How to deal with RCD tripping - external noise

[steptoe]

with a Ze that low on a TT I reckon they must have skimmed the neutral of the incomer with the rod!

either that, or they have hit the sewer ! :slap

 

[Brian 157]

with a Ze that low on a TT I reckon they must have skimmed the neutral of the incomer with the rod! either that, or they have hit the sewer ! :slap

Believe it or not I've actually done that! The place was earthed by the water pipe originally, around 70 ohms as I recall. I put in a new split load CU with 100mA type S main switch & 30mA on the split (16th Ed.) & banged a rod in by the back door step. 0.34 ohms...

I mentioned this back at shop & was told "either the house is built on an effing great copper plate or water board are going to kick your aris'!"

The place was at the bottom of a chalk hill, a couple of rainy weeks later the client had a power cut. The board were called & found a flippin' great notch blown out of the earth rod and the fuse blown on the tranny on the pole in the field opposite! Sure enough I'd nicked the concentric neutral..!

It's a funny feeling finding out you were half an inch away from death two weeks ago... bad day explode :coat

 

[apprentice87]

Hi All,

Another newbie stab in the dark now.....

Say you were on TT as Daba states he is, You would be unlikely to have a Ze, [if you measured it that way] of less than 20 something, never mind the 0.15 or whatever Daba has got.

Now, say a neighbour near to you IS on TNCS.

You measure your Ze in the way Daba's was, [incorrectly] could you end up with such a low figure because your met is bonded to the water pipe, THEIR met is bonded to the water pipe AND connected, [via their earthing conductor] to neutral. Sooooo, you are on "PseudoTNCS"

just a thought!!!

What you think??

john

 

[Brian 157]

Ze should be measured just on the main earth conductor (disconnected from MET) to avoid any parallel paths caused by bonding etc. If you measured directly from the MET without disconnecting the main earth conductor (whatever the earthing system) you will probably get a lower reading due to a parallel path. In the scenario I outlined in post 100 we measured below 0.5 ohms at the MET with the main earth conductor and main bonding disconnected, the lowest resistance parallel path was through the immersion flex to the immersion, the tank & the old cast water pipes under ground.

If the guys testing Daba's house just did a simple eath loop impedance test at the MET with main earth conductor, bonding conductors and final circuit CPCs connected the value they measured includes all the parallel paths and is not Ze.

 

[daba]

Ze should be measured just on the main earth conductor (disconnected from MET) to avoid any parallel paths caused by bonding etc. If you measured directly from the MET without disconnecting the main earth conductor (whatever the earthing system) you will probably get a lower reading due to a parallel path. In the scenario I outlined in post 100 we measured below 0.5 ohms at the MET with the main earth conductor and main bonding disconnected, the lowest resistance parallel path was through the immersion flex to the immersion, the tank & the old cast water pipes under ground.If the guys testing Daba's house just did a simple eath loop impedance test at the MET with main earth conductor, bonding conductors and final circuit CPCs connected the value they measured includes all the parallel paths and is not Ze.

I'm learning a lot from these later posts, thanks guys....

e.g.

1. Ze has been measured (twice) with all the "parallel paths" still connected and gives me no re-assurance of my own path to earth... BAD

2. IR tested globally across the board isn't a true test, probably devised by Haste because it is quicker (and therefore cheaper)... BAD

But, happy I haven't had to pay for these crappy cheap nasty tests... GOOD

We are waiting to see if the new RCD "immunises" me from the impulse the pub is generating - so far so good (8 days and counting).

 

[NozSpark]

I'm learning a lot from these later posts, thanks guys.... e.g.

1. Ze has been measured (twice) with all the "parallel paths" still connected and gives me no re-assurance of my own path to earth... BAD

2. IR tested globally across the board isn't a true test, probably devised by Haste because it is quicker (and therefore cheaper)... BAD

But, happy I haven't had to pay for these crappy cheap nasty tests... GOOD

We are waiting to see if the new RCD "immunises" me from the impulse the pub is generating - so far so good (8 days and counting).

What do you mean??? You still haven't proved that your installation (or appliances) are not the cause of your problems.

Bad testing is just that,,, it proves nothing!

 

[Sharpend]

Don't know why he didn't just have the rcd, taken out in the first place???? :C

 

[daba]

Don't know why he didn't just have the rcd, taken out in the first place???? :C

Would you do that ?

 

[Sharpend]

No but then I would test me place properly first.

 

[steptoe]

then again, I wouldnt have done a Ze on a TT install either,

anyone else wondering if its a 30mA RCD they replaced it with?

 

[apprentice87]

Hi Daba,

Global testing IR is perfectly in order, PROVIDING you do it correctly. In fact it is the best way, as you are testing the completed installation...

What i mean is, if you wanted to test each circuit individually, then a certain amount of dismantling would be required. By doing it globally, you test the finished job.

BUT, you have to make sure that there are no connected loads at all, as you obviously have to test with all breakers closed and all switches on, [needless to say the supply is isolated!!] and if there are any "two way" switched light circuits, you have to test with the switches in BOTH positions. [obviously you will have to take all the bulbs out!]

Although the MINIMUM is 1M Ohm, you want a reading above 2M ohms, as any less indicates a problem... Soooo, you would then have to do each circuit separately to track the problem down...

These would be absolute minimum figures, in practice, you would want to find readings MUCH higher than 2M Ohm

john..

---------- Post Auto-Merged at 00:39 ---------- Previous post was made at 00:36 ----------

Hi Steps,

"anyone else wondering if its a 30mA RCD they replaced it with?"

Good thinking!!!!

john..

 

[daba]

then again, I wouldnt have done a Ze on a TT install either,anyone else wondering if its a 30mA RCD they replaced it with?

THEY (as in the DNO.) didn't supply the new trip - I had to get it, at my cost (they will reimburse me if it don't cure the problem).

stop wondering, the new one is a 30mA trip ....

Old RCD legrand 086 31

New RCD legrand 089 12

I was told by the distributor - "same trip, just a different part number"

I tried to get the same device part number, was told the 089 12 was the same...

 

[steptoe]

so he has changed an old standard 200mS tripping RCD for a new EN one that is only required to trip in 300mS,

well, you have to hand it to the guy for his thinking outside the box.

 

[daba]

so he has changed an old standard 200mS tripping RCD for a new EN one that is only required to trip in 300mS,well, you have to hand it to the guy for his thinking outside the box.

i doubt this guy has a box small enough to contain his thoughts...

anyway, i've been reading the BEAMA "RCD Handbook", and there's a section on "nuisance" trips - interesting reading: they say a major cause of RCD trips is transient injection from another location - and even mention discharge lighting as a major cause - especially if PF correction isn't used.....

.... hmmm, didn't the landlord tell me last week that the brewery have been looking at electrical usage and are considering installing PF correction....

 

[Sharpend]

You now have something to support your argument, however your problem still remains, you need to 100% eliminate you side of the install, for even though the document says its a major cause, it doesn't say it is the only cause.

Now should you be able to prove that your side is clean and in good health then you would be in a stronger position with the DNO, however you might find that they will deflect the onus onto the landlord of the pub!

 

[steptoe]

OK,

daba, I have been without good internet for a few days, reasons irrelevant, but here are my leanings so far if you wish to digest them.

1st thing, your 'Ze' on a TT is totally wrong, I do not think this is a true Ze at all, if it is a true Ze then I think this may well be a cause of a lot of your problems.

you need an Ra of your earth rod, your testers have not tested your earth at all if they have not measured your Ra, very reminiscent of people that have no idea how to test TT systems, or simply do not have the necessary equipment to do so, I would go for the former.

this is my first major concern, so until you actually have a proper earth resistance test done you are still at a lose, I take it you understand the difference between Ra and Ze as opposed to Zs and Zdb.?

in my humble opinion everything else that has taken place after this most basic of tests can be regarded as irrelevant until this one thing is proven.

 

[daba]

OK,daba, I have been without good internet for a few days, reasons irrelevant, but here are my leanings so far if you wish to digest them.

1st thing, your 'Ze' on a TT is totally wrong, I do not think this is a true Ze at all, if it is a true Ze then I think this may well be a cause of a lot of your problems.

you need an Ra of your earth rod, your testers have not tested your earth at all if they have not measured your Ra, very reminiscent of people that have no idea how to test TT systems, or simply do not have the necessary equipment to do so, I would go for the former.

this is my first major concern, so until you actually have a proper earth resistance test done you are still at a lose, I take it you understand the difference between Ra and Ze as opposed to Zs and Zdb.?

in my humble opinion everything else that has taken place after this most basic of tests can be regarded as irrelevant until this one thing is proven.

I hear you. It seems that the so-called "professionals" take short-cuts, and adopt bad pratices when doing their tests....

1. The DNO tested my RCD with a device they plugged into a nearby outlet

2. Ze measurements were done with bonding connected

3. IR appears to have been done with all the breakers closed (sheesh 500V P-E and N-E applied to all the devices in the house!!)

Yet, my installation has stood up to all their mickey-mouse testing, and they still haven't investigated the CAUSE, not the EFFECT.

---------- Post Auto-Merged at 01:28 ---------- Previous post was made at 01:21 ----------

I meant to say "and they still haven't investigated the CAUSE, but investigated the EFFECT."

I have the evidence that another consumer is tripping my RCD - who is the governing body, the equivalent of Ofcom, or Oftel that I can make a written complaint to ?

 

[steptoe]

Have just spoken with Haste technical about the apparent low N-E reading, and he confirmed that it is a typical figure obtained when testing with CB's closed, i.e. all the devices in the house connected, and is due to all manner of things, including, he said, the main culprits being surge suppression devices built into equipment. He confirmed that the "Limited Electrical Condition Report" is satisfactory in every detail, and I have nothing to worry about.

He said it was a test they devised themselves - I'm not going to argue with them.

Never heard of anything like it! Anyone else?

I hear you. It seems that the so-called "professionals" take short-cuts, and adopt bad pratices when doing their tests....1. The DNO tested my RCD with a device they plugged into a nearby outlet

2. Ze measurements were done with bonding connected

3. IR appears to have been done with all the breakers closed (sheesh 500V P-E and N-E applied to all the devices in the house!!)

Yet, my installation has stood up to all their mickey-mouse testing, and they still haven't investigated the CAUSE, not the EFFECT.

---------- Post Auto-Merged at 01:28 ---------- Previous post was made at 01:21 ----------

I meant to say "and they still haven't investigated the CAUSE, but investigated the EFFECT."

I have the evidence that another consumer is tripping my RCD - who is the governing body, the equivalent of Ofcom, or Oftel that I can make a written complaint to ?

really?

well, why havent you told us that then?

because none of the information you have posted here is anything like near the sort of factual information you will require when it goes to court, all you have so far is opinions and circumstantial evidence, no actual facts,

if you do indeed take your test results,[as reported to us], into court, then I think you may have a lot of people laughing at your evidence so far!

 

[daba]

really?well, why havent you told us that then?

because none of the information you have posted here is anything like near the sort of factual information you will require when it goes to court, all you have so far is opinions and circumstantial evidence, no actual facts,

if you do indeed take your test results,[as reported to us], into court, then I think you may have a lot of people laughing at your evidence so far!

Okay, so here's the evidence I have - it's about the best I can do...

I have a ControlLogix PLC recording the the date/time of power outages....

When the CU has tripped, if it wasn't the DNO or Haste doing tests, I have telephoned the pub within 1 to 2 minutes, and they confirmed they had just turned their lights off, the telephone bill will have those calls time-stamped.

Is that good enough?

Of course, I could manufacture this evidence, but why would I ? I don't want to compromise the safety of the people who live here.....

 

[steptoe]

you dont have evidence,

you have coincidence.

you MUST have proof your install is NOT to blame,

first and foremost that is what any defence will ask for, without that your case has nothing to stand on.

the test you have had done will not stand up to any sort of scrutiny, that has been shown on this forum already.