Voltage stabilizer trips RCD ?

[Dannyx]

Good day folks. A friend of mine asked me to have a look at this fat servo-driven voltage stabilizer. It claims to be 10kVa ! He says it works but it sometimes trips the breaker at the panel (not its own at the front there), despite having a very light load connected to it, or none at all. Unfortunately, I don't know for sure whether it's an RCD that trips here or a regular dumb MCB. Either of them could cause the issue if they weren't sized according and they'd get tripped by the high inrush current - this was my initial hunch, but the thing is he says it doesn't happen at startup, but rather during normal operation, more specifically when the mains spikes/sags and the stabilizer SHOULD do its thing, but instead all it does is pop the breaker. I haven't witnessed this myself and it's hard to replicate, so I don't know for sure.

I plugged it in myself in a different location and sure enough it works as you'd expect: it fires up, the variac inside twitches a bit and you get 220v at the output, so the device itself works. What do you suppose could be causing this and what would a possible fix be, preferably still adhering to electrical safety rules ?

[stj]

well........
if you put 220v into a big inductor and then drop it to 190 the inductor charge will still be 220-ish.
that alone is not going to please a lot of rcd's and such!

[Dannyx]

Right - that's a big inductor after all. The current lags behind the voltage if I remember my basics. It'd be interesting to know if it's "residual current" part that trips because of an imbalance between L and N or the "overcurrent" part because of the current spike. The curve on the MCB/RCBO whatever it is is guaranteed to be C because that's the most common and it's extremely unlikely to see anything other than C around here for general purposes, unless it's a very specific and highly professional setup, which this ain't.....

[stj]

even the chinese battery-tab spot welders trip a C breaker

[Dannyx]

Originally Posted by stj

even the chinese battery-tab spot welders trip a C breaker

D-curve then ?