faulty RCD? i think its the supply cable.

the short version.

-Consumer unit change MK century 10 way special from Eddies.

-12:00  unit installed, RCD's all test ok.

-16:00  6 circuits tested and terminated, work fine when energised.

-7th circuit makes RHS, RCD trip when energised.

-Notice test button on RCD doesnt work, doesnt dissoconnect when testing.

-Swap for another identicle RCD, which does the same.

-Swap for an older MK RCD, test button works but it doesnt disconnect under test.

-Circuit tests OK, appliances unplugged. get it to hold.

-then a fridge made it trip, then a kettle, then a cooker, then it tripped with nothing plugged in.

-thought possible RCDs all faulty, circuits and appliances made it trip with no consistancy or logic.

-getting late put it all on the 1 good RCD

-That does the same.

-now all RCDs are bad.

-19:00  linked out RCDS left them with just MCBs which was no less safe then the old wooden wylex they had before i turned up.

-Getting ready to throw all the RCDs at Eddies and never buy MK again.

-Test the RCDs at home and all work and test perfectly.

-Now i think its the supply, have had it before at another customers. after weeks of tripping, DNO coming out and all sorts, turned out to be neutral conductor broken down in street.

-Tomorrow i plan to reinstall the RCDs, see if they do the same. Try putting loads on in the house ot see if that helps it trip, then phone DNO. i think i will be putting link in place of the RCDs until the supply cables gets repaired.

whats your thoughts?

pewter said:

the short version.

-Consumer unit change MK century 10 way special from Eddies.

-12:00  unit installed, RCD's all test ok.

-16:00  6 circuits tested and terminated, work fine when energised.

-7th circuit makes RHS, RCD trip when energised.

-Notice test button on RCD doesnt work, doesnt dissoconnect when testing.

-Swap for another identicle RCD, which does the same.

-Swap for an older MK RCD, test button works but it doesnt disconnect under test.

-Circuit tests OK, appliances unplugged. get it to hold.

-then a fridge made it trip, then a kettle, then a cooker, then it tripped with nothing plugged in.

-thought possible RCDs all faulty, circuits and appliances made it trip with no consistancy or logic.

-getting late put it all on the 1 good RCD

-That does the same.

-now all RCDs are bad.

-19:00  linked out RCDS left them with just MCBs which was no less safe then the old wooden wylex they had before i turned up.

-Getting ready to throw all the RCDs at Eddies and never buy MK again.

-Test the RCDs at home and all work and test perfectly.

-Now i think its the supply, have had it before at another customers. after weeks of tripping, DNO coming out and all sorts, turned out to be neutral conductor broken down in street.

-Tomorrow i plan to reinstall the RCDs, see if they do the same. Try putting loads on in the house ot see if that helps it trip, then phone DNO. i think i will be putting link in place of the RCDs until the supply cables gets repaired.

whats your thoughts?

Click to expand...

What earthing arrangement?

A RCD won't detect a high resistance neutral.

Put some load in it and test voltage L→N, L→E, N→E.

I did house same side but over a road few house along and that was over head.

This gaff has ground supply cable, clamp around lead sheith which is terminated in the head N-E. then has 16mm from head to earth block.

So i suspect was TNS, not shure if  the PME creation was done by DNO.  

I was considering asking DNO what it should have.

Tony S said:

A RCD won't detect a high resistance neutral.

Put some load in it and test voltage L→N, L→E, N→E.

Click to expand...

I shall be doing just that tomorrow,

thanks for the advice Tony.

Teaching granny to suck eggs probably but I assume you testes all circuits as you connected them?

Very often tripping for no reason, or failing to trip, is a fault on a different circuit, usually N-E fault.

ProDave said:

Teaching granny to suck eggs probably but I assume you testes all circuits as you connected them?

Very often tripping for no reason, or failing to trip, is a fault on a different circuit, usually N-E fault.

Click to expand...

I agree dave, it was what i thought, then appliance, or cross connected socket, or plug top. I always test circuits before i energise.

All help and ideas are help.

-installed board.

-RCDs test perfect.

-as i pull each cricuit in i do R1+R2,  i then test insulation resistance, L-E, N-E.  all test ok before i connect. If they dont test ok (one didnt) i find and solve the problem until insulation resistance test is clear.

-6 circuits on ok.

-C7 trips RHS RCD.

-Test C7 again, all clear, check everything unplugged

-Notice RHS RCD test button no longer works and it doesnt test ok, doesnt even disconnect on ramp test.

-Change RCD twice, all do the same. asume every MK RCD is rubbish.

-RCD holds when circuit connected.

-All most appliances drawing load make RCD trip.

-Consider it is faulty RCD.

- connect everything on the LHS RCD

-LHS RCD trips when larger load like kettle is applied, no problem with boiler and TV.

-Sometimes it would hold for 10 secs then disconnect.

-Sometimes hold for 5 mins.

-It all got worse between 17:00-19:00, (when other houses using there load to cook dinner?)

-19:00 linked out RCD and came home due to hunger and sadness as my sweet job went sour.

-Tested RCDs as soon i got in. All work perfect, test button, disconnection times, ramp, everything.

-This point i think it has to be to do with supply.

Forgot to mention i also checked to see if R1 or R2 was linked to any other circuits, i checked with low Ohms and Megga Ohms and no connection to any other circuit , especialy on the other RCD.

When i put it all on 1 RCD it still did the same.

Take circuit 7 out, and test IR from N on circuit 7 to ANY other point, e,g N of another circuit. Same with L

Borrowed neutral from circuit 7 me thinks.

ProDave said:

Take circuit 7 out, and test IR from N on circuit 7 to ANY other point, e,g N of another circuit. Same with L

Borrowed neutral from circuit 7 me thinks.

Click to expand...

i did that. clear to all other circuits.

i disconnected C7 then kettle on C3 tripped RCD. (earlier before 16:00 it didnt)

I put everything on 1 RCD and it still did it.

the RCD test buttons worked at 12:00 didnt work at 16:00.  i brought them home and test buttons work fine.

I struggled to find a pattern as to why it was tripping.

Towards the end TV and low current using equipment was ok. Kettle or fridge or any other larger load appliance made it trip, even though earlier it didnt make it trip

I considered that all 4 of the MK RCDs were faulty (2 it came with and 2 i had on my van).

I considered there ketle and fridges being knackered, even though there kettle is brand new.

The RCDs working at my house is what makes me think it is a supply problem

Before we had this and it took weeks of DNO putting analyser on, and eventuly they said it was a N fault in supply cable out side.

We couldnt prove it was that, and they took a few weeks before they dug up soem road and solved the problem.

Going to do what Tony S said.

wondering if i can do any other tests to prove if it is there cable.

The loop test on the N was a little bit higher, but nothing crazy high

Just stating obvious (only coz I've done it myself!) have you got the busbar in each clamp correctly, I've missed one before and had all the same as you've described?

Sharpend said:

Just stating obvious (only coz I've done it myself!) have you got the busbar in each clamp correctly, I've missed one before and had all the same as you've described?

Click to expand...

I have started checking with a dentists type mirror...just in case.

handy for outgoing side as well...some of those terminals are so far back it is hard to,tell

Sharpend said:

Just stating obvious (only coz I've done it myself!) have you got the busbar in each clamp correctly, I've missed one before and had all the same as you've described?

Click to expand...

I will double check. good call.

everytime i put one in i open up all of the clamps to full width, clamp, look, then tighten. After i found a neighbours one has been left the wrong side of the clamp, burnt the insulation off the supply bar and didnt look far from a fire.

Im going to go back tomorrow, reconnect the RCDs and start with a fresh atitude.

The RCD test button would still work ok if the outgoing bar wasnt connected properly wouldnt it.

Because 4 RCDs test buttons didnt work there after 16:00 but work at my house fine, makes me think there is a N problem and a neighbours N is back tracking to me.

Have you clamped the tails to see what the earth leakage is like?

Have you PA tested the kettle?

I will throw this one in without really thinking hard about it, reversed polarity on one circuit or rcd

SLIPSHOD & SLAPDASH said:

I will throw this one in without really thinking hard about it, reversed polarity on one circuit or rcd

Click to expand...

I was wondering if it was a plug top that had the N + E the wrong way round.

pewter said:

I agree dave, it was what i thought, then appliance, or cross connected socket, or plug top. I always test circuits before i energise.

All help and ideas are help.

-installed board.

-RCDs test perfect.

-as i pull each cricuit in i do R1+R2,  i then test insulation resistance, L-E, N-E.  all test ok before i connect. If they dont test ok (one didnt) i find and solve the problem until insulation resistance test is clear.

-6 circuits on ok.

-C7 trips RHS RCD.

-Test C7 again, all clear, check everything unplugged

-Notice RHS RCD test button no longer works and it doesnt test ok, doesnt even disconnect on ramp test.

-Change RCD twice, all do the same. asume every MK RCD is rubbish.

-RCD holds when circuit connected.

-All most appliances drawing load make RCD trip.

-Consider it is faulty RCD.

- connect everything on the LHS RCD

-LHS RCD trips when larger load like kettle is applied, no problem with boiler and TV.

-Sometimes it would hold for 10 secs then disconnect.

-Sometimes hold for 5 mins.

-It all got worse between 17:00-19:00, (when other houses using there load to cook dinner?)

-19:00 linked out RCD and came home due to hunger and sadness as my sweet job went sour.

-Tested RCDs as soon i got in. All work perfect, test button, disconnection times, ramp, everything.

-This point i think it has to be to do with supply.

Forgot to mention i also checked to see if R1 or R2 was linked to any other circuits, i checked with low Ohms and Megga Ohms and no connection to any other circuit , especialy on the other RCD.

When i put it all on 1 RCD it still did the same.

Click to expand...

Just 1 question for now..... Do you connect the CPC to the earth terminal before you do your IR tests?

pewter said:

I was wondering if it was a plug top that had the N + E the wrong way round.

Click to expand...

It would account for the problem. Pro Dave asked if you had PA tested the appliances.

pewter said:

I was wondering if it was a plug top that had the N + E the wrong way round.

Click to expand...

I was wondering if the customer could be an ex electrician and be tango'd with you!?

Problem solved, thanks for al lthe help guys.

I started at the beginning.

-checked the conenctions at the service head and loop tested

-checked connections at the meter and loop tested

-checked connections at consumer unit main switch and loop tested

-reinstalled the RCDs but only fed them and did not connect anything on the load side.

-RCDs tested fine, test button and the usual tests for the cert.

-Connected load N cable to the RHS RCD and the test button stopped working.

-Insulation resistance test E-N  and C6 had a low reading around 0.2 ohm.

(yesterday during testing C6 showed a low reading of under 1 ohm to earth. I went around the 1st floor and identified a socket with the lowest reading. I took the socket off and tested both legs of the cable and it was clear, so i asumed it must have being the socket. I tested the socket and that was clear. As it was getting on i didnt spend too long trying to find out what it was, replaced the socket and thought everything was ok, until i energised C7 a little bit later)

I did the same again which led me to the same socket, i took off the same socket and checked the legs, one was bad. I had a reading of around 0.14ohms N-E.

Other side of the room was wardrobes and draws with socket behind and a trailing lead plugged in. yesterday when looking at the problem the owner had being yanking the trailing lead around and it was clear when i tested the end of his lead.

-moved big wrdrobe and draws and tested socket

-0.07ohms or something like that.

-took socket off, looks ok

-tested legs, all tests ok

-tested socket all tested ok.

-examined cables close while squished behind wardrobe.

-found the tiniest knick in insulation, cable bent one way and i couldnt see it, bend it the other and i could just see a pin p****** of copper.

It was an old single gang box with the lugs top and bottom, i think the cable had been squishe against a lug.

-Heat shrink on the cable, bit of tape for luck. removed the top and bottom lugs. All tested ok, job done, got paid and charged a little extra for the fault finding.

Gutted im a day behind with other work as i have a trail of unfinished jobs right now (2 flats, 1 house, resturant, large studio shed and soem other stuff)

What threw me was the fault cleared yesterday after i changed the other socket. I wonder if the owner yanking his trailing lead about was enough to clear the fault, it was the smallest of knicks.

RCD test button not working due to the fault was interesting as i thought the RCD was faulty. The fault was so small N-E was not tripping the RCD, but making the test button fail (i have never had this before~). then a load on another circuit was then causing the RCD to trip.

energising C7 made the RCD trip which led me to examin C7 more in depth. Appliances on C7 made it trip, which got me examining them.

I did insulation resistance the entire N bar to E and kept getting clear which is why i thought it might be supply, or appliance or miswired plug or plug top.

The knick was so small on the adjustable lug, it gave me soem pretty unusual results.

So happy its up and running

NozSpark said:

Just 1 question for now..... Do you connect the CPC to the earth terminal before you do your IR tests?

Click to expand...

Yes i always do as GN3 says so, and especially after the case with the water tank and the lady that died.