In AC power systems you get capacitive coupling between life and non current carrying parts even if they are not conductive
In this photo we have a medium voltage cable Lets pretend for a second that we peel back just enough of the outer layers of an energized cable to expose the white layer of Kynar insulation.
It is an insulator so you would expect it to be safe to touch.
Let me assure you IT IS NOT...
You could be killed...
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I have on the other hand bare handed the cable as far in as the shield.
But let me tell you if you don't have that Semi layer and the copper to drain off the charge the capacitive coupling will build up enough potential its as dangerous as touching the actual conductor.
Lets have a look at another example a transformer
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In this case you can capacitvely couple the primary to the secondary without a bond to drain the charge off.
Look closely at a transformer and you will notice the primary is usually wound over the secondary and the core is.
So we want to bond both the secondary to ground and the core.
Sometimes on an grounded Delta power system you can still read some voltage from the line side.
But a properly designed and bonded instillation will be relatively safe ( but with stability problems, why its no popular to wire this way anymore )
Add some actual capcitors to a system now.
As they age they build up charges inside the caps in places that will not easily drain.
In time a disconnected used Cap might bounce back as we call it, this means even if you discharged it before hand the residual charge inside can work it way to the terminals and give you a nasty surprise.
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Add some high frequency electronics to the mix and it can be unpredictable how things will develop charges inside and out.
SO GFCI Good.
Bond where you can....
I assume no liability for your choices based on my little talk here.