Hi,i would like some advice please.My 73 year old dad likes to cut his lawn with his electric mower.So i bought a plugin rcd device to keep him safe.Well he proceeded to slice through the mower cable like i knew he would eventually do.The thing is the rcd didnt trip ,it did blow the 15 amp cartridge fuse at the fuse board....The elecrics are old type wylex cu and cartrige fuses....The mower was plugged into the rcd which was plugged into the extension cable which was plugged into the socket in the kitchen...The house electrics do not have a rcd-hence the rcd i bought....Can someone please tell me why the rcd didnt trip,and could a stand-alone rcd be fitted to the house electrics cu...Sorry if this post is abit long. kind regards Y.
rcd help
- Thread starter yuko
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An RCD trips when current leaks to EARTH. It constantly monitors the live and neutral. If there is an imbalance between the two (a leak), it trips.
Now, a lawnmower is double insulated. Its cable contains no earth core.
When your dad sliced through the cable, he shorted live and neutral. The RCD did not trip, because there was no imbalance. Despite there being hundreds of amps flowing for a brief moment, the live and neutral were balanced. No current leaked to earth.
An RCD is still a very important safety device though - had he nicked the cable, and not sliced it, the live would be exposed which would be very dangerous. This would probably leak to earth through the damp grass and trip the RCD. An RCD is very sensitive.
Now, a lawnmower is double insulated. Its cable contains no earth core.
When your dad sliced through the cable, he shorted live and neutral. The RCD did not trip, because there was no imbalance. Despite there being hundreds of amps flowing for a brief moment, the live and neutral were balanced. No current leaked to earth.
An RCD is still a very important safety device though - had he nicked the cable, and not sliced it, the live would be exposed which would be very dangerous. This would probably leak to earth through the damp grass and trip the RCD. An RCD is very sensitive.
First option is that you have a double insulated appliance which means that there will be no earth present in the cable through which fault current can flow, this means that when the cable is cut there is no current flowing to earth and it is this inbalance between phase and neutral that the RCD detects.
The other option is that the plug-in RCD is faulty, and is operating outside its required parameters. An electrician can test for this quite easily.
The other option is that the plug-in RCD is faulty, and is operating outside its required parameters. An electrician can test for this quite easily.
You've just learned why it's a good idea to still use a 3-core flex on DI appliances like that - increases the chance of cable damage creating a LE or NE fault that will trip the RCD...
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You're the first person I've ever seen say that, something that I have always thought was a good idea!
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