Mike Dolt Enterprises
Mike Dolt Enterprises
User: Npstewart, Location: Mountain View, CA
Asked on: Friday, June 3, 2011 at 1:59 pm EDT
Answered on: Tuesday, May 14, 2024 at 6:10 am EDT
Question: I have a residential project that we did a while ago, and now we are adding a generator right before construction. They sent me the specifications for a 80KW generator with a NON service rated auto transfer switch that they want to use.Right now I have the following setup:A meter can feeding the ATS, then the ATS feeds the MDP panel UNDERGROUND which is inside, NOT immediately adjacent to the meter.My question is, the feeder is outside the building the whole time because it is traveling underground. I think I should put a fused disconnect outside prior to the transfer switch correct? I know the easiest way would be for them to buy a service rated ATS, but I am trying to work with what I have already.I added a quick sketch, see attachment .Thanks
Yes, you should install a fused disconnect outside before the transfer switch.Reason
The feeder from the meter to the ATS is outside the building and thus exposed to the elements and potential damage. Installing a fused disconnect outside provides protection for the feeder and downstream equipment in case of a short circuit or ground fault.
Code Requirements
NEC 225.32(B) requires a disconnecting means for outdoor feeders supplying a building. NEC 225.32(F) requires the disconnecting means to be located at a readily accessible location outside the building.
Equipment Selection
The fused disconnect should be rated for the following:
Voltage
The voltage rating of the feeder
Current
The ampacity of the feeder
Interrupting capacity
Sufficient to clear potential short circuit currents
Installation
Install the fused disconnect outside the building, as close to the point of entry as possible. Ensure that the disconnect is readily accessible for maintenance and operation. Connect the feeder from the meter to the fused disconnect.* Connect the output of the fused disconnect to the ATS.
Note:
While using a non-service rated ATS is not ideal, it may be acceptable in some cases, such as when the ATS is only used as a backup power source. However, it is important to ensure that all safety precautions are in place, including the installation of a fused disconnect outside the building. Flag for review