# Workshop Isolation Transformer



## Conor McC (Oct 24, 2012)

Seasons greetings,

Regarding a 230Vac isolation transformer for a home workshop, output 230Vac and 250 to 500 VA power rating; working on smps units and want to protect myself and my expensive oscilloscope.

Question: does the output need earthing or does an output earth defeat the purpose of an isolation transformer?

Thanks,

(confused) Conor!


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## oliquir (Jan 13, 2011)

already use that for oscilloscope isolation, but it is very dangerous since casing of oscilloscope can become live, a battery oscilloscope is a lot more safe


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## retiredsparktech (Mar 8, 2011)

oliquir said:


> already use that for oscilloscope isolation, but it is very dangerous since casing of oscilloscope can become live, a battery oscilloscope is a lot more safe


With a plastic case.
When I was still working on drives for machine tools, I used to use a scope with a ground adaptor, to float the scope. The trucker was emptying the chip pan and bumped the drive cabinet door. The door bumped the scope and blew a hole in the aluminum scope case. The scope chassis was 277 volts above ground. An isolation transformer wouldn't have helped. :001_huh:


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## Big John (May 23, 2010)

retiredsparktech said:


> ...The scope chassis was 277 volts above ground. An isolation transformer wouldn't have helped. :001_huh:


 Eh? Isn't that the point of an isolation transformer, is that even with a fault you have no return path? What am I missing?


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## retiredsparktech (Mar 8, 2011)

Big John said:


> Eh? Isn't that the point of an isolation transformer, is that even with a fault you have no return path? What am I missing?


The positive and negative terminals were both above ground. It was one of the earlier DC spindle drives.


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## triden (Jun 13, 2012)

If you ground the output, you will start blowing stuff up as soon as you hook the scope ground lead up to the devices. That is unless you know what you are doing and avoid clipping the scope to the line side signals. Sometimes this is unavoidable (making differential measurements) and you still must isolate the ground.


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