MJRobinson
Member
- Location
- Chico, CA, USA
I don't do PV stuff, but agree - depends if you are feeding into the 800 amp main bus or into a 600 amp section bus.Through bus is the horizontal bus that connects the sections together. Section bus runs vertically in a section and is what supplies whatever is connected to the bus in that section. If you land a back feed breaker in the section then the bus rating is 600A for the 120% rule. For more info see this: http://electrical-engineering-portal.com/switchboard-construction-siemens-basics
Probably not what you were hoping for.
I don't do PV stuff, but agree - depends if you are feeding into the 800 amp main bus or into a 600 amp section bus.
To invoke the 120% rule you have to be at the opposite end of the busbar, which arguably isn't possible when you have multiple busbar sections coming off the main bus, presumably without individual OCPD. (i.e. you can't be at the opposite end of all those busbars) I think best case is that the main switch gear OCPD is not more than 600A and the AHJ lets you tie into the opposite end of the 600A section that is at the opposite end. I assume there is a stipulation that each 600A bus section can't have more than 600A load, and if that's followed then the logic behind the rule would deem such an installation safe. But article 705 doesn't explicitly address that. Probably it just needs an engineer to sign off on the details that simple code rules (or not-so-simple code rules, as the case may be) just can't fully address.
Why not? Supply side interconnections are frequently much simpler to design and install. They are just as legal and safe as load side connections. If the input OCPD in the switchgear happens to have space on its input bus to land PV connectors, it's easy-peasy.I agree, once you start interconnecting to switchboards there are few simple rules of thumb anymore. Switchboards are too highly customizable and you need to understand how that specific switchboard is put together. I've seen weird stuff out there. I've talked to many contractors who just default to supply-side interconnections because they don't want to get involved in what is going on in there, I don't agree with that choice but many do it.
Why not? Supply side interconnections are frequently much simpler to design and install. They are just as legal and safe as load side connections. If the input OCPD in the switchgear happens to have space on its input bus to land PV connectors, it's easy-peasy.
How many have you done where you used a landing point that was labeled "tap" and not just some convenient hole or stud that happened to be there? How many people drill holes in bus to land PV conductors? It might seem easy to do, but it's not easy to do correctly.
https://www.ul.com/global/documents...newsletters/electricalconnections/april10.pdf
I have never drilled a hole in a bus to land PV connection terminals. I have found open holes just like the ones the service conductor terminals are landed on and gotten the OK from the switchgear manufacturer to use them for PV interconnection.
I've talked to many switchboard manufacturers and have never found one that will approve landing at an unused hole that is not marked for taps. What manufacturers have you worked with who have approved it? Did they send you an approval letter or was it over the phone? I'd like to know who to work with.