RCD's and how they should work

[nickblake]

OK chaps RCD's we all know what they do ,they work if a fault to earth is detected basically an imbalance ,my concerns about these is that recently ive had three gardening tools in all class 2 two core , cables cut in half , didnt blow the fuse or trip the RCD so live ends floating about ,me being me sent a letter to the ESC sugesting earths should be in class 2 appliance cables ,got a reply back saying they dont need an earth because the RCD will trip if touched by some one touching the live end of the cable ,bit shocked at the reply
but before i reply just wonder what your thoughts were on this ill post the full reply at a later date

 

[Sintra]

An rcbo is an rcd with overload protection.

 

[Cj24]

Thank you, I don't exactly knw wat you mean tho sorry I knw an rcd will trip if there a fault across live and earth exp a flex cut but don't get wat u mean with rcbo sorry

 

[nickblake]

wasnt me that cut the leads , all leads were standard as supplied ,my idea would be to add the earth cpc in the cables thus increasing the protective capabilities of the cable ,connected at the plug end but not at the appliace this then chopping the cable in half will cause the inbalance and earth fault thus tripping the RCD ,items were brought to me to repair both cable haves ,items headge trimmer circular saw ,lawn mower

 

[davelerave]

screened/armoured would be theoretically safer as 'automatic disconnection' will cut the supply safely

a cpc makes no diference

your cut cables should have caused a short-circuit anyhow

 

[acat]

Thank you, I don't exactly knw wat you mean tho sorry I knw an rcd will trip if there a fault across live and earth exp a flex cut but don't get wat u mean with rcbo sorry

An RCD will trip on an earth fault thats it whereas an RCBO will trip on an earth fault short circuit or over current. An RCBO is basically an RCD and MCB combined into one unit.


Hope that helps


Chris

 

[Cj24]

Yes that's perfect thanx mate

 

[Risteard]

can you please tell me the difference and where they would be used between an rcd and an rcbo please

An RCBO is one specific type of RCD. It also provides overload protection. It is essentially both an RCD and an MCB.

 

[Risteard]

Sorry see that's been answered already.

 

[Jason Smith]

Just to give you the heads up, if a person is working in a garden it is likely that he/she wont be in contact with the general mass of earth, rubber wellies etc, most normal shoes, therfore if they cut a wire, and by some miracle dont cause a short. the two wires will, if touched will think the person is
now the lawn mower hedge trimmer and giveit a full dose of current. I.E. thinks you are the load.
If the cable included an earth wire,then as the blade etc sliced through it, the tempoary contact between the line conductors and CPC would cause the RCD to trip. Just the same as line to line should cause the MCB/Fuse to go.A cpcin the cable should provide more safety. I suppose it is possible to prtially sever a wire, and if there was a cpc in it as well it would increase the chance of contact between any of the three wires leading to automatic disconnection.

 

[nickblake]

Jason thats exactly my thoughts ,but not that of the ESC heres there reply :
Dear Nick

Thank you for your letter regarding the RCDS and electrical safety in the garden.

An RCD constantly monitors the electric current flowing along a circuit and any imbalance between the live conductors (L&N). It does not require an earth as a reference to detect a fault.

If it detects electricity flowing down an unintended path, such as through a person who has touched a live part (perhaps the end of a severed cable) an imbalance occurs and this is detected by the RCD, which automatically cuts off the power before injury or damage can result.

It is therefore not necessary for the supply cable to an appliance to be provided with an earth conductor.

We hope you find this response helpful and perhaps a reassurance that RCDs will operate correctly regardless of the classification of appliance or cable type.

I hope that the information provided is of assistance to you. If we can be of any further help please do not hesitate to contact us again.


Kind Regards

so when we read reg 131.2.1 were ment to be preventing shocks now matter how small ,so 5 to 10 ma throws you off painfull sensation 10 ma to 15 ma you cant let go ,20 ma to 30 ma impaired breathing ,50 ma and above ventricular fibrillation and Death ,

 

[Madmole]

So what if your wearing rubber boots (no earth) and put your thumb on the end of the wire touching line and neutral. There is no imbalance as you are just acting as a load (short). You get zapped and RCD doesnt trip. As your not a particularly good conductor, maybe thecurrent isnt sufficient to trip the MCB either!

Not good until you collapse with no heart beat and earth yourself thus tripping the RCD

What am I not seeing here?

 

[davelerave]

you're not mssing anything- there's no automatic disconection for that scenario

reduced voltage or isolated supply would help

scrren or armour will disconnect cut cables safely via the rcd/mcb- i've cut through a few live swas on t-n-cs with the hacksaw-not so much as a tingle


the mcb/rcd should protect in most scenarios when using a class2 appliance outdoors afaik

 

[Jason Smith]

I note the response and it is of course correct. It actually does take a set of circumstances before you can get a shock. Touch either of the conductors and the RCD should trip. Touch them both and you become the lawnmower. However, our original argument is should there be a CPC in the cables for equipment used outside. I say there should be, as it would provide an additional path to earth as if someone grabs a live and neutral together they are likely to grab the CPC as well. If there are for instance three hundred electrocutions in gardens this summer, I would bet that, had a CPC been included in the cables, then that figure would drop dramatically.

 

[R.Sparky]

Obviously a seperate issue, but in my opinion all MCBS should be fitted with RCD protection instead of just being over-current devices so it's easier to troubleshoot a fault with an appliance etc etc (making them RCBO's right?)

 

[Cj24]

Hi sorry to jump in half way, from what iv managed to gather an rcd is a mcb but with overload protection which is when the circuit is overloaded, but shouldn't an mcb do that anyway, little confused and I also don't quite get the rcbo