Just Curious

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GlennH

Member
Hypothetically, there is a piece of equipment protected with a fusible disconnect nearby with 30 amp fuses in it. This is fed from a panel with a 30 amp breaker.

This piece of equipment is replaced with a smaller one calling for a MOCP of 25 amps. A new 25 amp breaker is installed in the panel

Question is, is it ok to leave the 30 amp fuses in the fusible disconnect??

I'm aware it would be easier to just put 25 amp fuses in the disconnect but I'm curious if there is anything wrong with leaving the 30's in?
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
As long as the new piece of equipment does not limit the protection to "fuse protection" the 25 amp breaker satisfies the requirement. The 30 amp fused switch becomes a disconnect means.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
It is fine as long as the piece of equipment does not say fuse. On some A/C systems they call for fuses so a breaker would not qualify.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Some electric unit heaters we just hooked up say "Minimum circuit 35 amp fuse". $1600 worth of fused discs just because...:rant:
That instruction does not say, "use fuses, and put in nothing smaller than 35 amps." A breaker and branch circuit wiring rated at 40 amps would have satisfied the stated requirement.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
There may well be error in my thinking, but if I inspected a job where the equipment was marked "minimum circuit 35 amp fuse" I would be looking for a fuse or some documentation that led me to accept only a breaker.
 

Steviechia2

Senior Member
Location
Massachusetts
There may well be error in my thinking, but if I inspected a job where the equipment was marked "minimum circuit 35 amp fuse" I would be looking for a fuse or some documentation that led me to accept only a breaker.

This is interesting and one I never even would have thought of. I am just not sure the difference between a 35 amp fuse or a 35 amp breaker?
 

kwired

Electron manager
Location
NE Nebraska
This is interesting and one I never even would have thought of. I am just not sure the difference between a 35 amp fuse or a 35 amp breaker?

Trip curves will be different from one type fuse to another, and will be different for thermal-magnetic breakers also.

Different brands of thermal-magnetic may be different curve but will still be similar as compared to some fuse types.
 
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