Just signed a 4.6kW systems...

[solar_newbie]

Got an email from my installer that the city permit was approved yesterday. It was submitted on 09/22 and approved on 09/29. The installation is schedule for this coming Monday 10/5. Getting excited again

Congrats ... The wait is over.

[newe70]

Got an email from my installer that the city permit was approved yesterday. It was submitted on 09/22 and approved on 09/29. The installation is schedule for this coming Monday 10/5. Getting excited again

[sjsun]

Can you turn on your pm mode? My installer is locally here in LA area.

D'oh! Fixed my PM settings. I guess SF Bay Area would be a bit too far for your installer

Wondering why the huge difference between pricing. See, this is what keeps me from cutting a cheque - a 5-10% price swing in quotes might be ok but almost 20% price swing makes me wary of the market.

[foo1bar]

Additional sub panel is run directly from the metter.
Some houses have 2 main service breakers from metter. One is for the house sub-panel and one is for the AC. You can move the AC breaker to the new sub-panel and replace with 80A breaker there.

A "sub panel" by definition is not directly from the meter.
It is from another panel.

The subpanel is most likely going to be fed from breakers in a main panel which is very close to the meter (sometimes the main panel is an integrated unit with a main panel and a meter socket - my meter and main panel are one unit, as are many of my neighbors)

Of course, you need to make sure the cable from metter is 3/0 AWG or at least 2/0 AWG. Those cable can handle 200A.

I'd say that you need to make sure ALL wires are sized correctly.

3/0 is not always sufficient for 200A. I beleive 3/0 Aluminum would be too small.
2/0 copper usually will be sufficient, but you really should do the voltage drop calculations.
And I'd recommend Alum for larger wires like this due to price of copper vs. alum. (And there are many MANY large gauge alum wires in use - any electrician doing residential should be capable of doing 2/0 and 4/0 Alum, and have done it many times)

[newe70]

Can I please get the name too?

Can you turn on your pm mode? My installer is locally here in LA area.

[newe70]

It seems like there are at least three conversations going on here, so I'm not sure I understand your situation.

If you are connecting a 3.8 kW inverter to a 125 A end-fed MSP with a 125 A main breaker, then there is no reason to downsize the breaker to 100 A at this time. 20% of 125 = 25 A, which is enough to protect the 3.8 kW inverter circuit.

If your 125 A MSP is centerfed, or for some reason your PV breaker isn't going to be located at the opposite end, then the 120% rule doesn't apply and downsizing the main breaker to 100 A would give you up to 25 A of PV (100 A main breaker + 25 A PV breaker = 100% of the 125 A MSP rating).

What you have said is perfectly making sense and thank you for a cleared answer. My next concern now is the MSP rated at 100A, upgrading to a bigger AC system down the road and the MSP would not have enough load to handle.

[sjsun]

Ugpm.

Can I please get the name too?

[solar_newbie]

Adding a sub panel might end up being a line side (supply side) connection if the separate service conductors are run to the additional panel (and, of course, if local POCO allows line side connections.)
But if all you are doing is feeding the subpanel from a feeder breaker in the main panel that does absolutely nothing to help the 120% limit as applied to the main panel. You still have to count the PV backfeed to the main based on the sum of the inverter output ratings ([2014] NEC) or the sum of the breakers closest to the inverters ( [2011] and earlier NEC).

Additional sub panel is run directly from the metter.
Some houses have 2 main service breakers from metter. One is for the house sub-panel and one is for the AC. You can move the AC breaker to the new sub-panel and replace with 80A breaker there.
Of course, you need to make sure the cable from metter is 3/0 AWG or at least 2/0 AWG. Those cable can handle 200A.

[sensij]

You still have to count the PV backfeed to the main based on the sum of the inverter output ratings ([2014] NEC) or the sum of the breakers closest to the inverters ( [2011] and earlier NEC).

Just to be super-clear... it is 125% of the inverter's output rating in NEC 2014, instead of the breaker size in NEC 2011. For an inverter like the SE3800A, which was sized so that 125% of the output rating is an even breaker size (125% * 16 A = 20 A), there is no difference in the calculation in 2014 or 2011. The difference in calculation methodology matters more for some micro-inverter installations, or some larger installations that use more than one odd-sized string inverter.

[inetdog]

Curious, if adding a sub-panel is cheaper and provides more flexibility then why does anyone upgrade main panel and service at all?

Adding a sub panel might end up being a line side (supply side) connection if the separate service conductors are run to the additional panel (and, of course, if local POCO allows line side connections.)
But if all you are doing is feeding the subpanel from a feeder breaker in the main panel that does absolutely nothing to help the 120% limit as applied to the main panel. You still have to count the PV backfeed to the main based on the sum of the inverter output ratings ([2014] NEC) or the sum of the breakers closest to the inverters ( [2011] and earlier NEC).

[solar_newbie]

That is one obvious answer, installers trying to make more money but a lot of installers I talked to don't even do the electrical work anymore. Most work with another electrical contractor who bills you directly for panel/service upgrade work so nothing for the installer to make money on.

Alternately, did you talk to an electrical engineer about the difference? Or, call the city inspectors to figure out the difference?

I talk to hardware guy in my company. I would assume they are electrical engineer as they design million dollars enterprise systems . They do not see the different between 1 200A sub-panel vs 2 100 and 125A sub-panel.

The different is it might be more efficient to have 1 200A sub-panels since you can share load.
If I have 2 sub-panels, I need to manage load smartly.

For city inspector, I have no clue since they approved the permit with electrical diagram but not do final inspection yet.

[sensij]

Calling out sensij for help...I am in this exact scenario. The onsite plan called out the 125A main service panel to downsized to 100A. What is the reason to downsize? I am kinda confuse now. Sorry for the ignorant question, but can you please explain.

It seems like there are at least three conversations going on here, so I'm not sure I understand your situation.

If you are connecting a 3.8 kW inverter to a 125 A end-fed MSP with a 125 A main breaker, then there is no reason to downsize the breaker to 100 A at this time. 20% of 125 = 25 A, which is enough to protect the 3.8 kW inverter circuit.

If your 125 A MSP is centerfed, or for some reason your PV breaker isn't going to be located at the opposite end, then the 120% rule doesn't apply and downsizing the main breaker to 100 A would give you up to 25 A of PV (100 A main breaker + 25 A PV breaker = 100% of the 125 A MSP rating).

[sjsun]

Material cost for 2 are almost the same. The different is the labor cost. If you are installers, which option should you offer?

That is one obvious answer, installers trying to make more money but a lot of installers I talked to don't even do the electrical work anymore. Most work with another electrical contractor who bills you directly for panel/service upgrade work so nothing for the installer to make money on.

Alternately, did you talk to an electrical engineer about the difference? Or, call the city inspectors to figure out the difference?

[solar_newbie]

Curious, if adding a sub-panel is cheaper and provides more flexibility then why does anyone upgrade main panel and service at all?

Material cost for 2 options are almost the same. The different is the labor cost. If you are installers, which option should you offer?
For me, any installers offer me the upgrade option for 2-3K. I never response to them.
Any installers look at my 100% full load sub-panel and cry about they need to re-arrange it to get space for solar, I ask them if they do it for free. Otherwise, don't talk more as there is no cost to re-arrange the sub-panel circuits.

[sjsun]

There are reasons to upgrade a 125 A panel to a 200 A panel. PV installation, with no other expected changes to the load profile, does not usually require it. Most installers will be happy to sell the upgrade though.

And, that's what I was trying to highlight - design for expected load profile changes while you are adding capacity/source. Assuming a standard home with a 100/125A service/main-panel, upgrading to a 200A panel/service might give you sufficient room to expand in the future. I think there's hardly a thread about Solar that doesn't also talk about EV usage and EV consumption is only going to grow - bigger and more power hungry batteries. Gave me some food for thought in terms of having spare capacity in the entire system.