User avatar
drees
Moderator
Posts: 6221
Joined: Fri Apr 23, 2010 3:51 pm
Location: San Diego

Re: 125A Load Center, what are my options?

Mon Aug 26, 2013 12:17 am

Valdemar wrote:I've just realized that I may have misinterpreted what my electrician told me or he made a mistake. He said I can have a 4kW system with the 125A panel. Thinking about it, per the NEC's 120% rule I can back feed 25A of solar to a 125A panel with 125A breajer which translates to a 6kW array on 240V. Putting in a 100A breaker on the same panel would give me a total of 50A of solar current which is a 12kW array. I was shooting for a 7.2kW system, so I might be ok with a 100A breaker. Am I missing something?

As others have said - if your utility isn't OK with you installing a 200A panel with a 125A main breaker, not sure why they'd be OK with installing a new 125A panel with a 100A breaker.

Also, a PV system AC circuit also has to be derated as it's considered a continuous load - just like your EVSE. Your typical "4000W" inverter is rated at 20A and typically specifies that you can use a 25-30A breaker to protect it. A 50A breaker would only let you do 40A max or 9.6kW. As another example, Enphase M215 microinverters let you string up to 17 inverters per 20A circuit and each inverter is rated for 0.9A for a total of 15.3A per 20A circuit breaker.

Assuming you can't get around your dumb utility (which one is it, anyway?) not letting you install a 200A panel with a 125A main breaker (or a 125A panel with a 100A main breaker) or performing a line-side tap, another option is to oversize the solar panels to the inverter. You end up losing some potential energy as the inverter will max out before the solar panels during some situations, but you'll still get more power overall.

As I'm more familiar with micro-inverters, let's use Enphase for example.

If you are limited to 25A of backfeed, using the M215 inverter you could install up to 22 inverters, which would max out at 4730WAC (though in real life they will go up to 225W or 4950W total).

So that's already about 1 kW AC better than your typical DC inverter.

But you can plug in panels rated up to 270W into the M215 inverter (at least that's the largest one listed as compatible with it on their website) which would get you 5940W of panels - pretty close to your 7.2 kW goal.

The numbers change slightly with Enphase's new M250 inverter, but it's basically the same.
'11 LEAF SL Powered By 3.24 kW Enphase Solar PV

Valdemar
Posts: 2493
Joined: Tue May 10, 2011 10:32 pm
Delivery Date: 09 Sep 2011
Location: Oak Park, CA

Re: 125A Load Center, what are my options?

Mon Aug 26, 2013 1:00 am

Of course I will double check but I don't see why a 125A panel with a 100A breaker should raise any red flags, as the utility (SCE) only cares about not overloading their feed cables that can only handle up to 125A according to them. I suspect it is a lie and they just want to err on the safe side or they may have another reason such as a transformer already running at capacity that they do not want to upgrade. They won't tell.

It sounds like it might be best to postpone my solar install, as on one hand I'm not ready to upgrade to a 200A panel yet as there is no real need for it and it will be quite costly, and while getting a 125A panel with a 100A breaker will allow me to get to desired solar power a year or two down the road I may need to upgrade to 200A so the money spent on the new 125A panel upgrade will be wasted. I don't think I can keep my old Zinsco 100A panel and add solar to it unless there is some creative way to add a supply side connection for solar.

User avatar
drees
Moderator
Posts: 6221
Joined: Fri Apr 23, 2010 3:51 pm
Location: San Diego

Re: 125A Load Center, what are my options?

Mon Aug 26, 2013 1:25 am

Valdemar wrote:I don't think I can keep my old Zinsco 100A panel and add solar to it unless there is some creative way to add a supply side connection for solar.

Well, with a 100A panel you can do 20A of solar - using Enphase as I mentioned earlier you can use 17 M215 inverters - 3.6 kW AC of solar (up to 3.8 kW in reality since each one will do up to 225W AC) and up to 4590W of panels.

Then down the road should you decide to tackle the main panel issues for more capacity, you can simply add another string (or more) of micro inverters as desired.
'11 LEAF SL Powered By 3.24 kW Enphase Solar PV

QueenBee
Posts: 1564
Joined: Sun Aug 08, 2010 5:14 pm
Delivery Date: 20 Jun 2011
Leaf Number: 2062
Location: Bellevue (Seattle), WA

Re: 125A Load Center, what are my options?

Mon Aug 26, 2013 9:48 am

Valdemar wrote:
QueenBee wrote:So do they also disallow 125 amp panels that a 200 amp main breaker will fit into?! What if someone puts in a 200 amp breaker, think of the children!


They don't, or they don't care. If someone does it and home burns it won't be their problem, the fault will be clearly on the homeowners part. However if someone stays within the panel ampacity but burns underground cables and possibly the transformer, then at the very minimum it becomes their problem for repairs and possibly legal consequences if there is any damage to the property and worst case injuries or deaths as it is no longer all black and white as in the former case.

I disagree that the liability would be different in those scenarios. Just because the panels bus is rated at 200 amps does not mean that the wiring to the meter box, the meter box, the wires to the utility, the GECs, etc, etc. are all rated for that. AFAIC the utility has no more or less liability in those two scenarios. I actually think part of the problem is there doesn't seem to be any good way to know how many amps your service really is, at least around here, and there is nothing in place to protect the service wires. Your utility must be smaller and thus has the time to review panel upgrades and thus enforce this rule? My utility only did three things. Tested the voltage at the meter base and relocked the meter base after we opened it to cut power for the panel upgrade, reviewed the solar generation design, did the same test and installed the new production and net meters. Everything else they just assumed that because the inspector passed it was all fine.
Valdemar wrote:
QueenBee wrote:The funny thing is my 1969 house is it came with a split bus panel. The main breaker was 60 amps but the top of the bus allowed for 4 or 8 half breakers. So you could easily add more breakers than the service was rated for. No one cared when I had 30 amp for dryer, 30 amp for old water heater, and new 40 amp for the EVSE and the 60 amp main, all 240 volt.


There is no safety issue with having the sum of all individual breakers exceed the rating of the main breaker. As far as I understand it is fairly typical. The worst that can happen is your main breaker trips if you load several circuits at the same time, no harm is done.

No no, this was called a split bus panel. The main breaker was 60 amps and it only controlled the lower part of the panel. Then the top of the panel had 4 spaces (that could be doubled to control 8 lines, but would be against code as the limit is 5 throws to cut power). If you turned off the main breaker the top 4 circuits remained powered on.

But yes you are correct that the sum of all the breakers can exceed the service in a normal panel because the main breaker is there to trip and protect the main service, etc.
Valdemar wrote:
QueenBee wrote:
Do they make 125 amp panels with enough circuits to handle your house? Seems like you might need a sub panel to handle all the circuits.

How big of a system are you thinking? NEC/AHJ might not be happy with such a small main breaker but what about putting a 100 amp main breaker in a 125 amp panel? This would be safe and I doubt your house will ever have above an 80 amp draw. I turned on literally every thing in my entire house and barely got over 50 amp at 240 volt.


I've just realized that I may have misinterpreted what my electrician told me or he made a mistake. He said I can have a 4kW system with the 125A panel. Thinking about it, per the NEC's 120% rule I can back feed 25A of solar to a 125A panel with 125A breajer which translates to a 6kW array on 240V. Putting in a 100A breaker on the same panel would give me a total of 50A of solar current which is a 12kW array. I was shooting for a 7.2kW system, so I might be ok with a 100A breaker. Am I missing something?

So the math is like this:
125 *1.2-125=25 amp breaker for solar
125*1.2-100=50 amp breaker for solar

So depending on what kind of inverters you are looking at you could go into a sub panel powered by 25 amp/50 amp breakers. If you went with Enphase M215 microinverters:

25*.8 (continuous load derate factor): 20 amps
20/.9 (enphase amp rating): 22 M215s

50*.8 (continuous load derate factor): 40 amps
40/.9 (enphase amp rating): 44 M215s

If you were to connect your M215s up to 250 watt panels that would get you:
22*250: 5,500 watts DC
44*250: 11,000 watts DC

Basically you can have up to 20/40 amps of inverter output and then can add additional solar capacity above that. So a 4,800 watt central inverter or two of them. Then you'd add additional DC capacity to account for the conversion loss, wire loss, soiling loss, panel degradation, etc.

Note that the M215s are limited to 17 on a 20 amp circuit so to get 22 you would need a sub panel with two circuits.

QueenBee
Posts: 1564
Joined: Sun Aug 08, 2010 5:14 pm
Delivery Date: 20 Jun 2011
Leaf Number: 2062
Location: Bellevue (Seattle), WA

Re: 125A Load Center, what are my options?

Mon Aug 26, 2013 9:54 am

drees wrote:
Valdemar wrote:I've just realized that I may have misinterpreted what my electrician told me or he made a mistake. He said I can have a 4kW system with the 125A panel. Thinking about it, per the NEC's 120% rule I can back feed 25A of solar to a 125A panel with 125A breajer which translates to a 6kW array on 240V. Putting in a 100A breaker on the same panel would give me a total of 50A of solar current which is a 12kW array. I was shooting for a 7.2kW system, so I might be ok with a 100A breaker. Am I missing something?

As others have said - if your utility isn't OK with you installing a 200A panel with a 125A main breaker, not sure why they'd be OK with installing a new 125A panel with a 100A breaker.


Because if someone down the road comes in and reinstalls the 125amp breaker the utility has no risk that their services lines will be damaged. The risk is that the panels main bus would overheat but they certainly should not be making up rules for how the house is wired, that is NEC and the AHJ jobs.

wwhitney
Posts: 736
Joined: Sat Jul 17, 2010 10:10 am
Delivery Date: 01 Apr 2011
Location: Berkeley, CA

Re: 125A Load Center, what are my options?

Mon Aug 26, 2013 10:51 am

QueenBee wrote:But yes you are correct that the sum of all the breakers can exceed the service in a normal panel because the main breaker is there to trip and protect the main service, etc.

Just an FYI, this is also allowed (by the NEC, at least) in the case that a service panel has multiple main breakers (up to 6 are allowed). The only requirement in that case is that the NEC calculated load be less that the service size.

Cheers, Wayne

Valdemar
Posts: 2493
Joined: Tue May 10, 2011 10:32 pm
Delivery Date: 09 Sep 2011
Location: Oak Park, CA

Re: 125A Load Center, what are my options?

Mon Aug 26, 2013 11:40 am

Thanks all for your input, I'm still undecided whether I should add solar at this point but if I do it sounds like a new 125A panel with a 100A main breaker is the way to go. It'll be a while before I get an EV that can charge at 60A, if ever, and for now even though I might have to be more careful when I run big loads 100A should serve my needs in the observable future.

User avatar
RegGuheert
Posts: 6319
Joined: Mon Mar 19, 2012 4:12 am
Delivery Date: 16 Mar 2012
Leaf Number: 5926
Location: Northern VA

Re: 125A Load Center, what are my options?

Mon Aug 26, 2013 12:53 pm

Valdemar wrote:Are you sure they connected solar to the house side of the main breaker and not to the service side? This doesn't sound right as your panel would then surely see solar current that bypasses the main breaker, added with the service current it can then overload the panel and melt the bus bars without tripping the main breaker under the right conditions.

EDIT: unless your panel is rated high enough to handle max solar and service currents together, sometimes they derate the panel by putting a main breaker with lower amps to ensure that.
Your edit is what I was going to mention. Our PV is installed on the house side of the main breaker, but most modern breaker panels have the bus bars oversized WRT the main breaker rating. IIRC, one Siemens panel I looked at had a 200A breaker and bus bars rated for 225A. Can you find a 125A panel with bus bars rated up to 150A or more?
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

Valdemar
Posts: 2493
Joined: Tue May 10, 2011 10:32 pm
Delivery Date: 09 Sep 2011
Location: Oak Park, CA

Re: 125A Load Center, what are my options?

Mon Aug 26, 2013 1:01 pm

RegGuheert wrote:
Valdemar wrote:Are you sure they connected solar to the house side of the main breaker and not to the service side? This doesn't sound right as your panel would then surely see solar current that bypasses the main breaker, added with the service current it can then overload the panel and melt the bus bars without tripping the main breaker under the right conditions.

EDIT: unless your panel is rated high enough to handle max solar and service currents together, sometimes they derate the panel by putting a main breaker with lower amps to ensure that.
Your edit is what I was going to mention. Our PV is installed on the house side of the main breaker, but most modern breaker panels have the bus bars oversized WRT the main breaker rating. IIRC, one Siemens panel I looked at had a 200A breaker and bus bars rated for 225A. Can you find a 125A panel with bus bars rated up to 150A or more?


Possibly, I'll talk to my electrician about this option so he can investigate through his supplier.

QueenBee
Posts: 1564
Joined: Sun Aug 08, 2010 5:14 pm
Delivery Date: 20 Jun 2011
Leaf Number: 2062
Location: Bellevue (Seattle), WA

Re: 125A Load Center, what are my options?

Mon Aug 26, 2013 2:41 pm

Valdemar wrote:
RegGuheert wrote:
Valdemar wrote:Are you sure they connected solar to the house side of the main breaker and not to the service side? This doesn't sound right as your panel would then surely see solar current that bypasses the main breaker, added with the service current it can then overload the panel and melt the bus bars without tripping the main breaker under the right conditions.

EDIT: unless your panel is rated high enough to handle max solar and service currents together, sometimes they derate the panel by putting a main breaker with lower amps to ensure that.
Your edit is what I was going to mention. Our PV is installed on the house side of the main breaker, but most modern breaker panels have the bus bars oversized WRT the main breaker rating. IIRC, one Siemens panel I looked at had a 200A breaker and bus bars rated for 225A. Can you find a 125A panel with bus bars rated up to 150A or more?


Possibly, I'll talk to my electrician about this option so he can investigate through his supplier.


I'm not sure how common it is to oversize the bus bar rating vs the main breaker that it ships with but I'm willing to bet all of them that would even do that will also have a part number of a main breaker that supports the higher amperage. WHAT IF SOMEONE BOUGHT THAT AND INSTALLED IT?! I do have a feeling though that if you could find a part number of a panel that was "125 amp" because it came with a 125 amp breaker that you could get it passed the utility.

So back to my other idea. What if installed a meter base panel that was rated for 125 amp and only had the main breaker like this: TM12RMC
http://www.gepowercontrols.ru/catalog/i ... 42819.html Obviously finding the right model that would be a suitable replacement would need to be done but that's just an example.

Then you have that connected to a 200 amp main lug panel that powers your house and is backfed from your solar.

This seems like a nice solution because it gets your service panel up to modern standards, gives you lots of room in the new panel for circuits, etc. and then if you do need to upgrade to a larger service anytime in the future it's less wasted work as you would essentially just replace the meter base/circuit breaker and the wire to the service panel.

I wouldn't let this small pain in the neck stop you from moving forward. Also consider that generally speaking this upgrade would be part of the cost of installing solar so you would get the 30% tax credit for it.

Return to “Solar”