430.52 confusion

[Pham Van Hung]

1. 430.52(C)(1) requires motor BC SCGF OCPD rating or setting NOT exceed calculated value with factor given in Table 430.52.
2. However, in Anex D8 example, it does the opposite based on Exception No.1.

Let's say in D8 example, 102A is calculated for BC SCGF OCPD.
According to 1. above, 100A fuse should be selected as it does NOT exceed 102A calculated.
However, in D8 example, 110A fuse is selected based on 430.52(C)(1) exeption No1.

So between 100A and 110A which one is right? and where I get confusion here?

As far as I understand, 1. above requests when doing the calculation, you must NOT exceed the value in the table 430.53, that is Not exceed 300% for nontime delay fuse?

 

[Dan coulstring]

1. 430.52(C)(1)
As far as I understand, 1. above requests when doing the calculation, you must NOT exceed the value in the table 430.53, that is Not exceed 300% for nontime delay fuse?

This is where I think your confusion stems from. 430.52(c)(1) exception 1 allows next higher rating when calculated rating from table 430.52 is not a standard size as given in 240.6(A) So 110 A is correct not 100A.
Example D8 actually goes on to increase the rating even further using exception 2(a)

 

[Pham Van Hung]

This is where I think your confusion stems from. 430.52(c)(1) exception 1 allows next higher rating when calculated rating from table 430.52 is not a standard size as given in 240.6(A) So 110 A is correct not 100A.
Example D8 actually goes on to increase the rating even further using exception 2(a)

Well, I consulted from some examples and EC&M articles. Always the next higher rating is selected.
Do any one have any example which follows 430.52(c)(1) only, not fall into exception No.1 or No.2 ?

thanks

 

[Dan coulstring]

Well, I consulted from some examples and EC&M articles. Always the next higher rating is selected.
Do any one have any example which follows 430.52(c)(1) only, not fall into exception No.1 or No.2 ?

thanks

I f the full load current was 30 A rather than 34 as stated in the D8 example
300% x 30 = 90 exception 1 would not apply because 90 is a standard size fuse. Exception 2 could still be used if 90 A was not sufficient starting current you could go up to a maximum of 400% of FLC assuming non-time delay fuse and squirrel cage motor.

 

[Pham Van Hung]

I f the full load current was 30 A rather than 34 as stated in the D8 example
300% x 30 = 90 exception 1 would not apply because 90 is a standard size fuse. Exception 2 could still be used if 90 A was not sufficient starting current you could go up to a maximum of 400% of FLC assuming non-time delay fuse and squirrel cage motor.

It is clear now.
Thanks