knowledge become a bit patchy please help

[Andy 4482]

hello everyone, iv been doin re wires near enough constantly over past few years so my knowledge has suffered a bit so just tryin to brush up in some areas. 1,my understanding on how a rcd operates is that basically a current goes out on phase and if there is an in balance on what comes back on neutral this will cause trip indicating likely cause earth leakage. this being the case can anyone explain why shorting neutral to earth on an rcd causes it to trip when there is no load on ( current being used) .ie if u was to have an rcbo with nothing connected into it and u turned it on and then was to short the neutral terminal to the earth bar it would trip . why? there is no load. 2,iv recently run a cable ready to feed a garage the cable needs to go underground , dont particully want to joint my pvc cable to an armoured cable , so can i use the pvc cable underground if so what is the quikest cheapest way to do this and still lie within regulations . cheers

 

[telectrix]

1.RCD. shorting N/E will cause current to flow through the N of the RCD. as there is 0 current in the L of the RCD, inbalance = trip.

2. you can run T/E ubderground in conduit, but far better IMO to connect to SWA in an adaptable box.

 

[Andy 4482]

so where is the current coming from onto the n when earth is at zero potential and there is no load ?. will i get away with plastic conduit or need to be metal ? cheers

 

[gnselectricals]

Rcd tripping is due to the load on all the other circuits that are still connected, touch N-E on an isolated circuit and they are common to all other circuits so some current will flow to earth hence RCD trips
I'd 2nd SWA option as well much better
Regards Gram


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[telectrix]

plastic is OK buried sensibly with warning tape, but SWA is far easier than cutting tube, fitting bends/elbows etc. possibly work out cheaper in the long run.

 

[lmdawson]

Just wandering why the cable has to go underground? why not run it in pvc conduit at garage height?

 

[lmdawson]

or possibly get some flexible conduit/ copex? you can get metal copex covered in rubber both strong and watertight...