Supply problem or something else?!

Hi guys,
I have a big problem. We are making one machine in my client workshop and we have finished almost everything, tried every motor, every consumer and it was all ok when yesterday something happened with power supply from our utility and all DC components went to heaven except Mitsubishi PLC FX5U base, inductive sensors and Schneider Electric PSU... everything else died ... touch screen, step motor driver, photocells, all PLC modules which are additionally supplied by PSU etc...
So I changed everything today, and it was all ok, so I started to test all motors again but when I switched on hydraulic pump, AC, mono-phase, with two capacitors, one for starting and other for PFC, it short circuited and everything which I've replaced died again!!!
So I've sent motor for testing, and ordered again new components... also I will test earthing in workshop and I will measure earthing resistance... but I'm very confused how one short circuit on AC motor can kill all DC components?
Just to mention that I've respected all regulations during wiring and I've earthed everything. Grounding system is TN-C/S.
I need help/idea urgently as machine will go abroad in 3 days, and I'm afraid to ship it until I figure it why that short circuit made problem to other components!!!

If you break DC isolation then it can have the same potential as your AC supply. If a fault occurs then your DC side can carry the fault.

Not sure why that happened I think your on the right path checking your earth grounds.

If the customer standards will allow you could "float" all the 24VDC, that would surely isolate it.

I do not do this myself but I see a lot of people on here swearing by it.

Good luck to you!

MitsM83 said:

Not sure why that happened I think your on the right path checking your earth grounds.

If the customer standards will allow you could "float" all the 24VDC, that would surely isolate it.

I do not do this myself but I see a lot of people on here swearing by it.

Good luck to you!

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I do like not to connect 24VDC- to GND, but here we have several voltage analog inputs and outputs connected to PLC, from different sources (sensors and VFD), and FX5CPU has only one "0V" terminal for all built in analog inputs and outpus, so I was constrained to ground negative ends...

Maxkling said:

If you break DC isolation then it can have the same potential as your AC supply. If a fault occurs then your DC side can carry the fault.

Click to expand...

What do you mean when you say "breaking DC isolation", all equipment is isolated as per standards. If you think that I have connected DC-, and AC Neutral to GND, yes I did it... but GND should have much lower resistance and should path where current flows in case of error....

goghie said:

but GND should have much lower resistance and should path where current flows in case of error....

Click to expand...

If that was the case parallel and branch circuits would never work. Obviously you are getting AC current through your DC circuits during a fault. If you had DC isolation this wouldn't be an issue. I have done it both ways, grounding OVDC and floating, but it seems to be safer for equipment when floating, but no need to beat a dead horse.

Also an unbounded ground will not have less resistance than your neutral. When bonding ground to neutral they will have the same potential, but once unbounded it will be whatever code is or less, hopefully.

Your components went to heaven, but you are definitely near to hell:=) I would suggest to shutdown all breakers, fuses branches. Then start checking & turn it on one at the time

Also, let me add that I prefer grounding the zero reference for safety. I have seen multiple times AC being landed on DC controls. When someone then grabs a harmless 24VDC wire they have the potential of getting the AC line voltage to them. Call it a floating fault... Either way you have a bad fault, sure isolation can help protect the equipment, but doesn't change the fact you have a fault.