Strange RCD fault III

[securespark]

Had an odd one today.

RCD tripping when any item is plugged into a socket outlet.

Was an RCD incomer, so no wires crossed.

EFL ok, RCD testing OK in isolation, Ze OK.

Turned out it was a L-E / N-E fault with a gas cooker.

 

[Adam_151]

TN-C-S ?

 

[slider45]

EFL ok, RCD testing OK in isolation, Ze OK.

Turned out it was a L-E / N-E fault with a gas cooker.

Sounds interesting but means nothing. could you elaborate for those of us still learning?

If the cooker is at fault, why would plugging another appliance trip? And what was the fix?

Cheers!

 

[securespark]

Adamski. Top-hole, old chap!

It was indeed PME.

RCD's seem to often present strange faults on TN-C-S.

Slider- the fix was unplugging the faulty oven!

 

[RF Lighting]

It seems that all you do is cure arkward RCD faults just recently.

 

[securespark]

Tell me about it!

Because muggins here has the experience, he gets the fault-finding...

Still, don't feel too sorry for me: I love it really!

I hate inanimate objects getting the better of me & really love getting my teeth into a good fault that has baffled everyone else!

 

[Adam_151]

RCD's seem to often present strange faults on TN-C-S.

Without any load in the installation, neutral and earth are at the same potential on TNC-S, as soon as you plug something in, there is voltage drop on the neutral between where the earth branches off and the point of the fault, it only needs to rise a little above the earth to drive 30ma across the N-E fault.

With TNS it would have perhaps been easier to track down a neutral-> fault as it would likely trip it without any extra load becuase its volt drop on the neutral all the way back to the star point that matters in this case and there is bound to be load somewhere on the local lv distrubutuon system (and the chances of it being perfectly balanced at any time are... slim)

With TT its generally similar to TNS, but you need more voltage drop to drive 30ma through the fault (ohms law) due to the higher impedance earth path, also voltage drop in the earth can be quite significant due to its higher impedance, so someone testing EFLI somewhere else can cause a significant volt drop across the suppliers ground electrode which may be upto 21 ohms)


TNC-S is a rather horrible system in general in my opinion, but I admit it does have its place and works pretty well for most houses, and does at least have the fact that EEBADs works correctly without RCDs going for it I suppose its just the rich that present issues, you have to think carefully when you start adding pools and stables....

 

[ricicle]

I suppose its just the rich that present issues, you have to think carefully when you start adding pools and stables....

Or if you have enough bunce to have your own personal petrol station