Should I isolate other test equipment such as function generator or frequency counter/meter

Thread Starter

erictech7

Joined Mar 23, 2015
9
I have been reading on the use of isolation transformers and the need to use one when using an Oscope. I also want to hook up a function generator, and at times, a frequency counter while using the scope. Can or should I isolate the function generator and frequency counter (I know we don't need to and even shouldn't, isolate the oscope) and if so, can I use both of them on the same isolation transformer?

I was thinking of buying a large isolation transformer for all devices. Or should I buy separate transformers for each device? Or not at all?
 

AlbertHall

Joined Jun 4, 2014
8,301
Why do you need the transformer for the 'scope?
If it is so you can work on live equipment it would make more sense to isolate the live equipment.
 

Thread Starter

erictech7

Joined Mar 23, 2015
9
Why do you need the transformer for the 'scope?
If it is so you can work on live equipment it would make more sense to isolate the live equipment.
I don't need the isolation for the scope; it is for the device being tested and other test equipment.
 

MrChips

Joined Oct 2, 2009
19,269
Generally speaking, one does not require an isolation transformer for routine testing.
It really depends on your situation and what you are trying to do.

If you can elaborate on your particular test setup perhaps we can provide you with more informed advice.
 

rsjsouza

Joined Apr 21, 2014
200
There are several discussions online about the pitfalls and benefits of isolating equipment under test. If I recall correctly, the main ones were:

The ideal scenario is to ground everything and always use a differential probe when working on higher voltage equipment. That costs money.

Never float ONLY the test equipment, especially the oscilloscope. The reason is that its housing and exposed metal (on the BNC jacks, for example) will be raised to the potential of where you tied the ground clip of your probes, which can lead to shocks.

If ONLY the DUT is floated, the point where the ground clip of the oscilloscope is tied will always be at the earth's ground potential. This will only bring a hazardous situation if this potential is too high and breaks the dielectric insulation of the transformer.

If everything is floated (DUT + oscilloscope), all voltages will be floating in relation to the earth's ground, but care must be taken to not touch any exposed metal, close the circuit to the earth's ground (through YOU) and create a small surge of current due to capacitive coupling on the isolation transformers. This current surge may be very minimal or painful, which will depend on the test scenario. Also, the same situation above applies: if the voltages are too high, there is the potential to break the dielectric insulation of the transformer.

Regardless of the scenario, never forget the ground clips of a regular bench oscilloscope are always connected between them.

Also, don't get too confident the arrangement will prevent you from being shocked - always keep attentive to what you are doing.
 
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