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I was called out to a 5 year old Siemens SN26M253GB/44 with a partially blocked drain hose. This simply required flushing through to resolve.
As is my normal practice after appliance repair, I carried out a basic PAT test at the mains plug, comprising earth resistance and insulation resistance measurements. Both were perfect readings (practically zero and >200 MOhm). On plugging back into the mains, the mains supply RCD tripped. I quickly narrowed down the cause to the dishwasher main power module, which although perfectly dry with no visual imperfections, and giving perfect insulation test readings, repeatedly tripped out the mains when connected to the supply.
So on the face of it, the board was damaged by the PAT tester (my trusty Seaward Primtest 200). Luckily, the customer accepted my explanation that there must have been a pre-existing weakness in the board which had only come to light during the insulation test.
I don’t remember anything similar happening in 11 years of such testing, Has anyone else come across a similar example of standard insulation resistance testing triggering electronic failure? Or could the tester be faulty?
Re: PAT tester damages Siemens dishwasher module?
I can’t figure it. How did you know that the main board was causing the fault? Have you changed it to confirm that was the case?
Re: PAT tester damages Siemens dishwasher module?
Have had a faulty mains plug on plug in lead. It had a drip from the plumbing above it.
Re: PAT tester damages Siemens dishwasher module?
I removed the module from the machine, detached all the wiring connectors and plugged the mains cord into it – bang, the rcd tripped each time. As I said, no signs of damp on mains connector or pcb, no visible damage on the board, no hint of earth leakage showing on the insulation tester.
I can only assume a faulty component on the board was isolated from the mains terminals until connected to the ac mains supply. The odd thing is the dishwasher was working fine immediately before I did the pat test and there was no previous history of the dishwasher tripping out the rcd.
Re: PAT tester damages Siemens dishwasher module?
Is your pat tester set to 500v rather than 1000v for pat testing as I’ve damaged modules on washer testing at 1000v kai
Re: PAT tester damages Siemens dishwasher module?
The test voltage (fixed) is nominally >500V, with permissible tolerance range between 500v and 600V. I recall that on at least one occasion, I noticed a visible flash from the module housing when it tripped the rcd, but could see no evidence of PCB damage afterwards.
Re: PAT tester damages Siemens dishwasher module?
assuming this the type with the mains lead plug at the rear? The mains filter is also part of the PCB on these and I am guessing that’s where the issue is.
Re: PAT tester damages Siemens dishwasher module?
I was told during my course at Dixon training never to insulation test electronically controlled appliances via the plug due to the 500v causing damage to the electronics- but to insulation test the components individually?
The tutors had 70yrs experience between them so there must be something in it!Re: PAT tester damages Siemens dishwasher module?
I don’t believe for one moment that a PAT tester, whether it be 500v or 1000v would be the cause of the power board failure. We are talking about a tester that generates a DC voltage, not AC. PAT testing is the same procedure for computers, MOT test gear, Blood pressure monitors and so on.
Rearrange the following sentence : Barking, wrong tree, up, you’re and the. 😉
Yours truly
Doubting Thomas
Re: PAT tester damages Siemens dishwasher module?
well pat testing for a earth fault on Bosch appliances is a total waste of time in my opinion as I’ve been to so many with a earth fault on motor which a pat test does not pick up I had 1 last week which didn’t pick up low insulation on motor pass pat test motor was tripping electric. And the ex Bosch engineer I work with doesn’t use 1 on Bosch appliances which I found hard to believe
Re: PAT tester damages Siemens dishwasher module?
The peak voltage from standard 230V AC mains is 325V (230 x the square root of 2). From more typical 240V mains, the peak voltage is around 339V. so a standard 500V pat test does stress a component’s insulation more than experienced from normal mains voltage. The intention is to ensure the insulation can handle a significant margin above what it would experience from the normal mains supply.
eastlmark I think come up with the best theory. It is generally in remote rural areas, where mains voltage is subject to most fluctuation, that we see most cases of suppressor damage, especially the exploding type. So I suspect in this case, a weak on-board suppressor gave up the ghost when exposed to the 2 second long continuous 500V test voltage. The chances are the component would have failed at some point soon anyway.
Re: PAT tester damages Siemens dishwasher module?
kaibart wrote:well pat testing for a earth fault on Bosch appliances is a total waste of time in my opinion as I’ve been to so many with a earth fault on motor which a pat test does not pick up
At the risk of straying ‘off topic’ here but you are very much mistaken. A Megger or PAT would instantly pick up on that. The motor and all other components within are directly connected when power is applied.
:offtopic:
Re: PAT tester damages Siemens dishwasher module?
The only useful part of a pat test is the earth bond test as it will pick up a poor earth connection which may only be one strand of a severed earth wire.
Miele heater element earth faults for example will never show on any insulation test as they are wired direct from the terminal block via a double pole relay.
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