Grid Tie in Tucson Az

[posplayr]

It may/may not have power - the straddling breaker (and therefore the panel in the shed) will have 1 side live and the other side floating if the 60A feeding the lower is off.
So only if/when you have a 220V load connecting the two sides in your shed would you have the lower bus having voltage. (and that 220V load probably would be unhappy - it'd be seeing some weird voltages, since that side would not be driven by the POCO.)

Well I wont be using my tongue to find out.

[foo1bar]

Last night I just realized how bad that straddling breaker is. Unless both it and the house main are off the lower panel will still have power. Not good.

It may/may not have power - the straddling breaker (and therefore the panel in the shed) will have 1 side live and the other side floating if the 60A feeding the lower is off.
So only if/when you have a 220V load connecting the two sides in your shed would you have the lower bus having voltage. (and that 220V load probably would be unhappy - it'd be seeing some weird voltages, since that side would not be driven by the POCO.)

[posplayr]

One thing that I think has not been addressed yet is that at least one circuit in the lower left portions of the panel, using dual breakers, may be a MultiWire Branch Circuit (MWBC) with a red wire, black wire, and possibly a common neutral. If all you do is move the half size breakers up one position to fill in the blank, then you would end up feeding the black and the red wire from the same L connection. This will double the maximum current on the shared neutral, causing as fire hazard and a code violation.
An electrician can tell you how to rearrange the half sized breakers to make sure that this does not happen.

Thanks I'll check into that. Last night I just realized how bad that straddling breaker is. Unless both it and the house main are off the lower panel will still have power. Not good.

[inetdog]

One thing that I think has not been addressed yet is that at least one circuit in the lower left portions of the panel, using dual breakers, may be a MultiWire Branch Circuit (MWBC) with a red wire, black wire, and possibly a common neutral. If all you do is move the half size breakers up one position to fill in the blank, then you would end up feeding the black and the red wire from the same L connection. This will double the maximum current on the shared neutral, causing as fire hazard and a code violation.
An electrician can tell you how to rearrange the half sized breakers to make sure that this does not happen.

[posplayr]

http://ecmweb.com/code-basics/dwelli...r-calculations

http://iaeimagazine.org/magazine/201...ectrical-code/

Thanks

[foo1bar]

Perhaps I don't know what a load analysis is,

http://ecmweb.com/code-basics/dwelling-unit-feederservice-conductor-calculations

http://iaeimagazine.org/magazine/2013/05/16/residential-service-calculations-in-the-national-electrical-code/

[posplayr]

Not necessarily.

What you really need to do is a load analysis to see what is actually required for a main breaker for your property.

Most likely you have <200A when you do the load analysis.
Assuming that's the case, you can find a panel that has 225A bus
(ex. http://www.homedepot.com/p/Eaton-225...225R/202276723 )

200A main is at one end, 60A solar at the opposite end, and you're still less than 225*1.25
Possibly you can also do a 200A bus with 175A main and 60A at opposite end. (Assuming 175A or less from the load analysis)

Or possibly there are some designed-for-solar that have a separate breaker spot designed just for putting in a 60A breaker for solar.

http://www.downloads.siemens.com/download-center/Download.aspx?pos=download&fct=getasset&id1=BTLV_40907

I'm not sure if all of them are combined main + meter - they probably are.


Now if you're asking "How can I have 300A of breakers on a 200A main?" - the answer is the same as how you can have >10 of those 15A and 20A breakers being fed by a 60A right now. It's OK to do that - you just have to look at what's reasonable expectation for things being used together - which is basically what the load analysis does.


If I were looking at it, I'd possibly look at the combined meter-main panel.
I'd either replace the existing main and meter,
OR
have the breakers in the combo be 100A-shed, 60A-solar, and 100A-feeding-existing-split-bus-house-panel (assuming the house panel load analysis works for that - which my best guess is it would)

Good luck

Perhaps I don't know what a load analysis is, but I articulated one before to realize that it is pretty meaningless as breaker amperage levels are peaks attaining values of at least an order of magnitude above the average loads. So it is clear that the face value of load breakers are typically analytically merged in such a way to come up with a rationalized average load. The point is that unless you're talking peak loads analysis on a per circuit basis) and not averages the breakers arrived at will be wrong. Average loads are way way below peaks required on the breakers.

Other than the 60 amp house breaker and the 100 amp shop breaker, the rest are major loads like furnace, AC and swamp coolers which we are not going to be able to reduce. The house/light breaker is maxed out for what I understand is traditionally 60 amps so not likely to reduce that either. The "elephant in the room" is the 100 amp shop service that is being underutilized. It is driving up the breaker loads total on upper bus bar in the split panel and is making it appear as if the whole panel will go up in flames. Reality it is being way underutilized.

If it is allowable (which I think it is according to my previous post), dropping some of the amperage on the main feeder to the shop sub panel from 100A to 80A will give sufficient headroom on the 125A subpanel for the 60 amp backfeed PV breaker. This is putting more stress on the new sub panel, but takes some load off of the main panel. The #4 awg feeder to the sub panel should be plenty even with the PV and I don't have to trench then, just bore more holes in the brick wall. (it is actually easier to dig)

[posplayr]

Coming full circle, we are back to the solution that Solarix suggested at the beginning of the thread.

The shop is on a 100 amp circuit with a 125 amp sub panel is is basically not being used. The 125% rule would provide for for 1.25 x 125 Amps or 150 ampacity of the bus bar. Reducing the main breaker in the split bus panel to 80 amps and putting a 60 amp in for the PV in the bottom of the shop sub panel would total 140 amps total against the 125 amp limit. The house is safer as we reduced the 100A breaker down to 80A which can't be complained about and the new sub panel is below the 125% limit.

Apparently section (7) was omitted in NEC 2014, but since Az is still under NEC 2011 it must still apply.

http://solarprofessional.com/articles/design-installation/nec-section-70512-and-utility-interconnections/page/0/2

705.12(D)(7), “Inverter Output Connection.” Where distribution equipment is capable of supplying multiple branch circuits or feeders and the sum of the OCPDs supplying power exceeds the busbar rating, the ac inverter circuit breaker must be located at the opposite end from the input feeder supply conductors. The inverter’s OCPD also needs a permanent warning label indicating that the OCPD is for the output of an inverter and cannot be relocated. The label should have language such as: WARNING—INVERTER OUTPUT CONNECTION; DO NOT RELOCATE THIS OVERCURRENT DEVICE.

This subsection also clarifies the calculations needed when connecting an inverter’s dedicated OCPD to a subpanel. It states that for panelboards connected in series, the rating of the first OCPD directly connected to the output of a utility-interactive inverter is the only one used for all busbar and conductor calculations. Consequently, the inverter’s dedicated OCPD rating is used to evaluate all the conductors and busbars connected in series, not the rating of the OCPD protecting the subpanel.

For example, consider a building that has a 400 A main distribution panel protected with a 400 A OCPD. That main distribution panel feeds a 100 A subpanel protected at 100 A. Inside the subpanel, a 20 A dedicated inverter breaker is installed. The 20 A inverter breaker satisfies Section 705.12(D)(2) because the subpanel busbar rating is not exceeded by more than 120%. The 400 A main panel can accept up to 80 A of additional power sources (400 A x 1.20 – 400 A). Section 705.12(D)(7) states that the first OCPD, the 20 A breaker in this example, is used for all upstream conductors and busbars. Previous interpretations of the Code required that you use the subpanel’s 100 A OCPD when calculating the upstream conductors and busbars, and would have prevented a small 20 A PV array from being connected to the subpanel in this example.

[foo1bar]

Going through the new panel scenario, I added up (again) the 240V dual breakers:
60+50+30+30+60+100=330 amps @ 240V with 100A@240 for the shop.

...
I would need to drop the main breaker down to 140 amps to make room for 60 amps with a 200 ampacity

Fixing the main split panel with the 330 amps worth of breakers is a deal breaker as it would require a 400 amp service.

Not necessarily.

What you really need to do is a load analysis to see what is actually required for a main breaker for your property.

Most likely you have <200A when you do the load analysis.
Assuming that's the case, you can find a panel that has 225A bus
(ex. http://www.homedepot.com/p/Eaton-225...225R/202276723 )

200A main is at one end, 60A solar at the opposite end, and you're still less than 225*1.25
Possibly you can also do a 200A bus with 175A main and 60A at opposite end. (Assuming 175A or less from the load analysis)

Or possibly there are some designed-for-solar that have a separate breaker spot designed just for putting in a 60A breaker for solar.

http://www.downloads.siemens.com/download-center/Download.aspx?pos=download&fct=getasset&id1=BTLV_40907

I'm not sure if all of them are combined main + meter - they probably are.


Now if you're asking "How can I have 300A of breakers on a 200A main?" - the answer is the same as how you can have >10 of those 15A and 20A breakers being fed by a 60A right now. It's OK to do that - you just have to look at what's reasonable expectation for things being used together - which is basically what the load analysis does.


If I were looking at it, I'd possibly look at the combined meter-main panel.
I'd either replace the existing main and meter,
OR
have the breakers in the combo be 100A-shed, 60A-solar, and 100A-feeding-existing-split-bus-house-panel (assuming the house panel load analysis works for that - which my best guess is it would)

Good luck

[posplayr]

Anybody interested in this discussion here is another thread.

http://www.electriciantalk.com/f5/split-bus-panel-feed-72170/

Some interesting comments re split bus panels:

• you can't overload a protected load by adding additional supply (supply side feed).
• split bus is not protected by breakers it is protected by design..............

If the section the breaker is being installed in, has only service disconnects, it is a line side connection. There is no potential to overload the panel unless the rating of the PV breaker exceeds the rating of the panel bus. The PV is not a load, it is a supply. Installing it does not increase the load on the service or the panel bus. The current supplied by the PV system is just current that will not be supplied by the utility supply.

The potential to overload a service that has multiple service overcurrent protective devices always exists if additional loads are added. The service entrance conductors and panel bus for a service with multiple service over current devices is only protected by design, not by an overcurrent protective device.

[posplayr]

Going through the new panel scenario, I added up (again) the 240V dual breakers:
60+50+30+30+60+100=330 amps @ 240V with 100A@240 for the shop.

The real max load is obviously going to be much less. Summer usage is 1400 kwHr or 1.9 Kwatts average figure 10:1 peak to mean 19 Kwatts peak power. In the upper bus bar that is 80 amps peak at 240V. I could throw a factor of 30 at it and exceed the 200 ampacity.

If I try to put in a 330 Main and add a 60 amp PV source I'm at 390 amps just under the wire and have to run a 400 amp service (is the 4/0 is not sufficient) and put in a 400 amp panel. Now I'm playing this game of lower the main so I can add the PV. I would need to drop the main breaker down to 140 amps to make room for 60 amps with a 200 ampacity

Fixing the main split panel with the 330 amps worth of breakers is a deal breaker as it would require a 400 amp service. Is 60 amps of PV going to break the split camel's back? For the lower panel (assuming it is 200 amp rated ) there is no issue. The questions is , if the 330 amps is only there because of a mixed Amp load, then the 60 amp main for the lower has to be derated. But then the more that is coming in from the PV the lower that cue low panel supply breaker will be flowing.

You could make the argument if the house is shut down in the summer (but with furnace and/or AC on) and you might really really have 50 amps coming out of the lower main as supply and it is continuous. Will just have to find out what is required. I assume this will not be the first split panel PV system being applied for.

Here is a screenshot of the PV planning spreadsheet. It basically says if you don't pass you need a supply side tap. I entered the values for the split panel (60A/60A) and the answer is "Breaker per Service"=180 amps. My concern is obviously this is not for a split panel.

[foo1bar]

Hard to justify that if you do a panel upgrade a year after the PV install.

I agree - I'd do it at the same time or a little before.

[posplayr]

It does have a very important bearing on what size main breaker you would install if installing a new panel.
I believe 4/0 Alum. is rated for a 200A service. (table 310.15(b)(6))
So installing a 400A panel as was suggested above would likely be a problem.
But my main point is that if you replace the panel with a more standard setup, you need to look at the feeder to the meter. If your service is 200A service (and appropriate sized cable for it), then you should have a 200A main breaker. If your service is already with conductors that can handle 400A (and your meter and meter socket can do 400A) then you can upgrade those short wires from meter to panel if need be. My *guess* is that the wires coming into the meter from the POCO are your limiter though - but that's something for you to research.

I think the discussion has moved past the need to increase the panel bus bar ampacity beyond 200A at least due to PV. There is no need absolute need to support the PV install. However I did consult a "52 years in the business" electrician yesterday and he said even with a larger ampacity panel the 4/0 is all that would be needed. As mentioned I think it is mute.

Cost - yes.
Safety - I don't think so. I think a new main breaker is safer than what you have.

My safer statement was a relative one, specifically load side v.s. supply side connection for a PV install on this split bus panel, and I think I even qualified that even further by saying it was because it was easier to prove. I'm not going to argue that some combination of new panel might not be safer than a 50 year old split panel.

1> it's a split bus (they don't make those anymore)

2> it looks like you have >200A of "main" breakers on your panel, but only 4/0 AL wire. (may or may not be a code violation - I'm not sure, but less safe than if you had a 200A main breaker)

Yes I agree, the 200 amp main would put an absolute limit on the grid side that doesn't exist now where is the possibility of adding more than 200 amps of load. It apparently still meets code as the 100 amp service to the shop was added in 2000. However, as you noted below the shop breaker was not installed properly so it is not necessarily all legal or safe. Thanks for taking the time to look, I was debating shutting down the how house to verify 100 breaker was straddling upper and lower ; I'll not bother now. BTW, were are really not loading that shop to anything near it's capacity with little plans to do so.

3> Are you sure the bottom part of the split is rated for 200A (or at least 120A, since it's potentially 60A feed from PV and 60A feed from POCO)

It is something to check, but my guess is it is. I'm not qualified to determine the safety of this entire install so when we get that point somebody will have to review that. I have searched but online by part number but nothing comes up.

4> Is that 100A main breaker fully on the top portion of the split? It looks like it's straddling the top and bottom busses - which I would think isn't OK. Also it looks like maybe there are now 7 "throws" to turn off all power. (breaking the "6 throw rule", so a code violation.)

In order to feed the lower bus with the PV some adjustment in breaker locations will be required including removing the straddle.

5> It looks like you have a lack of open breaker spaces. (I'd want more - I suppose not really a safety thing though)

Add those to what you've already stated that it'd be nice for a master cutoff, and I think you have reason to change it out.

I agree, a newer panel would be nice, but I don't think it is the PV driving that decision. And while it would be nice to get it all wrapped up at once, I don't think that the panel swap is really impacted much by the PV in the first place.

And I think you can reasonably justify it as being a needed part of the solar install, and therefore eligible for inclusion when you are filing with IRS.
(I'm not a tax expert - but that's my opinion- and worth every penny you paid for it

)

This is really the only main reason that PV impact the main panel as you can lump it isn as a necessary upgrade for PV. Hard to justify that if you do a panel upgrade a year after the PV install.

Thanks for your time to detail out these issues and concerns. I think I'm getting a better handle on something that was a total mystery 48 hours ago.

[foo1bar]

I don't understand your point re: line feed. It is 4/0 aluminum wire and it runs through a 3" (yes inches) conduit from the panel box such that it apparently has no bearing on the discussion

It does have a very important bearing on what size main breaker you would install if installing a new panel.
I believe 4/0 Alum. is rated for a 200A service. (table 310.15(b)(6))
So installing a 400A panel as was suggested above would likely be a problem.
But my main point is that if you replace the panel with a more standard setup, you need to look at the feeder to the meter. If your service is 200A service (and appropriate sized cable for it), then you should have a 200A main breaker. If your service is already with conductors that can handle 400A (and your meter and meter socket can do 400A) then you can upgrade those short wires from meter to panel if need be. My *guess* is that the wires coming into the meter from the POCO are your limiter though - but that's something for you to research.

The most compelling reason to get a new panel is for a master cut-off and transfer switch for a generator. I don't believe the PV install is a driver at all to a panel replacement. From a safety and cost standpoint the load side breaker in the lower split panel bus is preferable.

Cost - yes.
Safety - I don't think so. I think a new main breaker is safer than what you have.

1> it's a split bus (they don't make those anymore)
2> it looks like you have >200A of "main" breakers on your panel, but only 4/0 AL wire. (may or may not be a code violation - I'm not sure, but less safe than if you had a 200A main breaker)
3> Are you sure the bottom part of the split is rated for 200A (or at least 120A, since it's potentially 60A feed from PV and 60A feed from POCO)
4> Is that 100A main breaker fully on the top portion of the split? It looks like it's straddling the top and bottom busses - which I would think isn't OK. Also it looks like maybe there are now 7 "throws" to turn off all power. (breaking the "6 throw rule", so a code violation.)
5> It looks like you have a lack of open breaker spaces. (I'd want more - I suppose not really a safety thing though)

Add those to what you've already stated that it'd be nice for a master cutoff, and I think you have reason to change it out.

And I think you can reasonably justify it as being a needed part of the solar install, and therefore eligible for inclusion when you are filing with IRS.
(I'm not a tax expert - but that's my opinion- and worth every penny you paid for it)

[posplayr]

Yes, sorry for ambiguity. I meant that the PV breaker could be located anywhere on the lower bus.

Thanks again