Additional Disconnect Switch for Automatic Transfer Switch

kwn

Member
Location
USA
Occupation
Automation
This request involves the Electrical supply system for a future gas compressor station. The station will be supplied from a customer-owned, pad mounted transformer (167 KVA 8320GY/4800 120/240 1PH). The Transformer has a Primary bayonet fuse for Overcurrent Protection. Primary Utility metering will be used, with a pad mounted disconnect switch (Service Point) located between the Utility meter and the Transformer Primary. The meter will be mounted on a Utility pole that's several hundred feet away from the Transformer, and the pad mounted Service Disconnect switch will located near the meter.

An Automatic Transfer Switch (800A) will be fed from the Transformer Secondary and from a standbye generator (80KW with 400A CB). The Transfer Switch and Generator will be mounted near the Transformer. My understanding of the NEC is that since there will be a disconnect switch (Service Point) located before the Transformer, the Automatic Transfer Switch isn't required to be Service rated, and so an additional Disconect switch before the Automatic Transfer Switch isn't required. Note that the output of the Transfer Switch feeds an Electrical building where an MCC with an incoming 800A 120/240 1PH CB for Feeder protection will be located. The Electrical Building will be located approx 300-400' from the Transformer/Gen/ATS location.

I'd appreciate some experience-based advice on whether or not, even though not required, it would be a good idea to include an additional Disconnect Switch (800A 120/240V 1PH) between the Transformer Secondary and the Automatic Transfer Switch. The pad mounted Service Disconnect switch is medium voltage (8000V), and will be located quite far from the Transformer/Gen/ATS location (several hundred feet). The operators also may not have extensive experience working with medium voltage electrical equipment, which might make working instead with a low voltage Disconnect Switch mounted close by, safer and easier to isolate the Transfer Switch and downstream equipment.

There is a cost consideration, but safety and ease of use may override that in this case. Your comments would be appreciated. Thank You.
 
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