Nuisance tripping when neighbour strims grass

[squarepeg77]

My consumer unit is in the kitchen, the meter is in an outside cupboard.

Attached another photo which hopefully shows where the cables go.

The cables that exit to the left go to the consumer unit AFAIK.

I guess the cables that exit to the bottom are the earths?

Untitled

• squarepeg77
• 10 May 2011
• 1

 

[JohnW2]

I'd say there is a 50-75% of my RCD tripping when my neighbour strims the grass.

That's a pretty strong link, but the fact that it's not 100% is also an interesting part of the equation.

I'd say it doesn't trip immediately, but usually happens after a few minutes. Last October when I was actually at home, I remember my RCD tripping three times in about 5 minutes of strimming.

Interesting. If it's literally true that trips can occur after the strimmer has been running for some time, that puts paid to some of the possible theoretical explanations (e.g those relating to start-up 'inrush' currents). However, when using strimmers, people commonly don't have them on continuously; rather, they use a series of 'bursts' of strimming. An experiment might be useful. If you got to her to repeatedly run the strimmer for short periods (a few seconds would be adequate) until your RCD tripped, you could ascertain whether the tripping is actually occurring 'as she presses the trigger', 'as she releases the trigger' or literally 'out of the blue' when it is running with the trigger pressed.

Kind Regards, John

 

[squarepeg77]

John,
Oh, I see what you were asking now!

Yes, when my neighbour uses the strimmer she does pulse it quite a lot. From memory I would say the trip happens either on pulling or releasing the trigger of the strimmer, not while it is continuously running.

I have borrowed her strimmer once for a few minutes, plugged it in to my house and pulsed-it on and off. But at that time I couldn't cause a trip. Unfortunately, whenever I broach this subject with her she gets quite defensive and there is no longer much spirit of cooperation. She is confident that nothing of hers is at fault and its up to me to fix, by myself.

Could it be that I need an appliance running in my house - like the fridge - at the same time to cause the problem?

Jonathan

 

[JohnD]

it might be

you are likely to have a bit of background leakage from all the appliances and all the circuits in your house (especially watery ones like CH boiler and pump; immersion heater; kettle; washing machine, shower) and although none of these leakages might be much, all of them together may be approachiong the trip current of your RCD, so it takes little extra to trip it.

fitting RCBOS will probably fix or reduce the problem instead of or until you find and fix the cause.

Inspecting all the earth connections and main and supplementary bonding would also be worthwhile and a good cheap start.

 

[JohnW2]

Yes, when my neighbour uses the strimmer she does pulse it quite a lot. From memory I would say the trip happens either on pulling or releasing the trigger of the strimmer, not while it is continuously running.

Thanks. That makes (some!) sense.

I have borrowed her strimmer once for a few minutes, plugged it in to my house and pulsed-it on and off. But at that time I couldn't cause a trip. Unfortunately, whenever I broach this subject with her she gets quite defensive and there is no longer much spirit of cooperation. She is confident that nothing of hers is at fault and its up to me to fix, by myself.

I suppose one can sympathise with her - and, indeed, she is very probably right.

Could it be that I need an appliance running in my house - like the fridge - at the same time to cause the problem?

Well, the whole thing is obviously rather mysterious. Even if your neighbour's strimmer were faulty (and we know it's happened with two different strimmers), that shouldn't affect any of the currents in your installation, and therefore should not cause your RCD to trip. However, as others have said, whatever the explanation, if other appliances in your house were running and already creating small amounts of earth leakage current, it would take less additional leakage to get to the 30mA or whatever needed to trip your RCD. So, yes, other appliances could be part of the equation - and that may, indeed, explain the fact that the strimmer does not always trip the RCD (e..g., the fridge compressor may, or may not, be on at the moment the strimmer trigger is pressed).

It would certainly be interesting to get an electrician to do some detailed testing to see if (s)he could get to the bottom of this. As has been suggested, replacing all your MCBs with RCBOs (and replacing the RCD with just a 'main switch' might solve the problem, but it might not - and would probably cost you around £170 in materials (for 5 RCBOs plus a main switch). Pragmatically, if one were going to do anything 'empirical' without actually having discovered the cause (not ideal, but there might be no altenative), I would have thought that the simplest and cheapest thing to try would be having the RCD replaced.

Kind Regards, John

 

[squarepeg77]

Thanks John for your detailed responses.

I will discuss with an electrician some testing and the possibility of replacing the RCD and/or using RCBOs.

Jonathan

 

[TheGayOwl]

Interesting topic and responses.

Another (cheaper) option to numerous individual cct RCBO's would be to put the kitchen power cct on a separate RCBO or RCD protected 'shower type' board by itself as it is likely that white goods/appliances will have the highest earth leakages. Say a fridge leaks 8mA; washing machine 15mA; thats 23mA already and close to the 30mA. Get a GOOD spark to ramp test the RCD.

And if you have lots of computers this can also be problematic.