Safe-t-cut

[PEP]

Hello everybody. I would like some advice from Qualified Electrical Personnel.

I have an electrical engineering background so I can understand the workings of a Safe-T-Cut core balance ELCB.

However I have identified a circuit in my home installation (the "normal" Thai two wire system.) that frequently causes tripping of the device. Obviously there is an earth fault that needs attention.

This, quite strangly, still occours despite the single pole circuit breaker for that circuit being open. I have phisically and electrically checked that there is correct connection for the Active and Neutral and that the circuit breaker is OK.

The main Neutral at my distribution board is not earthed.

I have checked and my conclusion is that the "floating" system Neutral has a potential of some volts above Earth.

My question now is that if I solidly "Earth" that Neutral will it possibly carry the whole village system Out-Of -Balance current? I do not wish to cause a major incident in my installation.

[bangkokumpalumpa]

this is an interesting one!!

I am going to leave this reply up to the others as they have lots more experience with village systems!

I have seen just the other day a neutral wire lighting up a neon test lamp, I have now seen this on two systems, one in an apartment that when all the safety cut and the mains breaker were off the neon was lighting up on the neutral.

this was tripping the safety cut, some wonderful Thai sparky had taken the money to install a new safety cut then found that it kept tripping so set it to direct, wow that worked!!!!

the end result to this is was that a neutral fualt in the wiring where another apartment has its neutral wired to this board, the whole 5 story block is a mess!!

the apartment managers were saying that this is one of the only old buildings about the place that has an earth system, this had me laughing my but off, yes it has an earth system there was the main earth wire going to the load center but there was not one wire contected to the earth bar!

welcome to the world of Thai electrical systems!

Edited October 31, 2009 by bangkokumpalumpa

[Crossy]

Interesting indeed.

Firstly, do NOT ground your neutral unless you are CERTAIN that MEN / PME is implemented in your village, you may end up with some interestingly large currents in the link.

Tripping even with the breaker open suggests a neutral => ground fault, try disconnecting the neutral of the offending circuit (with the breaker open) and see if the problem goes away. If it does you're looking for a neutral => ground fault.

You may want to measure the potential that your neutral is above ground, a big screwdriver in the lawn will provide a decent ground reference for this test.

[Daffy D]

Don't know if it's relevant to this particular post but some time ago an "Electrician" installed meters in some rooms near me. The new main switch box for all the rooms was on my outside wall (rented apartment) and I noticed a wire coming from it to ground.

Thinking this was a bit unusual (for Thailand) I had a look inside the box and saw that the "Earth" was connected directly to the neutral cable. and lit up my neon tester. I also checked with the tester right at the point of the connection to the grounding rod and it still lit up.

The thing was that it was my grounding rod that I used for all the computer stuff and I was now getting the neon test light up on my computer chassis.

I thought this was not right but it seemed to work and as we moved out soon anyway didn't worry about it.

[PEP]

Interesting indeed.

Firstly, do NOT ground your neutral unless you are CERTAIN that MEN / PME is implemented in your village, you may end up with some interestingly large currents in the link.

Tripping even with the breaker open suggests a neutral => ground fault, try disconnecting the neutral of the offending circuit (with the breaker open) and see if the problem goes away. If it does you're looking for a neutral => ground fault.

You may want to measure the potential that your neutral is above ground, a big screwdriver in the lawn will provide a decent ground reference for this test.

Thanks Crossy for your very sage advice. I have followed many of your previous posts with interest and despite my lenghty service in "the game" I have learnt much from you. Perhaps in my previous post I should have mentioned that the Neutral to Earth potential varies between 18 and 22 volts, hence my hesitation in grounding the Neutral. Thanks for your warning.

The offending circuit is an underground cable to a water fountain pump. This morning I dug up the lot and did find a bare spot in the insulation. No doubt caused by the "Keen Gardner's" (wifey's) efforts. All OK now with extra mechanical coverage (bricks).

Re Bangkokumpalumpo's post:-

I recently corrected a village installation similarly connected(?) where the Active and Neutral had been interposed when the Safe-T-Cut had been retro installed by a "Rice Farmer Electrician".