Service Size for 4 Unit Building

Old 10-24-02, 10:25 AM
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Service Size for 4 Unit Building

Hi -

I own a three family home that has 200Amp service to four electrical meters in the basement. I am currently renovating the attic of the building to create 4 units. My plan is to add the fourth unit onto the 4th meter which is right now the public one. My plan was to upgrade the current public panel from the 40A it is now to 100A so it can feed the top floor. This fourth apartment is going to run on all electric (heat/AC, stove, dryer, dishwasher, whirlpool tub, etc). There is no gas to this floor. I determined that 100A service would be sufficient for this. An electrician recently came out and told me the I would need to upgrade the entire service into my building from 200A to 300A. He said the best way to do it is to put in the service, with 4 new meters, 4 new service panels (125A each). He said that 200A was not enough to support four units, especially with the 4th floor I am putting in being all electric. I am curious as to is this sounds right? I was hoping to only have to upgrade the 4th floor panel to 100A off the public meter. I assumed 200A service into building would be sufficient. Any input on this would be appreciated. Below is what the major electrical units are in each apartment.

Electric Requirements
Floor 1 - Dryer
Floor 2 - Stove & Dryer, Dishwasher
Floor 3 - Stove, Dryer, Water Heater, Baseboard Electric HEat
Floor 4 - Stove, Heating/AC System, Dryer, DIshwasher, Whirlpool Tub

Old 10-24-02, 02:30 PM
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You can hope all you want,, but your going to need a service upgrade or switch a bunch of that stuff to gas.
Old 10-24-02, 03:55 PM
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You need to perform a demand calculation. In order for the electrician to have determined that you needed a service increase he must have done a demand calc., or measured the amps drawn through the current service. See the link below for the calc
Old 10-24-02, 04:49 PM
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I am curious how the meters are read if they are in the basement.
We need a little more information on how this is set up. Is there a single SEC coming into your house and then tapped off into three meters. If this is correct, how do you know what size your service is capable of? Is there an OCPD before the meters that is only rated at 200 amps. Either way I don't see the need to change panels in the house. You may have to change the Line coming from outside and install a 4th meter or a larger panel.
Let me know if this helps.
Old 10-24-02, 05:35 PM
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If you use the link that HandRon provided for a mulifamily unit you will have to add the square feet of each apartment together to get you total square feet of living area.

The small appliance branch cuicuits would not be 2 but two for each unit requiring 8 - 1500 watt small appliance branch circuits.

The laundry load would have to be calculated depending on whether you have a in house single and public laundry room for all renters to use or if you have a laundry in each apartment.

The laundry would be 1500 watts times one if a central laundry unit.

The laundry would be 1500 watts time 4 if a laundry is in each apartment.

The range would be added if four electric ranges as a total load of 17 KW if less than 12 KW per range but more than 8 3/4 KW rated ranges.

Typically you would be calculating four dwellings.

There is an optional method available for mutifamily dwellings found in NEC 220. 32 but suspect it would be about as confusing as the general method discribed in the link HandyRon supplied.

Remember you are doing a multifamily dwelling not a sinlgle family dwelling in your calculations.

Also remember each apartment is required to have a minimum of 100 amp panel serving that apartment as a living unit. However you would not just add the four 100 amp panels and say wow I need a 400 amp service to serve these units as a whole. The demand load calculation is designed to provide diversity due to intermittent loads regardless if you have 4 - 100 amp panels.

Hope this helps


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