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Electrical Question: Sizing of a MCB

Wed 12 Apr, 2017 07:36 am
Good Day,
I have 3 pumps that I want to put in a panel board, drawing 19A 19A and 11A.
What size should my main circuit breaker be? and what norm? NFPA? NEC?
and can you give me the formula, please?
Best Regard.
Nick.
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Type: Question • Score: 0 • Views: 1,491 • Replies: 6

Ragman

3
Wed 12 Apr, 2017 07:46 am
@Nick0201,
If it were me, I'd hire a licensed electrician. How will this building get insured or pass the building code without one?

Obviously you're not an electrician. Why risk taking the chance or endanger property or safety?
Nick0201

1
Wed 12 Apr, 2017 07:59 am
@Ragman,
No No, I'm just having a debate with a friend, I'm an electronics engineer, and do panel board assembly, in my design, I pick the highest rated current, multiply it by 2, then, add the other two rated currents:
19A 19A 11A
so I do this:
(19x2) + 19 + 11 = 68A
so I use and MCB 3x80A.
but I lack norm, I use this formula because I'm taught about it.
I just need some norm or regulation to follow.
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centrox

1
Wed 12 Apr, 2017 12:54 pm
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dalehileman

-2
Wed 12 Apr, 2017 02:04 pm
@Nick0201,
My guess Nick wold be 50 amps. However you can be fooled if they're all switched on at once

I presume they're each fused

Quote:
(19x2) + 19 + 11 = 68A
so I use and MCB 3x80A
---leaves me in the cold. But do listen to the others as I depend on the intuitive
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Sou004

0
Thu 26 Oct, 2017 08:52 pm
I am a electrical engineer i must say that higher rating mcb it's not a safety device as well as a lower rating mcb it's not a safety device. U must calculate the A using ohm law. If your power supply 120v then current will be high as well as if you using 220v then current will be low same as 440v. I don't know what is your power supply in your area. U can calculate easily. So if u r 220v area then 63A will be ok for this because when a fault occur then mcb will be trip. If u have 120v then u can use higher rating. U must know the wattage of all the machine. Then u can calculate the actual A. So better called a professional electrician and check it.
0 Replies

Guzel

0
Sat 4 Nov, 2017 12:10 pm
@Nick0201,
Use the NEC ampacity table for CB calculations.
0 Replies

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