remove a sidewalk, and remove a retaining wall to run a new power feed. I will need to bring in a contractor with an excavator to dig a trench as it will be five feet deep at one spot.

[GRickard]

Reader, if you can run the solar AC side back to the meter socket you could use the "MILBANK K5022-INT HEX INTL TAP CONNECTOR". A lot cheaper (at $35) and faster than a panel upgrade. Milbank also has a solar ready meter base available.

Greg

[reader2580]

I think it would actually be easier to replace the panel than to do a supply side tap, but I could be totally wrong. It appears I could just replace the main breaker with a 175 amp one, but replacing the main breaker will be almost as difficult as replacing the whole load center from the looks of it.

[GRickard]

The tap would be on the load side of the meter base. With either option you will have to have the utility pull the meter and the jacks on the pole, but with the taps all you do is replace the existing lug plates with the new ones and install conduit and wire to the disconnect within 10 feet (of wire). That's a lot easier than a panel change out and with the right prep work and communication could be done in a few minutes with the utility and the inspector there to minimize outage time.

Greg

[peakbagger]

FYI , the local utility in my area does not allow any PV wiring in their meter enclosure and does not accept meter adaptors. Apparently other utilities have the same attitude. The local utility requires the line side tap in a separate enclosure downstream of the meter enclosure. If there is room in the main panel upstream of the main breaker that's okay but most folks apparently are cutting a new enclosure into the conduit.

[tyab]

Reader2580 - (all of this may be mute since your AHJ wants you to be a qualified person), but lets step back a moment. How big of a system were you planning on needing. Just want to run the calcs starting with that garage subpanel.

[reader2580]

Reader2580 - (all of this may be mute since your AHJ wants you to be a qualified person), but lets step back a moment. How big of a system were you planning on needing. Just want to run the calcs starting with that garage subpanel.

My plans are to use a Fronius Primo 8.2 KW inverter which has output of 34.2 amps at 240 volts. I plan to replace the garage subpanel with a 12 circuit panel that has a 125 amp bus. The feed is 60 amps from the house. The garage subpanel should be fine since the bus bar is 125 amps.

The house panel is 200 amps. The garage is fed from a 60 amp breaker. I will be slightly over the bus bar capacity. The options are a new load center with 225 amp bus and 200 amp main breaker, or putting a 175 amp main breaker in the current load center. Replacing the main breaker is probably just as much work as replacing the load center.

Another option I am considering is just going with a 7.6 KW inverter that will not require changes to the main load center. With thirty 300 watt panels I will be at 118% of inverter capacity which is within specs. The ideal string size seems to be 10 panels with the panels I am getting.

[inetdog]

Replacing the main breaker is probably just as much work as replacing the load center.

Another option I am considering is just going with a 7.6 KW inverter that will not require changes to the main load center. With thirty 300 watt panels I will be at 118% of inverter capacity which is within specs. The ideal string size seems to be 10 panels with the panels I am getting.

I am not sure it would be as much work, especially when you take into account removing and repulling all of the branch wiring (unless you just swap the guts inside the enclosure.)
But the new main breaker may well cost as much as the new panel with breaker as a bundle.
If you change the panel to a 225A bus you may find yourself changing brands and that may mean replacing all of the branch breakers too.

[reader2580]

I am not sure it would be as much work, especially when you take into account removing and repulling all of the branch wiring (unless you just swap the guts inside the enclosure.)
But the new main breaker may well cost as much as the new panel with breaker as a bundle.
If you change the panel to a 225A bus you may find yourself changing brands and that may mean replacing all of the branch breakers too.

The current panel is an ITE panel. Siemens bought the company and current Siemens/Murray breakers can be used in the panel. Many of the breakers have been replaced with AFCI due to major electrical work to the house. Siemens makes a 225 main lug amp panel that uses the same breakers. The panel is $160 and a 200 amp main breaker is $84. A 175 amp main breaker for current panel is also $84. (Yes, Siemens still sell main breakers for a panel type that was discontinued in 2002.)

The wire from the meter is very stiff aluminum wire. I highly doubt I could pull the wire out of the main breaker lugs to replace the main breaker. I think I would need to disconnect everything from the panel board and then unscrew the panel board and pull it down to get free of the free cables.

The idea of just going with an 7.6 KW inverter and losing 10% of output on the best day is starting to sound better the more I think about it,

[reader2580]

I can't find a Siemens 225 amp panel that has a 200 amp main breaker. I would need to buy a main lug 225 amp panel and then buy the 200 amp main breaker separately. Eaton and Square D both make "solar ready" panels that have a 225 amp bus with 200 main breaker. The only Siemens "solar ready" product is an outdoor load center with meter socket. My load center is in the basement.

[inetdog]

There is nothing stopping you from using a meter-main panel inside and just not using the meter socket!