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From where is this stray 14VAC coming and what can I do about it?


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This started when my wife told me one evening that she had just gotten an electrical shock when she touched the shower head and then when she turned-off the shower valve. I checked both with my little pen voltage meter and it showed 12+VAC at both.

 

 

 

My set-up is, the Mains are split into three consumer units, two in the house and one in the parking area. The two in the house are about twelve years old with no connection between the Nbar and the Gbar, the Mains going directly to the main CB. The one in the parking is newer with the Main L going directly to the main CB and the Main N going to the Gbar and then to the main CB. I have a heaver gauge Ground (Earth) wire going from a two meter copper ground rod driven between the house and septic tanks and then that wire is split to each of the CU's Gbars. All of my receptacles and main appliances are attached via ground wires to their respective CU Gbars.

 

Quick checks that evening with my little pen VM showed 220VAC on all Ls and 12+VAC on all Ns, including those at the Main CB s, and all Gs including those inside the shower unit. Further checking with the multi-meter the next day showed:

 

with all Main CB s on or off, ~225VAC between Ls and Ns at all CU s and the same between Ls and Gbars at all CU s. No VAC between Ns and Gs anywhere (as they are connected in the parking CU but still 12+ on both with the pen VM.). With the heavier G (Earth) detached from the CU Gbar in the parking area and all of the Main CB s off, the reading between Ls and Ns were the same as above. The difference in the readings was that I had 14 to 15 VAC between the Ns and heavier G wire at the CU in the parking area and 14 to 15 VAC between N and Gbars at the other CU s. The shower unit showed 14 to 15 VAC between N to G, and, 11 to 12 VAC N to the shower head and shower valve (with main and dedicated CB s off.)

 

All this is to say that it appears that I have 14 to 15 VAC coming-in through my Main N and grounding does not mitigate it. As a note, the power pole from which my meter originates has a cable running down the back from somewhere above into the ground.

 

Suggestions please.

vac pen on shower.jpg

cu in parking.jpg

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Number one is that you probably won't feel 12V AC, it's certainly not hazardous.

Number two, at low voltages those pen units are less than accurate.

 

Try measuring (with a proper meter) between neutral and a known ground (not your rod, leave that connected, stick a big screwdriver in the lawn).

 

You appear to be wired as MEN, so as long as your rod is good you should get very little N-E.

 

I assume that one of the green wires is the rod, the other is the water heater.

 

Very often those "tingles" are actually just muscular, I get them in our shower which is on 2m of plastic pipe from a properly grounded water heater.

 

Does your shower heater have metallic pipe fittings for the shower head, most are plastic these days.

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Ah, you say "CUs", multiple consumer units? Are their ground bars bonded to each other? Each one have it's own rod?

 

Please post a sketch of how everything is hooked up.

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2 hours ago, ellobo said:

As a note, the power pole from which my meter originates has a cable running down the back from somewhere above into the ground.

 

That will be the N-E bond, good that means you actually have MEN implemented in the street.

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2 hours ago, ellobo said:

As a note, the power pole from which my meter originates has a cable running down the back from somewhere above into the ground.

As was the case on the power pole outside of my house here, and when I investigated it, the cable was wound around something akin to a 6 inch nail and pushed into the ground....duh?

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11 minutes ago, xylophone said:

As was the case on the power pole outside of my house here, and when I investigated it, the cable was wound around something akin to a 6 inch nail and pushed into the ground....duh?

 

Yeah, it should be a proper rod, report to your local PEA office.

 

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1 hour ago, Crossy said:

Does your shower heater have metallic pipe fittings for the shower head, most are plastic these days.

Even with a plastic pipe to the shower head, if there was a fault wouldn't you get a shock through the flow of water?

 

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Thank you for your responses.

 

2 hours ago, Crossy said:

Number one is that you probably won't feel 12V AC, it's certainly not hazardous.

I am not disagreeing with you, however, if you can convince the wife of that, problem solved. * laughing *

 

2 hours ago, Crossy said:

Number two, at low voltages those pen units are less than accurate.

I realize that. Please note from my post, “Further checking with the multi-meter the next day showed:  ….. 14 to 15 VAC between N to G”

 

2 hours ago, Crossy said:

 

Try measuring (with a proper meter) between neutral and a known ground (not your rod, leave that connected, stick a big screwdriver in the lawn).

You like your screwdrivers in the lawn don't you? * laughing again * Hay, I have read every post in this section that may give a clue to my problem, hence your previous mention of screwdrivers was noted.  But I agree that all possibilities should be checked and I should have done so already, so in the morning.

 

2 hours ago, Crossy said:

 

You appear to be wired as MEN, so as long as your rod is good you should get very little N-E.

I will double check in the morning but is 14 to 15 very little?  Seems to me that it should be close to zero.

 

2 hours ago, Crossy said:

 

I assume that one of the green wires is the rod, the other is the water heater.

The photo is of the newer CU in the parking area, sorry I should have labeled it, but yes. The CU in the house with the water heater is a twelve CB unit with two water heaters, each with its own ground back to the Gbar.

 

2 hours ago, Crossy said:

 

Very often those "tingles" are actually just muscular, I get them in our shower which is on 2m of plastic pipe from a properly grounded water heater.

 

Does your shower heater have metallic pipe fittings for the shower head, most are plastic these days.

This could be another thread but all of the hose connections in the water heater are plastic but there is still a 11 to 12V charge on the shower head and the shut-off valve measured with the multi meter (to N.)

 

 

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2 hours ago, xylophone said:

As was the case on the power pole outside of my house here, and when I investigated it, the cable was wound around something akin to a 6 inch nail and pushed into the ground....duh?

Was this causing you any problems?

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1 hour ago, Crossy said:

 

Nope.

 

Pure water (tap water is pretty pure) is a very poor conductor of electricity it just doesn't have the free ions, it needs dissolved salts (like from your skin) to become conductive to any appreciable degree. 

The key here is "pure water."  We are on a well with very hard water.  A little demonstration.

water test.jpg

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13 hours ago, Daffy D said:

Even with a plastic pipe to the shower head, if there was a fault wouldn't you get a shock through the flow of water?

 

Not if the shower unit is grounded to the above system earth and the internal element sheath is grounded also within the fitting.

It is possible to get a slight rise in potential on the neutral/earth as one gets further away from the MEN.

Even so, most of the units I've seen have a local safety cut in the unit themselves.

 

Best option with the installation is have individual safety cut combos ( circuit breaker/ safety cut) on each circuit radiating from the final sub-circuit switchboard.

Edited by bluejets
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11 hours ago, ellobo said:

Was this causing you any problems?

Actually I never found out what it was for!! However I did have to install an earth rod as no earth in the place, in order to stop getting shocks off the kitchen appliances, and this worked.

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15 hours ago, xylophone said:

As was the case on the power pole outside of my house here, and when I investigated it, the cable was wound around something akin to a 6 inch nail and pushed into the ground....duh?

As with many construction things in the Kingdom, this is non-functional, for appearance only.

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off the top of my head  ... dont use the tiny tools .. not accurate    second find an electrician let them do it 

 

CAREFUL   ask here for recommendations for GOOD KNOWLEDGEABLE  electricians      

most i run into do not even know what how grounds work  

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16 hours ago, Crossy said:

Number one is that you probably won't feel 12V AC, it's certainly not hazardous.

Number two, at low voltages those pen units are less than accurate.

 

Try measuring (with a proper meter) between neutral and a known ground (not your rod, leave that connected, stick a big screwdriver in the lawn).

 

You appear to be wired as MEN, so as long as your rod is good you should get very little N-E.

 

I assume that one of the green wires is the rod, the other is the water heater.

 

Very often those "tingles" are actually just muscular, I get them in our shower which is on 2m of plastic pipe from a properly grounded water heater.

 

Does your shower heater have metallic pipe fittings for the shower head, most are plastic these days.

My experience is very limited but in the past when a plastic fitting/valve is introduced into the system it has a metal strip connecting the two threaded ends. Probably bad earthing with all the plastic pipes etc.

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Whilst there are many respondents to this subject it is worth while understanding some basics.

1: Electricity and wet areas don't mix well.!

2: Effective earthing in these areas is essential.

3: Multiply earthed neutral system, with or without ELCB (safety switch) is appropriate.

Effective earthing in Thailand is often overlooked.

The length of an earth spike is irrelevant, it's effectiveness is.!

A 60ft earth spike into dry ground is almost as ineffective as a 6ft spike into dry ground.

A spot where the ground is permanently moist is essential for an earth spike to work.

So a spikes into the ground near the septic leach drain long enough to be well into the moist area should work.

Several spikes spaced out within the moist area are more effective than one.

If this is not available then a spike long enough to reach into the ground water table should be used.

Earth spikes that join together (male and female screw ends) can be assembled and driven into the moist ground at what ever depth is required.

Testing (megameter) of the effectiveness of earthing is advised.

Multiple earthed neutral systems are appropriate.

This is the long brass bus bar in the main switchboard, it will have all the neutral wires (black or blue) from the house circuits connected into it as well as the main earth wire (green).

This can be divided into two sections connected together by the earth leakage circuit breaker safety switch (ELCB) as a fail safe.

It should be noted that ELCBs (safety switches) do not work when there is no effective earth.

In pre plastic pipe days, electrical safety in wet areas was taken care of by effective earthing of steel and copper pipes and fittings.

In this plastic pipe era safety is now taken care of with ELCBs.

And thus where there is no effective earth ELCBS are useless.!

In this specific situation it may be worth while opening the hot water heater to see the actual heater (boiler), many are small copper tanks with electric elements within, some are now made of heat proof plastic.

If the boiler is copper, test the tank body with the pen volt meter, it should test at 0v, if a voltage is detected and the tank is not earthed, earth it.

Plastic boiler tanks are more difficult to test, the heater element within the tank will have a copper outer shell, some of this outer may be protruding from the tank, test this, it too should be at 0v.

If a voltage is detected and the tank is earthed, the earth is faulty (ineffective).

Refer to above on how to ensure the earth is effective.

Some water heaters come with built in ELCBs but as previously mentioned become useless when there is no effective earth.

ELCBs trip on less than 1v, if the voltage detected is 12v - 14v this suggests, 1: there is no ELCB on the circuit or 2: the earth is ineffective.

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Reminds me of the situation in my apartment in Bangkok, where I stayed my first 12 years in Thailand.  It was two one-bedroom apartments joined together.  I placed my computer desk in front of where the kitchen sink in one apartment had originally been.  A caped galvanized water pipe had been left sticking out about 1.5"/8cm from the wall.

 

All the building wiring was only 2 wires, no ground wire.  I used my meter to check the voltages between the two wires and the pipe, hoping that the pipe would serve as a ground.  I got something like 208V and 12V, give or take a couple of volts, from the two wires.  I quickly installed a three wire socket with a ground wire attached to the pipe.

 

You simply can't expect things to be like they are in more advanced countries, after all TIT.

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It is entirely possible there is an induced voltage between the supply ground and your grounding rod.

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29 minutes ago, millymoopoo said:

This can be divided into two sections connected together by the earth leakage circuit breaker safety switch (ELCB) as a fail safe.

It should be noted that ELCBs (safety switches) do not work when there is no effective earth.

The majority of you post is excellent but in your concentration on an ELCB as the safety switch and the way it works you have made a significant error which is drawing a dangerously wrong conclusion (in that if believed people may decide not to install one) 

The function of the vast majority of RCCBs (a common term for your ELCB) that are required to be installed in Thailand and many other countries, is to measure the current on both the line and neutral and if there is an imbalance to cut the circuit NO PERMANENT EARTH CONNECTION IS REQUIRED FOR THEM TO FUNCTION, they work if enough (a very tiny amount) of difference is detected.
 

Effective earthing may allow them to trip before a human is involved and is an absolutely good thing 

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A lot of great posts, thank you one and all.  I will try to work through them.

 

7 hours ago, Crossy said:

 

Yes. Because it is the only way to get an absolutely known earth. It should also be at leat 3m from any system earth (doesn't actually matter much so long as you are not right next to the rod).

OK, screwdriver ground installed and connected directly to the water heater.  224VAC L-E, 14VAC G-E.  Does this tell us anything?  What else do I need to check with this?

 

7 hours ago, Crossy said:

 

These voltages N-E are inconsequential particularly as you seem to have created TT islands on the TNC-S system (this is why I asked for a sketch of what you actually have, working in the dark somewhat).

I am working on a sketch, however, I think you are correct re the TT islands.  For one, I am over 150m from the "grounded" power poll.  As I mentioned, the two consumer units in the house, one of which the showers are connected, are old boxes with no connection between G-E which if I understand correctly could make them TT islands.  So I am guessing I should connect G-E in these CU s.  Am I close?

 

7 hours ago, Crossy said:

 

Have you checked the continuity of the earth from the heater to the ground bar and from the ground bar to the rod?

No, and I think this should be the next step, to the rod and to the screw driver.  Can you tell me how to do this (with a multi-meter?) 

 

 

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OK, since you do seem to be TT islanded then 14V N-E isn't excessive, since you also appear to be MEN enabled in the street linking N-E in your CUs would be advantageous (and get rid of the 14V). But these CUs do still need a link to the rod.

 

Checking continuity to the rod etc. just needs a long wire and your meter on "ohms". With the mains off put one end of your long wire on the rod/shower and measure resistance between the other end of the wire and your earth bar. Should be low ohms.

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1 hour ago, Crossy said:

Should be low ohms.

A hundred or two (though not great) is low~ish, low double digits  or better single is what you should hope for. 

Edited by sometimewoodworker
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Just now, sometimewoodworker said:

A hundred or two (though not great) is low~ish, low double digits  or better single is what you should hope for. 

 

With a direct copper connection I would hope for as close to zero as a cheap DMM can get.

 

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11 minutes ago, Crossy said:

 

With a direct copper connection I would hope for as close to zero as a cheap DMM can get.

 

Set on 2k it reads .001, the same as touching the two probes together.

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Th

2 minutes ago, ellobo said:

Set on 2k it reads .001, the same as touching the two probes together.

 

That's a good connection, is that shower to CU or CU to rod?

 

Doesn't it have a 200 ohm range?

 

 

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