drinkingbird
Member
- Location
- Massachusetts
I'm an electrical engineer but not an electrician, hope I can still post here.
I'm working on planning out an upgrade to a 2 family that I own. Currently 2x100A service (single 4/0-4/0-4/0 Alum. SEU, dual pan).
Would like to go to 2x200A panels. I assumed this meant a 400A capable SE to the (new) dual meter pan, which using residential table means 400MCM copper or 600MCM aluminum. Then I saw something mentioned about only sizing the SE to the calculated load and not to the main breakers themselves, but that makes no sense to me. My understanding was the SE must always be sized to the sum of the main breakers, but wondering if there is something different since its two meters and two distinct units? I think what I read was incorrect or not clearly stated, and that they meant to say to size both the mains and the SE to the calculated load, but was curious for confirmation. I'm aware the POCO does their own calc and their aerials will likely be 1-2 sizes smaller than my SE but wondering about my portion of it.
It actually looks like my POCO will require a significant payment to do 400A service, so I'm considering a somewhat non-standard 2x150 instead as that falls under their "we'll pay for it" limit and would save me money on the SE as well, but still thinking it through. A very generous load calc with lots of buffer only puts them at about 110-125A peak load each and technically the dwelling is still served by 200A or greater service which seems to be what most authorities want these days.
An aside question - code clearly requires each unit to have access to their main disconnect, which is fine, each will have the panel in their unit (they actually don't now), but I saw mention that for multi-dwelling, that all disconnects go in one place, meaning at the meter and wiring the panels as subs. Wasn't sure if this was a code requirement or just a locality thing. Most 2-fams around here don't have disconnect at the meter. I understand the benefit of doing it that way for a fire or other emergency, just wondering if its actually required.
I'm going to run this by POCO and inspector when the time comes but I like to have a clear view in my head before relying on their sometimes assinine requirements/recommendations. Thanks for any thoughts/input.
I'm working on planning out an upgrade to a 2 family that I own. Currently 2x100A service (single 4/0-4/0-4/0 Alum. SEU, dual pan).
Would like to go to 2x200A panels. I assumed this meant a 400A capable SE to the (new) dual meter pan, which using residential table means 400MCM copper or 600MCM aluminum. Then I saw something mentioned about only sizing the SE to the calculated load and not to the main breakers themselves, but that makes no sense to me. My understanding was the SE must always be sized to the sum of the main breakers, but wondering if there is something different since its two meters and two distinct units? I think what I read was incorrect or not clearly stated, and that they meant to say to size both the mains and the SE to the calculated load, but was curious for confirmation. I'm aware the POCO does their own calc and their aerials will likely be 1-2 sizes smaller than my SE but wondering about my portion of it.
It actually looks like my POCO will require a significant payment to do 400A service, so I'm considering a somewhat non-standard 2x150 instead as that falls under their "we'll pay for it" limit and would save me money on the SE as well, but still thinking it through. A very generous load calc with lots of buffer only puts them at about 110-125A peak load each and technically the dwelling is still served by 200A or greater service which seems to be what most authorities want these days.
An aside question - code clearly requires each unit to have access to their main disconnect, which is fine, each will have the panel in their unit (they actually don't now), but I saw mention that for multi-dwelling, that all disconnects go in one place, meaning at the meter and wiring the panels as subs. Wasn't sure if this was a code requirement or just a locality thing. Most 2-fams around here don't have disconnect at the meter. I understand the benefit of doing it that way for a fire or other emergency, just wondering if its actually required.
I'm going to run this by POCO and inspector when the time comes but I like to have a clear view in my head before relying on their sometimes assinine requirements/recommendations. Thanks for any thoughts/input.