Fused Switch

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Alwayslearningelec

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If you have a 2000A switched fused at 1600a conductors would have to be sized for the 1600A fuse?

Your conductors could be rated for more than 1600A but not less?
 
The general order of things kind of is determine load - we need 1540 amps - then determine what size conductor you need, then determine what overcurrent protection you need.

Now you might be well under 1600 amps with actual load but still want to design for 1600 amps - remember the rules in 240.4 if overcurrent device is over 800 amps the conductor ampacity must also be equal or greater than the overcurrent device, no next size up rule for over 800 amps. Specific applications in (G) could be different though.
 
kwired said:
The general order of things kind of is determine load - we need 1540 amps - then determine what size conductor you need, then determine what overcurrent protection you need.

Now you might be well under 1600 amps with actual load but still want to design for 1600 amps - remember the rules in 240.4 if overcurrent device is over 800 amps the conductor ampacity must also be equal or greater than the overcurrent device, no next size up rule for over 800 amps. Specific applications in (G) could be different though.
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Helpful, thanks.
 
FWIW Washington state does have a kind of similar rule, where if the ampacity of the service entrance conductors is less than the overload protection allowed in 230.90(A) exception 3 (2-6 rule), a permanent plaque must be installed indicating the ampacity of the service entrance conductors.
 
electrofelon said:
FWIW Washington state does have a kind of similar rule, where if the ampacity of the service entrance conductors is less than the overload protection allowed in 230.90(A) exception 3 (2-6 rule), a permanent plaque must be installed indicating the ampacity of the service entrance conductors.
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Which only has a chance of meaning anything to electrical professionals like EE's EC's and inspectors...
 
infinity said:
Dumb rule. Who other than a professional will be working on a 2000 amp switch?
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I had only one jurisdiction that wanted that, large suburb of Atlanta. 400 amp fusible service disconnects, but engineers had them fused at 350. You would see stencils on disconnects all over that City.
 
hillbilly1 said:
I had only one jurisdiction that wanted that, large suburb of Atlanta. 400 amp fusible service disconnects, but engineers had them fused at 350. You would see stencils on disconnects all over that City.
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I'm trying to understand what purpose that would serve. You open the switch and see that the 400 amp switch has 350 amp conductors and you don't put in 400 amp fuses.
 
infinity said:
I'm trying to understand what purpose that would serve. You open the switch and see that the 400 amp switch has 350 amp conductors and you don't put in 400 amp fuses.
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He probably figured if the tenant blew a fuse, he (or their handyman) would just stick in a higher rated one, just like a homeowner.
 
hillbilly1 said:
He probably figured if the tenant blew a fuse, he (or their handyman) would just stick in a higher rated one, just like a homeowner.
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400 amp fuse is getting about borderline on what you might be able to go to the local hardware store or even big box store to purchase.

Did they also require this for 125/150/175 amp fuses (in 200 amp fuse holder of course) or 35-50 amp fuses in 60 amp fuseholders?

I run into this sort of issue the most with farmers and fertilizer injection pumps on their irrigation systems. Pretty typical to see a 1/2 HP three phase (480 volt) motor on those. They want to go the cheap way of course and it gets connected to the output circuit from pivot panel with miniature fuses, I always put in 2 amp fuses. That is high enough to allow starting in nearly all cases yet low enough it will blow if there is phase loss or mechanical issue with pump. Whenever I get called because it "wont work anymore" the motor is burned out and the blown fuses are at least 6 amps if not higher. which lets it run at/near locked rotor without blowing the fuse, but you can't explain this to them. Instead just sell them another motor. 1/2 HP not too terribly priced and they don't think much about that.
 
hillbilly1 said:
I had only one jurisdiction that wanted that, large suburb of Atlanta. 400 amp fusible service disconnects, but engineers had them fused at 350. You would see stencils on disconnects all over that City.
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I’m going to guess Cobb Co.

Probably the single most difficult jurisdiction i work in.


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