Two Houses Having Random Power Trips.

[LiveWire Electric]

Hi all,

I have a customer that has their main RCD isolator tripping at the same time as there next door neighbour.

The electricity board has put them on separate phases or at least says they have and the tripping continues.

They said the have carried out a ZE from the house and its 55ohms, no I agree this far to high for and system, let alone a TT.

But am I right in assuming that the early path has nothing to do with this, and if anything a high resistance would reduce the chance of tripping?

Any ideas on why both houses are tripping, they are both TT's?

Could it be that one house trips due to a short circuit and the fault current spikes up the next houses's earth rod?

Steve.

 

[binky]

are they both fed from same overhead pole? Can't think why external fault would cause RCDs to trip, but have previously had neutral issues with DNO supplies. Does sound more like DNO issue. I would suggest dead testing a few circuits in each house, just to confirm no internal issues.

 

[SPECIAL LOCATION]

Hi all,

I have a customer that has their main RCD isolator tripping at the same time as there next door neighbour.

The electricity board has put them on separate phases or at least says they have and the tripping continues.

They said the have carried out a ZE from the house and its 55ohms, no I agree this far to high for and system, let alone a TT.

But am I right in assuming that the early path has nothing to do with this, and if anything a high resistance would reduce the chance of tripping?

Any ideas on why both houses are tripping, they are both TT's?

Could it be that one house trips due to a short circuit and the fault current spikes up the next houses's earth rod?

Steve.

55Ohms is quite good for a TT...

have another read of the bottom of page 11 OSG...

how old are the properties (and the CU's & "RCD"s) ?

are they actually old Voltage operated Earth Leakage Breakers by any chance??

Ive had adjoining properties trip each other with VOELCB...

 

[LiveWire Electric]

The houses are 100 years old protected by 100mA RCD's.

Sorry I was thinking of a TN system regarding ze reading, my bad!

If there were to be a Neutral spike then that would imbalance both houses rcd's even if they are fed from different phases right?

 

[Steve3948]

Well a few months ago there was a post where every time a pub up the road switched their car park lights on his RCD tripped in his house.

I don't think he ever came back with the resolve so who knows, it could be a supply issue.

Do you have a looped supply through the wall to your neighbours.

 

[sparkytim]

They may be on different phases but they will share the same nuetral. A dodgy nuetral on the supply can cause RCDs to trip ( Transient Voltages )

Get the DNO to check the L - N Loop at the service head.

 

[Doc Hudson]

How often is it happening, daily, weekly monthly greater? You say the electricity board has tested Ze as 55ohms. Have you done any tests yourself, and have you tested both properties, or are we saying they both are 55ohms? I presume they have their own individual earth rods? have you double checked polarity and incoming voltages. How stable do the voltages appear?

Doc H.

 

[Evans Electric]

Can't really help with the exact problem other than agreeing with others but can add that when doing a PIR some years ago we had two MK RCD sockets on a stage , when we tested one for trip times the other one adjacent also tripped. 

Also had it on a 20 way doubled up board last week , each bank protected with an RCD ,  press for the X1 test and both trip .  

 

[Jono Pashley]

Had a similar issue recently, Office supply and a kitchen supply off the same RCD, Office has a small garage type board with rcd main switch and their circuits off it. Dodgy appliance in the kitchen would take both out. Perhaps when tripped their is a imbalance which affects other devices.

 

[SLIPSHOD & SLAPDASH]

I can also add a story, i shorted live to earth out when screwing back a badly designed MK switch (well its never my fault). It tripped all 6 RCBO's in the board.

 

[Evans Electric]

HHhhhmmmm ! Curiousor and curiousor  .

 

[Phoenix]

Perhaps both houses have a neutral - > earth insulation resistance fault of of a high enough impedance that when N and E are say 5 volts apart that not enough current flows to trip an RCD, lets say 1K-ohm ... water in an outside fitting perhaps. 5/1000 = 5mA leakage

Lets also assume that the 55 ohms Ze is made up of 45ohms installation earth electrode, 10 ohms for the supply electrode at the transformer and negliable impedance of the tx windings and supply phase conductor.

Now say you turn up at another property supplied by the same Tx and take a Ze reading, Your loop tester pushes 10A through the fault path which includes that customers electrode AND the supply authority electrode at the tx and back to the star point. 10A x 10ohm = 100v between earth and neutral (Just as well we insist on isolation of the neutral in TT systems...) now back to our 1k-ohm fault. 100v/1000ohm = 100mA leakage