60 Amp AC combiner panel/feeder to 200A loadcenter

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ggunn said:
Yes, of course, but that would have to be in a panel that is, obviously, not an MDP for a service. We use that option for AC inverter combiner panels but it still leaves the problem of how to interconnect it.160A would not be less than 20% of any residential service that I have heard of, so that panel could not be a residential subpanel. It would have to be supply side interconnected.
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There is another option: You use 230.40 exception #2 to feed a new main breaker (service disconnect) panel and also use it as your combiner qualified under the sum of all breakers rule.
 
jaggedben said:
The third rule, the 'sum of all breakers' rule, occasionally works for a residential MDP.
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I'm reluctant to use the 3rd rule on anything but PV AC combiners. While at a point in time it might apply to an MDP those panels will most likely get loads added to them over the years and by electricians or homeowners who are not aware of the restriction on the panel that it was qualified under when the PV was installed. Now the sum of all breakers is more than the allowable amount. PV AC combiners will most likely never have any loads installed, particularly if properly placarded to not allow additional loads.
 
pv_n00b said:
I'm reluctant to use the 3rd rule on anything but PV AC combiners. While at a point in time it might apply to an MDP those panels will most likely get loads added to them over the years and by electricians or homeowners who are not aware of the restriction on the panel that it was qualified under when the PV was installed. Now the sum of all breakers is more than the allowable amount. PV AC combiners will most likely never have any loads installed, particularly if properly placarded to not allow additional loads.
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Yep.
 
pv_n00b said:
I'm reluctant to use the 3rd rule on anything but PV AC combiners. While at a point in time it might apply to an MDP those panels will most likely get loads added to them over the years and by electricians or homeowners who are not aware of the restriction on the panel that it was qualified under when the PV was installed. Now the sum of all breakers is more than the allowable amount. PV AC combiners will most likely never have any loads installed, particularly if properly placarded to not allow additional loads.
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Well, there is the required label. And if the sum of breakers is at the max you can add a 'Do Not Add Additional Loads' sticker that costs about $1. I often stick these labels right over unused twistouts in the deadfront to increase the likelihood that they get read and thought about. We also usually put an engraved placard with our company info that says to call us with questions. If someone willfully ignores all that ... that's on them. Further, I don't think it's that much more prone to abuse than other rules. A number of times I've seen that a homeowner had a panel upgrade after solar was already installed and the electrician failed to put the solar breaker at the opposite end of the busbar as required, or did something technically disallowed with feed through lugs. None of these rules are safe from a yahoo showing up later. And finally, all the rules are incredibly conservative and the likelihood that the kind of mistakes you describe would actually lead to an incident remains exceedingly small. For all these reasons, while I hear you, I don't hesitate to use the rule where appropriate.
 
jaggedben said:
Well, there is the required label. And if the sum of breakers is at the max you can add a 'Do Not Add Additional Loads' sticker that costs about $1. I often stick these labels right over unused twistouts in the deadfront to increase the likelihood that they get read and thought about. We also usually put an engraved placard with our company info that says to call us with questions. If someone willfully ignores all that ... that's on them. Further, I don't think it's that much more prone to abuse than other rules. A number of times I've seen that a homeowner had a panel upgrade after solar was already installed and the electrician failed to put the solar breaker at the opposite end of the busbar as required, or did something technically disallowed with feed through lugs. None of these rules are safe from a yahoo showing up later. And finally, all the rules are incredibly conservative and the likelihood that the kind of mistakes you describe would actually lead to an incident remains exceedingly small. For all these reasons, while I hear you, I don't hesitate to use the rule where appropriate.
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Something we have run into recently is a customer of ours who had us install a grid tied PV system via a backfed breaker in the MDP later installing a whole home generator with an ATS between the MDP and the meter. This is a dangerous (to the generator) thing to do and we would never have known had he not also contacted us to add to his PV system. The PV system interconnection needs to be moved to the line side of the ATS.
 
jaggedben said:
Further, I don't think it's that much more prone to abuse than other rules. A number of times I've seen that a homeowner had a panel upgrade after solar was already installed and the electrician failed to put the solar breaker at the opposite end of the busbar as required, or did something technically disallowed with feed through lugs. None of these rules are safe from a yahoo showing up later. And finally, all the rules are incredibly conservative and the likelihood that the kind of mistakes you describe would actually lead to an incident remains exceedingly small. For all these reasons, while I hear you, I don't hesitate to use the rule where appropriate.
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If the panel is correctly rated and the PV CB is at the opposite end then no one installing additional CBs later needs to be concerned with, or even aware of, the special requirements for PV. It's baked into the setup and much safer than expecting that every time a load is added that the person doing it is aware of and able to comply with 705. Also limiting an MDP to the sum of all CBs rule puts a huge restriction on how the homeowner can use the MDP in the future. It's not right in my mind to do that to someone just so I can check a box in 705.
 
pv_n00b said:
It's not right in my mind to do that to someone just so I can check a box in 705.
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Certainly we can come up with plausible scenarios where the alternative is to spend an additional $2,000+ on panel upgrades, and the homeowner is happy to accept the limitations on future expandability for the present dollar savings.

Cheers, Wayne
 
pv_n00b said:
If the panel is correctly rated and the PV CB is at the opposite end then no one installing additional CBs later needs to be concerned with, or even aware of, the special requirements for PV. It's baked into the setup and much safer than expecting that every time a load is added that the person doing it is aware of and able to comply with 705. Also limiting an MDP to the sum of all CBs rule puts a huge restriction on how the homeowner can use the MDP in the future. It's not right in my mind to do that to someone just so I can check a box in 705.
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In addition to the scenario I mentioned above (subsequent main panel replacement) I can think of more scenarios under the other rules where the person who comes later needs to be aware of the special requirements for PV. For example, adding breakers often involves figuring out space around quads and tandems, so someone might very well move the PV breaker for that reason. Or if the main breaker has been downsized, someone might upsize it back to what it was because they think additional load needs it. So I just don't buy that the opposite end rule doesn't have the same issues.

Also with the sum of all breakers rule, there's a pretty big difference between, say, leaving a 200A panel full of 200A of breakers, and leaving it with something much less. Or for example there's the cases where you're really not restricting them very much. For example a 200A panel with two 100A subpanel breakers, and plenty of leeway to still do whatever you want in the subpanels.

What I'd agree is 'not right' is failing to inform the customer, especially if you know they are planning specific additional load in the future. But the same logic applies to main-breaker-downsizes which we do to meet the other rule.

You're entitled to your opinion of course, I just don't see avoiding 'sum of all breakers' as a general rule is very objective.

wwhitney said:
Certainly we can come up with plausible scenarios where the alternative is to spend an additional $2,000+ on panel upgrades, and the homeowner is happy to accept the limitations on future expandability for the present dollar savings.
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Yup. Except you're understating the typical amount by half. At least in our area. For overhead.
 
pv_n00b said:
. Also limiting an MDP to the sum of all CBs rule puts a huge restriction on how the homeowner can use the MDP in the future. It's not right in my mind to do that to someone just so I can check a box in 705.
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Not an issue.....The future person can just counter with their own label 😂
 

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