How to check your earthing system

[Forkinhades]

How to check your Earthing.

Earthing is very important, and will have many different values in an installation, these values are important, as if they are too low (<0.038 ohms) under fault conditions can cause explosions, and if they are too high (>1677 ohms for Safe-T-Cut set at 30mA) then our safety devices will not open. If you do not have a Safe-T-Cut installed then a 32A Type C MCB requires a value <0.71 ohms to open in time.

For reference I will use phase to describe the live/hot

The easiest way to test is with a multimeter at a socket.

First we should check between phase and neutral, this will tell us that there is voltage there on the phase, and indeed that the meter is working.

Set the multimeter to the 750Vac setting

Insert one probe into neutral first. As we do not want the other probe to become live, and then the other into phase, you should get a reading around 220V

Now you can check between phase and earth

You need to insert one probe into the earth terminal first. As we do not want the other probe to become live, then the other into the phase.

If you get a reading of around 220V, then you have a good indication of an earth.

You can also check between Neutral and Earth, and will possibly have 1 or 2 Volts

Doing this test will also prove polarity

How to calculate incoming ‘values’ of earth

If you have your MEN connection at your DB then your values will be low, we can calculate this as we know the resistance of different cable sizes.

R1R2 Chart.pdf

From the chart above I will give my example.

From my PEA meter I have a 10mm cable supply, for the full earth path we use the neutral as we have done our MEN connection.

The cables are 20 meters in length, so from my chart I know that the phase and cpc (Circuit protective conductor (MEN connection)) is 3.66 milli ohms per meter.

So a simple calculation 20x3.66/1000 = 0.0732 ohms so all good there.

This does not take into consideration that the meter will have a value as well, which would need to be added to the 0.0732 already calculated. You would also need to take off your resistance for your parallel earth rod. Mine was 15 ohms, so product over sum would bring the resistance down to 0.0728 ohms

Again this calculation can only really give us an indication as to what we might have.

EDIT : added product over sum calculation for the earth rod.

[Forkinhades]

Just saw this on Amazon UK

http://www.amazon.co.uk/Martindale-EZ150-Check-Impedance-Indicator/dp/B002L651LY/ref=sr_1_4/276-8035793-9097428?ie=UTF8&qid=1388905735&sr=8-4&keywords=martindale+tester

That is just an awesome piece of kit

RS Malaysia might do one, but their site is down at present.

[Crossy]

Just saw this on Amazon UK

http://www.amazon.co.uk/Martindale-EZ150-Check-Impedance-Indicator/dp/B002L651LY/ref=sr_1_4/276-8035793-9097428?ie=UTF8&qid=1388905735&sr=8-4&keywords=martindale+tester

That is just an awesome piece of kit

RS Malaysia might do one, but their site is down at present.

Wherever you get it from, you'll need to make a correctly wired adaptor to use in Thailand.

[Forkinhades]

Schneider do a very good range, and are available in all good outlets.

The socket on the left will accept any plug I do believe. This is what I have had installed in the house.

Can easily adapt above, just put a surface back box on, flex it up with a 3 core cable, and put your type of thai plug on.

[Naam]

Schneider do a very good range, and are available in all good outlets.

20140105_163946.jpg

The socket on the left will accept any plug I do believe. This is what I have had installed in the house.

Can easily adapt above, just put a surface back box on, flex it up with a 3 core cable, and put your type of thai plug on.

looks as if it even accepts a crooked Aussie plug.

[Deke]

Just saw this on Amazon UK

http://www.amazon.co.uk/Martindale-EZ150-Check-Impedance-Indicator/dp/B002L651LY/ref=sr_1_4/276-8035793-9097428?ie=UTF8&qid=1388905735&sr=8-4&keywords=martindale+tester

That is just an awesome piece of kit

RS Malaysia might do one, but their site is down at present.

Also available from RS Thailand:

http://thailand.rs-online.com/web/p/mains-socket-testers/7190901/

but I like this one better:

http://thailand.rs-online.com/web/p/mains-socket-testers/7190905/

[Forkinhades]

^ well done that man

[Gunnin25]

thank you so much for posting this, i've been looking for this info for ages

[Mudcrab]

Just saw this on Amazon UK

http://www.amazon.co.uk/Martindale-EZ150-Check-Impedance-Indicator/dp/B002L651LY/ref=sr_1_4/276-8035793-9097428?ie=UTF8&qid=1388905735&sr=8-4&keywords=martindale+tester

That is just an awesome piece of kit

RS Malaysia might do one, but their site is down at present.

Also available from RS Thailand:

http://thailand.rs-online.com/web/p/mains-socket-testers/7190901/

but I like this one better:

http://thailand.rs-online.com/web/p/mains-socket-testers/7190905/

This is where the uninformed give dangerous advice. The meter in question is rated at category 2 only. Could be good for working on cars.

The slightest fault - lightning strike, overvoltage or static discharge on the system will have this blow up in your face. Agreed unlikely for the domestic user but I will stick with Cat 4 meters, Type A fused leads thanks!

[Forkinhades]

You want fused leads in case of lightening strike as you are testing a socket? Which takes seconds to do.

God give me strength

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

[Crossy]

A nonsense troll post has been removed along with another in the same vein.

If you cannot post reasonable seriously in this forum please do not post at all.

Any more and holidays will be handed out.

YES! This means YOU!

[EmptyHead]

Thanks! This is a useful thread.

How do i know if my house is properly earthed? There is as earth cable visibly going into the ground (only 4mm cable), but i can't tell if it is attached to an earth rod or if the cable is just buried on its own. The area is now concreted over so i don't have access.

I would like to know if there is a test i can do to figure out if the earth grounding connection is good enough? (I suppose I could create an earth to phase fault with a plug and some connector block to see what happens...but maybe dangerous?)

We do have an RCD mains switch, however.

I have attached a pic of our consumer unit, just incase anyone is interested (or sees a problem)

If you look closely at the earth bar, you will see the blue 4mm earth connected along with all the other green 2.5mm earths for the household circuits. That 4mm blue one is going into the ground.

[Crossy]

Looks like a reasonable job, shame he didn't stick to an internationally recognised colour code

Testing a ground without proper equipment is not easy, you can get an idea if the rod is any good by following the steps below.

WARNING Anything to do with electricity is potentially lethal, take great care. Send the kids to play with their mates, have someone with you just in case.

1. Get yourself a low-wattage (15W or so) conventional light bulb and a holder for it.
2. With the RCD turned off disconnect the wire going to the rod from the earth bar.
3. Connect one end of the lamp to the wire going to the rod.
4. Dab the other end of the lamp onto the incoming live.
5. If the rod is making a reasonable connection the lamp will light. How brightly depends upon how well the rod is working.

[EmptyHead]

Thanks for the advice. I will try this when i get back up to the house. It could be a couple of months though.

By the way, is there proper testing equipment available here for testing the ground? I would consider buying it.

Thanks again!

Yeah, pity about the weird colours he used.

And they also decided to use wood screws to screw the socket outlets and switches into their metal backboxes (rather than the correct screws) which means the threads are all chewed up

[Crossy]

The proper kit is available here, you'll have to visit one of the electrical specialist outlets to find one.

If you're serious about ensuring you're installation is totally safe it may be worth buying an installation tester, there are quite a few on Ebay, a "16th Edition" tester like these http://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2050601.m570.l1313.TR0.TRC0.H0.X16th+installation+tester&_nkw=16th+installation+tester&_sacat=0 would likely be less expensive than a dedicated earth tester.

By the way, Thailand (mostly) uses the US colour code:-

Black - Live

White - Neutral

Green - Earth (sometimes this is red in flexible cables)

[EmptyHead]

Thanks

[technologybytes]

Every socket I ever looked into in Thailand has two wires the same colour for the power, and if you are lucky (not normally) a different colour for earth.

The concept for neutral and phase wires may work in the west, but not here.

Couple of years ago I bought a extension bar with a little light on it that tells me if earth is OK, it cost about 400 baht and works good.

[CTO]

Earth? Earth? This is Thailand, they don't earth.

But I so wish they did!

[TPI]

I've been using a copper rod, 1 metre long with flex soldered onto it to earth my computers. It works really well and no zaps from the computer frames!! I use the standard "under 3 ohms to earth" construction rule of thumb!

[stgrhe]

This is an article by Fluke about how to test the 'Earth-Loop Impedence'

Impedence Looptesting by Fluke.pdf

[Rorri]

Naam, on 05 Jan 2014 - 18:26, said:

Forkinhades, on 05 Jan 2014 - 17:49, said:

Schneider do a very good range, and are available in all good outlets.

20140105_163946.jpg

The socket on the left will accept any plug I do believe. This is what I have had installed in the house.

Can easily adapt above, just put a surface back box on, flex it up with a 3 core cable, and put your type of thai plug on.

looks as if it even accepts a crooked Aussie plug.

Ah, the good old aussies plug, no matter if 3 pin or 2, it can only go in one way and not to bulky. Time for the world to change.

[Rorri]

OP, just where did you reference the earth being too low can cause an explosion? In fact, as far as I'm aware, the lower the better.

[Brian Robson]

Absolutely a shocking state of affairs in Thailand when it comes to earthing!

As CTO states.

In South Africa it is compulsory to have a 20mA earth leakage breaker on the main switchboard.

I can feel current leaking from laptop and DVD player chassis on occasion in Thailand.

No wonder fires and electrocutions are common.

Thanks for the info on how to sort this out fairly cheaply

[bluejets]

You want fused leads in case of lightening strike as you are testing a socket? Which takes seconds to do.

God give me strength

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

Don't know where you get your information but it is incorrect.

Using a Cat 2 meter to check anything other than an appliance is out and it certainly isn't rectified by added a fuse to the leads.

Earth loop impedence is a rather comples issue and not just a simple measurement.

I could go into it in depth but as i said, a complex issue and over the head of most general users.

Suffice to say it involves conditions, equipment used as to ratings and type, along with supply authority transformers and distribution system.

I also do not know how you get your "explosion" or how you intend to measure these low ohm levels.

We do, (in hospital environments), with specialised equipment I might add.

The >1600 odd level and it's connection to trip levels has me completely baffled.

[KKr]

Earth? Earth? This is Thailand, they don't earth.

But I so wish they did!

Who are "they"?

maybe the same "electricians" that wanted to finish the repair of my apartment in Europe quickly.

As some sockets didn't have power, I found that they plastered about 25 cm of wire behind the socket.

"must work, have wire" the kind of Russian speaking gastarbeiter said.

He then further explained to me that Earth was not necessary: simply connect the Neutral to the Earth and, according to him, all is working fine. (Don't try this one, a lot of people in Moscow get shocked every day, many metal keyboards give a nice tingle, and when the socket of white goods is connected the wrong way around, the cabinet has 220 V live)

Also, I have seen hi-so places where the Earth-safety device is connected to the ceiling lamps, but not to the electric water heater.

In short,in the LOS it is not as bad as some may think.

[sandrabbit]

I've been reading your article and generally it is very good, I just want to make a point about the safe-t-cut devices as I always thought it was a normal rcd (residual current device) but I've just been on their website to read up on their devices as I didn't understand your point about the earth having to have a certain impedance to ground - I use the word impedance as we are discussing ac power. I see from the manual ( it's in Thai but the diagrams have English as well) that the neutral inside the safe-t-cut has a busbar (it looks like a busbar in the diagram) and this has to be connected to earth via a ground spike.

Now I come to the point I want to make. a normal rcd doesn't have a ground connection and doesn't require it as it looks at the imbalance between the live and neutral currents and if the neutral current is for example more than 30mA difference it will trip the breaker as there is less current returning through the neutral as the assumption is that it has found a path to ground. This also means that you can retrofit a normal rcd into 2 wire circuits to provide protection but never rely on it completely, most western countries require you to bond any metal pipework to ground as well as have a rcd if you have electric water heating.

In my condo they have wired the earth to neutral but I still have 3 pole sockets which is acceptable as long as you only use 3 pole multi extenders so that the live and neutral can never be plugged in in reverse. What I don't like about this system is that it requires the full fault current to trip your circuit breakers the same as if there was a full short across the live and neutral which is what happens when there is a fault to earth. The idiots who modernised the condo for the previous owner made such a bad job of the wiring in the kitchen that it prevents me fitting a rcd in the dist board so for the shower heater I fitted a rcd just for that circuit. I can measure the insulation resistance with a multimeter ........

One tip with rcd's when you press the test button, which you should be doing regularly, is to do it without high loads such ac's or water heaters on as you could burn the contacts on tripping which could lead to them welding closed on tripping in the future when tripping with high currents. If you don't know you're doing leave well alone and find somebody who does which sometimes is hard to find in Thailand.

[lucifer666]

I used to own a socket tester that was simply a 3 pin plug with 3 LED's built in. That would test for live, earth and neutral connections.As recall, it only cost maybe a quid or so. Surely, there's someting similar over here for the not so technically minded, so they could just plug it in and get an instant indication of a bad/no earth.

[sandrabbit]

I used to own a socket tester that was simply a 3 pin plug with 3 LED's built in. That would test for live, earth and neutral connections.As recall, it only cost maybe a quid or so. Surely, there's someting similar over here for the not so technically minded, so they could just plug it in and get an instant indication of a bad/no earth.

I have one with 3 neons but it gets confused by the earth being connected to the neutral but it is good for showing if your earth is connected to the live but the same test is easily done with a multimeter and then you see if the earth and neutral are connected together. In Europe the neutral point of the local transformer is connected to ground so the neutral/earth voltage will vary depending how far you are from the transformer although I'm not sure if they carry out this practice everywhere in Thailand.

[Mudcrab]

You want fused leads in case of lightening strike as you are testing a socket? Which takes seconds to do.

God give me strength

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

Seconds are very long time relatively speaking. God won't give you strength but a good priest may give the last rites!!

Take the piss all you want. I take electrical safety VERY seriously.

Of course fused leads would be no good in the case of a lighting strike,in fact with a direct lightning strike you are in real trouble.

However a direct hit is quite rare, but lightning striking a powerline or a static discharge (yes wind can create a static charge) or even an HV switching operation, many kilometres away can create a very high short duration voltage pulse (with current in the kilo amp range) that can destroy the lower rated meters. If you are making a measurement at the same time......luck of the draw. With a CAT III or CAT IV meter, the chances are you would never even know it happened.

I merely made mention of the fused leads to give some guidance to the amateur sparkys who read this thread. I have repaired many analogue meters in the old days from people measuring current while ohms are selected. The fused lead can help save the meter (and the user).

As I have posted on TV before, Fluke have a very good video about multimeters and show a few cheaper Cat I and Cat II meters being destroyed by a high voltage impulse - measured in micro/milliseconds. I would recommend watching it.

You've never seen the aftermath of an arc fault? - I have - not a pretty sight. One bloke had his eyes fused shut for quite a while, another bloke was luckier as he had PPE on.

[Forkinhades]

OP, just where did you reference the earth being too low can cause an explosion? In fact, as far as I'm aware, the lower the better.

Your MCB's can only handle 6KA or 10KA of fault current depending on make. Perhaps Crossy can advise what is distributed in Thailand.

So ohms law tells us that with an MCB of 6KA, and earth value less than 0.038 ohms, under fault conditions the MCB cannot handle the fault current, and thus 'jumps' over the MCB, which will then explode a unprotected devices upstream. Which is exactly what Thailand has, no upstream protection.

Result : PEA meter explodes.