Duplex service conductor

[Ponchik]

Based on 2014:

I was reviewing my code book and got to thinking about duplex service conductors and I did my own practice load calcs and here is what I came up with.

1.Unit A & B each calculated load is 67A and 62A
2.Minimum service rating for each is 100Amps based on 230.79(C)
3.Single overhead riser conduit with single set service conductors is based on 129 amps
4.Based 310.15(b)(16) my over head service conductors are based on the calculated load of both units 129 amps = #1 copper conductors

Am I correct?

Or size of the service conductors is based on the main over current protection times two (so 200Amp and use 3/0)

Thank you

 

[kwired]

If 310.15(16) applies you are correct.

But 310.15(16) is for not more then 3 current carrying conductors in raceway cable or earth with ambient temp of 30C.

conductors in free air get to use a different table, which one applies to your conductors?

Quite often this is POCO's service drop cable and they don't have to comply with NEC either. Many of them around here would drop a #2 aluminum to this service.

 

[Ponchik]

If 310.15(16) applies you are correct.

But 310.15(16) is for not more then 3 current carrying conductors in raceway cable or earth with ambient temp of 30C.

conductors in free air get to use a different table, which one applies to your conductors?

Quite often this is POCO's service drop cable and they don't have to comply with NEC either. Many of them around here would drop a #2 aluminum to this service.

The service conductors in my question is not the service drop. I know the service drop is under the POCO jurisdiction. The 3 CCC does not apply because I have two hots and one neutral in the service riser conduit.

 

[kwired]

The 3 CCC does not apply because I have two hots and one neutral in the service riser conduit.

You are looking at that aspect the wrong way, it says "not more then" 3 current carrying conductors, but still if they are in free air another table may apply and actually allow for higher ampacity from same conductors.

Are you selecting size of the "overhead" conductors that are in free air or are you selecting size of the conductors in the riser conduit? Maybe I misunderstanding what you were asking about?

 

[Smart $]

...
Are you selecting size of the "overhead" conductors that are in free air or are you selecting size of the conductors in the riser conduit? Maybe I misunderstanding what you were asking about?

#3 in OP. The conductors will not be in free air.

3.Single overhead riser conduit with single set service conductors is based on 129 amps

 

[Smart $]

The service conductors in my question...

You did not post your load calculation. For combined service entrance conductors you may be able to take advantage of 75% demand for four or more fixed-in-place appliances if the individual units could not.

Is this new construction? ...one meter or two? If one meter I have to question here whether or not the duplex units can legally be under one meter and billed as one service by the power company.

You will not be able to take advantage of 310.15(B)(7) the way it is worded.

 

[Ponchik]

You are looking at that aspect the wrong way, it says "not more then" 3 current carrying conductors, but still if they are in free air another table may apply and actually allow for higher ampacity from same conductors.

Are you selecting size of the "overhead" conductors that are in free air or are you selecting size of the conductors in the riser conduit? Maybe I misunderstanding what you were asking about?

Which aspect I have the wrong way?

 

[Dennis Alwon]

Edward, to answer your question the risers can be based on the calculated load however if you want to leave room for growth then you may want to up the size of those conductors

 

[Ponchik]

Edward, to answer your question the risers can be based on the calculated load however if you want to leave room for growth then you may want to up the size of those conductors

:thumbsup:
That is all i wanted to learn if in this case the service conductors are based on calculated load or based on the main OCPD.

 

[Smart $]

That is all i wanted to learn if in this case the service conductors are based on calculated load or based on the main OCPD.

The minimum is based on the calculated load. However, service ocpd rating has a mutual relationship with the service conductor ampacity... and vice versa.

 

[kwired]

#3 in OP. The conductors will not be in free air.

The more I look at OP, #3 is conductors in the riser, #4 is the overhead conductors. Majority of my responses has been concerning those overhead conductors, which don't necessarily get sized the same method as those in the riser conduit.

I think OP is asking about both.

129 amps is the correct load to use based on information provided.

 

[kwired]

Which aspect I have the wrong way?

That 3 current carrying conductors doesn't apply, the table is for three or less so same table applies to ony 2 current carrying conductors.

Seems to be a lot of confusion (at least on my part) on which conductors you are sizing.

Then you kind of switched your tune to the 129 amps being primarily what you are asking about. If that is what you were after, then yes you must have at least a 129 amp conductor in this application, though many would probably install a 180-200 amp conductor just to allow for some additional load in the future.

 

[Smart $]

The more I look at OP, #3 is conductors in the riser, #4 is the overhead conductors. Majority of my responses has been concerning those overhead conductors, which don't necessarily get sized the same method as those in the riser conduit.

I think OP is asking about both.

129 amps is the correct load to use based on information provided.

I believe he is referring to the service entrance conductors only. He states "over head service conductors" in regards to the service delivery type—overhead vs. uderground.

 

[kwired]

I believe he is referring to the service entrance conductors only. He states "over head service conductors" in regards to the service delivery type—overhead vs. uderground.

Which to me "overhead service conductors" is typically aerial cable, those that are in the mast are not "overhead conductors"they are just conductors in a raceway.

Both are still "service conductors" though.

To be honest, the "duplex service conductor" in the title first had me thinking he was talking about a 120 volt only service (no 240 volts). 120/240 services are supplied with "triplex".