Duplex service

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mbrooke

mbrooke

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Ok, 100amp service to each dwelling. My understanding is that I can reduce the size of the conductor from the meter to the panel by 83%, however does code permit me to do an 83% reduction using 2/0 conductor or do I have to use 3/0?

My thinking is that 83 amps x2 is 166 amps so I can do the same between the weather head and meter.
 
I think that in general if a wire serves more than one dwelling unit the reduction does not apply, although a duplex may also be covered.
 
GoldDigger said:
I think that in general if a wire serves more than one dwelling unit the reduction does not apply, although a duplex may also be covered.
Click to expand...

I guess the question is how do I size the conductor between the weather head and meter? Do I just add the two? Or does a diversity factor apply (although I cant seem to find anything in the code).
 
jumper said:
Go back and look at (1) and (2) of that section. You can use it for the service conductors and the feeders.
Click to expand...

Half my question is already answered (it was right there lol), however what do I apply that 83% to? Do I use my calculated load of both units, 83 amps or 100amps?
 
There seems to be some confusion here between calculated load and service size. If the calculated load is 100A, then it is 100A. The wire, however, can be sized to 83A.
If the calculated load is 70A, the wire can be sized to 70 times .83
If you did not calculate the load you cannot just set it to 83A.

You also cannot blindly add 83 and 83 and then take 83% of that for the service conductors.
 
mbrooke said:
Half my question is already answered (it was right there lol), however what do I apply that 83% to? Do I use my calculated load of both units, 83 amps or 100amps?
Click to expand...

It says: service conductors supplying
the entire load associated with an individual dwelling
unit in a two-family or multifamily dwelling, shall
be permitted to have an ampacity not less than 83 percent
of the service rating.

If you are installing a 200A service I imagine it would be 83% of 200A
 
GoldDigger said:
There seems to be some confusion here between calculated load and service size. If the calculated load is 100A, then it is 100A. The wire, however, can be sized to 83A.
If the calculated load is 70A, the wire can be sized to 70 times .83
If you did not calculate the load you cannot just set it to 83A.

You also cannot blindly add 83 and 83 and then take 83% of that for the service conductors.
Click to expand...


Isnt the wire sized to the service disconnect rating with an 83% reduction rather then the calculated load?

I would not add 83 amps and the reduce by 83%, rather my thinking was add 83 together getting 166 amps and using 2/0 on the 75*C column.
 
mbrooke said:
Isnt the wire sized to the service disconnect rating with an 83% reduction rather then the calculated load?

I would not add 83 amps and the reduce by 83%, rather my thinking was add 83 together getting 166 amps and using 2/0 on the 75*C column.
Click to expand...

2/0 CU is what I get. Either my way or your way it still comes out to 166A.

I just took 83% of 200A instead.

2/0 CU matches the old resi chart also.
 
So 2/0 to meter and #4 cu from meter to panel?

For future reference do I calc the weather head to meter after the 83% reduction or do I go by the service disconnect and then apply the 83% to that?
 
mbrooke said:
So 2/0 to meter and #4 cu from meter to panel?

For future reference do I calc the weather head to meter after the 83% reduction or do I go by the service disconnect and then apply the 83% to that?
Click to expand...

Yes, 2/0 CU to meter base pack, I assume 2 meters for a duplex, tap off 2/0 with #4 to each meter. Meter base to each disconnect or panel.
 
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