Tap 400Amps Board with new 400Amps circuit breaker

[monitaverma]

Can we tap a 400A main electrical service board with a new 400A breaker to feed temp load? See attacehd SLD. Thanks for your guidance in this matter.

 

[infinity]

Hard to read but it appears that it's not code compliant with 500 kcmil tap conductors for 400 amps. Also it needs to be seen if the existing service can support the additional load. If the tap conductors are changed to 600 kcmil then the tap rules would not apply so there would be no 25' limit.

 

[monitaverma]

Thanks. We have checked and confirmed that the existing service can handle the load. We are using 500 kcmil THHN conductors, which are suitable for a 400A breaker.
By tapping the board’s bus bar, this setup would not be considered a parallel disconnect. The tap can be taken via either a 350A or 400A breaker. I also confirmed with the manufacturer that a 350A breaker is acceptable for use with the phase converter.

 

[infinity]

We are using 500 kcmil THHN conductors, which are suitable for a 400A breaker.

500 kcmil tap conductors have an ampacity of 380 amps and cannot be used to terminate in a 400 amp OCPD. They would need to be increased to 600 kcmil or terminate in a 350 amp OCPD.

 

[electrofelon]

Thanks. We have checked and confirmed that the existing service can handle the load. We are using 500 kcmil THHN conductors, which are suitable for a 400A breaker.

Note tap conductors are one of the situations where you cannot use the "next size up" rule