Confirming sizing for small apartment building

[jdrive]

Hi all,

I am working on a service upgrade in the Chicagoland area for a low rise apartment building. It is a bit larger service than I normally handle so I just wanted to confirm that I have the sizing correct. Total building load is 410amps (calculated). Overhead service.

Wire from weatherhead to meter socket: Based on 310.15(B)(16) it looks like I need to go with 600 MCM copper. I don't think I can use aluminum as the meter socket lugs are rated for 600 MCM max.

Side question: On paper, I should be fine with a 3" conduit for the 600 MCM copper. Will I have any issues bending this size wire through a 3" weatherhead? It's a pretty straight shot from the meter socket except for the turn that I would have to do coming out of the head.

Each apartment panel will be 200amps so 3/0 copper would be used in 1 1/2" conduit from the meter socket to each panel.

Interior GEC from the panel to the water service - sizing based on 250.66 and 600 MCM service conductor would mean 1/0 copper in 1" EMT. Can I use #4 copper to bond the panels together per 250.102(C)(1)?

Exterior GEC from meter socket to ground rod - #6 copper in 1/2 EMT

Thank you in advance!

 

[augie47]

First thing I would do would check with your Power Co about metering. Our POCOs don;t have a self contained meter for a 410 amp load (They use CTs)
Depending on your Code cycle, if you don;t have a main for a 410 amp calculated load, you could parallel 4/0s..
much easier to handle.
You can use 310.15(B)(7) for the individual apartment feeds so 3/0 would not be necessary.
Use PVC to sleeve and GEC ( if you need to sleeve them). With EMT you have to bond.

(This being out of the relam of your normal work, you might come out ahead to work with someone familiar with this scope of work this time)

 

[jdrive]

Each apartment has a separate meter, which would just be the standard 200amp rated meters ComEd uses on almost all residential service around here. A CT would only be necessary if I had a single unit running 400+ which we definitely don't have. We can't use PVC around here, all RMC or EMT.

I will go back and review 310.15(B)(7)

 

[augie47]

I should have realized that (separate meters), but your term "meter socket" caught me
If this is a meter module I would think it would accept parallel conductors which would make your work easier.
Unless local rules required, you would not need to sleeve your GEC and avoid the bonding issue.

 

[don_resqcapt19]

What code are you working from? There are a lot of different editions of the NEC in use in the Chicago area, and Chicago has it own code which is a highly amended version of the 2017 NEC.

 

[kwired]

Each apartment has a separate meter, which would just be the standard 200amp rated meters ComEd uses on almost all residential service around here. A CT would only be necessary if I had a single unit running 400+ which we definitely don't have. We can't use PVC around here, all RMC or EMT.

I will go back and review 310.15(B)(7)

If you have separate meters to each unit what is it that only accepted 600kcmil max? A multiple meter assembly? If so chances are the main lug section would accept parallel conductors, or possibly needs to be at least a 600 amp version if you want larger lugs?

If individual meter sockets, you would likely be running your main service conductors to a gutter or tap box then running smaller conductors to each individual meter.

310.15(B)7) would only apply to conductors to individual dwellings and not to the common supply conductors for multiple dwellings.

 

[jdrive]

What code are you working from? There are a lot of different editions of the NEC in use in the Chicago area, and Chicago has it own code which is a highly amended version of the 2017 NEC.

Chicago's special edition

If you have separate meters to each unit what is it that only accepted 600kcmil max? A multiple meter assembly? If so chances are the main lug section would accept parallel conductors, or possibly needs to be at least a 600 amp version if you want larger lugs?

The meter socket (multiple meter assembly) is a single unit with separate positions for each meter. The meter socket specifications state "(2) #2-600" for the main lugs, so yes it appears to support parallel conductors.

I was originally assuming that it would be easier (and possibly cheaper) to just run a single 3" conduit than to parallel two sets of conductors...

 

[kwired]

Chicago's special edition



The meter socket (multiple meter assembly) is a single unit with separate positions for each meter. The meter socket specifications state "(2) #2-600" for the main lugs, so yes it appears to support parallel conductors.

I was originally assuming that it would be easier (and possibly cheaper) to just run a single 3" conduit than to parallel two sets of conductors...

Often if it says two #2-600 it usually states an even larger conductor for single conductor applications. Physically there should be room for larger than 600 if it will accept two 600's unless there is other reason to not allow a larger conductor.

Such gear may even have options for using different lugs, say you wanted to run single conductor or maybe parallel three conductors instead of two.

 

[jdrive]

I spoke with Milbank (the meter socket manufacturer) last week and they said it is only listed for up to 600MCM. I suppose I could use different lugs, but the mfr says that is not officially a supported application. I think 600MCM should be large enough though, right?

 

[kwired]

I spoke with Milbank (the meter socket manufacturer) last week and they said it is only listed for up to 600MCM. I suppose I could use different lugs, but the mfr says that is not officially a supported application. I think 600MCM should be large enough though, right?

Do you have a single main or multiple mains?

Single main needs to be at least 450 amps if your load calculation is 410.

If you have the allowed 2-6 service disconnects you only need common supply conductor ampacity of 410, but sum of the overcurrent devices can be more than the ampacity of common supply conductor. Taps to individual mains need to be sized per the ocpd it supplies though, but if you have a meter center it will be listed as is so those taps wouldn't be of any concern for you.