Making sure a circuit is "dead" before doing any work on that circuit

[grs90]

I recently noticed a water leak from inside one of our shower water heaters.  So, I turned off the power at the breaker for that circuit, checked the heater was no longer working when the water flowed which, rightly or wrongly,  indicated to me that the power was off, and then removed the shower unit which was taken to a local shop to get the leak fixed. 

 

Picked up the repaired box today and have just reinstalled it.  Everything now seems OK.

 

However, when reconnecting the wires to the shower I accidentally touched the neutral and earth together.  This tripped the main incoming circuit breaker for the house which surprised me as I’d assumed I was working on a “dead” bit of wiring due to the breaker for the circuit being off.

 

Is what happened when the neutral and earth touched normal or does it mean there is a fault somewhere?  I had always thought that turning off the breakers for a circuit meant it was safe to work on but maybe I should be turning off the main breaker instead of just the one for an individual circuit?

[OneMoreFarang]

If you want to be sure switch everything off at the main breaker.

IMHO especially in Thailand you can't be sure about anything.

Cable colors don't matter, neutral and earth are mixed up, and and and.

[NoDisplayName]

Do you have a multimeter, pen-tester, or some other way to confirm there is no current in the lines?

 

 

[Moonlover]

The first house that I stayed in here in Thailand had the consumer unit wired in such a way that all the circuits still had  'live' going to them, even when the main breaker was off. Even changing a light bulb could be hazardous!

 

And what was really crazy about it was that the circuit diagram stuck to the inside of the cover showed that to be the correct way to do it! So I assume that every house on the mobaam was wired the same.

 

I've always been super suspicious ever since and check all exposed connections with a simple pen tester, at the very least, before touching anything. If in any doubt, bang the main incoming breaker off and even then check again.

[grs90]

14 minutes ago, NoDisplayName said:

Do you have a multimeter, pen-tester, or some other way to confirm there is no current in the lines?

 

 

Hi.  No I am very much an amateur and don't have anything to test a circuit,  I just assumed that "off" at the circuit breaker meant off at  the shower.  Disconnecting the 3 wires in the shower unit and then reconnecting them later is about as complicated as I want to get!  I just want to make sure, if I have to do something similar in the future, that I can do that as safely as realistically possible.

[HauptmannUK]

My wife has several houses that she rents out. Earlier this year the shower packed up in one of the houses. I went to replace it. Turned off power at main breaker in fusebox. Took the precaution of checking for voltage at the shower - it was live!  On further investigation the shower was found to be wired direct to incoming mains from the meter!  There are two showers in the house and both the same.  Fitted by local 'electrician' when the house was built 8 years ago.  All sorted now with breakers...

[Celsius]

Just another statistic on thaiger very soon.

 

Mind boggles why would you even attempt to do something like this yourself.

[Crossy]

16 minutes ago, grs90 said:

 No I am very much an amateur and don't have anything to test a circuit,  I just assumed that "off" at the circuit breaker meant off at  the shower.

 

As an absolute minimum go and spend 50 Baht on a neon screwdriver, trying to work on 'lectrics here "blind" is definitely risky.

 

"Proving dead" is an incredibly difficult thing to guarantee absolutely, too many (even pros) have died when a dead circuit wasn't!!! 

 

Test first on a known live circuit, then your "dead" circuit. Always assume any wire is live (even the "neutral" or "earth"), even if the main breaker is off. You wouldn't be the first to find their shower is till "on" coz the sparks tapped into the incoming supply!

 

Get a local sparks to do the job for you.

[Crossy]

51 minutes ago, grs90 said:

However, when reconnecting the wires to the shower I accidentally touched the neutral and earth together.  This tripped the main incoming circuit breaker for the house which surprised me as I’d assumed I was working on a “dead” bit of wiring due to the breaker for the circuit being off.

 

This would trip an RCD / RCBO, nothing to worry about, your circuit is still dead.

 

But go and buy that neon and a cheap multimeter.

[OneMoreFarang]

9 minutes ago, Crossy said:

"Proving dead" is an incredibly difficult thing to guarantee absolutely, too many (even pros) have died when a dead circuit wasn't!!! 

If you think all is dead, then touch all the wires.

Are you scared to do that? Remember, it's all off.

What I do sometime is to touch wires with a swipe of my hand. If they are life I will know. But because I swipe my hand the contact will be only for a fraction of a second, no big risk.

After I did that, I feel more confident that the wires are really dead.

[BritManToo]

1 hour ago, grs90 said:

However, when reconnecting the wires to the shower I accidentally touched the neutral and earth together.  This tripped the main incoming circuit breaker for the house which surprised me as I’d assumed I was working on a “dead” bit of wiring due to the breaker for the circuit being off.

 

Is what happened when the neutral and earth touched normal or does it mean there is a fault somewhere?  I had always thought that turning off the breakers for a circuit meant it was safe to work on but maybe I should be turning off the main breaker instead of just the one for an individual circuit?

You are correct assuming the wiring has been done correctly.

However if the live and neutral were reversed before the breaker, what you thought was 'neutral' would be in reality live and permanently connected.

 

MY house had live and neutral reversed coming out of the PEA meter, neutral was constantly live until I had it fixed. Sam as you, I found it (with a test screwdriver) when installing a shower heater on the first day I moved in the new build.

 

Mains testing screwdrivers are well worth the 20bht.

Always touch every bare wire with one, before you put your hands on it.

Edited May 29, 2023 by BritManToo

[Crossy]

Just now, OneMoreFarang said:

If you think all is dead, then touch all the wires.

Are you scared to do that? Remember, it's all off.

What I do sometime is to touch wires with a swipe of my hand. If they are life I will know. But because I swipe my hand the contact will be only for a fraction of a second, no big risk.

After I did that, I feel more confident that the wires are really dead.

 

I'd rather use a neon or a known good non-contact tester, I've had too many buzzes in my life ???? 

[NoDisplayName]

29 minutes ago, grs90 said:

Hi.  No I am very much an amateur and don't have anything to test a circuit,  I just assumed that "off" at the circuit breaker meant off at  the shower.  Disconnecting the 3 wires in the shower unit and then reconnecting them later is about as complicated as I want to get!  I just want to make sure, if I have to do something similar in the future, that I can do that as safely as realistically possible.

NONONONONONONOOOOOOOOOOOO!!!!

 

You're working on a building constructed by local dudes who may or may not be literate, and only on a good day may be half-sober.  They don't label, they don't worry about matching color codes, they're not interested in building codes or standards, and they use whatever is at hand.

 

NEVER assume the circuit breaker is correctly labeled, or that the wires are correctly connected, or that the ground is grounded.  Assume nothing.  Double check everything.

 

First stop, watch some Youtube videos on how to check circuits.  Then stop by Mr. DIY and get you some inexpensive test equipment.

[Robin]

I have a simple rule;  never trust any Thai electrics that you have not wired and checked yourself.  

In particular, do not trust simple on/off wiring.  Just because the light is off does not mean the supply is off, or safe.  Thai eletricians have no qualms about witching the neutral (return) supply.  "What's wrong with that, the light still switches off"   "This is done Thai style, not as in Farang  places"

Second rule is not to trust wiring colour codes in Thailand.  Wires come in many colours and even given a "correct" blue/brown/ Green-yellow coloured cables, there is no reason to believe that the wires are connected correctly.

Buy a Neon Tester and check every time you work on some-one else's wiring.  

I am amazed that there are so many Thai Electricians still living.

[sometimewoodworker]

There is one fun thing that I don’t think anyone has pointed out.

Just because you have done everything right and all the circuits have breaker’s on the correct live line so that when off no circuits has a live line doesn’t stop the PEA switching the line and neutral connections before you supply. It has happened and enough times for it to be a standard check.

 

Bottom line. NEVER work on electrics without checking that they are completely dead and don’t assume that another house may not suddenly have a fault that energies the neutral. 

[OneMoreFarang]

1 hour ago, Crossy said:

I'd rather use a neon or a known good non-contact tester, I've had too many buzzes in my life ???? 

Yes, you are right.

My comment was about the time after you checked with a test screwdriver and/or a multimeter.

[Crossy]

16 minutes ago, OneMoreFarang said:

Yes, you are right.

My comment was about the time after you checked with a test screwdriver and/or a multimeter.

 

Yeah, I still avoid touching the bare copper even when I know it's dead!

[OneMoreFarang]

2 minutes ago, Crossy said:

Yeah, I still avoid touching the bare copper even when I know it's dead!

That is kind of my point. If you touch it once intentionally then you know you can touch it without problem.

That doesn't mean you have to touch the copper, but "you" are not afraid anymore that it could happen. 

[grs90]

Well thanks for all the comments and I agree that I should have tested for a live connection rather than assuming it was dead just because the circuit breaker was off.  Lesson learned and the tester is now on the list for my next visit to Mr DIY!

 

[billd766]

3 hours ago, grs90 said:

Hi.  No I am very much an amateur and don't have anything to test a circuit,  I just assumed that "off" at the circuit breaker meant off at  the shower.  Disconnecting the 3 wires in the shower unit and then reconnecting them later is about as complicated as I want to get!  I just want to make sure, if I have to do something similar in the future, that I can do that as safely as realistically possible.

I use a SAFE-T-CUT from the incoming power and that feeds the main breaker box. By using the SAFE-T-CUT I can disconnect its output before the main circuit breaker box.

 

I also know that no showers, a/c etc is connected to the main PEA input, as I can physically see it.

 

When I kill that I know the whole house is dead, electrically speaking, and I do have a small multimeter that cost about 1,000 thb, and proved it.

 

Electricity is unseen, sneaky, usually silent and can kill you if it bites you.

Edited May 29, 2023 by billd766
added extra text

[billd766]

As a coincidence I wanted to change a light switch in my work area which is powered from the small house.

 

I got my wife to turn off the SAFE-T-CUT while I changed the switch. It was still live and I had the wrong switch anyway.

 

I abandoned the job and she turned the power on but nothing happened. No power to the small house at all.

 

She called out the guy that does the jobs I can't do any more and the fault was in the main breaker in the main circuit box which has been there some 19 years.

 

She gave him some money to get another and I had a vague memory of another box from long ago that I part cannibalised. Luckily the main switch was still there so we used that, which worked.

 

I still have no idea why the switch was live though.