Best position for RCD.

[conny]

Now that summer is here a lot of people will be using electricity outside such as when mowing the lawn, trimming the hedge etc

This raises the question of where to plug the RCD in. Is it better/safer to plug it into the fixed outlet inside the house/garage or into the extension lead that will, in all probability, be being used?

 

[Spark123]

Into the house/garage at the start of the extension lead, then the lead is also protected when you run it over with the lawn mower. Also saves smashing the RCD accidentally.

 

[conny]

Thanks Sparks. Very valid point about protecting the extension lead as well.

 

[PrenticeBoyofDerry]

I would also use the socket outlet that is supplying the power as the point to introduce RCD protection, that is if there is currently non-existing on the installation protecting the circuit being used. If there is and functioning correctly there would be no need for additional RCD protection.
The issue with a lot of electrical garden equipment, is that the flex provided is often two core and no earth. So the RCD would not operate even if the flex was cut or the equipment submerged in water!

 

[ericmark]

The issue with a lot of electrical garden equipment, is that the flex provided is often two core and no earth. So the RCD would not operate even if the flex was cut or the equipment submerged in water!

Not really ground is still connected somewhere to neutral and 30ma will still likely flow to ground and still cause the unbalanced situation required to trip the RCD. There are also 10ma RCD's which can be plugged in seen for sale in caravan shops but quite rare really.

Yes at the house socket is correct place if required. My wife came home with new lawn mower and plug in RCD which the salesmen assured her was required which I had to return. Other than with caravans and boats we don't use multi RCD's of same rating. They come in four standard sizes.
300ma for fire protection and for TT supplies.
100ma was used for TT supplies before new rules came out.
30ma protects personnel and now required for nearly all socket outlets.
10ma used to discriminate so a fault will trip that trip rather than main one.

The trip is tested at half and full rating to show non trip and trip so where one feeds another they are approx 1/3 of rating to previous RCD. However with something like a nail hammed through a cable I have seen the 30ma, 100ma, 500ma and 1amp RCD all trip together.

The old ELCB-v would not trip with a fault in the garden but the new ELCB-c (Now called RCD) will trip there are still some ELCB-v around but rare. The v stands for voltage operated the c stands for current operated. The voltage type was discontinued around 20 years ago as it could be easy shorted out by bonding stopping it working.

 

[PrenticeBoyofDerry]

I would have thought in the case of an unearthed flex, that any fault would be detected as a short between line and neutral, rather than an imbalance/earth leakage.
Although an active controlled RCD would operate due to power-loss.

 

[ebee]

the flex does not require an earth for RCDs to work.

If you system is earthed (TNS, TNC-S, TT) then a fault to earth (you hold of a flex whilst standing on earth for example) could still trip it.

 

[PrenticeBoyofDerry]

fair point!

 

[ebee]

The RCD would probably operate if the appliance is submerged in water unless in a pond formed with a plastic liner and the liner isolated the pond from surrounding earth!

A pal of mine discovered the truth of this when he laid on the side of the pond (true earth) and put his hand in the water containing a faulty pump (Daft twit) - I knew what he was going to say when he started telling me - customer had complained his water pump tripped the RCD on his outside socket but did not trip the RCD when he used an inside socket and his flex extension, therefore the outside socket that I fitted was faulty, the sockets were both on RCD - guess what? his extension was two core .( no earth!).
LOL - he got a belt off the live water

 

[JohnW2]

I would have thought in the case of an unearthed flex, that any fault would be detected as a short between line and neutral, rather than an imbalance/earth leakage.

The scenario people talk about is chopping through a 2-core cable (without an OPD operating, for whatever reason) and then someone picking up the cut end of lead and touching the L (whilst standing on wet soil with bare feet, of course!).

I'm not sure that there is any real excuse other than cost (if cost is an excuse) for allowing 2-core flex for these things. The presence of a CPC has got to increase the chances of some protective device operating if the cable is chopped.

Kind Regards, John

 

[ebee]

a cpc in a flex can not be said to protect the cable when cut and must not be relied upon to do so(if not needed by the appliance) but in practice it might just fortunately do such that in some cases.

Each extra bit affecting your safety is worth considering, so havinga cpc even if the appliance does not require it is probably a better option than not having one

 

[PrenticeBoyofDerry]

In total agreement John and regardless of RCD, would offer another path to earth for disconnection.

 

[JohnW2]

a cpc in a flex can not be said to protect the cable when cut and must not be relied upon to do so(if not needed by the appliance) but in practice it might just fortunately do such that in some cases.

I don't think anyone is suggesting that one should ever 'rely on a CPC' to offer protection to a cable when chopped. However, the presence of a CPC may increase the chances of an OPD operating and is essential to cause an RCD to operate in response to a 'simple cut' (by something which isn't earthed).

Each extra bit affecting your safety is worth considering, so havinga cpc even if the appliance does not require it is probably a better option than not having one

Exactly my point!

Kind Regards, John