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Old 11-05-2019, 17:48   #1
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Hammond isolation transformers

Has anyone had experience with 2-3 KVA Hammond power/isolation transformers? There are some good deals out there that are priced reasonably low. I am curious if anybody has experience and can comment as to whether they are quite or produce an audible hum.
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Old 12-05-2019, 05:32   #2
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Re: Hammond isolation transformers

All transformers produce an audible hum.
According to NEMA ST-40, a Sound Rated ‘A’ or ‘B’ <3KVA transformer should operate at no more than 40 dB. Sound rated ‘C’ will be at 67dB or less.

https://www.nema.org/Standards/Secur...20-2014WMS.pdf
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Old 12-05-2019, 06:54   #3
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Re: Hammond isolation transformers

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Originally Posted by GordMay View Post
All transformers produce an audible hum.
According to NEMA ST-40, a Sound Rated ‘A’ or ‘B’ <3KVA transformer should operate at no more than 40 dB. Sound rated ‘C’ will be at 67dB or less.

https://www.nema.org/Standards/Secur...20-2014WMS.pdf
Thanks Gordon!!! Your above post started me on my information hunt where I learned they comply with ‘’Meets NEMA ST-20 standards.’’ There I found that transformers rated between 0-9 KVA are 40db maximum.

Again thanks Gordon
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Old 12-05-2019, 07:40   #4
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Re: Hammond isolation transformers

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Originally Posted by foggysail View Post
Thanks Gordon!!! Your above post started me on my information hunt where I learned they comply with ‘’Meets NEMA ST-20 standards.’’
Oops! I misstated NEMA ST-40; whereas you are correct as ST-20 Standard.
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Old 12-05-2019, 07:46   #5
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Re: Hammond isolation transformers

Gordon, prior to your post I didn’t even know they had a sound standard and I spent years in circuit design. Don’t concern yourself about the wrong spec/standard
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