250 amp branch circuit tap?

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Electron_Sam78

Senior Member
Location
Palm Bay, FL
I have a 208 volt, 3 pH. , 250 amp branch circuit with a safety switch at the equipment. The equipment has been removed from service and replaced with a unit that only requires 35 amp ocpd. Can I make a branch circuit tap at the 250 amp safety switch and feed a new 60 amp fused safety switch with 35 amp fuses to supply the new equipment? The old circuit is considered a branch circuit but if a "tap" is made like I suggested it would become a feeder. Is this even code compliant? We're using 2008 NEC.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
It is Code compliant as long as you follow the appropriate 240.21 tap rule as to size & length of conductor, etc.
 

Electron_Sam78

Senior Member
Location
Palm Bay, FL
So, with my transformation of the branch circuit to a feeder then the feeder tap rules would apply? I will be under the 25 ft or less in that case and would need to run #4 copper from the old 250 amp switch to the new 60 amp disconnect the where I can fuse and resize the new brach circuit accordingly. Does that sound right?
 

kwired

Electron manager
Location
NE Nebraska
I have a 208 volt, 3 pH. , 250 amp branch circuit with a safety switch at the equipment. The equipment has been removed from service and replaced with a unit that only requires 35 amp ocpd. Can I make a branch circuit tap at the 250 amp safety switch and feed a new 60 amp fused safety switch with 35 amp fuses to supply the new equipment? The old circuit is considered a branch circuit but if a "tap" is made like I suggested it would become a feeder. Is this even code compliant? We're using 2008 NEC.
The old circuit was maybe considered a branch circuit, but once you removed the load - you were left with just a non specific circuit that really has no designation as feeder or branch circuit until you add load to it again.

You can reduce overcurrent protection at the supply end and make this a branch circuit, or you can take advantage of extra capacity available and use it as a feeder, maybe even replace the safety switch with a panelboard and make it easier to supply other loads.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
So, with my transformation of the branch circuit to a feeder then the feeder tap rules would apply? I will be under the 25 ft or less in that case and would need to run #4 copper from the old 250 amp switch to the new 60 amp disconnect the where I can fuse and resize the new brach circuit accordingly. Does that sound right?

:thumbsup:
 

Electron_Sam78

Senior Member
Location
Palm Bay, FL
The old circuit was maybe considered a branch circuit, but once you removed the load - you were left with just a non specific circuit that really has no designation as feeder or branch circuit until you add load to it again.

You can reduce overcurrent protection at the supply end and make this a branch circuit, or you can take advantage of extra capacity available and use it as a feeder, maybe even replace the safety switch with a panelboard and make it easier to supply other loads.


We're actually looking for an option where we can leave the original ocpd and safety switch. We don't need a new panel for sure and need the cheapest and quickest option while remaining code compliant.
 

kwired

Electron manager
Location
NE Nebraska
We're actually looking for an option where we can leave the original ocpd and safety switch. We don't need a new panel for sure and need the cheapest and quickest option while remaining code compliant.
Well then if you can keep the tap under 10 feet you can use 8 AWG for the tap, or possibly even smaller if the load supplied is a motor. A little change of wording in 240.21(B)(1) may make this a little trickier then it was before 2014, but I think you still could have a motor that needed at least 25 amp minimum conductor (10 foot tap can't be less then 10% of supply side OCPD so that is why 25 amp) but because it is a motor circuit it could likely still be protected at more then 25 amps to allow starting. Otherwise the general rule is the conductor would need to be at least 35 amps if that is what the load end overcurrent device is. The 2014 change in 240.21(B)(1) may mean if your tap supplies a 60 amp fused switch you may need a 60 amp conductor - I haven't given it much thought or done any reasearch on this change yet, just now noticed a change there.
 

kwired

Electron manager
Location
NE Nebraska
It's not a motor it's a water heater that was downsized due to a change in needs for the facility.

If there is such a thing as 400 amp to 60 amp size fuse reducers that is possibly the cheapest option., then again they still may cost more then simply adding a two space loadcenter and 35 amp breaker right next to the original disconnect.
 

Electron_Sam78

Senior Member
Location
Palm Bay, FL
If there is such a thing as 400 amp to 60 amp size fuse reducers that is possibly the cheapest option., then again they still may cost more then simply adding a two space loadcenter and 35 amp breaker right next to the original disconnect.

Don't have to worry about that. The 400a switch is non - fused safety switch :thumbsup:
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
you might be able to get some 60A class J fuse holders and install them inside the 400A switch enclosure. Maybe on the side or floor of the enclosure. can probably get a class J 60A fuse block and fuse for < $50 a pole.

you might have an issue with the minimum size wire you can put on the lugs of the switch versus the maximum size wire the fuse blocks will take though.
 
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