How can this be

[sometime]

How can this be

The power went out last night but since it came back on I get the readings below.

Between grounded earth & neutral 110 volts

Between grounded earth and live 300 volts

Between live & neutral 226 volts.

Thanks

[Crossy]

Such a large N-E voltage is worrying (and could be damaging to equipment). Did you make the same measurements before the power failure (to be sure this is something new)?

It's possible that the star point ground at the transformer has gone bad, or (worse) one of the phases has been grounded instead.

A few checks you can make before calling the power company.

Verify your ground really is grounded, check the continuity between your main earth bar and the ground rod (power off).

You could also try making the same measurements as before but using a big screwdriver in the lawn as a known good ground.

Connect a small conventional lamp between N and E, does it light, does the N-E voltage go to zero (or near)? Do the same with the lamp between L & E (it should light).

If your ground is good and you get the same results to a known ground (the screwdriver) or the lamp lights, call the power company.

[sometime]

Thanks Crossy, ever since they upgraded the area to 3 phase its gone tits up, we know when they are messing with the lines, the power can range from 226 180 and even down to 30 volt.

I put a screwdriver in the lawn connected from that to N and the conventional lamp NO LIGHT although voltage showing 120

lamp between L & E far too bright voltage 300

Lamp between L & N ok voltage 226

Thanks Sometime

Such a large N-E voltage is worrying (and could be damaging to equipment). Did you make the same measurements before the power failure (to be sure this is something new)?

It's possible that the star point ground at the transformer has gone bad, or (worse) one of the phases has been grounded instead.

A few checks you can make before calling the power company.

Verify your ground really is grounded, check the continuity between your main earth bar and the ground rod (power off).

You could also try making the same measurements as before but using a big screwdriver in the lawn as a known good ground.

Connect a small conventional lamp between N and E, does it light, does the N-E voltage go to zero (or near)? Do the same with the lamp between L & E (it should light).

If your ground is good and you get the same results to a known ground (the screwdriver) or the lamp lights, call the power company.

[Crossy]

Your Neutral to Screwdriver lamp test that resulted in no light, did you check the voltage across the lamp (110V should have put it on dimly)?

I think it's time to call the power company as something is certainly amis.

[CharlesHH]

The phases are mixed up either by accident or just negligence. You have a bad situation and should call power company immediately. Skip doing your own dangerous tests. Turn off all power in your home at the main breaker box, as North Americans call it. Do not turn that power back on until electrical co shows you their correction.

In Nakhon Pathom, sometimes electric co. just changes the phase after a brief outage, which likely is them turning it off and changing the phase and turning back on.

You definitely need company help.

[Crossy]

I think we're both on the same page Charles, there's something well amiss on our OPs supply (although a phase-neutral swap would result in catastrophic voltages for 60% of users, I can't believe that the supply company wouldn't have fixed that by now).

The reasoning behind suggesting some simple tests is that you can get similar readings if you measure a floating (unconnected) ground with a high Z meter, unconnected grounds are not unusual here.

Experience with the PEA shows that if you cannot demonstrate the problem to them it does not exist

EDIT Of course the really scary thing is that if he hadn't made his initial measurements he would never have known about the potential hazards

[wayned]

Experience with the PEA shows that if you cannot demonstrate the problem to them it does not exist

I agree, my voltage cycles from 150 vac to 220 vac every weekday in the afternoon. I have voltmeter connected to the line in my living room. It's definitely cyclic as I can see it going down for about 3 seconds and then back up and then down again. PEA has been out twice and, of course, it never did it when they were here. I think that it's caused by the gravel quarry down abort 1 kilometer away , but everything works fine when they are here.

You need to be able to show them something that they understand, I haven't been able to yet so nothing is resolved.

[Forkinhades]

I have recently experienced a similar situation. Friend was getting shocks off metallic devices. When measured the voltage was between 50V and 130V from earth at the socket to sink or other equipment.

Tested supply at DB, all voltages to earth and each phase 220V, and to each phase to Neutral. We tested from the DB earth bar to the ground nearby as was getting 90V even with main switch off.

The 3 phase DB had the MEN link in place, and a cable going to the earth rod, although we could not see the earth rod.

Disconnected the earth rod cable, and the MEN connection, then got readings of 300V to the earth rod cable , on one phase and 50V on another, and 180V from earth rod cable to earth bar! Somehow the earthrod has become live! This is still being dealt with with the install sparky who knows exactly where the earth rod is buried. I think a call to the PEA is in question indeed.

In the meanwhile can anybody possibly throw some light on this, as it's been a long day and my head is frazzled.

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[sometime]

Very strange, I placed an item on the aircon unit outside and got a slight shock although this unit is turned off on the DB.

All this came into play when all the power went out after a storm on Sunday, not just in our area, (Silverlake)all the way down Sukumvit.

I have recently experienced a similar situation. Friend was getting shocks off metallic devices. When measured the voltage was between 50V and 130V from earth at the socket to sink or other equipment.

Tested supply at DB, all voltages to earth and each phase 220V, and to each phase to Neutral. We tested from the DB earth bar to the ground nearby as was getting 90V even with main switch off.
The 3 phase DB had the MEN link in place, and a cable going to the earth rod, although we could not see the earth rod.

Disconnected the earth rod cable, and the MEN connection, then got readings of 300V to the earth rod cable , on one phase and 50V on another, and 180V from earth rod cable to earth bar! Somehow the earthrod has become live! This is still being dealt with with the install sparky who knows exactly where the earth rod is buried. I think a call to the PEA is in question indeed.

In the meanwhile can anybody possibly throw some light on this, as it's been a long day and my head is frazzled.


Sent from my SM-G900F using Thaivisa Connect Thailand mobile app

[Litlos]

First question: Has it been raining in your area recently? If not (and even if it has) take a walk down to your local transformer and see if there is an earth rod with a cable connected back to the transformer? If so is the earth rod loose in the ground? Maybe check with a screwdriver with insulated handle.

I have seen similar strange readings when up in Isaan particularly during dry weather. The family thought I was a screw loose taking a jug of water down and carefully wetting the area around the earth stake whilst wearing rubber flip flops. I still used a splash technique to drop the water in batches rather than a steady (conducting) stream. All of a sudden the strange effects disappeared though. I waited for the next downpour and went back and stamped the earth tight against the earth rod though.

Still sounds like there is something amiss and PEA are not going to be able to discount your readings as it appears to be a (semi) floating earth.

Cheers

[sometime]

Just an update, after the PEA being notified regarding the fault they arrived two days later, they have just rectified the problem ten days later, I think they went up and down every pole in the area.

Fingers crossed they have not just passed the problem on to someone else.

Thanks to all for your advice