How to select circuit breaker ?

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Hiiii, i have single deweling unit .i want to calculate c.b & feeder size . I applied demand factors And get the demand load Ampere To size c.b : demand load ampere *1.25 . My question sometimes iam getting the value like such as 56 AMPERE AND SHNIDER C.B SELECTED
In this case i have 56 ampere i want to know go next standard 63 AT or previouse 50 AT ampere my consultant engineer told to me apply 5% rule for c.b 50 A 5% is 2.5 the max ampere 52.5 if the current more than this value must be 63A C.B SELECTED. ,for 63A c.b 5% is 3.1 the max ampere is 66 if the current is more than this value .must be 80A c.b selected .finally,this rule is correct or not
Please help me
 
Not sure where you are at but your standard sizes are not the same as ours. section 240.4(B) allows us to use the next size overcurrent protective device rated 800 amps or less as long as the wire is rated for the calculated load.

If you are using the NEC then a dwelling would need a minimum of 100 amps. Section 230.79 and 230.42(B)
Specific Installations. In addition to the requirementsof 230.42(A), the minimum ampacity for ungrounded conductors for specific installations shall not be less than the rating of the service disconnecting means specified in 230.79(A) through (D).
 
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