Isolation transformer - Voltage between output and ground

[Oldtestgear]

I read this thread with interest as my isolation transformer was causing the bench RCD to trip intermittently.  I removed the cover & there was the problem. A RIFA capacitor from live to earth was leaky. It was not cracked or obviously damaged but removing it solved the problem.  Just my observation.


Phil

[tom66]

I spent over 45 years working professionally with all kinds of electronic and electrical equipment. Voltage levels from 5V or less to 40,000V or even more. I worked on high power transmitters and on flea power logic circuits and virtually everything between. I NEVER WORE ANY KIND OR ESD OR GROUND STRAPS. NEVER!


Why not? Because I valued MY LIFE more than some static sensitive IC which cost mere pennies. If you or I touch a point that is hot, that ground (ESD) strap COMPLETES the circuit and current can then flow.

ESD straps have internal resistance, usually 1Mohm or so, which limits the fault current in cases of device voltage up to 1kV. You should not use ESD straps on higher voltage equipment without additional precautions, but those situations are very rare.  The idea that you have 'never' damaged ESD sensitive parts is farcical... sorry... I can point to tens of devices I know were only damaged after handling or numerous images of devices with on-die damage from ESD, plus the precautions the electronics industry take.

[Ian.M]

@Phil,
The RIFA was there for a reason, but as you probably know that with age their casings micro-crack and allow ambient humidity to attack their dielectric which  effectively makes them become incendiary timebombs, waiting to burn your equipment or even your whole workshop!  Obviously it works without it, but is likely to be more vulnerable to mains transients and conducted EMI.   You were lucky it was line to ground that tripped the RCD, rather than line to neutral, for which the first warning is a nasty smell if you are lucky, and smoke and flames if not.

I would therefore strongly recommend removing any other RIFA capacitors present, then replacing them with modern non-RIFA capacitors of similar value and voltage rating, class X for Line to Neutral and class Y for either live wire to Ground/PE.