frank mazeski
Member
Can any one enlighten me on the ramifications of this section of the code. I am told that under this code wire size is bumped up to 600 mcm from 500 mcm.
NEC code 240.4C
- Thread starter frank mazeski
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Re: NEC code 240.4C
Frank, all it means is that after you go past 800 amps the conductor(s)must meet or exceed the OCP, this would mean where parallel 500 KCMIL conductors would only give you 760 amps at 75 deg you would have to use parallel 600's which would give you 840 amps.
Below 800 you can go to next higher standard breaker which would allow the parallel 500's to supply a 800 amp breaker.
Roger
Frank, all it means is that after you go past 800 amps the conductor(s)must meet or exceed the OCP, this would mean where parallel 500 KCMIL conductors would only give you 760 amps at 75 deg you would have to use parallel 600's which would give you 840 amps.
Below 800 you can go to next higher standard breaker which would allow the parallel 500's to supply a 800 amp breaker.
Roger
frank mazeski
Member
Re: NEC code 240.4C
russ
Senior Member
- Location
- Burbank IL
Re: NEC code 240.4C
Just to clarify 800 amp is ok with parallel 500 kcmil.
240.4(C) kicks in at, over 800 amp.
Just to clarify 800 amp is ok with parallel 500 kcmil.
240.4(C) kicks in at, over 800 amp.
Re: NEC code 240.4C
Unless it is a 4-wire wye service and the neutral carries a fair amount of neutral current such as harmonics in which case you would need three 500 KCM copper in parallel to get 800 amps ( could also use a 900 amp circuit breaker ) with conduits in free air.
Actually, if you are using PVC conduit you can take advantage of 300.3 (B)(3) and run 4 pipes with 3 A phase wires in 1 pipe, 3 B phase wires in the next pipe and so forth. You would need to cut a slot between the knockouts in metal box walls in accordance with 300.20(B). This simplifies making the conductors of the same phase the same length.
The explanations of 240.4(C) are as follows:
1. Less frequent circuit breaker ratings over 800 amps - 1200 amps to 1600 amps is a bigger jump than 125 amps to 150 amps.
2. Popularity of 100% rated circuit breakers and fusible switches above 800 amps.
Also, the only real way to connect 600 KCM and larger copper wire is to use Burndy's lugs that are exothermically WELDED onto the end of the wire. Sefcor also makes aluminum alloy weldment lugs for welding onto the end of 3/0 and larger aluminum wire using the tungsten inert gas process.
I have also discovered in the process of doing amp checks that electromagnetic ballasts tend to send about 10% of the neutral current back through the equipment grounding conductor and 90% back through the neutral. How I found this out was that I was using a clamp-on ammeter to dope out which hot wires shared which neutrals when energizing 1 circuit breaker at a time in an auditorium that had 7 fluorescent lighting circuits with 7 fixtures on each circuit. Some branch circuits were 120Y208 4-wire and the rest 3-wire network. The ammeter readings of neutral current did not square up with the nameplate ratings of the ballasts when 1 breaker at a time was energized. After a few more tests I convinced myself that about 1 to 1.5 amps for each circuit was flowing through the conduits rather than the insulated neutral!
Unless it is a 4-wire wye service and the neutral carries a fair amount of neutral current such as harmonics in which case you would need three 500 KCM copper in parallel to get 800 amps ( could also use a 900 amp circuit breaker ) with conduits in free air.
Actually, if you are using PVC conduit you can take advantage of 300.3 (B)(3) and run 4 pipes with 3 A phase wires in 1 pipe, 3 B phase wires in the next pipe and so forth. You would need to cut a slot between the knockouts in metal box walls in accordance with 300.20(B). This simplifies making the conductors of the same phase the same length.
The explanations of 240.4(C) are as follows:
1. Less frequent circuit breaker ratings over 800 amps - 1200 amps to 1600 amps is a bigger jump than 125 amps to 150 amps.
2. Popularity of 100% rated circuit breakers and fusible switches above 800 amps.
Also, the only real way to connect 600 KCM and larger copper wire is to use Burndy's lugs that are exothermically WELDED onto the end of the wire. Sefcor also makes aluminum alloy weldment lugs for welding onto the end of 3/0 and larger aluminum wire using the tungsten inert gas process.
I have also discovered in the process of doing amp checks that electromagnetic ballasts tend to send about 10% of the neutral current back through the equipment grounding conductor and 90% back through the neutral. How I found this out was that I was using a clamp-on ammeter to dope out which hot wires shared which neutrals when energizing 1 circuit breaker at a time in an auditorium that had 7 fluorescent lighting circuits with 7 fixtures on each circuit. Some branch circuits were 120Y208 4-wire and the rest 3-wire network. The ammeter readings of neutral current did not square up with the nameplate ratings of the ballasts when 1 breaker at a time was energized. After a few more tests I convinced myself that about 1 to 1.5 amps for each circuit was flowing through the conduits rather than the insulated neutral!
- Location
- Massachusetts
Re: NEC code 240.4C
Very few people will spend the money for 100% rated equipment.
That is simply not true and I have no idea why you would think that.
I sure would like to see a link to that product, as I really doubt it is aimed at typical building wiring under 600 volts.
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