I HAVE A 120VAC CIRCUIT COMING INTO MY PLC CONTROL PANEL. INSIDE THE PLC PANEL, I WILL BE PLACING A 60 AMP FUSE. AFTER THE 60 AMP FUSE, WE ARE GOING TO BRANCH OUT TO OTHER MISC. CONTROL & INSTRUMENTATION CONTROL PANELS WHERE EACH PANEL WILL HAVE ITS OWN MAIN CIRCUIT BREAKER TO SHUT OFF POWER TO JUST THAT PANEL. MY ELECTRICAL ENGINEER THINKS WE NEED TO SIZE THE CONDUCTORS FOR THE 60 AMPS, I THINK WE ONLY NEED TO SIZE IT TO WHAT THE MAIN CIRCUIT BREAKER IS RATED FOR IN THE REMOTE PANELS. CAN SOMEBODY HELP? THANKS!
CONDUCTOR SIZING
- Thread starter samiam12
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wanderer20001us
Senior Member
Re: CONDUCTOR SIZING
What you need to ask yourself is why are you going to use a 60A OPD if the connected load is going to be equal to or less that the breaker rating for one the sub panels. It doesn't make sense.
Listen to your electrical engineer. If the connected load warrents a 60A OPD, then size the conductors accordingly.
What you need to ask yourself is why are you going to use a 60A OPD if the connected load is going to be equal to or less that the breaker rating for one the sub panels. It doesn't make sense.
Listen to your electrical engineer. If the connected load warrents a 60A OPD, then size the conductors accordingly.
charlie
Senior Member
- Location
- Indianapolis
Re: CONDUCTOR SIZING
And, please, turn off the "Caps Lock" so you are not shouting. That also makes your posts difficult to read.
And, please, turn off the "Caps Lock" so you are not shouting. That also makes your posts difficult to read.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: CONDUCTOR SIZING
A conductor is sized at its protected ampacity. The downstream device does not affect the fault current that can be deliverd thru the 60A fuse.
A conductor is sized at its protected ampacity. The downstream device does not affect the fault current that can be deliverd thru the 60A fuse.
B
bthielen
Guest
Re: CONDUCTOR SIZING
Am I missing something? I do know that within a given enclosure wires are allowed to be sized for the load, at least with regard to our machinery. But to my understanding, wires exiting the enclosure are required to be sized per the supply OCPD.
Bob
So, let me get this straight. If I install a 60A subpanel in my home and supply it from a 100A circuit breaker in my main panel, I only need to size the wire for the 60A main OCPD in my subpanel? A ground fault between my main panel and my subpanel could then conceivably draw up to 100A before tripping the OCPD in my main. In the mean time, my wire and along with it, my house is burning.
Am I missing something? I do know that within a given enclosure wires are allowed to be sized for the load, at least with regard to our machinery. But to my understanding, wires exiting the enclosure are required to be sized per the supply OCPD.
Bob
charlie
Senior Member
- Location
- Indianapolis
Re: CONDUCTOR SIZING
Bob, I don't think anyone was saying that at all. If you have a 60 ampere circuit, you have to use 60 ampere wire and a 60 ampere overcurrent device. If you are not protecting the wire, you then have to meet the requirements of 240.21.
Bob, I don't think anyone was saying that at all. If you have a 60 ampere circuit, you have to use 60 ampere wire and a 60 ampere overcurrent device. If you are not protecting the wire, you then have to meet the requirements of 240.21.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: CONDUCTOR SIZING
This is covered by the tap rules in 240.21.
Paraphrasing 240.21
If the conductors leave the enclosure, they need to be 60A. If the conductors are less then 10' long, they can be sized to the OCPD at the end of their run. If they are between 10' and 25' they can be sized to their OCPD but cannot be smaller than 20A. If they are longer than 25', they need to be 60A rated.
This is covered by the tap rules in 240.21.
Paraphrasing 240.21
If the conductors leave the enclosure, they need to be 60A. If the conductors are less then 10' long, they can be sized to the OCPD at the end of their run. If they are between 10' and 25' they can be sized to their OCPD but cannot be smaller than 20A. If they are longer than 25', they need to be 60A rated.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: CONDUCTOR SIZING
If the conductors are longer than 25' they are not covered by any tap rule, so they need to be fully rated (60A).
If the conductors are longer than 25' they are not covered by any tap rule, so they need to be fully rated (60A).
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