240.100 Feeders and Branch circuits. (A)(1)

[d-decherd]

Does anyone have a schematic of what is discussed in this article? I avoid 3 phase 3 wire Delta circuits as not being bonded and having a path for returning fault current. The equipment is severly damaged when a ground fault occures on an ungrounded system.What is residual current of current transformers? What is meant by where the neutral is not regrounded on the load side of the circuit?

 

[kiloamp7]

Re: 240.100 Feeders and Branch circuits. (A)(1)

240.100(A)(1) is about ckt. bkr.OCP in medium voltage ckts.

The basic principles are the same as 600V. & below, in that conductors are protected against overcurrents. - However, a medium voltage ckt. bkr. is physically totally different than a typical 600V. & below bkr.

Instead of having "series trips", in which the load current passes through a tripping element, a medium voltage bkr. can be thought of as an electrically-operated switch with a close coil & a trip coil.

Protective relays (driven by the output of current transformers that monitor the load current) are used to energize the trip coil from a control circuit source. The control ckt. source is frequently DC from batteries.

There are common ways that these protective relays are connected.

These statements are a greatly simplified introduction to medium voltage ckt. bkrs.
OCP above 600V. is a subject in itself. You could even consider it a speciality.
Some rather intense engineering publications are available. The IEEE series of books & mfgr's. such as, Square D, Westinghouse/Cutler Hammer, ABB, Basler, etc. offer info on the subject.