duplex service

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hotblueelectric

hotblueelectric

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Dallas Texas
Normally dont rewire old duplexes but the way things are need the work. I am building a new service for a duplex. My load calculations call for 150 amp load center for each unit. They are not total electric but if they do become total electric 150 amps will be enough. Service entrance conductors will be sized at 250mcm. I am using a dual meter base 300 amp. 150 amp outdoor loadcenters are hard to find and very expensive. Can I use (2) 200amp panels? Can I size the feeders from the meters to the panels for 150amps? And last can I keep the service conductors at 250mcm? Trying to keep the cost down. What is standard in this situation?
Thank you for any advise.
 
Yes 220.40, You use the calculated load.
4/0 AL. Would be plenty.

BTW if you don't want to re-wire any old duplexes send them my way,:D $$$$$$$. They can be more profitable then a new house.
 
Unless they are real big duplexes. No way the total calculated load is 300. More like 70 each unit.
The power company is going to hook #2 AL to it.
So why should you go out of your way. 4/0 would be more then adequate.
If you must use bigger wire look at table 310.16- 60 degree column.
 
hotblueelectric said:
My load calculations call for 150 amp load center for each unit.

They are not total electric but if they do become total electric 150 amps will be enough.

... each units calculated load is 150, ...
Click to expand...
It can't be both, and certainly not all three.

A calculated load isn't a guess. See Art. 220.
 
about the panel you can use 200a panel with 150A mains. 250 mcm to meter line. 2/0 AL from double lug on load side to feed main, unless the meter has factory busses. we sell 200a service because they are cheaper to buy and the customer feels like they are getting more than they should.
 
duplex sizing service cond. for a dual meter

duplex sizing service cond. for a dual meter

Ive run the load calculations on Mike Holts residential calculator.
750 square ft
10kw heat load
2 small appliance
1 5kw dryer
1 micro
1 dish wash
1 disposal
1 water htr
1 range 8kw
I come up with 148 load this is not a guess.
The spread sheet for main and panel options says to use 3/0 cu feeder conductors (from the meter load to each 200 amp panel)with #6 cu neutral, and 2/0 cu ungrounded conductors from the meter line to the weatherhead with #4 cu neutral.
I want to know why it is sizing the service conductors at 2/0 instead of sizing them for the total load. Is there a demand factor here? Still can not get a clear answer. Help.
 
hotblueelectric said:
I come up with 148 load this is not a guess.
Click to expand...
Sorry, but something is wrong. My house is 3000 sq.ft., and my load is nowhere near 148a. You'd need a 200a service for that, and that's with little room for expansion.

... with #6 cu neutral, and 2/0 cu ungrounded conductors from the meter line to the weatherhead with #4 cu neutral.
Click to expand...
That's two different neutral sizes. Is that for each unit, or the building total?

I want to know why it is sizing the service conductors at 2/0 instead of sizing them for the total load. Is there a demand factor here?
Click to expand...
There is, but we'd need to see your numbers. You figure each unit, then do the calc again for the whole building, not just add the individual unit numbers.
 
You might also want to run the "optional" calculation from Mike's site. I think you will come up with a load of about 110 amps.
 
LarryFine said:
My house is 3000 sq.ft., and my load is nowhere near 148a. You'd need a 200a service for that,
Click to expand...

I disagree, if the load calcs come up with 148 amps then all you are required to provide is a 148 amp service, of course those 148 amp mains are tough to come by so I might go to 150. :cool:
 
duplex 1500 = 4500va
4 small app = 6000va
2 laundry = 3000va
gen light , sm app and laund load = 13500va

3000va @ 100% =3000va
10500 @ 35% =3675va

2 water heat = 9000va
2 refrig = 2800va
2 dish wash = 2060va
2 disposals =1380 va
2 microw = 3260va
2 ahu 10kw ea =22400va

gen light demand load = 6675 va
total heat load = 22400 va
appliance demand = 13875 va
dryer demand = 10000 va
range demand = 11000va

Service demand = 63950 va
demand load = 266 amps
neutral demand = 119 amps

This is what I come up with using the standard load calculator on Holts website.

2 200 amp panels with main breaker
overhead riser to meter line = 2/0 copper
feeders from meter load to panels = 3/0 copper

I have read art 220 and still do not see where the reduction (demand % factor) on the service riser conductors comes from.

266 amps would require a 250 mcm
the residential load calculator says to use 2/0.
This is where I am confused.

Article 220.84 mentions 3-5 dwelling units nothing for 2.
220.85 mentions 2 dwelling units but I dont understand it.

Thanks
 
The way I'm reading what you are showing is that there are (2) 200 amp services with panels, not a shared service drop. Per Table 310.15(B)(6) the conductor size for a single phase residential 200 amp service is 2/0 cu. If you were to combine the service drop it would indeed be different as you suggest.
 
I would agrree with calculated load of 266 amps, 250 cu would be required for a combined service drop with 2/0 required for 200 amp main breakers or #1 required for 150 amp main breakers split from there. 310.15 (B)(6) is where you should be looking.
 
That is exactly where I looked and also came up with 250mcm for the service conductors. BUT when I enter all the info into mike holts calculator and scroll over to the right where the panel section is for (2) panels, it tells me to use 2/0. This is where I am confused why 2/0 and not 250?????
 
I used the same program, got basically your numbers, and I don't see where it calls for the 2/0 under tjhe standard method. I see 1/0 to two panels.
When you change to the optional method, I see 187 amp demand and (2) 125 amp panles.
 
I believe it is only telling you the size required for 1 of 2 200 amp services, not the combined service. I have never used this calculator, but it makes sense from your description and sizes called for. Maybe someone who is familiar with this calculator could comfirm this.
 
standard

standard

augie47 said:
You might also want to run the "optional" calculation from Mike's site. I think you will come up with a load of about 110 amps.
Click to expand...

I agree. Even doing a standard calc for both units, unless I missed something, the total for each will be 125A per unit using 1/0Al tenant feeders [310.15(B)(6)] with a 250McM meter center per [310.16]. rbj
 
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