Newbie question re rcd plugs\fuses

[JohnnyRhodes]

Hi all,

I've just joined this forum to generally improve my knowledge such that I can do basic DIY tasks. I've no formal training, and no knowledge other than a very rusty memory of ohms law from o-level physics at school ( showing my age there ). So my stupid first question is :

My wife read somewhere that you should always use an rcd plug with a lawn mower in case you accidentally cut through the wire. Why do you need such a thing? I understand what they do, but wouldn't the fuse in the plug fitted to the mower do the same job? Apologies if this is a daft question but everyone has got to start somewhere right?

Also, anyone know any good online resources for learning the basics (as I think i'm gonna need it !!)

Many thanks,

Johnny

 

[steptoe]

good choice to come here,

firstly, and I'll try do this is laymans terms,

the fuse in the plug is 13amps, most likely,

an RCD will most likely be rated at 30 milli-amps,

so I think you can see already where this is going,

the plug fuse will take at least 13amps to blow, in reality it will take much mkore than this for a sustained period of time, and by time I mean seconds.

the RCD will stop the electricity in milliseconds as soon as it detects/senses an imbalance of 30 milli-amps,

the thing that must be borne in mind is that an RCD will not detect a direct fault from live to neutral, that is why you still need a fuse.

any help?

 

[batty]

Well my father in law managed to cut through the hedge trimmer cable years back now as this had a two core flex on it it did not trip the RCD but it did blow the fuse. The thing is though RCD's may not trip if you do have a two core flex but if you do grab hold of the live cable on a wet lawn or the severed cable touches a wet lawn it just may save your life so RCD's are a good idea as far as I am concearned and welcome to the forum.

 

[Lee321]

just to add to the above. typical humans would die with anymore current flowing through them than 30Ma so rcd's would turn off the supply at or above 30Ma saving the victim if they were in contact with earth and live

 

[ian932]

Hi welcome to the forum

Some video's on the benefits of RCD's

https://www.youtube.com/embed/i-pkBogaciU?feature=oembedanother link on garden safety Garden safety : Electrical Safety Council

The TLC website has a lot of good info

 

[Doc Hudson]

Welcome to the forum Johny, RCDs and fuses actually detect different types of faults. Fuses protect against overload or too much current flowing to protect the cables. RCD's detect leakage or as steptoe describes it imbalance between the live and neutral. They protect people and animals from electric shock due to very small currents that would never blow a fuse. This link to the Electrical Safety Council may help.

RCDs Explained : Electrical Safety Council

Doc H.

 

[Evans Electric]

I think all that needs to be said has been said, without causing confusion . Don't worry about the technical side, You always need an RCD for outside use, for the reasons given above.

A personal foible is I'd rather have a fixed socket than a plug-in jobbie (rules out the " Oh I can't find the damn thing situation" ) Better still , have one fitted at your fuseboard , protecting all your sockets .

 

[tom1]

4-Socket Extension Reel with RCD - 20m from Homebase.co.uk

not as good as an rcd in the cu but i have something similar to this in the van,

 

[kme]

[quote name='Lee

 

[Sidewinder]

There is actual research published by the IEC on this under document number IEC/T* 60479, it has several parts some with differing characters where I have put the *.

You can find the titles on the BSI Online website.

There is a summary here:

The Electric Shock Questions

I am not sure as to how this relates to the actual IEC documents as I don't have them all, nor have I cross referenced it, nor am I sure as to how current (ha ha) this is!

Also it only gives 60Hz, not 50 so it is really "Yank".

OP: Sorry if this is a bit over your head, it is aimed at the professionals on the forum, I don't feel that I can add anything to the info you have already been given as it is all sound IMHO. Sorry if you feel that this is a thread hijack, it is not aimed that way.

HTH.

 

[Lee321]

I used 30 K as it was more relative to the 30ma rating. Less than 1ma AC directly could cause defibrilation while interestingly DC would need to be inexcess of 300ma