Simple Motor Short Circuit/Ground Fault Protection

[new_ee]

I have a 30 HP, 3 Phase, 208V motor that I am sizing the SC/GFP device for. As I calculated and look at 430.52 (C)(1) I am a little confused.

Motor FLC = 88

88 X 1.75 (Dual element fuse) = 154A 150A or 175A protection?

88 X 2.5 (Inverse time breaker) = 220A 200A or 225A protection?

It's 430.52 (C)(1) exception no. 1 that has me questioning. It says that when the value does not correspond to the standard values that using the next higher rating is permitted. Does that mean you have to use the next higher? Should you use the next higher?

 

[iwire]

90.5 Mandatory Rules, Permissive Rules, and Explanatory Material.

(A) Mandatory Rules. Mandatory rules of this Code are those that identify actions that are specifically required or prohibited and are characterized by the use of the terms shall or shall not.

(B) Permissive Rules. Permissive rules of this Code are those that identify actions that are allowed but not required, are normally used to describe options or alternative methods, and are characterized by the use of the terms shall be permitted or shall not be required.

(C) Explanatory Material. Explanatory material, such as references to other standards, references to related sections of this Code, or information related to a Code rule, is included in this Code in the form of fine print notes (FPNs). Fine print notes are informational only and are not enforceable as requirements of this Code.

You are not required to increase the SC/GF protection above the table values at all if you think your motor will start.

However you are allowed to move up to the next standard size if the SC/GF protection is inadequate to get the motor started.