Isolation transformer for SMPS spike protection?

[Circlotron]

Had several field failures of a ~200 watt SMPS in the same location and want to try something different. Leaving aside MOVs and GDTs etc, how well would an iron cored double-wound isolation transformer function to reduce mains borne transients? Could the iron be expected to saturate above a certain level and clip, or at least round off a spike? Maybe soften it enough so that the existing MOVs etc inside the SMPS could have a better chance of saving the day? Maybe even the added impedance of the transformer's leakage reactance might help? Any ideas regarding this approach? We need to get something that is ready to wire in, not construct from scratch because of safety certifications and legal liabilities. Was considering the following:

https://au.element14.com/block/tim500/transformer-isolating-500va/dp/1131600?ost=1131600&ddkey=https%3Aen-AU%2FElement14_Australia%2Fsearch

[Berni]

Yep 1:1 transformers are one of the best ways of protecting mains powered electronics.

They are usually designed to be pretty close to saturation at the rated voltage (copper is expensive) so in a overvoltage condition they indeed start clipping the waveform.

Still its not a magic pill. If some resistance + MOV doesn't fix it there could be a different problem related to common mode voltage surges. Long wires can have a lot of inductance and so sharp transients can cause all 3 wires of the mains line jump together. This won't cause a MOV to clip because the differential voltage between the wires is still ok. For isolated devices (Like a FM radio) this is not really a problem since the whole device just rides along and keeps seeing the correct differential voltage across the live and neutral. But this can become a problem when the device is connected to other things (Like a TV connected to the coax cable network). Whatever else is connected to it might not want to follow along the common mode wave, when grounds are connected there could be excessive currents flowing between the two. When the grounds are not connected a excessive common mode voltage difference might develop between the input and output of the switching PSU, eventually becoming large enough to arc over the PSU transformers insulation or the internal EMI capacitors.

In any way a isolation transformer should help but you should also take a look at the whole system as it could be as simple as adding a thick wire between two earthing points.

[Circlotron]

Okay, I'll try the isolation tranny and ground the centre of the secondary winding. That should take care of any common mode noise. Maybe also put somewhat more than the usual amount of X capacitor across the secondary too. 500VA transformer is hardly working so it should tolerate a bit of reactive power just fine.