current feed ratings for a service panel

In california I hear the service panel feeds cannot exceed 125% of the named rating. Meaning.....on a 100 amp service you can install another 25 amps from alternative energy, yet there are no 25 amp breakers, so in a nutshell, a 100 amp service can have a 20 amp breaker feeding the service. Now if you look at the sunnyboy 6000U it appears to have a maximum AC maximum output rating of 25 amps, which would require a 30 amp breaker, and needs a larger service. The home owner is not feeling responsible for this after the initial bid was delivered.

Now...I am looking as an installer at a supply-side-tap. meaning I will tap into the incoming wires, inbetween the meter and the 100 amp service. From there I plan to run a 50 amp service, and put my required 30 am breaker to feed all this through the existing meter.

Cities, counties and un-incorporated areas tend to make their own rules, and the inspectors are generally a bit un-knowledgeable about such things.... solar being a bit of a wildcard in the construction industry.

I am just looking for input, I don't like to be part of a red flag for the local inspectors. I am up against 2 jobs with this current issue, so I with the background I have given here are my questions;

1. What is the protocol for maximum amps fed to a service panel in a residential setting?
2. Do the inspectors even care?
3. What are the physical dangers for over-feeding current to an old service? (aside from fire, death and dismemberment)
4. Has anyone done a sub-panel that was tapped inbetween the meter and the original service?


Comments

  • Patman3Patman3 Solar Expert Posts: 62 ✭✭✭✭
    Re: current feed ratings for a service panel

    I don't know how to answer the last 4 questions, but as it started out, could you just use a combination of 10 amp and 15 amp breakers in parallel? Spaced 1 breaker apart to be on the same half of the 220 and put a connecting arm to the 2 breakers.
    Would the subpanel between original service and meter really become the new main panel?
  • BB.BB. Super Moderators, Administrators Posts: 31,907 admin
    Re: current feed ratings for a service panel

    I am not an electrician--but I would have grave concerns about having one service with, basically, no master breaker / disconnect (or two master disconnects... depending on how you look at it). It probably would be best to bite the bullet and see if you can get the customer to cover the direct part costs of the new panel(s) and you eat the labor. Here, checking the main service feed is one of the check lists when I did solar on my home. You also might be able to sell them on a new panel if they plan on adding loads in the near future.

    Second, you only need 25-30 amp breakers if you have a full complement of panels... If you have (like my home) only 3.5 kWatts of panels, you can probably get away with a 20 amp set of breakers (I think that you can undersize the breakers based on actual loads, not on design capability of the Grid Tied inverter).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RoderickRoderick Solar Expert Posts: 253 ✭✭
    Re: current feed ratings for a service panel

    The idea of paralleling breakers makes me cringe - I don't know why. But if it fails the gut check, it might disturb an inspector.

    I can confirm that the amps fed into the panel cannot exceed 120% in San Jose, CA, where I live. This is from NEC 690.64. I'm not saying that it isn't 125% where you live, but it would be worth checking, again. You would normally use a 20A breaker to backfeed into a 100A panel, or 25A to backfeed into a 125A panel. And I think you can buy 25A breakers - check the internet. My understanding is that this is to avoid overloading the busbars of the panel, and my guess is there's an assumption that a residential situation won't be drawing in excess of the panel rating in general (otherwise, the main 100A breaker would keep popping before you put in your solar). This exception of 120% only applies to a single-family house (and maybe a duplex, I'm not sure); for a commercial installation, you need to simply have a panel that's rated for full amperage.

    And, as the other poster mentioned, you probably don't even need a 20A breaker. The solar panels are inherently power-limited, and unless your installation is huge, the inverter won't be putting out anything near 20A continuous. If your installation is huge, then I'd say you really need to replace the main service panel with a higher-rated one.

    Do the inspectors care? It's against my personality to think this way. I'm a coward, so even if the inspector didn't check, I'd want things to be as compliant as possible. In fact, if they find violations in my work, I will thank them for correcting me.

    Risks of overcurrent, other than fire and death? Again, I'm a coward, so fire and death would be enough. However, I would add the threat of a lawsuit if this were a job for someone else. Knowingly violating safety standards would be choice meat for lawyers.

    I believe that the NEC no longer allows running another panel directly after the meter. But even if you wanted to do this, you would have to call the power company to remove the meter, so as not to work on the live mains. If it were me going through all that trouble, I would just bite the bullet and put in a big, 200A panel at that time.
  • BB.BB. Super Moderators, Administrators Posts: 31,907 admin
    Re: current feed ratings for a service panel

    By the way, building inspectors are not legally responsible for any decisions (or lack of proper decisions) that they may make.

    No matter the inspector's decision, if something goes wrong (as in violating NEC, local Building Codes, and/or UL/NRTL requirements)--you (as the installer) will be left holding the bag.

    If you do the installation per applicable code and NRTL requirements (as per date of installation)--you are pretty much golden (legally speaking).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • halfcrazyhalfcrazy Solar Expert Posts: 720 ✭✭✭
    Re: current feed ratings for a service panel

    sounds like time to upgrade the service. here in maine they make us have a seperate meter for outgoing from the inverter so it isnt really a issue. we usually just swao in a double meter socket with disconnects makes the power co happy and gives you the lockable disconect they want
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: current feed ratings for a service panel

    halfcrazy,
    the meter has little to do with it as they are refering to the capacity of the main electrical box. that same meter would handle reading the wattage from a 200 amp service as it does the 100 amp service being talked of.
    pmosier,
    if i understand this correctly they are saying you need to add the max power coming in from the utility along with the outgoing renewable energy max and it's not to exceed 125%. this makes no sense to me because if you are generating even 100amps of renewable ac power(i know that's huge) and use 200amps and you have a 100amp service there is not 200amps flowing through that service from the utility, but only 100amps and this does not exceed the 125amp max for the service. they should not add together is all i'm saying, but they would have a point on the size and numbers of the breakers. a subpanel should take care of that in my opinion with no increase in the size of the original 100amp service box. i'd be curious if they are insisting on increasing the size of the service entrance wires too to go along with the box. it is my opinion none of it is needed unless the renewable power is being fed from the utility, which it is not. do realize my opinion doesn't supercede any dumb laws or stupid inspectors.
    note here that you could not generate to send to the utility higher than the rating of the service max though. i don't think there's any danger of that happening now as that would be one big system. 125vx125a=15,625w after accounting for any losses that would occur. not many home owners have pv systems that big.
  • RoderickRoderick Solar Expert Posts: 253 ✭✭
    Re: current feed ratings for a service panel

    I think the issue is as follows (I know, unlikely):

    No solar:

    Everybody decides to turn on their space heaters. We have 10, 15A circuits in the house, each drawing 13A. Ok, so none of those branch breakers pop. But there is 130A being drawn from the main service, so the main 100A breaker trips. No problem there. Turn some stuff off, and go reset the breaker.

    With solar:

    Same thing, but the solar is providing 40A backfeed. Now, the mains are providing 90A, no circuit breaker trip there. Each circuit is within its rating, no circuit breakers trip there, either. But there is now 130A of current continuously flowing through the busbars of the main service panel, which is only rated for 100. It is the heating of these busbars that would be the concern.
  • RoderickRoderick Solar Expert Posts: 253 ✭✭
    Re: current feed ratings for a service panel

    Hi, sorry to keep chiming in. Another solution came to mind.

    What you might do is reduce the customer's main breaker to (say) 80A instead of 100A (this is betting that they don't often draw such a heavy load). That would leave enough headroom on the busbars to safely inject another 40A, if you really needed to. I would advise the customer that this was what I was going to do. It would be safe, legal, and hopefully within the bounds of your bid. If the customer insisted on continued 100A service from the power company, you would then advise them that this can certainly be done cleanly, but there would be an extra charge.

    Personally, I like the previous solution of just using a 20A breaker to backfeed the solar. Clean, no extra subpanel. And if the present panel is out of space, you could use one of those twin-ganged 240V skinny breakers (actually, 2 skinny breakers with tie bars). If the customer later opted to upgrade to the full 6000 watts later, well, that would be the next installer's issue.
  • System2System2 Posts: 6,290 admin
    Re: current feed ratings for a service panel

    To add insult to injury, there is no main breaker, the meter is wired directly into the bus bar. I am still chewing on the information I am receiving. Thanks for all the replies and I'll let you all know what happens.
    Pat
    http://affordenergy.com/gallery
  • halfcrazyhalfcrazy Solar Expert Posts: 720 ✭✭✭
    Re: current feed ratings for a service panel

    Neil what i was trying to say was here we have to have 2 meters so the situation they have wouldnt occur as the solar"outgoing" would go into the second meter thru its own panel or disconect we cannot feed into the house's main panel as the local power co's want seperate meters to record stuff so the meters would have a lot to do with this as if i have 2 100 amp meter sockets the house can draw its 100 amps and the solar could put out 100 amps as the meter enclosure would handle 200 amps and each meter would have its own 100 amp breaker. so my question is why cant this work for this particular case? if you put a double meter enclosure in with 100 amp breakers feed meter A to the house subpanel and feed meter B with the solar? seems simpler then trying to figure a way around the 125% of the sub panel and then if they ever upgrade solar you would still have plenty of room?
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: current feed ratings for a service panel

    ok i follow as it's seperate panels into seperate meters and that sounds ok to me, but they have to be joined together with the service wire so i believe another box is needed for that, unless it is accomplished another way?
  • halfcrazyhalfcrazy Solar Expert Posts: 720 ✭✭✭
    Re: current feed ratings for a service panel

    neil the ones we use are made that way one service cable two meters and disconnect breakers under them usually all that is needed is to take customers old meter socket out and put this in and upgrade the cables from meter socket to the service mast. they are basically the same meters used on apartment buildings
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