I am being told that if I supply a service disconnect with my equipment, that I have to size the conductors to the disconnect to the maximum size fuse that fits inside the disconnect.
For example, if my machine needs a 120A fuse, and I use a 200A disconnect, then the conductors to the disconnect need to be sized for a 200A ampacity.
I can see this as being a good practice, to an extent, but I don't think it is mandated anywhere in the NFPA 70. I have never seen this in NFPA 79, or UL 508A either....Since it is a service disconnect, NFPA 70 would be the ultimate authority...
Does anyone know if this is an actual rule in NFPA 70? If i specify a fuse size for the equipment, I still have to size my wire ampacity to the disconnect and not the fuses? Sounds like an invitation for someone to monkey around with the fuse size on the equipment...
For example, if my machine needs a 120A fuse, and I use a 200A disconnect, then the conductors to the disconnect need to be sized for a 200A ampacity.
I can see this as being a good practice, to an extent, but I don't think it is mandated anywhere in the NFPA 70. I have never seen this in NFPA 79, or UL 508A either....Since it is a service disconnect, NFPA 70 would be the ultimate authority...
Does anyone know if this is an actual rule in NFPA 70? If i specify a fuse size for the equipment, I still have to size my wire ampacity to the disconnect and not the fuses? Sounds like an invitation for someone to monkey around with the fuse size on the equipment...