UK RCD adaptor issue

[Confused user]

I am seeking professional advice. I have no electrical qualifications. On the last 2 occasions I have cut my lawn the RCD adaptor did not trip BUT when I disconnected the mower the RCD was completely dead (ie would not reset nor test nor allow power to any device) . On the second occasion I borrowed a friends RCD adaptor and consequently destroyed his! Obviously I suspect the mower but as a novice I would have expected either of the RCDs to trip. On the occasion before these lawn cuttings I had some difficulty connecting the power lead to the mower hence my suspicion of the mower having a fault. I would like an explanation as the only other cause could be the house socket (its in a newish build and has not had any previous problems!) Many thanks Paul

 

[westward10]

If it is a newish build do you need an rcd adaptor, I assume this adaptor you plug to the socket outlet first.

 

[Confused user]

The answer to that is probably not. But the new build is an extension and as I understand it on a different circuit to the rest of the house. But to do the front lawn I use the other circuit. (I said I am not an electrician) and the use of the adaptor is basically habit. I am chasing an explanation so I know whether to ditch the lawn mower or have the extension electrics investigated. Thanks for replying

 

[pc1966]

It sounds odd. An RCD adaptor should survive OK even with the switching on/off of a load such as a lawnmower.

Were they both the same brand of RCD adaptor?

True, in a new house the sockets should already be protected, but equally you ought to test the main RCD (at the CU = consumer unit = fusebox) regularly (which will cut the 13A socket power temporarily, so best to trun off PCs and TIVO recorders, etc, beforehand).

 

[radiohead]

What you experienced is exactly what would be expected on cutting a mower flex. Most mowers are Class 2 appliances, or double insulated, and do not have an earth conductor. An RCD trips with a leakage to earth, so cutting the mower cable would not trip an RCD because fault current would not flow to earth. It would however cause a short live to neutral which would blow the 13a fuse in the RCD adaptor rendering it non functional. All you had to do is replace that fuse and the RCD adaptor would be functional again.
The RCD would protect you if you (for example) damaged the flex without blowing the fuse and came into contact with a live conductor, if you received an electric shock in that situation the RCD should do it's job and trip before the current flowing through your body to earth reached a fatal magnitude .

 

[freddo]

Does the RCD adaptor work in another socket? Many do not reset/can't be switched on if the socket they are plugged into has no earth connection.

 

[Confused user]

What you experienced is exactly what would be expected on cutting a mower flex. Most mowers are Class 2 appliances, or double insulated, and do not have an earth conductor. An RCD trips with a leakage to earth, so cutting the mower cable would not trip an RCD because fault current would not flow to earth. It would however cause a short live to neutral which would blow the 13a fuse in the RCD adaptor rendering it non functional. All you had to do is replace that fuse and the RCD adaptor would be functional again.
The RCD would protect you if you (for example) damaged the flex without blowing the fuse and came into contact with a live conductor, if you received an electric shock in that situation the RCD should do it's job and trip before the current flowing through your body to earth reached a fatal magnitude .

Brilliant and highly logical answer. Thank you very much for sharing your expertise. I shall change the fuse on one RCD appliance asap. I shall also change the flex on the mower once lockdown is over. I am ever so grateful

 

[davesparks]

What you experienced is exactly what would be expected on cutting a mower flex. Most mowers are Class 2 appliances, or double insulated, and do not have an earth conductor. An RCD trips with a leakage to earth, so cutting the mower cable would not trip an RCD because fault current would not flow to earth. It would however cause a short live to neutral which would blow the 13a fuse in the RCD adaptor rendering it non functional. All you had to do is replace that fuse and the RCD adaptor would be functional again.
The RCD would protect you if you (for example) damaged the flex without blowing the fuse and came into contact with a live conductor, if you received an electric shock in that situation the RCD should do it's job and trip before the current flowing through your body to earth reached a fatal magnitude .

But the OP hasn't mentioned anything about cutting the mowers cable

 

[radiohead]

But the OP hasn't mentioned anything about cutting the mowers cable

You are correct, I misread the post. Perhaps then there is a short circuit on the mower or flex connector which has blown the fuse. A blown fuse would still account for the dead RCD adaptors.

 

[pc1966]

Certainly it is worth trying a change of fuse if it has one, but not all RCD adaptors do (RCD plugs obviously have to!).