National Electrical Installation Standards

Standards as High as Your Own

Thursday, August 19, 2021



Thanks for this great forum. It answers a lot of questions related to the NEC. My question relates to the minimum number of transfer switches required for a hospital. I was told that only one is required. I did see that if the load is less than 150 KVA that only one is permitted. Your insight would be appreciated.

Arnie Stall



Hi Arnie,

Thanks for the question. Based on the information provided, the minimum number of transfer switches for a hospital shall be based on reliability and design. The minimum number of transfer switches is three, one in each branch of the essential electrical system. See Section 517.31(B). Often essential electrical system designs in hospitals include more than one transfer switch in each branch. This is related to better localizing any outages to a smaller portion of the facility. As you mentioned, there is an exception for only one transfer switch if the continuous load on a  facility does not exceed 150 KVA. 

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