250.24(C)(1) - last sentence

[dana1028]

This last sentence has me puzzled.

"The grounded conductor of a 3-phase, 3-wire delta service shall have an ampacity not less than that of the ungrounded conductors."

I understand the ampacity part - but how do you have a '3-wire' service with 3 phases and a grounded conductor?

[This was new language in 2002 but I never paid any attention to it before.]

Thanx for any enlightenment.

 

[C3PO]

If it is a corner grounded delta.

 

[roger]

If it is a corner grounded delta.

I second that.

Roger

 

[dana1028]

Thanx for the feedback.

 

[LarryFine]

I understand the ampacity part - but how do you have a '3-wire' service with 3 phases and a grounded conductor?

Just to reiterate: Let's say "a 3-wire service including a grounded conductor."

 

[dana1028]

Just to reiterate: Let's say "a 3-wire service including a grounded conductor."

I looked in Philip Simmons 'Electrical grounding & Bonding' - he has a color illustration showing the 3-wire system consists of red, black, and white phase conductors - the white phase conductor serves the dual purpose of also being grounded.

Did I get that right?

 

[LarryFine]

I looked in Philip Simmons 'Electrical grounding & Bonding' - he has a color illustration showing the 3-wire system consists of red, black, and white phase conductors - the white phase conductor serves the dual purpose of also being grounded.

Did I get that right?

Basically, yes.

Just as with a typical 120/240 1ph service, the grounded conductor is to be bonded with the usual EGC/GEC stuff, colored white, and otherwise treated like any other circuit conductor, which it is.

The grounded conductor should never be fused, but may be switched with switches, disco's, or 2- or 3-p breakers. It's a basic 3ph system that just happens to have one circuit conductor grounded.