Service & OCPD size

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Designer69

Senior Member
Hey guys I'm a little unclear on this:

Industrial type facility.

Two (2) 10HP motors.
Two (2) 7.5HP motors.

About 50A of LTG/RCP type loads.

Facility has single phase service 120/240.

The motors are basically one lead and one stand-by of each but the service should be sized worst case scenario meaning all are on at the same time.

All motors will be connected to with 240V.

So right now I have the service size at 400A. but am worried it's a little high.

Same w/ OCPD.

Some comments would be appreciated TY
 

Jraef

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Assuming you want CBs as OCPDs;
Your 10HP motors each need 90A CBs, but are 50A FLC, so 100A total,
Your 7.5HP motors each need 80A CBs, but are 40A FLC, so 80A total,
Your other loads are 50A as you stated,
So 100 + 80 + 50, I see a 230A max. load, that means a 400A service.
Definitely not a 200A service. So what's the controversy?
 

Designer69

Senior Member
Well I just wasn't too solid on it because I remember some NEC rule that says something like ... take the highest motor load and multiply by 75% and add all other motor loads to it or so I can't remember

but essentially J I was just looking for a double check on the numbers

thanks for the help
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
75%, 125%... ah come on... what's 50% between friends?

Yes, that would be the way to be more exact about it, especially when you want to size a main CB. I wasn't meaning to be inexact, just when looking at a service size, 200A, then 400A are the available options so this was definitely over 200A.
 
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