Earth Proving device

[WaterSparky]

Hello,

Recently been tasked with putting in a supply for a hot wash (pressure washer) This is quite the beast, diesel powered for the heating of the water and small 1Ph 230V supply for the actual pressure side.

Bit of background, will be supplied via 10A C type MCB fed via 3C 2.5mm2 SWA to a IP67 16A plug and socket with RCD protection on the socket then via some 3C 1.5mm2 H07 to the pressure washer it will be housed inside a small wooden shed (for me to make...) Fed from a board inside, pressure washer will be outside, 10m max.

But I've just been told by one of the old hands, that this needs to supplied via a earth proving socket (Basically checks for the continuity of earth) Never really heard of one before Im un-sure if this is true or not? And couldn't find a reg that applied? Anyone got any ideas/regs or help to say if this is needed or not? or just legacy stuff?

Thanks
WS

 

[Richard Burns]

Whilst an earth proving unit may be a useful addition to the equipment I would not have thought it necessary for your installation.
The only relevant current regulation may be for high protective conductor currents 543.7, but use of earth proving can be useful for the equipment you describe but the RCD should ameliorate some of the risk.

 

[Knobhead]

I’ve worked on many earth proving units. You can still get plugs and sockets with a pilot pin. The pilot has 12V which returns via the cables earth core. Break the earth and the supply switches off. In the later units we also installed a RCD.

I can see why it’s been recommended considering the likelihood of water ingress and cable damage.

There are two methods of wiring them:

The best has a diode between the pilot and earth at the appliance. The proving unit has two relays each with a diode in opposing directions. Under normal conditions half wave DC pulls in the proving relay. If there is short between pilot and earth the fail relay pulls in and latches. So with either a broken core or shorted cores the supply will shut off.

The basic system uses a single relay so there’s no protection against a damaged cable allowing the continuity relay to close. I wouldn’t recommend this method.

 

[WaterSparky]

Thank you Rich & Tony for your answers, I thought it seemed a bit OTT maybe for the installation. Tony, I did wonder what that small pin on the some plugs was cheers!
Rich, cheers for the reg number I will bat that one back and see what he says

The original one that was in the old spot measured the resistance it seemed also not allowing it to be over 1.5 ohms, if i recall correctly.

Thanks guys.

 

[Engineer54]

We used pilot pin safety sockets extensively in the industry i did my training in. Later with the advancement of RCD protection, the pilot safety pin became less and less used throughout the factories....