Sizing protection for 3/0 THHW

[Malywr]

I am relocating safety disconnect. Now is located above 9’ of floor and is protected with 225A breaker disconnect
My question is if I bring that to 6’6” of the floor I and move it few feet to right I increase distance conductor run approximately 10’ can I reuse existing disconnect or I have to protect with new code which is 200A for #3/0


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[jumper]

I am relocating safety disconnect. Now is located above 9’ of floor and is protected with 225A breaker disconnect
My question is if I bring that to 6’6” of the floor I and move it few feet to right I increase distance conductor run approximately 10’ can I reuse existing disconnect or I have to protect with new code which is 200A for #3/0


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New code for 3/0? When was 3/0 CU ever listed for 225A?

Assuming non resi app here.

 

[ptonsparky]

Is this a disconnect for a motor?

 

[kwired]

I agree with others, 3/0 was never rated for over 200 amps (@ 75C anyway and your terminations are going to be 75C in this case), and if it is supplying a motor it may be allowed to be over 200 amps.

Need more details.

 

[infinity]

If no motors are involved and the protection ahead of the switch is 225 amps then you need a 400 amp switch.

 

[jumper]

If no motors are involved and the protection ahead of the switch is 225 amps then you need a 400 amp switch.

I thought we were talking about the OCPD/breaker rating and 3/0 CU conductors?

 

[Malywr]

New code for 3/0? When was 3/0 CU ever listed for 225A?

Assuming non resi app here.

I do not know when this tap was install but is protected tap 225A breaker inside box 20x14x6” from breaker this supply power to 200A panel.
I think there was something in 2002 cod referring to dwelling units single phase service entrance conductor



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[Malywr]

I am relocating safety disconnect. Now is located above 9’ of floor and is protected with 225A breaker disconnect

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Feeder is 500A then is my tap we are discussing breaker 225A 9’ of the floor. Second tap is for oven 125A. Third tap 200A was for 2 motors 40HP and 10HP. Currently third tap is disconnected not in use.
So since I am relocating 225A breaker hopefully it was up to code years ago can I reuse same breaker and box? Or I should use ampacities 310.15.B.16 , 75*F ,3/0, 200A Disconnect and 200A fuses.


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[Cow]

Do you know how to do branch and feeder calcs?

Determine what this feeder serves, do a quick calc, and see where your calculated load ends up. If it's well south of 200 amps, fuse the run at 200 amps, extend the wire to the new disconnect location and be done with it.

 

[roger]

I do not know when this tap was install but is protected tap 225A breaker inside box 20x14x6” from breaker this supply power to 200A panel.
I think there was something in 2002 cod referring to dwelling units single phase service entrance conductor

Your situation doesn't sound like it's for a dwelling unit and even if it was it wouldn't fly. From what you are saying, your 225 A OCPD is to big.

Roger

 

[Malywr]

Your situation doesn't sound like it's for a dwelling unit and even if it was it wouldn't fly. From what you are saying, your 225 A OCPD is to big.

Roger

Roger I taught too OCPD was too high for this conductor a specially it feed panel not individual motor. On the other hand if was done many years back maybe back then was good and up to cod. Now from all input I hear I probably never was correct.


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[Malywr]

Do you know how to do branch and feeder calcs?

Determine what this feeder serves, do a quick calc, and see where your calculated load ends up. If it's well south of 200 amps, fuse the run at 200 amps, extend the wire to the new disconnect location and be done with it.

That panel is energizing lab years ago now this area is empty we want to keep it for future use. So if years ago it was in use and feeder was sufficient now I will install 200A disco and 200A fuses and will be as new with correct protection.


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[roger]

Roger I taught too OCPD was too high for this conductor a specially it feed panel not individual motor. On the other hand if was done many years back maybe back then was good and up to cod. Now from all input I hear I probably never was correct.

That is correct, it never was per code however, if this was an industrial application there are some provisions for "Engineering Supervision" but that is probably a long shot.

Roger

 

[infinity]

I thought we were talking about the OCPD/breaker rating and 3/0 CU conductors?

The OP said he's relocating a "safety disconnect", it would likely need to be a 400 amp disconnect if the upstream protection is 225 amps.

 

[Malywr]

Yes it is industrial 3ph, 208V

I guess I relocate OCPD to 6,6’ of the floor install new disco 200A with 200A fuses and change building diagrams documentation from 225A to 200A

Now since I am thinking about that violation maybe oven is over protected too. Monday I will need to check conductor size and fuse size. Also tap is approximately 25’ so suppose to be 1/3 of the feeder and I don’t think it is.
Question if it is same situation OCPD is to high I should correct it or can leave it alone because I am not touching that one tap


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[kwired]

Roger I taught too OCPD was too high for this conductor a specially it feed panel not individual motor. On the other hand if was done many years back maybe back then was good and up to cod. Now from all input I hear I probably never was correct.


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75C ampacity of 3/0 has been 200 amps for a very long time AFAIK, maybe at least for however long it has been since they started using thermoplastic insulation.

 

[Malywr]

Yes it is industrial 3ph, 208V

Now since I am thinking about that violation maybe oven is over protected too. Monday I will need to check conductor size and fuse size. Also tap is approximately 25’ so suppose to be 1/3 of the feeder and I don’t think it is.
Question if it is same situation OCPD is to high I should correct it or can leave it alone because I am not touching that one tap


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Ok so today I checked oven tap it is approximately 15’. Size #3. 200A disconnect and 125A fuses
So this one is in violation too. Tap size 240.21.B.2. Supposed to be 1/3 of feeder OCPD which is 500/3=166.7A tap should be size #2/0 and oven protection has to be 100A inside 200A disconnect
Please correct me and explain because I am confused why someone would protect #3 wire with 125A fuses and what should I do I am not touching oven tap should I fix it ? At least install 100A fuses or don’t touch it?


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[Adamjamma]

Now, I am definitely not an expert and am only making a bad guess here, but could they be sizing the breakers for the expected surge, but then putting fuses in for normal current, so that if a fault happens normally, the fuse catches it, but they do not have to always deal with the surges from a process? Kind of like the UK using 16 amp breakers for a circuit using 13 amp outlets, then using fuses in the plugs?