Nuisance trip?????

[BMelectrics]

Evening gentlemen,

got one I want to run by you.


Did a new kitchen install a couple of months ago, within this installation there was an induction hob and single oven.

A new 10mm cable was run to supply both appliances, through a 45A cooker switch, which supplies the cooker outlet behind the appliances.

at the time, all tests were done, all perfectly passed.

Customer contacted me recently saying that whenever she switches the cooker switch off at the wall, the rcd sometimes trips. It was a new switch that was installed.

I'm wondering if the switch is the problem?? all the cables are sound, doubt it could be the new appliances. Could it have anything to do with the magnets in the induction hob?

Once again, the rcd sometimes trips when she turns the 45A cooker switch on the wall off, I dont know why she does this as it resets the clock on the oven every time!

any thoughts???


thanks guys.

 

[Darkwood]

What happens when you break an inductive load? Although I would have thought this isn't the issue as I doubt they switch it off while loaded....Is it possible a trapped cable behind the switch is the issue and its the mechanical shock from switching it that causes a temp leakage or S/C

 

[stuartcourt]

I once had a 20 amp isolator doing the same thing (but on immersion) so I would guess is switch. I took apart but could not find anything jumping out at me so thought maybe switch was shutting off one side before other and caused in balance tripped R.C.D but prob silly guess

 

[BMelectrics]

I once had a 20 amp isolator doing the same thing (but on immersion) so I would guess is switch. I took apart but could not find anything jumping out at me so thought maybe switch was shutting off one side before other and caused in balance tripped R.C.D but prob silly guess

Thanks for the replys guys.


I checked inside the switch to make sure all cores were sound, they were!

I was thinking the same about the DP switch isolating the L and N at different rates to trip the RCD also, a god damn nuisance what ever is causing it!

 

[Des 56]

I would change the isolator to be sure the poles are disconnecting together

Whilst I have heard,on this forum,about some DP switchess on final circuits in domestic installations tripping the rcd,I can't remember who it was posted the link to some interesting facts about this problem,so I just googled and found this bit of somebody s post from elsewhere

quote
Double-pole switching within the fixed wiring is known to produce a strange phenomenon
whereby switching OFF a double-pole switch supplied through an RCD can cause the RCD
to trip. Single-pole switching does not produce this effect, and it is known that changing
over from double-pole to single-pole switching can overcome the problem, where such
replacement is permissible and safe.
The phenomenon is explained by the fact that while capacitance between neutral and earth
will exist in all installations, the earth leakage through this capacitance will be negligible due
to the low (almost zero) potential between neutral and earth. When the neutral pole of a
double-pole switch is opened, the voltage across this capacitance will suddenly increase,
with a subsequent increase in neutral-to-earth capacitive earth leakage currents. This
increase will be at a maximum if the neutral opens first and will be aggravated by arcing at
both switch contacts which will cause high frequency voltage spikes to cause even higher
neutral-to-earth leakage currents.The effect may be aggravated further by the slow-break
feature of the switch often found in domestic a.c. switchgear.

 

[RyanCheetham]

I would change the isolator to be sure the poles are disconnecting together

Whilst I have heard,on this forum,about some DP switchess on final circuits in domestic installations tripping the rcd,I can't remember who it was posted the link to some interesting facts about this problem,so I just googled and found this bit of somebody s post from elsewhere

quote
Double-pole switching within the fixed wiring is known to produce a strange phenomenon
whereby switching OFF a double-pole switch supplied through an RCD can cause the RCD
to trip. Single-pole switching does not produce this effect, and it is known that changing
over from double-pole to single-pole switching can overcome the problem, where such
replacement is permissible and safe.
The phenomenon is explained by the fact that while capacitance between neutral and earth
will exist in all installations, the earth leakage through this capacitance will be negligible due
to the low (almost zero) potential between neutral and earth. When the neutral pole of a
double-pole switch is opened, the voltage across this capacitance will suddenly increase,
with a subsequent increase in neutral-to-earth capacitive earth leakage currents. This
increase will be at a maximum if the neutral opens first and will be aggravated by arcing at
both switch contacts which will cause high frequency voltage spikes to cause even higher
neutral-to-earth leakage currents.The effect may be aggravated further by the slow-break
feature of the switch often found in domestic a.c. switchgear.

What an interesting nugget of information. Cheers chap. I love little facts like this

 

[baldsparkies]

I remember following an electrical consultants spec regarding rcd's supplying floor sockets in a call centre. (commercial install).
The call centre had PCs at every work station, about 70 in total. The RCD's didnt stay there long. Nuisance tripping would be an understatement.
Also seen similar problems with economy seven circuits on RCD's when the E7 kicks in all those N/S/Heaters loads come on and click!!!
My night stores are all cold in the morning ?????
Rcd's have there place. But rcbo's provide dedication to individual circuits. And if suitable for the aplication, time delay units can also help.
Inductive loads under switching without a clean balanced disconection can often cause these kind of issues though.
Tell them the Isolation switch is only to be used for servicing or emergencies. So leave it alone.

 

[LlandrilloSpark]

Top post Des

 

[stuartcourt]

agreed hate it when my misses keeps turning stuff off like kettle at wall, come back a few minutes later and realise does my head in