Short Circuit Current Rating for 4000 Amp Switchgear

[sepanolo]

I have a project where the facility has a 4000 Amp RL Siemens Switchgear lineup as part of a double ended substation. The gear is fed from a 2000KVA transformer and the available fault current is about 69kA at 208 volts. The 4000 Amp main is rated 85kAIC but some of the feeders are rated 30kA for example: A Siemens RL-800 feeder breaker. What is the short circuit current rating for this switchgear? Conventional wisdom would state that the switchgear is rated for the lowest rated device in the switchgear. Does any one know which standard states that the switchgear would be rated for the lowest device? Is it possible that this switchgear is not over duty? I am going to need to reference the applicable standard to explain why I think the switchgear is over duty.

 

[davidbeach]

Unless there is some form of series rating between the 30kA feeder breakers and the 85kA main that gives the feeders at least a 70kA rating you are stuck with an expensive boat anchor.

 

[wareagle]

I agree with David. Not only is the 800 amp breaker under rated , but the panel and breakers that it feeds may also be under rated.
Yuo need to calculate the fault current at these locations also.

 

[Zogzog]

Have you calculatesd the fault current at the feeder breakers? It should be a little lower than 69kA. If so you can replace your RL-800's with RLF-800's. I am pretty sure they have 65kA ratings at 480V, might be more at 208V if that is what you are using. They made RL's in many different versions, RLE (42kA I think), RLI, RLH, and the fused RLF.

I have plenty of the RLH's in stock if that is the solution, and will even give you credit for your old RL's, I will check the ratings Monday to verify, the RLH may even be good for 85kA @208V.