jbbotello@hotmail.com
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- washington
480v, 1600A breaker feeding a capacitor bank rated at 800kvar, what size should the in coming conductors be? distance is about 25 feet from capacitor bank to service disconnect
conductor size
- Thread starter jbbotello@hotmail.com
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cduranph2006
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- Philippines
3 sets of 4-250mm2 THHN would be okay. The code says the size of conductor rating must be equal to or greater than the breaker's capacity if the breaker is equal to or greater than 800A. If you will use metallic conduit, bundling of phase conductors must be properly observed.
ramdiesel3500
Senior Member
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- Bloomington IN
Am I missing something here?? Looks to me like you need 4 runs of 600Kcmil THHN.
800 kvar = 964 amps. 460.8A requires a 1.35 factor to be used for caps. 964x 1.35 = 1301 amps. so for 3 ckts you need # 700 kcm. For 4 ckts you need #400 kcm. However, since the breaker is over 800 amps the conductors must match the breaker rating. 460.8B requires the breraker setting to be "as low as practicable". It appears that you need to dial down the setting.
ramdiesel3500
Senior Member
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- Bloomington IN
Do you think that 460.8 (A) and (B) overrides the requirement for overcurrent protection of the conductors as per 240.4?
ramdiesel3500
Senior Member
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- Bloomington IN
Sorry I was not very clear with my question. What I am wondering about is this. The original poster stated that he had a 1600A breaker. Would he be required to have a total conductor ampacity of at least 1600A per table 310.16? (assuming the 1600A breaker is not adjustable). 460.8 B almost seems to be an override that would allow overcurrent protection ampacity that exceeds conductor ampacity similar to what is allowed with motors. What do you think?
You have 2 requirements. 240.4 requires the the conductor match the OC device. 460.8B requires that the OC device setting be as low as practicable. If you assume the inspector will allow a 1600 amp OC device
then the conductor must match that rating. Someone will have to make the decision regarding 460.8B requirements. Then you can choose the conductor to match.
then the conductor must match that rating. Someone will have to make the decision regarding 460.8B requirements. Then you can choose the conductor to match.
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