Melting Furnace OCPD Requirements

So I have a research furnace I need to install with a single point connection, Per the vendor specs the equipment is rated at 118A. The vendor has a 200AF/175AT breaker at the connection point. I'm planning to install a disconnect with 150A fuses to supply the equipment, since at 125% the amperage is 147.5A. I would rather have my disconnect blow a fuse, than the vendor's breaker trip. This will also reduce the arc flash incident energy. So my obvious question is does anyone see an issue with this installation per the code or should I install 175A fuses? I haven't contacted the vendor yet, but plan to do so.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
Not sure why the manufacturer has such a high ocpd so unless there is some design reason I don't see why 150 amps wouldn't work. I am not sure what is entailed with a melting furnace either.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
So I have a research furnace I need to install with a single point connection, Per the vendor specs the equipment is rated at 118A. The vendor has a 200AF/175AT breaker at the connection point. I'm planning to install a disconnect with 150A fuses to supply the equipment, since at 125% the amperage is 147.5A. I would rather have my disconnect blow a fuse, than the vendor's breaker trip. This will also reduce the arc flash incident energy. So my obvious question is does anyone see an issue with this installation per the code or should I install 175A fuses? I haven't contacted the vendor yet, but plan to do so.
In a short circuit there is no guarantee that your 150 fuse will open before the 175 breaker without knowing the trip curves. Also, assuming that the incident energy will be less is not valid.
There must be reason the manufacturer has 175 trip. I would want to know the full specs before making any assumptions.
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
Is it an induction furnace or does it use resistive heating? An induction furnace will typically have more variability in its load current. I agree that more info should be obtained from the manufacturer.
 
In a short circuit there is no guarantee that your 150 fuse will open before the 175 breaker without knowing the trip curves. Also, assuming that the incident energy will be less is not valid.
There must be reason the manufacturer has 175 trip. I would want to know the full specs before making any assumptions.
Don't disagree about knowing more about the full specs, just wanted to know if there is any code violation with the proposal? Thanks
 
Top