NEC 240.21 Point of Supply Definition

[fun ee]

NEC 240.21 states conductors should be protected at their point of supply. What is the formal definition of point of supply?

Point in case, a feeder that is protected upstream by a breaker terminates on a safety disconnect switch (has no fuse or breaker). The conductors on the load side of the switch could be considered in violation of 240.21 because their point of supply (load terminals of switch) has no protection at or within that switch. I am sure I am mis-interpreting, so a clear understanding of point of supply is probably where I am mixed up.

Thanks Again

 

[GoldDigger]

The language is simply intended to require the protection to be somewhere upstream rather than downstream of the conductors in question. For a complete circuit protection absent any wire fault, anywhere in series works. But if there is a fault in the conductor(s) downstream protection is no help.
The tap rules set specific conditions under which downstream protection is sufficient.

 

[charlie b]

I think it is an interesting question. Suppose we change your example to say that a 225 amp feeder that is protected by an upstream 225 amp breaker has two safety disconnects that are connected at the same point somewhere downstream of the feeder breaker. Suppose one of the disconnects has a 225 amp feeder connected to its load side. Suppose the other disconnect has a 150 amp feeder connected to its load side. Suppose that we follow the 10 foot tap rule for the 150 amp feeder, and provide a 150 amp MCB panel at the load end of that feeder.

What we have is the feeder attached to the first disconnect being protected by the 225 amp breaker further upstream. What we also have is the feeder attached to the second disconnect being protected by the 150 amp breaker further downstream. Where do these two feeders have their ?point of supply?? Both actually get their power from the same point, the point at which they connect to the original feeder. But the code says that they both have to have their overcurrent protection at that point, except if we follow one of the tap rules. The first one does not follow a tap rule, and is in fact not a tap at all (per the definition in 240.2).

I am sure that the intent of the code is that a conductor be protected against overcurrent either (1) At the point at which it gets its power, or (2) At a point further upstream, or (3) At a point further downstream, provided that the tap rules are followed. But that is not how the code is worded. I believe we can safely apply this interpretation. I also believe a code revision is in order. But if I am not mistaken, that code revision cannot be suggested until the NFPA starts accepting suggestions for the 2020 NEC.