Thread: Earth Leakage Safety Switch

Hi Austastar

The devices are now called RCD's (residual current devices) and trip by comparing the current between the active and neutral. Therefore an earthless extension cord will cause a trip just the same if some of the current goes out through a leak. Just think of double insulated tools, they don't have an earth.

When my sparkie was last at my place he just threw out every individual power-point circuit breaker and installed the new type of RCD breakers. They aren't that dear any more.

Hi bee utey,

I guess mine needs updating at some stage then, it is 24 years old and has 'earth leakage circuit breaker' written on it.
thanks and cheers

And if you happen to have a small A/C inverter split system wired into a circuit with an RCD you will often get nuisance tripping,particularly if it is a Daikin.The larger A/C units should be on their own dedicated circuit so don't have an RCD.

Hi All,

I'm a sparky and just want to let you know that there are two types of RCD's/ELCB's

The first is just RCD only. These are fairly older units and used to be installed adjacent to the existing fuses/circuit breakers, usually the width of four circuit breakers, and were mainly protecting the power circuits only.

The second type are RCD/MCB. These look exactly the same as your standard circuit breakers but have a built in RCD. Some are the width of two circuit breakers, but newer ones are only one circuit breaker wide. They may also have a small window that changes colour when a fault occurs. This differentiates from a residual current fault or just an overloaded circuit breaker. When you reset the breaker the window clears and is reset.

Some manufacturers make their RCD/MCB work in a way that when there is a fault, the breaker switch will only drop half way. To reset these you just turn the breaker off and back on again.

Individual RCD/MCB are the way to go. You only need to put these on lights, power, garage, pool/spa, etc. They are not needed on stove, hws, a/c circuits.

All new homes will have the lighting circuits protected but it was not necessary to protect these circuits in older homes.

I strongly recommend that the lighting circuits get protected in older homes as well. There was an accident near where I live about 10 years ago, where a young boy was electrocuted when he attempted to climb onto the family metal carport roof to retrieve a ball. When he touched the carport whilst standing on the ladder, his muscles contracted and he couldn't let go. It was later found out that when some backyard wannabe sparky run the wire to the carport light, it was run too close to the roof. At a later date a screw was put through the roof and caught the carport light switch wire (which meant that whenever the carport light was on, the carport was live). A RCD would have saved this boy's life.

Just another point I'd like to make regarding RCD's. It's important to press the test button on these regularly to make sure that they are working properly. Nothing lasts forever and they have been known to fail. I have a RCD tester which tells me the RCD trip time in milliseconds. When I have checked RCD's that have not been tested for a while the trip time has been as high as 45milliseconds. That will kill you! They should trip between 18 and 30 milliseconds.

I apologise for going on about this but I hope this information helps.

Jim

Originally Posted by JA1969

........................................ I have a RCD tester which tells me the RCD trip time in milliseconds. When I have checked RCD's that have not been tested for a while the trip time has been as high as 45milliseconds. That will kill you! They should trip between 18 and 30 milliseconds.

Jim

When you say haven't been tested for a while, do you mean tested by pressing the test button, or tested by meter/test equipment etc.

My understanding from that would be that if they are not tested by actuation then they may become a bit 'sticky'. Have I got this right ?



Martyn

That's right Bushie. Test by pushing the test button is all you need to do. Most manufacturers recommend testing monthly.

Originally Posted by VladTepes

Saved my wife when she stood on an extension cord that evidently had a short in it. Thing went BANG, the power cut out in a poofteenth flat, and wifes foot was blackened with sooty stuff as was the floor.

If you got a BANG, a blackened foot and sooty stuff, it is more likely that the fuse/overload circuit breaker is what tripped. A ELCB/RCD will trip too quick to display any of these symptoms. If a short exists between active and neutral, with no earth involved, the ELCB/RCD will not trip.

Aaron.

Well after 50 years living without a earth leakage switch or the other one it got used the other day - was only fitted just over a month ago.

A friend was over and using his laptop while sitting in my recliner. I was in another room and heard a zap and the power points were all off. I asked what happened and he said that there was a flash in the room and the sound of a zap - he also indicated that his laptop was now on battery. On investigating I found that the 240v power cord to his laptop power supply had been cut to the copper in the wires. He had moved from the recline to situp position in the chair and the metal frame had acted like a pair of scissors and cut through the insulation shorting out the wires.

Thankfully he would not have been electrocuted as the leather and padding would have insulated him from the frame and it seems the earth leakage switch cut to power so quickly that the laptop did not suffer a power surge. On checking the switch board - all circuit breakers were still on and only the earth leakage safety switch had tripped.

So a clear demonstration of how these things work to not only save lives but protect equipment.

Garry