http://cr4.globalspec.com/thread/24666

I agree with Mr Slacks comments.

Unplug all of your accessories and text your RCD. It might be that the RCD is off spec.

If you have lots of stuff such as computers, TVs, printers etc with a filter installed you will cause a small amount of leakage. The more you plug in the greater the leakage gets until you get to 30mA and off it goes.

What is the RCD for? Is it there for personnel protection or simply because you have a bad earth or TT system. Personnel protection needs to be 30mA. A bad earth system and it might be you can increase things safely to 100mA.

You might consider protecting your sub circuits with 30mA devices and increase the main incomer to 100mA. This won't guarentee you discrimination but likely would solve your problem. On a system where you want to guarentee the 30mA device trips before the 100mA you really need to look to time grading.

First thing though get your existing RCD tested.

The regulations in the UK state that all new installs of residential DBs must be fitted with a 30mA RCD. It's also forbidden by the regs to cascade RCDs. I suspect the Indian regs are going the same way.

Some of the local villages with TT systems had serious issues with tripping. At the time the electricity board agreed to increase the incoming RCD from 30mA to 100mA. Remember the incoming device is not installed to give life protection.

I agree 30mA would give better protection but its a nice to have rather than a need to have. The installation must meet section 411 of the regs.

Having an incomer at 30mA and then, dependent on installation method, virtually every other circuit protected by a seperate 30mA device you would trip sub circuit and incomer every time. Bit pointless really.

Is the service a 40 A 3phase and neutral? If so why 4 pole breaker? As stated the 30 ma setting does not provide personal protection. The dwg below is a single pole breaker but the concept would be the same. The circuit is 1 power conductor and neutral. The green wire is called an equipment grounding conductor(EGC). The protection setting is 5 ma. The green wire would be bonded to the appliance and if there was leakage or fault current on the EGC over 5 ma the breaker would trip. There are also GFI receptacles available that may be used inplace of the breaker.

30mA does provide personnel protection. check I.E.E. regs (BS7671)

5mA on an incomer???

Thanks to know that there was an earlier similar posting in CR4,http://cr4.globalspec.com/thread/24666

It was suggested in that discussion,quoted below:

""Measure the resistance from neutral to earth downstream of the main distribution point, so as to establish the correct connection of the downstream circuits. If the reading is low, disconnect the neutrals from the neutral bar one at a time to see which circuit(s) is(are) presenting the earth-to-neutral fault(s)""

How to determine the reading is low? What is the limit below which the resistance is considered low,with reference to 'earth-to-neutral fault'?

Anything below, oh, say 0.5MΩ between earth and neutral on the downstream circuit would indicate an insulation break-down and an earth trip because of it will not be far away.

An electric kettle (if you use one) is a good suspect, since the internal turn-off-thermostat is activated by steam; the steam could also create a conductive surface-path to earth that would disappear soon after.

Another intermittent source may be mice or other creatures trying to chew through cable insulation and tripping the RCD...

Guys,

I have always done my own wiring and been perfectly happy with the results. No problems in a number of properties over 50+ years. I am a Member of the IEE. If I want to change the Distribution Box I call my Brother in Law, who is very safety concious but can replace a Dist box in well under an hour.

My safety precautions would take 2 hours at least, I work MUCH slower than he does - he is a professional.

I had cause to redo a complete room with a lot of electrical changes; this caused me to let a contract , for the first time, to an external provider who had his own electrician. Apart from a few bungled contracts. electrician #1 did not want the job, electrician #2 did not want to travel that far!! and so on, These were all subys!

I took on a local company to do the work, which included a complete gut of the room, electrical supply of about 15 lights with all their controls, mostly 3 way switched. Power sockets for 18 sockets. I had set up the house ring mains to accommodate this so that all the electrician had to was wire from Point A to Point B to keep it in the ring. he was happy. New furniture, new plumbig, new floors ( old ones squeaked!)new entertainment system etc.etc. Complete redecoration.

When the jpb was done, there were a number of intermittent trips but it seemed to settle down.

Before this contract was let this electricain and I had been around the whole house making sure that every circuit was AOK, no leakage! He was insistent from his safety and responsibility aspects and I was happy that I had a second view on everything that I had done over the years - including ring splits, external wiring the lot.

After the Electrician had left Trips continued, not every 4 hours but intermittently.

I kept calling the electrician back; I even kept a log book of these occurrences!

Eventually I managed to call him back on one occasion, he said as he walked in the door "now where is this trip" - Bang - and the whole house went off all the MDFs etc.

So I said ; there you are, here is the log it is somthing that you must have done because this has never happned before in this house in about 20 years.

He was a trifle miffed because he realized that he would not be able to walk away from this one. Several hours later he had checked and rechecked all of his work and surprise, surprise it has never tripped again. He would not tell me what he had done to put matters right but he obviously had found and fixed a fault. I knew the boss and was Ok with talking to him about it but the following day the boss called and closed the business down- they had run out of money; (all of the guys got new jobs quite quickly! They were good workers apart from the recalcitrant electrician!)

We are a few years further down the line; I will never know what he did but it all works now! I have an inkling as there is a circuit on another ring in the loft which is only there as a Power source if I am working up there and this socket is now dead; I know where it should be conected and I will summon up the energy to check it out one day!

I believe that if you get into a situation like this you just have to persevere until you have solved it.

Use a log book, check which circuit it affects each time. keep the log book as a serious piece of evidence and be prepared to measure everything in sight. Everytime.

One thing that I have done is to make sure that all loads which require trip ccts have trips And those that don't don't have them. I have also used my knowledge to increase the number of MDFs, the number of individual circuits so that when a circuit goes down I can rapuidly diagnose what, where, why? I have 19 circuits on the Main MDF, There are three other MDFs in the property. one for the Garage, one for each Shed. I am contemplating another workshop which will obviously involve another MDF. Almost all external circuits use SWF cable. Some lighting ircuits do not.

Have heart, there will be a resolution, but you must be prepared to fix it, otherwise, you and everyone who lives/works there is in possible danger.

Sleepy

Check and verify that the ground and neutral conductors have not been "crossed" on any/all primary/incoming and secondary/outgoing wiring.

Make sure the neutral and ground busses are not shorted together. (Remove bonding screw if installed and/or any cross wiring/jumpers.)

Make sure you do not have any power carrying conductors wrapped around any neutral or ground conductors.

If all of this proves to be ok, check all of your primary and secondary circuit conductors with an oscilliscope for induced "noise" and/or harmonics.

If the noise is present on any of the conductors you will need to stop the noise/harmoonic(s) by installing shielding and/or filtering the noise off to ground.

Be sure to research and install the proper capacitor, diode, and/or resistor required for proper filtering.

If none of the above yields the culprit, replace the unit.

Surely you would prove the integrity of the RCD before embarking on this lot.

I'm sure you will eventually get to the right answer but I wouldn't like to think I was paying for your fault finding time.

Any crossed wires and the system will trip straight away - its not going to hang about.

I'm not happy about removing bonding bits. If anything is crossed ...

The scope - surely we are looking for leakage not induced noise and harmonics wherever they may be coming from.

I'm not certain how a diode is going to help and a resistor simply can't help.

Surely you would prove the integrity of the RCD before embarking on this lot.

OP : After every trip, installation tests are conducted. After confirming that there are no earth leakages in the wiring or through connected appliances (tested one by one),RCCB is reset and the electrical circuits are restored to function normally. But again after 3 or 4 hours,nuisance trip recurs.

I'm sure you will eventually get to the right answer but I wouldn't like to think I was paying for your fault finding time.

I have yet to experience an unhappy client/customer with my troubleshooting skills, time billed, or quality of work. Most of the time the previous troubleshooters fail to prove out the basics and have overlooked simple mundane wiring errors whether induced during the installation or at the factory during assembly. The mislead and misguided attempts that follow these errors fail to identify the root cause issue and lead to extensive down time of the equipment as well as excessive cost to the client.

Any crossed wires and the system will trip straight away - its not going to hang about.

OP: Since the nuisance trip repeats often,request advice to solve this problem.Thanks.

I'm not happy about removing bonding bits. If anything is crossed ...

I'm am not certain about India but in the US four (4) wire electrical service requires separation of the earth ground(s) and neutral(s) and bonding of the busses therefore is not allowed. Since this regulation is based upon proven competent electrical design and protection methods I am assuming the same would apply to India.

The scope - surely we are looking for leakage not induced noise and harmonics wherever they may be coming from.

All GF and other circuit protection devices utilize solid-state electronic circuitry that trigger SCR, FET, NPN, PNP, or other components that are all very suseptible to noise as the firing voltage of the gates is well below 1 VDC. (.3VDC or .7VDC either pulsed or maintained)

Any noise injected into the control circuirty that exceeds the .3VDC or .7VDC limit (threshold voltage of the circuit component design) will cause intermittenet and uncontrolled activation/firing of the transistors and/or other components of the protective device and most definitely will trigger "trip" circuit(s) whether GF, PTG, PTP, DIFF, or other type of protection device. Removing this noise and stabilizing the circuitry is exactly what an RLC or RDC filter accomplishes in the circuit. The reverse biased diode drains off all unwanted DC, The resistor or inductor limits the magnitude of current drained, and the capacitor is "tuned" by size to match the fequency of the unwanted noise/harmonic.

I'll stick with my guns - test and prove the RCD.

Now pull all the fuses / mcbs and fuses and bring the circuits back on one at a time. Bring the lights on first and wait an hour or so. Its going to take time but something the home owner should be able to do.

You say circuits are tested but you do not say what with. I had a similar situation in one of my rental properties - ground floor sockets would trip about every 40 minutes. It took a while to suss that it was the house wiring and not an appliance. (the rubbish the tenants plug in needs to be seen to be believed) Its a UK ring main so I disconnected the circuit in legs. The fault only showed up when blasted with a meggar. The resistance was still high and likely high enough to have passed a test but it was a magnitude lower than other legs of the circuit. circuit leg now isolated and replaced and no reason for the cable degrade.

The RCD is pretty immune to noise on the line. Don't understand the comments on silicon and germanium semiconductors. FETs?? Is this straight out of a book cos its not really applicable here

Never been to India .....

Good hunting with the fault.

NVMANI,

I hope that using some/all the suggestions above you will be able to find the cause and correct it.

When you have the results, please post a reply here and report the cause; it would be very interesting and educational.

Quote Silverfox "30mA does provide personnel protection. check I.E.E. regs (BS7671) 5mA on an incomer???"

From Wikipedia

RCDs are designed to disconnect the circuit if there is a leakage current. By detecting small leakage currents (typically 5-30 milliamperes)
and disconnecting quickly enough (<30 ms), they may prevent electrocution. There are also RCDs with intentionally slower responses
and lower sensitivities, designed to protect equipment or avoid starting electrical fires, but not disconnect unnecessarily for equipment
which has greater leakage currents in normal operation. To prevent electrocution, RCDs should operate within 25-40 milliseconds at leakage
currents (through a person) of 30 milliamperes, before electric shock can drive the heart into ventricular fibrillation, the most common
cause of death through electric shock. By contrast, conventional circuit breakers or fuses only break the circuit when the total current is
excessive (which may be thousands of times the leakage current an RCD responds to). A small leakage current, such as through a person, can
be a very serious fault, but would not cause the total current to become high enough for a fuse or circuit breaker to break the circuit,
let alone do so fast enough to save a life.

GOOGLE ARTICLE

How GFCI Receptacles Work

GFCI Receptacles, are not the grand mystery most people conceive them to be. They are actually very simple devices. General-purpose, 120-volt
household circuits have current flowing to and from the load on two insulated wires: the white and the black. Power is brought to the load
the black wire, flows through the load and then returns via the white. As long as these two currents are equal, the GFCIs, is happy and provides
power like a standard receptacle. But if some of the return current is missing, the GFCI will immediately open the circuit.

The logic is that if some of the electrons that leave the device don't come back, they must be going somewhere else. Usually,
this "somewhere else" is through a hapless tool holder to ground. The actual amount of missing current needed to trip the GFCI
is 4 to 6 milliamps (thousandths of an amp). This is the maximum amount of current the normal person can take without his or her
heartbeat loosing its rhythm. Instead of a steady thump, thump, thump, a shocked heart starts beating to an irregular rhythm. Such
syncopation is great for music but deadly for hearts.

Apparently there is disagreement as to how many ma will stop the heart.

GA

I liked your simple but correct explanation, are you a teacher of electrics by any chance?