An interesting read

[andrew1210]

And another question, would this situation lead to the issues i've noticed....

IE, RCD and next doors (God knows who elses) trips when you plug in double insulated, unearthed appliances ie, lappy's, dvd players, lamps etc. but NOT when you plug in earthed appliances like washing machines, tumble dryers, fan heaters, power showers, industrial arc furnaces (lol)....... you get the jist

 

[matt1e]

Hi, they are great drawings! that was quick! .

Thanks but I wasn't that quick, the first drawing I started months ago and then forgot about!!

The current disappeared when they connected it at A, the MET
We have the highest current reading of the effected houses, and are nearest to the transformer

Read more: http://www.diynot.com/forums/viewtopic.php?t=258233&start=45#ixzz1RiEp8q5F

In that case The neutral fault lies between the transformer and your propety

None of the properties have a Neutral as such

some of the neutral return is returning to the starpoint as net currents via bonding and E/N faults
the rest is returning to the starpoint via the intact common neutral between the properties(easiest route) and your bonding

Matt

 

[matt1e]

And another question, would this situation lead to the issues i've noticed....

IE, RCD and next doors (God knows who elses) trips when you plug in double insulated, unearthed appliances ie, lappy's, dvd players, lamps etc. but NOT when you plug in earthed appliances like washing machines, tumble dryers, fan heaters, power showers, industrial arc furnaces (lol)....... you get the jist

yes absolutly
you have net currents from differing phases all over the shop
not to mention transients,common mode noise,already present E/N faults all over the shop
its likely that switch mode power supplies etc will effect the rcd
if you are sure that about the table lamp and all unearthed appliances then my money is on common mode noise/interference
its all related though

 

[andrew1210]

It was always something that bugged me, thanks for explaining, I'll be armed with this tomorrow morning!

It is really frustrating every time a laptop is switched on..... *toinnggg* RCD goes plunging house into darkness (one RCD for the lot!) we then have to reset clocks, timers and all that usual rubbish

I was interested about the "dirty" supply comment, surely that can't be good for our "sensitive electronic equipment" to quote!

 

[andrew1210]

I....GIVE.....IN! INQ contractors came out at 8:15 this morning to 'investigate deeper'

STILL no further forward... All 150 odd houses in our area are wired as PME whereas according to Scottish Power, we should be TT providing our own Earths. . . OK, an easy mistake to make???? (lol)

So now another team are coming out at some point this week to test the RCD as this team couldn't do it... even though the RCD was tested last week and tripped at 28mA

They think it could be to N to E fault in someones house that us returning via the water/gas bonding

So, here we go again, engineer team number 8, and still no further forward

 

[andrew1210]

Latest - Voltage monitoring device being installed on Friday for 1 week to see what actually happens with this current when the RCD trips . . .

 

[xr4x4]

I'm a little bit lost with this post but can't you just solve your problem by going TT?

 

[andrew1210]

I don't blame you!

Well after today's light shed on the subject I'm thinking YES, just go TT and hope everything stops...

Whats concerning me now is that 150 odd houses are wired as PME. . .

But Scottish Power are admitting at this moment "They can't be 100% sure due to lack of solid evidence" ie no one has bothered to look anywhere bar our meter cabinet

anyways, there fitting this voltage monitoring device on Fri, tbh if it is as easy as go TT, I will be!

 

[matt1e]

tbh if it is as easy as go TT, I will be!

Not without a neutral you wont

Is this still not sorted?

 

[andrew1210]

No, and I'm getting pi**ed of now, big time. This is going on far too long.

SP are aware of 2-6/7A on Earths in at least 3 houses, but send out 'electricians' who are probably not even allowed to change a 13A plug without getting permisson from their seniors.

The boss phoned this morning to see how the matter was progressing and I blew up on the phone. I set it out straight that 7 teams of Scottish Power engineers have been out and 1 specialist contractor on behalf of SP and between them, the harsh reality is all they have done is put a multimeter on the Earth wire and witnessed this fluctuating current, or watched in disbelief as the RCD trips with all unearthed appliances and not with earthed ones. nothing else.

What a waste of, time, manpower and money!

Edit: And to make matters worse we're off on holiday in a couple of weeks, and are going to have to find someone to check the RCD twice/three times a day otherwise fridge/freezer/alarm etc will go off! Because trust me, it will happen.

 

[JohnW2]

tbh if it is as easy as go TT, I will be!

Not without a neutral you wont

I don't think anyone is suggesting, or could be suggesting, that there is no neutral. After all, all the affected houses seem to have usable supplies, give or take the RCD tripping.

Kind Regards, John.

 

[bernardgreen]

RCD and next doors trips when you plug in double insulated, unearthed appliances ie, lappy's, dvd players, lamps etc. but NOT when you plug in earthed appliances like washing machines, tumble dryers, fan heaters, power showers, industrial arc furnaces (lol)....... you get the jist

Double insulated items can only trip an RCD if they have leakage currents via stray capacitive coupling to near by earthed objects. At 50 Hz this is unlikley to create enough unbalance to trip. But at higher frequencies the same capacitance will pass more current. At 150 Hz the third harmonic of 50 Hz stray capacitive coupling might pass enough current to trip the RCD which itself could be far more sensitive to unbalance at higher frequencies than it is at 50 Hz.

Defective transformers can create 3rd and 5th harmonics so maybe the problem is caused by a defective transformer superimposing 150 and 250 Hz onto the 50 Hz sine wave. You could ask that SP use an oscilloscope to check the purity of the 50 Hz sine-wave.

 

[andrew1210]

Thanks Bernard for your reply. A monitoring device is being fitted on Friday by SP for 1 week to record data.

Will this record this information? I assume they are just hoping something obvious shows up in this data! The only instruction given to us is to note down the times when the rcd tripped and they can zoom in on the graph this machine will have recorded.

Hopefully know more soon!

Thanks everyone

 

[bernardgreen]

Hi Andrew

The normal equipment ( as I understand it ) will record voltage and times to produce a graph and little more than that. Probably not enough to solve your problem. Unless the time of RCD trip is very accurately noted then the graph might show a sharp rise in voltage at that time. This rise may be considered as the reason for the trip when in fact the trip reduced the the load and the voltage rose after the trip occurred.

I doubt they will have harmonic measuring equipment other than maybe an oscilloscope to look at but not continuously record the amount of harmonics and / or other disturbances to the mains supply.

One thought just occurred. Are there any common services other than gas water and electricity such as district heating supplies. Or distributed TV and or radio services from a communial aerial ? In fact are you anywhere near a transmitting mast for radio and / or TV broadcasting that could be inducing radio frequency energy onto your mains. The inductance of the magnetic winding in an MCB will act as a filter to that so the live conductors are "clean" but the neutrals are not clean. That could cause significant un balance with minimal capacitive coupling to earth.

 

[andrew1210]

Thanks again Bernard. No, no other communual services apart from Gas and water, and no transmitters as far as I am aware. Our block of houses that are 'affected' the worst is the block closest to the transformer, which only again seems like too much of a coincidence to me.

The trip is really easy to simulate, ie, just plug in a charger. I will see if the engineer on Friday could hook up an ocilliscope and watch while I plug in laptop charger or the like so he could possibly check this, unless he again needs special permission from his boss to do anything other then what he has been told to!

Then again, no one has bother even batting an eyelid at the transformer...