Clearance Requirements for +600V

[nvpowerdoc]

Referring to Table 110.34(A), Minimum Depth of Clear Working Space at Electrical Equipment under "Condition II", what is the appropriate clearance for a medium voltage starter on an indoor enclosed 12kV system? Our AHJ inspector interprets this as 9001V - 25,000V, thus requires 6' clearance (based on equipment name plate rating of 12kV), though "Nominal Voltage to Ground" is 7200V.

The table specifically states "Nominal Voltage to Ground" in determining the voltage class.

Referencing 100 Definitions:
Voltage, Nominal. A nominal value assigned to a circuit or system for the purpose of conveniently designating its VOLTAGE CLASS (e.g., 120/240 volts, 480Y/277 volts, 600 volts).

and

Voltage to Ground. For grounded circuits, the voltage between the given conductor and that point or conductor of the circuit that is grounded; for ungrounded circuits, the greatest voltage between the given conductor and any other conductor of the circuit.

Definition 1 places the starter in the 9001V-25kV class as a system, however definition 2 places the starter in the 2501V-9kV class.

The Engineer indicates 5' is required (based on phase to ground voltage). As the electrical contractor we can see both sides of the argument. What is the best way to interpret this table since the voltage ratings cross classes?

 

[charlie b]

Definition 1 places the starter in the 9001V-25kV class as a system. . . .

No it doesn't. The Inspector is wrong, and the engineer is right.

The words that appear in the column heading of Table 110.34(A) are not "nominal voltage." The words are "nominal voltage to ground." That four-word phrase does not appear in Article 100. You don't get to exclude two of the words (i.e., "to ground"), when you look for the meaning of the four-word phrase.

A system that has a "nominal voltage" of 12kV might, from moment to moment, have an actual phase-to-phase voltage of 11,600 volts or 12,500 volts or who knows what. So to determine the voltage to ground, for the purposes of finding your way around that table, you do not take the value of 11,600 and divide by 1.732, and you do not take the value of 12,500 and divide by 1.732. You take the "nominal voltage" of 12,000, and divide that number of 1.732. That is the reason that the word "nominal" appears in the phrase "nominal voltage to ground."