I am trying to understand the use of the optional calculations for high rise condo services with 5 meter centers (22 meters each) on common bus duct (total 110 units). After applying the demand factor for the one meter center (22 units served), can you then take an additional demand for the total number of meter centers on the bus.
Multi family optional calculations
- Thread starter msmoe
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- Windsor, CO NEC: 2017
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- Service Manager
Re: Multi family optional calculations
I am confused by your question. (Not suprising, as it's a little outside my normal scope of work!)
It seems to me that you would need to have the bus at the lowest level (closest grade) sized for the total demand load for the building.
I am confused by your question. (Not suprising, as it's a little outside my normal scope of work!)
It seems to me that you would need to have the bus at the lowest level (closest grade) sized for the total demand load for the building.
wirenut1980
Senior Member
- Location
- Plainfield, IN
Re: Multi family optional calculations
I would say yes, you should take into account another demand factor, because otherwise your total demand factor will only take into account 22 units, when in actuality you have 110 total units. And IMO, when you add more and more units into the mix, generally the overall demand decreases. This is all just my gut intuition, by the way.
[ September 27, 2005, 08:16 AM: Message edited by: wirenut1980 ]
I would say yes, you should take into account another demand factor, because otherwise your total demand factor will only take into account 22 units, when in actuality you have 110 total units. And IMO, when you add more and more units into the mix, generally the overall demand decreases. This is all just my gut intuition, by the way.
[ September 27, 2005, 08:16 AM: Message edited by: wirenut1980 ]
- Location
- Lockport, IL
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- Retired Electrical Engineer
Re: Multi family optional calculations
Take care that you do not "double dip" into the demand factor pool. The simple way to say this is that when you look at any single wire, you first add up the load that is downstream of that wire, then you use the demand factor that applies to the number of units that are included in that load.
I presume you are in 220.84, "Multifamily Dwelling." When you look at the feeder to a single apartment, there is only one unit downstream of that feeder, and you have no demand factors available. When you look at the feeder to a meter center, you add up the load on the 22 units, and apply the demand factor of 36%.
Now look at the service to the set of 5 meter centers. You have to add up the loads on all 110 units, without using the results of the previous step. You do not get to take the 36% demand factor (from each meter center), and then apply another demand factor 45% for 5 meter centers) to that sum. That would be "double-dipping." Rather, you add all the loads on 110 units, without using any demand factor in obtaining that sum. When you get that sum, you then apply a demand factor of 23% (for having more than 62 units).
Take care that you do not "double dip" into the demand factor pool. The simple way to say this is that when you look at any single wire, you first add up the load that is downstream of that wire, then you use the demand factor that applies to the number of units that are included in that load.
I presume you are in 220.84, "Multifamily Dwelling." When you look at the feeder to a single apartment, there is only one unit downstream of that feeder, and you have no demand factors available. When you look at the feeder to a meter center, you add up the load on the 22 units, and apply the demand factor of 36%.
Now look at the service to the set of 5 meter centers. You have to add up the loads on all 110 units, without using the results of the previous step. You do not get to take the 36% demand factor (from each meter center), and then apply another demand factor 45% for 5 meter centers) to that sum. That would be "double-dipping." Rather, you add all the loads on 110 units, without using any demand factor in obtaining that sum. When you get that sum, you then apply a demand factor of 23% (for having more than 62 units).
wirenut1980
Senior Member
- Location
- Plainfield, IN
Re: Multi family optional calculations
Charlie, you are one of the most eloquent posters I have ever seen. I was trying to say what you were saying and it came out garbage. Good thing you are here.
By the way, love the Seinfeld reference.
Charlie, you are one of the most eloquent posters I have ever seen. I was trying to say what you were saying and it came out garbage. Good thing you are here.
By the way, love the Seinfeld reference.
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