An Electrical Q

[lujanit]

I am hoping that there is an electrician out there who can help me solve a problem.

When our house went under we lost power in a couple of circuits. I managed to get two of them working again but the third is causing me some frustration. Firstly this circuit seems to cover half the house. There are power points and lights upstairs and downstairs on it as well as the water pump.

As soon as I switch the circuit breaker to ON it immediately trips out the main breaker. So I disconnected the water pump completely but the problem still exists. I then went and checked every outlet to check if there was water in them and yes one had a fair bit of water so I completely disconnected that as well. Still no joy. I am at a loss as what to do now. Any ideas would be welcome. Obviously getting an electrician is out of the question as our moo baan is completely flooded.

TIA

[ShopBoy]

Do you have doorbell if yes check your doorbell.

The doorbell might be connected somewhere along the circuit line and runs on the ground. If yes try to isolate it and see what happens.

[VocalNeal]

First priority which you have probably done already is to wire the water pump to a working circuit with an extension cord.

Is it possible you have missed an outlet. Car port, outside etc. Maids quarters? Connection for garden lights that you have never used?

Sorry I can't be more specific.

Edited November 14, 2011 by VocalNeal

[impulse]

Diagnosing a problem like that over the internet isn't too safe for you.

If it were me, I'd go buy a $10 VOM meter (Volt-ohm-milliamp meter) at Home Pro or just about any hardware store and start looking for my short with no power on at all. If I couldn't find the short without turning on the power, I'd seriously consider making due without the power for a few more days. But then, I'm a coward who designs and sells 3000 volt pump systems for a living- and they don't scare me nearly as much as household wiring in Thailand..

There's also the possibility that the main breaker is no good. If it has a higher capacity than the branch circuit breaker, the branch circuit breaker (lower amp capacity) should be the one that trips. If the main breaker isn't bigger than the branch breakers, there's something fundamentally wrong. Breakers do wear out and go bad- and they're only a few bucks so it may be worth a shot.

And if you have a GFI (ground fault interrupter) on one or more of the circuits, that adds another level of complexity to your troubleshooting.

One last edit- your problem may be in one of the 2 circuits that is working. It could be a short that leaks enough amperage to almost trip the breaker, then when you add the third circuit, you add enough load to trip it. You may want to test the third circuit by itself and see what happens. If I've given you the idea that it could be complicated, I've succeeded.

Edited November 14, 2011 by impulse

[lujanit]

Do you have doorbell if yes check your doorbell.

The doorbell might be connected somewhere along the circuit line and runs on the ground. If yes try to isolate it and see what happens.

The doorbell is indeed on that circuit. I pulled it out and changed the connectors as they were pretty cruddy. I am unable to trace the wiring as it all runs underground below concrete.

First priority which you have probably done already is to wire the water pump to a working circuit with an extension cord.

Is it possible you have missed an outlet. Car port, outside etc. Maids quarters? Connection for garden lights that you have never used?

Sorry I can't be more specific.

Yes that is one of the first things I did. Nada. The wiring to the pump is now disconnected so the pump cannot be the problem.

Diagnosing a problem like that over the internet isn't too safe for you.

If it were me, I'd go buy a $10 VOM meter (Volt-ohm-milliamp meter) at Home Pro or just about any hardware store and start looking for my short with no power on at all. If I couldn't find the short without turning on the power, I'd seriously consider making due without the power for a few more days. But then, I'm a coward who designs and sells 3000 volt pump systems for a living- and they don't scare me nearly as much as household wiring in Thailand..

There's also the possibility that the main breaker is no good. If it has a higher capacity than the branch circuit breaker, the branch circuit breaker (lower amp capacity) should be the one that trips. If the main breaker isn't bigger than the branch breakers, there's something fundamentally wrong. Breakers do wear out and go bad- and they're only a few bucks so it may be worth a shot.

And if you have a GFI (ground fault interrupter) on one or more of the circuits, that adds another level of complexity to your troubleshooting.

One last edit- your problem may be in one of the 2 circuits that is working. It could be a short that leaks enough amperage to almost trip the breaker, then when you add the third circuit, you add enough load to trip it. You may want to test the third circuit by itself and see what happens. If I've given you the idea that it could be complicated, I've succeeded.

I appreciate your concern regarding diagnostics over the net. Thanks. I should have mentioned that I changed the breaker for another one which I knew was okay and the problem persisted. So not the breaker. There are 10 circuit breakers plus the main breaker which is 50 amp. Also there is a GFI (60 amp). What is interesting is that it isn't the 50 amp main breaker that trips but the GFI.

I agree what you say about thai household electrical wiring. When we had a large air con installed last year it kept tripping the main breaker. There were guys here from Home Pro and Hitachi trying to work out why on several occasions. They couldn't so have a guess what they did? They bypassed the board altogether and wired the air-con into the street supply side of the board. They said it would be fine!

[soundman]

I am moving this to the DIY forum where there are quite a few members with good understanding of electricity, applications, problem solving and safety.

[paulchiangmai]

Do you have doorbell if yes check your doorbell.

The doorbell might be connected somewhere along the circuit line and runs on the ground. If yes try to isolate it and see what happens.

The doorbell is indeed on that circuit. I pulled it out and changed the connectors as they were pretty cruddy. I am unable to trace the wiring as it all runs underground below concrete.

First priority which you have probably done already is to wire the water pump to a working circuit with an extension cord.

Is it possible you have missed an outlet. Car port, outside etc. Maids quarters? Connection for garden lights that you have never used?

Sorry I can't be more specific.

Yes that is one of the first things I did. Nada. The wiring to the pump is now disconnected so the pump cannot be the problem.

Diagnosing a problem like that over the internet isn't too safe for you.

If it were me, I'd go buy a $10 VOM meter (Volt-ohm-milliamp meter) at Home Pro or just about any hardware store and start looking for my short with no power on at all. If I couldn't find the short without turning on the power, I'd seriously consider making due without the power for a few more days. But then, I'm a coward who designs and sells 3000 volt pump systems for a living- and they don't scare me nearly as much as household wiring in Thailand..

There's also the possibility that the main breaker is no good. If it has a higher capacity than the branch circuit breaker, the branch circuit breaker (lower amp capacity) should be the one that trips. If the main breaker isn't bigger than the branch breakers, there's something fundamentally wrong. Breakers do wear out and go bad- and they're only a few bucks so it may be worth a shot.

And if you have a GFI (ground fault interrupter) on one or more of the circuits, that adds another level of complexity to your troubleshooting.

One last edit- your problem may be in one of the 2 circuits that is working. It could be a short that leaks enough amperage to almost trip the breaker, then when you add the third circuit, you add enough load to trip it. You may want to test the third circuit by itself and see what happens. If I've given you the idea that it could be complicated, I've succeeded.

I appreciate your concern regarding diagnostics over the net. Thanks. I should have mentioned that I changed the breaker for another one which I knew was okay and the problem persisted. So not the breaker. There are 10 circuit breakers plus the main breaker which is 50 amp. Also there is a GFI (60 amp). What is interesting is that it isn't the 50 amp main breaker that trips but the GFI.

I agree what you say about thai household electrical wiring. When we had a large air con installed last year it kept tripping the main breaker. There were guys here from Home Pro and Hitachi trying to work out why on several occasions. They couldn't so have a guess what they did? They bypassed the board altogether and wired the air-con into the street supply side of the board. They said it would be fine!

Interesting how they bypassed your breaker box when installing the air conditioner, a few years ago I had an air conditioner installed in a bedroom and at the same time the installers put a main switch for the A/C on the wall. A short while later I decided to add an additional power point from this A/C main switch, I turned everything off at the breaker box and took the cover off the main A/C switch previously installed by the A/C installers, I put my meter on the wires to make sure it was all dead and would you believe it was all alive, the sons of bitches had bypassed the breaker box and luckily for me my habit of always using a meter paid off. I called the installers back and this time they did it properly.

[Crossy]

If the GFI (RCD) is tripping it's almost certainly wet still in the circuit somewhere.

With the breaker off, remove the covers from all the outlets and let it all dry out naturally, if you have a working outlet and a hair dryer you can help things along a bit, but there's no real substitute for a bit of patience.

[Forkinhades]

You have a fault to earth, caused by the flooding, thank goodness you had a GFI, (RCD), or you could have been in much more serious trouble.

Easiest, and safest solution, is that you have to wait until everything dries out.

With the right test equipment and knowledge you can identify EXACTLY where the fault(s) is (are). Some cheapo meter for $10 will not give you the information required to pinpoint it. The correct equipment will be in the region of 55,000 to 60,000 baht.

Most circuits are just radials her in LOS, ie do not have a return cable going back to the DB

so if you could identify what outlets are on what circuits, then after switching OFF you could go to a midway point, and disconnect one of the pairs of cable, then try and turn on again, this will eventually narrow down where the fault(s) is (are) but this is a very timely exercise.

Best left the to the experts

the GFI (RCD) will trip at 30 milliamps with a fault to earth (in this case water), but has an overload of 60 amps.

Without this device installed, you would have effectively made live all water in your dwelling!!!

[ShopBoy]

The doorbell is indeed on that circuit. I pulled it out and changed the connectors as they were pretty cruddy. I am unable to trace the wiring as it all runs underground below concrete.

The wiring would definitely have to appear somewhere to tap on the power. You would need to find where does that wiring goes to and try isolating that particular wiring again.

Does your car porch still have any low lying sockets or lighting that uses electrical ? Are the wiring looping from one sockets to another ?

Edited November 14, 2011 by ShopBoy

[electau]

Locate the circuit that is tripping the RCD. You have an earth fault caused by water in a fitting. Leave this circuit off and allow fittings to dry out.

An RCD will trip on earth fault between 50% and 100% of rated current in mA.

If the circuit still trips you will have to use an 500V insulation tester and split the circuit until the fault is found. Insulation between L and E. and N to E. You will have to disconect the circuit to do this. You may have to obtain the services of an electrician to do this test.

Check to see if there are any fittings still under water first.

　

　

　

[bankruatsteve]

I suggest you also - first disconnect power - pull out all receptacles, junction boxes, switches, etc.,. that went under water. Clean out any muck, dry any visible dampness, and make sure wire fittings still tight. Testing for no continuity (ohm meter) between L/N/E would be helpful. Then replace or reinstall if tests OK. Even after drying, a muck filled receptacle will likely trip a RCD.

[impulse]

You guys correct me if my math is bad, but to get 30 mA (0.030 Amps) to leak from a 220 Volt system and trip the GFI, you need your insulation resistance to drop to 220/.030= 7300 ohms or less. Even my cheapo Chinese digital VOM's will find that short.

I don't think you need a $2,000 set of equipment, or even a $200 megger to identify that kind of ground fault. In fact, I have to remind our service guys occasionally to pull out their Flukes' when their meggers show zero megs. The last time that happened, we found 72,000 ohms on the Fluke, though the megger went to zero.

I stand by my recommendation that an inexpensive VOM meter is the most cost effective tool for the job- with the power turned off. More and better gear is great and speeds thing up, but not necessary if you're willing to take the diagnosis in steps to isolate the problem. As folks have said, it sounds like a wire or two is still wet and leaking current to ground. The GFI was probably doing exactly what it was designed to do and may have saved someone from a nasty- even tragic result.

Still, I do recommend getting a professional out there. Here's why:

http://www.armytimes.com/news/2009/02/ap_sailor_electrocuted_020309/

[InterestedObserver]

In fact, I have to remind our service guys occasionally to pull out their Flukes' when their meggers show zero megs. The last time that happened, we found 72,000 ohms on the Fluke, though the megger went to zero.

Certainly a standard 500 volt megger will read zero megohms while the 9 volt Fluke reads 72,000 ohms. Nothing unusual there. Not the same test conditions.

Edited November 15, 2011 by InterestedObserver

[Forkinhades]

my old megger set to ohms would read that

[InterestedObserver]

my old megger set to ohms would read that

True, but then it is no longer a megger, but a VOM with an ohms scale.

[Forkinhades]

no it is an high reading ohm meter when set to meg ohms, and a low reading ohm meter when set to ohms

Edited November 15, 2011 by Forkinhades

[InterestedObserver]

no it is an high reading ohm meter when set to meg ohms, and a low reading ohm meter when set to ohms

The open circuit test voltages are normally not the same for the two (high/low) scales. A decent megger would use at least 500 VDC to test insulation resistance of type NYY, 750V cable. You cannot do that with the equivalent of a VOM.

[Crossy]

Whilst a regular meter is far better than nothing, the correct equipment (in this case a Megger) is easier and more reliable.

The problem with damp induced leakage is that it is not like a simple short, the leak is distributed around the circuit and may become undetectable with a normal meter when the circuit is split in order to locate the problem, the Megger will do the job easily.

To our OP.

While you have the outlets open look for Thai-style taped joints which may be retaining water, open them up and let them dry out thoroughly.

To be honest, the best solution would be to isolate the offending circuit and use traily leads from a working circuit until things have totally dried out. At this point you really will need an insulation tester if you want to do a thorough test.

[electau]

A VOM test voltage is 300mV. An insulation tester is 250/500V. One does not use a VOM to check insulation resistance.

Edited November 17, 2011 by electau

[Forkinhades]

^ totally agree with crossy and electau on their last comments!

[Crossy]

A simple insulation tester can be got for less than 5k Baht (from Electronics Source), probably cheaper if you shop around a bit.

EDIT NPE have this one http://www.mynpe.com/more.php?data=028220009001 for 2900 Baht.

As a compliment to a simple DMM a good investment for those who have been flooded.