Domestic electrical query

[Captain Kernow]

I have a general question for any electricians, please.

 

In a typical domestic house setting, apart from plug sockets, what else may be connected to the RCD switch in the fuse box? 

 

Or put another way, if one was to turn the RCD circuits off at the fuse box, apart from the plug sockets, what else might typically become isolated, please? 

 

Many thanks. 

 

[Clagsniffer]

Electric showers and cookers, but could be anything really. What is your current set up? Is it an RCD on the front end supply or do you have a split board? My father has an RCD on the supply side to his old Wylex board, so if he has an earth fault or if he turns the RCD off he loses everything. My house has a split board as shown in the attached picture.

[96701]

My split board has RCD protection on all circuits.........

[Dagworth]

Depends on how old your wiring is. 

 

Andi

[Dave John]

Depends when it was wired and by whom capt K. 

 

Generally up to about 1990 it would be a switched incomer , followed by mcb for fixed load with an rcd covering socket outlets and possibly a shower .  

Before that if there was an earth fault device it might well be of the voltage detecting type, rather that one in the current domain. 

 

Towards 2005 we are beginning to see split boards with 2 rcds and mcbs covering individual circuits.

 

I would now tend towards individual mcbos for all circuits . The plastic box shown by clagsniifer would now be inadequate as a new installation. 

 

Last year I upgraded a dental practice. All circuits rcbo with integral arc fault protection, surge protected incomer and full voltage stabilisation for the chair system. Price of a small car. 

 

That said, I have seen far too many inadequately protected installations over the years. 

 

Take a few photos. I will try and advise. 

[Captain Kernow]

Photo will follow. Installation dates from 2003, though. 

[Stubby47]

A) if this is an April Fool joke, I don't get it

B) if it is an April Fool joke, you posted it too early

C) if you need to work on any part of your domestic wiring, turn lights, lamps, tv, etc. on, then turn off everything at the main switch. If some electrical stuff stays on, call an electrician!

[Phil Bullock]

Our RCD tripped every time a lap top was plugged in - any socket.

 

So just had main board replaced - RCBOs on all circuits. Cost not too bad - £400 including parts and labour

[chris p bacon]

48 minutes ago, Phil Bullock said:

Our RCD tripped every time a lap top was plugged in - any socket.

 

So just had main board replaced - RCBOs on all circuits. Cost not too bad - £400 including parts and labour

 

How did you get that lot in the laptop ?

[meil]

52 minutes ago, Phil Bullock said:

Our RCD tripped every time a lap top was plugged in - any socket.

 

So just had main board replaced - RCBOs on all circuits. Cost not too bad - £400 including parts and labour

SMP well known source of RCD tripping. You just needed a new power supply to the Laptop.

[Phil Bullock]

1 hour ago, meil said:

SMP well known source of RCD tripping. You just needed a new power supply to the Laptop.

 

Cheers - tried that! And it was any laptop, not a specific one. Too many trips out the the garage in the dark to reset!

[sharris]

1 hour ago, meil said:

SMP well known source of RCD tripping. You just needed a new power supply to the Laptop.

 

My first thought was that it was more likely to be a problem with the inlet filter on the laptop power supply (Phil, were you trying all the different laptops through their own power bricks, or just using the same power brick for each laptop tried?)

 

[Captain Kernow]

1 hour ago, meil said:

SMP well known source of RCD tripping. You just needed a new power supply to the Laptop.

Electrical dunce here asks what 'SMP' means (apart from the maker of flexible track)?

 

[Dagworth]

Just now, Captain Kernow said:

Electrical dunce here asks what 'SMP' means (apart from the maker of flexible track)?

 

Switch Mode Power Supply

 

Andi

[kevinlms]

3 minutes ago, Dagworth said:

Switch Mode Power Supply

 

Andi

For which the normal abbreviation is SMPS, not what was given. Although whether that makes any difference to the Captain, I don't know!

[Captain Kernow]

 

This is the circuit board (installed 2003) in Kernow Towers.

 

The issue is one that has happened only very occasionally, but manifested again last night.

 

About 18 months ago, we had a small number of spurs fitted off existing plugs in the small room that we use as a study. The purpose of these spurs was to provide electrical sockets at desk level, so that we didn't have to scrabble around on the floor to turn a computer on or off at the switch.

 

The spurs were installed by a professional, accredited local electrician and we have the appropriate certificate for the work etc.

 

Prior to the installation of the new spurs in 2018, there had been no problems whatsoever with the RCD tripping.

 

A short while after the spurs were installed, we had a couple of mysterious RCD tripping incidents, which turned all the electrical sockets in the house off. CTMK initially noticed this and we eventually narrowed the cause down to when she turned the computer off at the wall socket, after using it.

 

This then happened to me a few days later, when I was turning the same computer off at the wall socket. Having looked into what other items might have been drawing power at the same time, I was satisfied that the RCD tripped when I turned that switch off at the wall.

 

We stopped using that particular socket and informed the local electrician. He replaced the socket with a new one and the problem stopped.

 

Now the same has happened again last night. Because there was very little drawing power from the various wall plug sockets in the house at the time (certainly no lights in any rooms that we were in, or TV, which would have immediately notified us), it was only discovered a few minutes after CTMK had turned the computer off, when she found that the wall sockets upstairs were not working. I checked the RCD switch on the fuse box and found that it had tripped. It reset with no problems when I pushed it back up into the 'on' position.

 

Once again, there was virtually nothing else, apart from a couple of lamps in unoccupied rooms, drawing power from those circuits at the time, so the obvious conclusion to us is that it is the same cause as before.

 

Of course now, this is not likely to be considered an urgent matter, so there is little likelihood of an electrician attending until the current health crisis has improved.

 

Appliances that draw much more current than a computer have since been used and don't trip the RCD switch.

 

We are continuing to use the socket for now, but monitoring it carefully. Unless we are actually using the computer (or TV or other appliance), it isn't normal practice in our household to leave anything turned on at the wall socket.

 

 

Edited April 1, 2020 by Captain Kernow

[meil]

RCD tripping has little to do with "drawing power". There is a leakage to earth (more properly called the CPC, Circuit Protective Conductor) somewhere - and I suspect it's live to earth rather than neutral to earth. If it were Neutral to Earth disconnecting the MCB wouldn't take the problem away.

 

If you can you should disconnect each MCB on the RCD protected circuits and see if you can identify which circuit is causing the circuit to trip.

 

However the proper way is to measure the resistance of each circuit to earth. For that it sounds like you need an electrician to do that.

Edited April 1, 2020 by meil

[Phil Bullock]

1 hour ago, sharris said:

 

My first thought was that it was more likely to be a problem with the inlet filter on the laptop power supply (Phil, were you trying all the different laptops through their own power bricks, or just using the same power brick for each laptop tried?)

 

 

Different power bricks....

[Dave John]

My suspicion would be the computer power supply. 

 

Simply put, switched mode power supplies, such as those commonly found in computers and similar, leak a little bit of electricity to earth all the time as part of the way they filter electrical noise. There tends to be some electricity stored in the smps when in use.

 

Even with the computer shut down the smps is still running. If you switch off at the socket it may be that the live and the neutral are not disconnected at the same time, perhaps only milliseconds of a difference, but modern RCDs are very fast. The result is that stored energy is discharged through the slowest bit of the switch, the RCD sees an imbalance between the live and neutral currents, decides that there is a fault and trips. 

 

Note that although the RCD is rated for 30 mA / 30 mS it is not uncommon fro them to be a lot more sensitive than that.

 

In electrical terms there is always a tradeoff between protection of the installation of a whole and what we call nuisance tripping, particularly under transient conditions. 

 

The RCD seems to be working properly, which in safety terms is the main thing. Longer term, a new computer or power supply, but for now don't worry too much it is just a nuisance. 

 

 

 

 

[kevinlms]

1 hour ago, Dave John said:

My suspicion would be the computer power supply. 

 

Simply put, switched mode power supplies, such as those commonly found in computers and similar, leak a little bit of electricity to earth all the time as part of the way they filter electrical noise. There tends to be some electricity stored in the smps when in use.

 

Even with the computer shut down the smps is still running. If you switch off at the socket it may be that the live and the neutral are not disconnected at the same time, perhaps only milliseconds of a difference, but modern RCDs are very fast. The result is that stored energy is discharged through the slowest bit of the switch, the RCD sees an imbalance between the live and neutral currents, decides that there is a fault and trips. 

 

Note that although the RCD is rated for 30 mA / 30 mS it is not uncommon fro them to be a lot more sensitive than that.

 

In electrical terms there is always a tradeoff between protection of the installation of a whole and what we call nuisance tripping, particularly under transient conditions. 

 

The RCD seems to be working properly, which in safety terms is the main thing. Longer term, a new computer or power supply, but for now don't worry too much it is just a nuisance. 

 

 

 

 

Perhaps a solution to the computer tripping the RCD, is to get a UPS for the computer? That way the load to the mains is the UPS rather than the computer.

It's s good idea anyway to have the computer connected to a UPS, as it enables the computer to be shut down in an orderly manner in the event of power failure, rather than crashing off and potentially causing problems with the HDD.

[Grovenor]

Quote

If you switch off at the socket it may be that the live and the neutral are not disconnected at the same time,

You can pretty well guarantee that since in 99% of sockets the neutral is not switched.

[meil]

38 minutes ago, Grovenor said:

You can pretty well guarantee that since in 99% of sockets the neutral is not switched.

Correct, in the UK normal sockets do not switch the neutral. The ones that come to mind that do are cooker switch units and electric shower switches.

[John ks]

 

3 hours ago, Captain Kernow said:

I was satisfied that the RCD tripped when I turned that switch off at the wall.

 

The RCD tripping when you turn the switch off (I assume you mean the switch on the power point) Has me perplexed

Have you tried plugging the computer into a different power point(via an extension lead if necessary) & trying to replicate the fault 

if the fault followers the computer than it is most likely the computer

 

Regarding nuisance tripping

With a single circuit on a RDC or RCBO ( Residual Current Circuit Breaker with Overcurrent Protection) if there is a small leakage (say 10to20mA) a 30mA RCD wont trip

 

With multiple circuits on a single RDC/RCBO & each circuit leaking a few mA it adds up to a point where adding an otherwise OK device (that has a leakage of a few mA) will trip the circuit 

Or

With multiple devices on a single RCBO & each device leaking a few mA it adds up to a point where adding an other leaky device  will trip the circuit 

 

Trying to find a leaky device by plugging in each device until the RCBO can be problematic 

If you had 3 devices each with a earth leakage of 12mA, plugging any 2 devices wont trip a 30mA RCBO, but as soon as you plug the third item the RCBO will trip

 

 

One expensive way to reduce nuisance tripping might be to replace all CBs with RCBOs

 

I have RCBOs installed (10 years ago) on all circuits except stove & a hard wired AC Unit & so far I don't recall any nuisance trips 

 

Hope some of this helps

John

 

 

 

 

 

 

[Sidecar Racer]

5 hours ago, Captain Kernow said:

 

 The purpose of these spurs was to provide electrical sockets at desk level, so that we didn't have to scrabble around on the floor to turn a computer on or off at the switch.

 

 

 

 

Forgive me if this is wrong , a friend of mine had her computer fail to boot up one day , it came up with

list of things to reset that she did'nt understand so took it to the local computer shop , the problem turned

out to be the CMOS battery having died , after it was sorted and when she went to collect it she was asked

about her normal shut down routine which included turning off at the mains , it was suggested that by

doing that the machine then uses the CMOS battery to keep all the set up data live , as she does not use the

computer a lot , sometimes maybe for several days this speeds up battery drain , by not switching off at the

mains there is still some residual power in the machine to keep memory circuits live .

 

I don't know how much power a shut down computer consumes , but if it is minimal then maybe just

leaving it like that would be an idea .

 

Edited April 1, 2020 by Sidecar Racer

[stewartingram]

L/N/E screw loose in a wall socket maybe?

 

Stewart