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George-Allsorts
George-Allsorts, Senior Appliance Technicial Manager
Category: Appliance
Satisfied Customers: 1448
Experience:  A whitegoods technician with 30+ years service in Domestic Appliance Service & Repair, and General Mechanical & Electrical Repair
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A Bosch fan assisted oven trips an RCD when the cooling fan

Customer Question

A Bosch fan assisted oven trips an RCD when the cooling fan stops
The oven is connected to an mcb on the non protected side which does not trip
Submitted: 9 months ago.
Category: Appliance
Expert:  George-Allsorts replied 9 months ago.
Hello Martin, my name is***** you let me know the Enr of the appliance please. This can be caused in a few ways... First and foremost, can you check the connections and condition of the wall terminal wiring.. This is the most common cause. Next, have you got an insulation tester or a 20M ohm multimeter to test the insulation of some of the components of the appliance? regards
Customer: replied 9 months ago.
Hi I do have the instruments if needs be
what is puzzling me is how a non protected circuit can trip an RCD protecting other circuits.
What is even more puzzling is why it trips when the fan times out and switches off.
If the oven is manually turned off via the cooker switch whilst the fan is running no trip occurs, then switched back on after a few minutes and the fan does not run and no trip occurs.
nothing else in the property causes any tripping of the RCD
The cooker circuit is individual and non protected and causes no tripping apart from when the fan times out.
The cooker is at a friends house and they asked me to explain what was happening, I was stumped!
Regards
Martin
Expert:  George-Allsorts replied 9 months ago.
Fault in the connection of the neutral wire at the power source for the oven. Neutral to earth, or live to earth, leaking from the switch for the fan or from the fan itself... I would need to look at the wiring diagram for confirmation of this.. but my first action would be to check the wiring at the connection to the wall (make sure all is tight and not overheated); and then check the socket itself; the thermal switch for the fan, then the fan itself.
Customer: replied 9 months ago.
Thanks George
I would agree with you if the oven was on the RCD that is tripping, but it is not, it is on a non protected mcb on a separate feed and neutral bar.
Please explain how you think the fault is affecting the separated RCD
regards
Martin
Expert:  George-Allsorts replied 9 months ago.
Can you describe or diagram me which way you have it all set upregards
Customer: replied 9 months ago.
hi George
the board is a 16th edition with 3 non protected mcbs then an RCD followed by five protected mcbs
the mcbs are lights-lights- cooker- RCD - sockets- sockets- lights -shower -sockets
there is no further nuisance tripping which makes me think a neutral earth fault or/and mixed neutral highly unlikely
regards
martin
Customer: replied 9 months ago.
hi George
the board is a 16th edition with 3 non protected mcbs then an RCD followed by five protected mcbs
the mcbs are lights-lights- cooker- RCD - sockets- sockets- lights -shower -sockets
there is no further nuisance tripping which makes me think a neutral earth fault or/and mixed neutral highly unlikely
regards
martin
Expert:  George-Allsorts replied 9 months ago.
Mmm.. I would disconnect the cooker and use an insulation tester on the lead to look for a neutral earth issue in the cooker taking the RCD over limit.. regards
Customer: replied 9 months ago.
hi George
I have sorted many neutral earth faults on 17th edition boards and I have never seen a fault take the wrong rcd out or take both out, i have also never seen an appliance run perfectly then trip an rcd when it turns off.
can you give me any tech thoughts as to why this could happen
Expert:  George-Allsorts replied 9 months ago.
Neutral or Earth surges or Insulation breakdowns are the only circumstances I can think of at the moment. Here is a bit of reading that may help
Customer: replied 9 months ago.
read that stuff thanks
it suppose a neutral earth fault on the protected side, which I can understand might cause a non protected circuit neutral fault to trip the rcd. however in my situation there is no other nuisance tripping on the rcd which would be the case as load increased on the protected circuits.
could the fan be dc and cause an inductive surge as the motor winding field collapses when it swtches off ?
Expert:  George-Allsorts replied 9 months ago.
The fan motor is 240vacThe fans usually operate via a cut-in thermal switch and it is possible that a failure within the switch is causing the issue, but again, without a wiring diagram I could not confirm this scenario. Without having the appliance in front of me and fully testing it I have no other thoughts.

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