What if I connect this wire to this wire

IF I get my multi meter and check the voltage of Live and neutral I should get 220V approx.

If I connect live to Earth through the multi meter I should get 220V

If I got 150V what would that mean.

A that I have a bad earth or

B that I have 70 v in the earth?

C and how would I check the earth for voltage?

 

Er. I'm not an electrician either, and normally I would not reply to this because I'm not confident that I know the answer, but I'm pretty sure the above answer is wrong and I hate to leave it there misleading people. So, until an actual expert comes along ...

There are various electrical setups that use three wires. As I understand it (which may be wrong) you can have a split-phase system with two hot wires and a ground. You should see 220 between the two hot wires and 110 between either hot wire and the ground. There are also 3-phase systems where you should see 220 between two hot wires and 127 between either hot wire and ground.

There may be other three-wire systems as well. Basically, you have to find out what your house or marina is supposed to be supplying before you can decide if it is correct.

 

Hi Frosty - lets see if I can throw some more mud on they answer - Dave is correct in that there are more than one "3 wire" systems - it looks like from my looking a bit on the internet (if it's on the internet is must be the truth ) - is that Thailand is a 220 volt two wire system for household type use. However Ground or Earth should always be at zero (give or take for bad wiring) - you should have 220 V from hot to neutral and 220 v from hot to ground. (I am assuming that you are not using a 3 phase system, which if that was the case there would be a 4th wire that is ground or earth)

My guess from halfway around the world is that the marina has a floating ground, first thing to check is at the receptical in the marina (also check your cord) - and see if the ground is still floating in the marina or if you have a problem on your boat.

One of the problems using a multimeter is that they have such a high impedance (not much current flow to get a measurement) you can get fooled when a wire is broken or there is a bad connection you might see voltage that is just a bit of leakage (as in the case where you have voltage to a piece of equipment but it will not run when turned on) I have seen a couple of very smart electricians get fooled by that problem.

When you are checking the ground, also look around and find some conduit or water pipe (they should both be at ground if they are not plastic) and use one of them as a double check to your ground wire. Try looking at your ground against the above two sources.

Standard disclaimer - I am not in your marina, I used to do electrical control systems, I am a bit rusty and with all troubleshooting, there is sometimes a "did not feel right" aspect - however your 70 V ground reading is not correct to the best of my knowledge.

Good luck

 

Do a continuity and/or ohm check between the common bus and the ground wire you're employing.

 

It is not clear if you're talking about your house or about your boat, but generally I'd say thet the measurements indicate that you have a current leakage towards ground wire. Until you find out where the leakage is, do not touch appliances with metallic or wet parts with bare hands, have your electrical system checked and install a leakage breaker (RCD) in your switchboard. RCD is rightly called "salvavita" (life-saver) in italian language.

And I believe you should also hear CDK about this problem.

Cheers!

 

In English "salvavita" is "GFCI" short for "ground fault circuit interrupter".

 

Apparently (at least according to Wikipedia), it has different names in different English-speaking countries: http://en.wikipedia.org/wiki/Residual-current_device

Cheers!

 

You're right. I should have been more specific.

 

Frosty,

I am taking a guess at your AC Marina installation.

For Thialand based on the following:

http://en.wikipedia.org/wiki/Mains_electricity_by_country

With commando style Marina plug of:

http://en.wikipedia.org/wiki/IEC_60309

...and the assumption that the system is supposed to use AC grounding (earth) and bonding (connection of grounding to grounded at source).

Then; Based on your description, I would say you have problem with bonding between Earth and Neutral at the source (output of a transformer). Such that the 70VAC difference is really a drop across earth grounding rods, or earth connections.

I will try and answer your questions:

If I got 150V what would that mean.

A that I have a bad earth or

Bad bonding connection between earth and Neutral at the source.

B that I have 70 v in the earth?

Potential is across grounding rods, or earth connections.

C and how would I check the earth for voltage?

Really, the earth has no potential until we use it as a reference. Then, through ground and source misapplication, we can start to have problems with this connection through earth. Earth grounding is important as a reference relative to a source. So connection to earth between the ground rod and neutral should be at the output of the transformer source. For bonding issues start with the source.

Mark

 

Just to clarify I am talking the boat, it is a 3 wire live neutral earth 220 V

The question was fictional I do not have problem but if the boat next to me had a 70 v leak into the earth and I connected live to earth with the multl the 70 would come off the 220.

If there was power in the earth how do I test it, against what, there is no water pipes or anything with zero potential. I thought that if I get 220 from live to earth then earth must be zero.

 

No if the boat next door is leaking 70V to earth, it goes to earth, not to your boat.

 

So If I do,-- then the marina earth is faulty. But how would I be able to see that there was leakage in the earth system what has less potential to read it from.

As far as I know the marina is fitted with earth leakage trips but a lot dont work (fact) and In any case it just cuts your supply off and maybe not the faulty one.

 

Frosty, I'm glad the question was only fictional.

If the wiring was done the way I recommend, the on-board ground would not be connected to shore ground but to whatever metal parts you have in the water and there would be a gfi to protect you against current leakage. Should the voltage reading be 150 in that case, you'd have a defective multimeter and need a new one.

If the boat were hardwired to shore ground, there are two possibilities:

a. What you assumed to be ground is in fact an open wire because a terminal somewhere nearby in a junction box got corroded to the point where it is no longer conductive. That is the most likely cause.

b. The ground wire on the shore is pulled 70 volts away from zero because a heavy electrical load has been connected between one phase and an interrupted neutral wire. On land neutral and ground are interconnected at every ground electrode, if the neutral between the power station and the user is cut, the current flows through ground, pulling the voltage towards the phase potential.

There is one 3rd way to create the phenomenon, but a very rare one in civilized countries.
The power company installed new concrete poles between my beach house and the village and connected a live wire to the ground terminal on a pole. The armored concrete drew approx. 30 KW from the grid and converted that to heat.
I called them but was stonewalled because I was a customer, so a proverbial harebrain and they left that situation unchanged from nearly 6 months.
Depending on the moisture of the soil there was between 25 and 50 volts on the ground wire, making showering a painful experience.

Then they noticed the constant loss of electricity and started looking. I invited the electrician to touch the pole and after he did that they corrected the problem and later his boss called me to apologize.

 

So how do I check the earth.?

 

Assuming your DC ground is bonded to engine, rudder etc, measure the AC voltage between DC ground and the yellow/green earth wire. It should be near zero or just a few volts (fluctuating). If it is, measure the resistance between these two. Do that twice, once with the red read on DC ground, once on the earth wire. The average reading must be near zero (one may even be negative).

In all other cases the yellow/green wire is dangerous and should be disconnected..