wasasparky
Senior Member
IMHO this is a tap.
The 100A lugs/bus are tapped to a 125A feeder.
Conductors are wire, lugs, bus...
The 100A lugs/bus are tapped to a 125A feeder.
Conductors are wire, lugs, bus...
Can you provide a Code reference?
It is stated periodically within these fora that "If the Code does not prohibit it, then it is allowed." I'm not sure I would always agree with that, but is that all we have here?
thanks
db
charlie,
i am not aware of anything in the nec that requires the feeder and it's overcurrent protective device for a fused disconnect to be sized for the full rating of the disconnect.
Chris
May I infer that the phrase "100 amp rated fused disconnect" means that that is the highest rated fuse that the component is rated to contain, and not the level to which it must be protected by an upstream device?
Let me try to explain my logic in this case.
What we have is a 125 amp feeder between a 125 amp breaker and a fused switch. The fused switch has 70 amp fuses installed. From the fused switch we have a 70 amp branch circuit to the load. The 70 amp fuses protect the disconnect and the branch circuit (and possibly the load) from overcurrent. The 125 amp breaker only protects the feeder conductors from overcurrent.
If you have a 100 amp rated non-fused disconnect then the 125 amp breaker would be a branch circuit overcurrent protection and it would exceed the rating of the 100 disconnect.
Chris
I'm not sure I agree that the 70A fuses protect the line side of the switch. Everything up-stream of the top of the fuses is under the influence of the 125A breaker.
This is fun
db
This is fine if the disconnect's label states MCA and MOC numbers (which I seriously doubt.)The 70 amp fuses will provide overload protection for the line side of the disconnect, and the 125 amp breaker will provide short circuit and ground fault protection.
This is fine if the disconnect's label states MCA and MOC numbers (which I seriously doubt.)
Otherwise, only tap rules would allow the disco's feeder to be smaller than its supplying OCPD.
Got it. I'd say no, the disco must be rated for the OCPD supplying its feeder.The feeder in the OPer's question is sized for the 125 amp breaker, the question is can this feeder terminate in a 100 amp rated fused disconnect that has 70 amp fuses installed.
Got it. I'd say no, the disco must be rated for the OCPD supplying its feeder.
The 70 amp fuses will provide overload protection for the line side of the disconnect, and the 125 amp breaker will provide short circuit and ground fault protection.
Otherwise, only tap rules would allow the disco's feeder to be smaller than its supplying OCPD.
The feeder in the OPer's question is sized for the 125 amp breaker, the question is can this feeder terminate in a 100 amp rated fused disconnect that has 70 amp fuses installed.
Got it. I'd say no, the disco must be rated for the OCPD supplying its feeder.
That's what I said in my first response, and you had an issue with it! Make up your mind, man!What if I apply the tap rules in 240.21(B)(1) to the line side of the disconnect?
1. 125A breaker, 1/0 conductors, one 100A Fused switch - Legal?? YES NO
2. 125A breaker, 1/0 conductors, two 100A Fused switches - Legal?? YES NO
Isn't it Lazlo's signature that says "Just because it works, doesn't mean it's right." ??
That's what I said in my first response, and you had an issue with it! Make up your mind, man!
(I'm not really fussing, it was just more fun this way. :grin
All that matters is the actual load, not the size of the fused disconnects.
iwire - Is there a code refererce for #1 (single switch)? Are there limits? ie 250A breaker feeding a 30A switch?