RCD tripping on high power appliances

[carlramsay]

Hi
I have a Volex new consumer unit, and have a problem with the RCD tripping when ever a appliance is plugged in to the upstairs ring circuit. Only higher power appliances power tools, henry hoover, hair dryer. It even trips with the tv 40" samsung but not on the same plug with a lesser watt 180w samsung 32"tv. I was told it was probably a faulty appliance, but cannot believe they all have faults. The lights up/down have there own circuits, and also up/down elecs own circuits, and kitchen cooker / heating have there own circuits. I do live in a semi rural area and do have overhead cables entering the house have heard of earth problems ?
Any ideas. The RCD is a 80

 

[JohnD]

new consumer unit,

New, eh?

Who fitted it, what skills did he have, and what tests did he carry out?

 

[1john]

Can you post the test results on the certificate and a pic of the CU?

 

[ajrobb]

I'm a novice DIYer but it sounds like a TT supply with an RCD (80?) to limit fault currents to a local earth. I think there should also be 30mA RCD protection on general circuits up to 32A for sockets and lights. Elsewhere concentric earth protection (earthed steel conduit or earthed SWA etc) on dedicated supplies for boilers and freezers etc.

I'd be interested to see the insulation test figures.

 

[Taylortwocities]

RCDs do not trip on over current.
The most likely reason is that the neutrals (or lives) have been mixed up on one of the ring finals. How many RCDs do you have in your board?

Let's see a picture but I am not sure why you are asking on here.
Surely you should be getting the electrician who did the work to resolve HIS/HER problem..?

 

[bernardgreen]

It could be a neutral to earth fault on another circuit protected by that RCD even if there is nothing plugged in on that circuit.

The diagram shows a neutral to earth short. Leakage between neutral and earth due to damp or large filtering of the mains in an appliance on the other circuit can have the same effect as the short circuit shown.

Neutral_Earth_trip

• bernardgreen
• 16 Jan 2011
• 48

EDIT added "" can have the same effect as the short circuit shown. ""

 

[flameport]

Who fitted it, what skills did he have, and what tests did he carry out?

We all know that the answers are a. an 'electrician' who is on holiday, b. very few, and c. switching it on.

 

[jaysean1]

I had a mem rcbo pod trip out when an iron was switched on, was due to a fautly pod

 

[RF Lighting]

It's usually a high(ish) resistance N>E fault somewhere on the installation.

If the RCD holds in with a load of 180W, then it is not a wiring fault like a mis-connected ring.

 

[ericmark]

It could be a neutral to earth fault on another circuit protected by that RCD even if there is nothing plugged in on that circuit.

The diagram shows a neutral to earth short. Leakage between neutral and earth due to damp or large filtering of the mains in an appliance on the other circuit can have the same effect as the short circuit shown.

Neutral_Earth_trip

• bernardgreen
• 16 Jan 2011
• 48

EDIT added "" can have the same effect as the short circuit shown. ""

Not the best diagram but likely the right answer. I would agree that a device with an earth neutral fault will likely only trip the RCD when a load is placed on the circuit. The load may be from a different device.

If the earthing system is TT however this is less likely as likely there is a larger differential between earth and neutral to start with.

But assuming it is a TN system likely TN-C-S then yes as load is increased so will the leakage and so any large item will trip the RCD.

If the fault is in wiring not much Joe public can do other than get electrician back. However if the fault is some other appliance then maybe he can find the appliance which is faulty.

Step one unplug and switch off every item on ring main.
Step two get a known good device with heavy load lets say a fan heater best if double insulated. If this works OK continue if not then likely wiring fault so need to get electrician to test.
Step three one by one reconnect the items unplugged while fan heater still running. Better to unplug once tested and sure power has not tripped.

At some point something you plug back in will trip the RCD likely it is that item that is faulty.

Step four take suspect item for testing.

If it is in the wiring then sockets will likely need removing to test and test equipment will be required. Since in the supply earth and neutral are connected the tests will require all power to be switched off at the main double pole isolator. Then with a special ohm meter which uses 500 volt for the test the neutral and earth, the line and earth, and the line and neutral are all tested.

To me the standard forms need an extra box. They have Live/Earth and Live/Live but the Live/Earth is the lowest of two readings Line/Earth and Neutral/Earth however so many people think of live only referring to line (the phase) and forget it also refers to neutral.

 

[ajrobb]

Step four take suspect item for testing.

Would that be PAT?