rcd tripping from streetlight switch on

[equipotential]

Hi everyone,

i have a question reegarding rcd tripping.
i know that this has been discussed before but i cannot seem to find the threads so i have to start this thread.


i work on street lighting and infrequently come across residents who claim that their house rcds trip when the street light switches on.
i tell them the same thing every time
check to see if the fridge is switching on at that time, or the immersion or an outside light or a boiler etc.

today i was called to a house and the lady said that she had called a qualified electrician to check her installation because of nuisance tripping.
they carried out a thourough examination but found nothing untoward and put it down to an intermittent fault.

however she noticed that the trip operated every night at the same time as the street light came on.
i explained the usuall checks for her to do
coincidence i said!
and to prove it i would switch the street light outside her property on at that moment

to my unbelief the 30ma rcd operated
as it did for several times in a row afterwards.

the rcd resets ok when the light is on it just trips on start up.
the street light is fed from an overhead 4-wire network, off the brown phase,
and the house is fed from the grey phase

i have left the light on burn to prove if that particular light causes the rcd to trip or if other lights cause the rcd to trip.

the house supply is a single phase overhead supply feeding two other properties looping from the first house to the ladys and then to the next house.

any ideas as to what the cause may be!

gratefull for any ideas folks

 

[Lectrician]

What type of trip operates?

Is it an old voltage operated ELCB? These used to be renown for doing this.

 

[Spark123]

What make of RCD is it? Is it an electronic one, usually have a functional earth wire?

 

[JohnD]

What type of trip operates?

Is it an old voltage operated ELCB? These used to be renown for doing this.

30ma rcd

I can certainly believe it

One of my RCBOs went through a spate of tripping after midnight while people were upgrading the road near my house out of hours. They've now finished working on the road and my RCBO has stopped tripping.

 

[Spark123]

Is your RCBO one of the electronic ones?

 

[JohnD]

of course

MEM

The others didn't trip.

 

[equipotential]

apologies everyone
i should have been more clear in my post

the rcd is a current operated type rather than the old voltage types which as you rightly say were suseptible to importing faults

i am unsure what you mean when you refer to an electronic trip

my basic understanding of the workings of a rcd is basically the measurement of current flowing into the circuit against the current returning.

a difference of calibrated milliamps being the monitored leakage rating of the rcd, in this case being 30Ma, is achieved by the strength of magnetic fileld set up by the current flowing through the live and neutral conductors.

i got a bit more history today from the tennant

apparantly she has lived there for three years the rcd operated occasionally when high winds occured, then since june this year the rcd has operated nearly every evening
it wasn't until after the installation had been checked by an electrician that she realised that the tripping of the Rcd occured when the street lights fired up.

i had a thought about it down the lines of a high resistance on the neutral supply agriveted by the load of the street lights activating which effects the flow of the return current through the Rcd on the neutral conductor

but it is an unproven theory

also
interestingl there has been recent roadworks outside of her home!

thanks for eveyones input

oh by the way not sure what you mean john D MEM ? of course?

do you mean Mem electronic rcds are noted for this nuisance tripping?

 

[Spark123]

MEM RCDs are quite often electronic. One give away of electronic RCDs is they tend to have a functional earth wire. They can also monitor the voltage between neutral and earth, if this exceeds a preset value then it opens.

 

[JohnD]

sorry

I meant that I use MEM ones (they are very good quality, mostly used on industrial and commercial applications) and they have an electronic sensor which reacts to pulsating DC faults which might not trip the older type of RCD. I have an RCBO for each socket circuit. They have a thin white wire that goes to the earth block. I am not sure if this makes them more sensitive to surges from street lamps or external plant, will have to think about it

some other makes are also electronic these days but I am not up to date on which.

If you know the type and model of yours someone is bound to know.

edited: bah too slow!

p.s. I am TNC-S so would not expect much N-E potential