Over Christmas I've got the power supply built and most of the electrical cabinet wired up but I've got a little bit of a problem which has left me scratching my head.

As far as I can tell the power supply is correctly wired but I'm getting an annoying number of nuisance trips from the breaker it's running off. The transformer I'm using is this 1000VA 24+24V part and at the moment the only load is the bleed resistors.

I initially wired it up with an 8A regular fuse but after blowing a couple of fuses I switched it over to a 6A Type C MCB which I had and this stayed in about 70% of the time on power up. Since the Type C was almost enough I figured a 6A Type D would do the trick so off to the shops, one quick swap over later and.... trip. The Type D stays in 90 to 95% of the time but I'm still getting some trips on power up.

I suppose it's possible there's a wiring fault but I've had the power supply powered up for 40 minutes and the blue smoke didn't escape so I think the problem is just the initial inrush current. I found somewhere that gave a rule of thumb for the inrush as 8* the nominal current for 0.1 seconds for transformers under 2500VA. If I'm understanding it correctly new for this coil that would be 4.3 * 8 = 35A which is well inside the 60A my Type D breaker should handle as an instantaneous load. This page gives a maximum inrush of 104A if the AC voltage is at 0V at power on, that seems more believable considering the trips I'm getting.

Right now I'm kicking myself for getting such a big transformer, I think a more moderately sized one would probably have run fine on the D6 but it's too late to change that now. I think the solution is probably to fit an NTC thermistor in series with the primary supply to provide a soft start. I'm hesitant to do that as I've not seen any other power supply builds like that so I'm concerned I'm doing something wrong.