Mastech HY3005F-3 trips 20A breaker.

[freak]

I purchased a Mastech HY3005F-3 power supply. It typically works fine but maybe 50%-75% it trips a 20A breaker with nothing else connected to it. Reset the breaker and then it's usually ok.  It has a toriodal transformer and is connected on the secondary entirely with plug connectors.  I disconnected all secondaries and powered up and the breaker still trips.  I have used two different circuits/breakers and am not overloaded on either.  I removed three MOV's which two were parallel to the each side of the switch (but I cannot see how a MOV failure here could cause a problem) and a third which was across line/neutral.  Still trips the breaker.  Could the circuitry on the secondary side somehow limit the inrush current and there is a failure there or is inrush always limited on the primary side?  If so there's really nothing there to do it.  I appreciate any tips.

[Kleinstein]

Large (e.g. > 100 VA) toroidial transformers sometimes do trip a normal mains fuse. They can have quite significal inrush current as the core can be driven all the way to saturation.  Ideally there should be some extra circuit to limit the inrush current: this could be a NTC inrush limiter or a resistor and relay to bridge the relay after a few 100 ms.

[freak]

Is it as simple as selecting the right NTC limiter and putting it in series with the transformer?

[Kleinstein]

With lower power ( < about 300 VA) just a suitable NTC and a suitable environment (allow the NTC to run relatively hot without damage) should be enough.