Automatic Transfer Switch: Disconnect/Overcurrent protection needed on line side?

[RobbieR]

2000A service, 480/277V, 3PH, 4W.

Normal power feeders are coming in from a 1500kVA pad mounted transformer, through the ATS mounted inside the building and into the adjacent Main Switchboard with a 2000A Main Breaker.

We have a 1.5MVA generator backing up the entire building. Genset is protected by a 2000A breaker in the generator enclosure. Emergency power feeders are coming in through the ATS.

The ATS is NOT service entrance rated. Do I need a fused disconnect upstream on the line side of the ATS to meet 230.70 and/or 230.90? I thought the 2000A Main Breaker at the Switchboard covered this?

 

[kingpb]

Sounds like you need a service entrance rated disconnect ahead of the ATS and protection. Why not get a SER ATS? Eaton makes a good one that uses breakers.

 

[qcroanoke]

2000A service, 480/277V, 3PH, 4W.

Normal power feeders are coming in from a 1500kVA pad mounted transformer, through the ATS mounted inside the building and into the adjacent Main Switchboard with a 2000A Main Breaker.

We have a 1.5MVA generator backing up the entire building. Genset is protected by a 2000A breaker in the generator enclosure. Emergency power feeders are coming in through the ATS.

The ATS is NOT service entrance rated. Do I need a fused disconnect upstream on the line side of the ATS to meet 230.70 and/or 230.90? I thought the 2000A Main Breaker at the Switchboard covered this?

I think you need a fused disconnect in front of the ATS since it is not service rated and would not be considered a service disconnecting means.
You may be able to use an unfused service disconnect but it would have to be in line with your ATS and
main switchboard but I'm not sure if the NEC allows that.

 

[RobbieR]

I think I answered my own question.

I'm going to move the Switchboard sections around a little. Main service coming into the main disconnect of the switchboard. Feeder from main disconnect to normal side of ATS. Genset to emergency side of ATS. Load side of ATS to distribution section. BAM! Problem solved.

Thanks for the help!

 

[augie47]

It's amazing how often this happens. An ATS is not recognized by 230.82 as a piece of equipment allowed to be on the supply side of your service disconnect, therefore your ATS would need to be service rated or have a service disconnect ahead of it.

Unless your generator install complies with 701.11 or 702.11 a disconnect may also be required in/at the building per 225.31

 

[Mike01]

transfer switch

transfer switch

I agree the transfer switch would have to be service entrance rated if not protected by an upstream device either a circuit breaker or fused switch will work (there are many manufacturers that have these types of transfer switches), also if you move you transfer switch below or after you switchboard main circuit breaker make sure you adjust your grounding appropriately (neutral-to-ground bond), because of the service size I assume the main will be equipped with ground fault protection in which case you may want to switch the neutral conductor / pole. I know you mentioned switchboard construction but just as a side note the transfer switch will need to be protected by a 3-cycle device most transfer switch manufacturers require this unless the device is 30 cycle listed (in this case switchboard would be use a UL489 listed breaker so you're ok).