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Comment by jandrese | Hacker News Reader

> We had to be careful about those AC utility jacks. The tester ground was at -11 volts at several hundred amps. If you clipped a scope to a ground, it would happily melt the insulation off the scope probe until it stunk up the room and pooled on the floor. We had to use a three-prong adapter with the ground cut off.

You don't get this kind of excitement anymore with modern electronics.

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Not exactly this, but you can easily make big sparks and trip RCD (GFCI) breakers if you accidentally probe something with a grounded scope that isn't isolated. In the past we've used battery powered scopes to get around this (cutting the ground pin off anything isn't a good way to do things!)

I have the same issue today when I fix old tube radios. Once side of the mains is connected to chassis -- and there are no polarized plugs. I use an isolation transformer, otherwise if I try to use a scope, I'd blow it out immediately--50% of the time.

I am cheap.

So I've never used an isolation transformer, I measure from test equipment chassis to chassis and check voltage potential, then roll the plug as needed.

It also reduces the risk of shock. Spend the $100 and get one.

How so?

An isolation transformer will prevent electric shock should you accidentally put your body in contact with the hot side of the device and earth.

https://en.m.wikipedia.org/wiki/Isolation_transformer#Electr...

An isolation transformer also completely prevents a GFCI from working.

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