Hammond isolation transformers

[foggysail]

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.

[GordMay]

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

[foggysail]

Originally Posted by GordMay

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

[GordMay]

Originally Posted by foggysail

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.

[foggysail]

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