isolation transformers

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Esteemed Member
Re: isolation transformers

engy: Don and I have been kicking this dead horse around for over three years now.

Don is correct in his statements. They are in line with the handbook and Soares Grounding Book.

My statements are in line with technical documentation in the NEC definitions and history of the origin of the term "Separately Derived System".

I was working in the trade in 1956 when the words were changed from "Electrical Systems Without External Connections" to Separately Derived Systems".

Check out the 1947 Handbook.

The diagrams in the Soares Book are indicating the neutral is multi-grounded. This is my complaint. The reason for a separately derived system is to eliminate the multi-point grounding within the premises.


Senior Member
Re: isolation transformers

in the cctv world one of the most common uses for an isolation transformer is to interrupt a "ground-loop" condition whereby a current is found to flow between two points [say a camera and a monitor] that indicate a difference in ground potential. since the video signal is a mere 1V Pp it doesn't take much current to
overwhelm the signal and cause havoc with your picture.

an isolation xfm can often solve this problem.

similar issues are common with rs422 and rs485 communications runs, alarm systems, etc.

generally not a safety issue, but often an intermittent or otherwise mysterious problem with the signal path.
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