Both legs of the RCD in the pic will both be at 500v with respect to the circuit protective conductor as they are tied together, as hairyben says - as long as the RCD is not one of those with a functional earth lead then it will be fine.
It's like this- If you touch a 500v supply in your bare feet, you'll get a belt as it finds it's way to earth.
If you touch the same supply fully insulated from earth, you won't get a belt, as, although you have a potential of 500v, you're not "completing" a circuit.
by linking out the RCD, you've no potential difference to complete a circuit and damage anything.
Now.. that's live conductors to earth covered what about between live conductors? Megger haven't supplied an image of the recommended method to do that. I know we can test each circuit's lines to neutral with all loads etc removed but is there a common method using a link at all?
By
1. Removing all voltage sensitive equipment, pilot lamps and lamps removed. All switches on.
2. Main switch on.
3. RCD shorted out on both legs.
4. Test across live and neutral at main switch (live side if initial verification; load side if periodic)
??
Would that work out? Tests all circuits in one hit.
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