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Mike G.
Mike G., Master Electrician
Category: Electrical
Satisfied Customers: 7088
Experience:  Proven Professional 46 years Experience
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Sinclair talked to you before about a year ago. I am

Customer Question

Hi Mike, Steve Sinclair talked to you before about a year ago. I am planning on doing a 400a service project and need some questions answered please if you could help me out. i read in an article 310.15 believe that the entire load to a service can be squeezed ( as far as the riser service conductors are concerned ) to 83% is that correct? so my question or series of questions, sorry im a little confused and absolutely in need of your help .. so the project i am in the middle of ordering stock for the home owner through a supply house Standard Electric down here in Lowell, MA is a 3 metered 400 amp service i believe because the property owner mentioned to me since he spoke with National Grid that they only can have a 200 amp service or a 400 amp service? no 300? either way the guy David the property owner wants his existing panels demo'd and a new 400 amp service. the man wants copper conductors. so with 3 metered off locations, 1 powering a 100 amp service seperately metered for 1st floor a second seperately metered off 200 amp panel for the 2nd and 3rd floor and he wants out of the 200 amp main to power each floor seperately with a sub panel so i was thinking a (2) 100 amp overcurrent devices powering subs on both the 2nd and 3rd floor. is that legal to have two 100 amp subs out of a 200 amp main panel? and then lastly a 3rd seperately metered off 100 amp panel to be a common panel but he wants to run a sub panel off of it to his 3 flr garage? is that legal? because i could have sworn he even mentioned it wasnt legal but like wants to do it anyways? confuseinf. so if the 83 percent to the riser service conductors for a 400 amp service powering (2) 100 amp main panels in basement as well as (1) 200 amp main panel, as copper and with 90degree temperature rated sheathing would be 350 kcmill that are good for 350 amps?
Submitted: 6 months ago.
Category: Electrical
Expert:  Mike G. replied 6 months ago.

Hey Steve. Code requires a demand factor for the 4 units at 100A have a 45% factor which makes a 200A service. See Art 220.84

Customer: replied 6 months ago.
you are saying that i do not need to size the service to 400 amps but only to 200 amps if i am metering off 3 locations 1. being a 100 amp main panel basement to power 1st floor 2. a 200 amp main panel with 2 100 amp sub panels ran off of it and 3 being a 100 amp common panel/garage 100amp sub panel?
Customer: replied 6 months ago.
if you'd prefer me to call thats fine. thank you
Expert:  Mike G. replied 6 months ago.

I can call tomorrow if that works for you.

Customer: replied 6 months ago.
i will be working all day tommorow on a basement remodel. i just wiped out my bank account asking a couple more individual questions i dont think i now can pay to call you it wouldnt take my credit card anymore. anyways, thanks for the help Mike appreciate it. my number is *****
Expert:  Mike G. replied 6 months ago.

To avoid the phone charges we can continue via the site.. Do you have a code book?

Customer: replied 6 months ago.
nec 2014
Expert:  Mike G. replied 6 months ago.

Art 220.84 Table is all that is needed for calculating the demand factor of the service size.

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