Voltage difference ground to neutral

[PMK]

Hello,

I hope everyone is well. I'm getting mild and sometimes not so mild shocks playing electric guitar if i am grounded. None if not. I'm repeating here what a friend has told me is the probable cause and solution. He says there is a good ground but there is a 75 volt difference at the mains between ground and neutral. When he checked each circuit it sometimes went down to to 45 volt. He suggests running a wire between the ground and neutral bus as he has done himself in Thailand (in the USA they would be on the same bus) but with only a few volt differential and is hesitant with such a large one. He also thinks this is the reason I have to set my Safe-T-cut GFI to lowest sensitivity.

 

What do you guys think about both the diagnosis and suggested solution?
 

[bankruatsteve]

The voltage between N and E is a concern but you are not likely getting a shock from the neutral.

What is the voltage between L and E?

Is your guitar/amp connected to ground?  (3-pin plug)

I would not bond the N and E bus without more information of your grid supply.

Unless things have changed recently, US boxes have separate N and E bars which are bonded.

[Crossy]

Is your ground really good? (how do you know)

 

Try measuring to a known-good ground (big screwdriver in the lawn), a floating ground would give you something like you are seeing.

 

Are you in a house or a condo??

 

I wouldn't go around connecting N-E unless you KNOW that you have a TNC-S supply with MEN.

 

[PMK]

58 minutes ago, bankruatsteve said:

The voltage between N and E is a concern but you are not likely getting a shock from the neutral.

What is the voltage between L and E?

Is your guitar/amp connected to ground?  (3-pin plug)

I would not bond the N and E bus without more information of your grid supply.

Unless things have changed recently, US boxes have separate N and E bars which are bonded.

Hi. Thanks. The amp is grounded. I don't know about the voltage between Line and ground - and won't measure myself because I don't know what I am doing! But will try and find out.

[Crossy]

1 minute ago, PMK said:

The amp is grounded.

 

Is that ground actually connected to the ground at the box and then the rod? A LOT of extension leads hve 3-pin plugs and outlets with 2 core cable!

 

[PMK]

2 minutes ago, Crossy said:

Is your ground really good? (how do you know)

 

Try measuring to a known-good ground (big screwdriver in the lawn), a floating ground would give you something like you are seeing.

 

Are you in a house or a condo??

 

I wouldn't go around connecting N-E unless you KNOW that you have a TNC-S supply with MEN.

 

House, and I can drive in a good ground rod and try that. Thanks.

[PMK]

Just now, Crossy said:

Is that ground actually connected to the ground at the box and then the rod? A LOT of extension leads hve 3-pin plugs and outlets with 2 core cable!

OK. I will do my own ground. I actually started to do that but backed off because of the other opinion.  I'm familiar with the ungrounded 3 pin extensions in Thailand. ????

 

[Crossy]

Since you are in a house take a walk and look at your power poles, a supply with MEN will have a ground wire from the neutral (usually the top wire of the ones on small insulators), if you are definitely MEN then a N-E link is a good idea.

 

Can you post a photo of your distribution board with the lid off (care) so we can see what's going on in there too.

 

[PMK]

1 minute ago, Crossy said:

Since you are in a house take a walk and look at your power poles, a supply with MEN will have a ground wire from the neutral (usually the top wire of the ones on small insulators), if you are definitely MEN then a N-E link is a good idea.

 

Can you post a photo of your distribution board with the lid off (care) so we can see what's going on in there too.

 

What is MEN?

[Crossy]

3 minutes ago, PMK said:

What is MEN?

 

It means "Multiple Earthed Neutral", it needs the multiple grounds to keep the neutral at a safe level to permit you to connect it the your house ground.

 

[PMK]

I will drive in a proper grounding rod but what size wire should i use?

[bankruatsteve]

3 minutes ago, PMK said:

OK. I will do my own ground. I actually started to do that but backed off because of the other opinion.  I'm familiar with the ungrounded 3 pin extensions in Thailand. ????

Measuring the voltage between L and E is just a simple (for me) way to determine relative quality of ground.  IE: if voltage is pretty much the same between L-E and L-N, then you likely have a decent ground.  if voltage between L-E is same as N-E then your ground is not good.  Of course a stake in the ground will give you what it should be.

[shaemus]

75 Volts is potentially lethal.

 

it my be possible that you have lost your service Neutral or it has a bad joint.

 

I would be on the phone to your service provider and  asking them to check the connection to your supply.  

 

Shaemus

[PMK]

2 minutes ago, bankruatsteve said:

Measuring the voltage between L and E is just a simple (for me) way to determine relative quality of ground.  IE: if voltage is pretty much the same between L-E and L-N, then you likely have a decent ground.  if voltage between L-E is same as N-E then your ground is not good.  Of course a stake in the ground will give you what it should be.

I'm not comfortable messing around in the panel with power on.

[shaemus]

11 minutes ago, PMK said:

What is MEN?

2 meanings.

 

Multiple earthed Neutral : A UK term for multiple earth spiked on the service neutral

Mechanically earthed Neutral. An Australian term  for a permanent link between Neutral and earth, required by standards at the consumers Switchboard to equalise the potential difference due to poor ground conductivity in some areas  (sandy)

[bankruatsteve]

2 minutes ago, PMK said:

I'm not comfortable messing around in the panel with power on.

Fair enough.  What do you plan to do with a ground rod?  BTW: any size wire you have laying around that is long enough can be used for temporary ground and testing.  1.5-2.5 mm2 best.

[PMK]

7 minutes ago, bankruatsteve said:

Fair enough.  What do you plan to do with a ground rod?  BTW: any size wire you have laying around that is long enough can be used for temporary ground and testing.  1.5-2.5 mm2 best.

Hook it up to the bus with the power off!

[Crossy]

Earthing systems https://en.wikipedia.org/wiki/Earthing_system

 

Thailand is TNC-S with MEN, but there are areas which are still TT so you need to check.

 

Do post that photo of the board with the lid off so we can be sure what you have.

[Crossy]

If you are going to buy wire for your rod I would go with at least 6mm2 preferably 10mm2 for mechanical robustness.

[PMK]

I'll be back later or tomorrow. Thank you.

[PMK]

[Jack 0009]

2 hours ago, bankruatsteve said:

The voltage between N and E is a concern but you are not likely getting a shock from the neutral.

What is the voltage between L and E?

Is your guitar/amp connected to ground?  (3-pin plug)

I would not bond the N and E bus without more information of your grid supply.

Unless things have changed recently, US boxes have separate N and E bars which are bonded.

I was at PMK's house with my multimeter today

between Line and N was about 156VAC between Line and Earth was about 238VAC and between N and Earth was about 75 VAC.

I suspect his ground is okay but I agree with installing a new one. I believe that MEN situation is not correct but I'm not sure the correct solution to that problem.

[Crossy]

10 minutes ago, Jack 0009 said:

I was at PMK's house with my multimeter today

between Line and N was about 156VAC between Line and Earth was about 238VAC and between N and Earth was about 75 VAC.

I suspect his ground is okay but I agree with installing a new one. I believe that MEN situation is not correct but I'm not sure the correct solution to that problem.

 

Some somewhat alarming voltages there, but testing to a known earth (screwdriver in the lawn) should be task A.

 

Check for MEN by looking at the incoming poles as noted earlier.

 

The number of wires on each bus looks OK. 

 

Is that green/yellow on the ground bus making good contact (is that the rod wire)?

 

What about the two whites on the ground bus?

 

I also note no earth-leakage protection in place so an upgrade of incomer is probably in order (fix the interesting voltages first).

 

EDIT Try checking incoming L-N with the main breaker off.

EDIT 2 There could be a bad joint in the incoming neutral which I've seen before giving similar issues.

[bankruatsteve]

5 minutes ago, Jack 0009 said:

between Line and N was about 156VAC between Line and Earth was about 238VAC

Is that reversed maybe?  IE:  L-N at 156V and L-E at 238V is not what I would expect in any condition of earth.

[86Tiger]

4 minutes ago, Crossy said:

 

 

 

What about the two whites on the ground bus?

 

 

 

 

 

My immediate reaction any time some one sees voltage on ground is some one has connected neutral conductor to earth bus.

 

 

Correct guess more times than not.......

[PMK]

Just now, 86Tiger said:

 

 

My immediate reaction any time some one sees voltage on ground is some one has connected neutral conductor to earth bus.

 

 

Correct guess more times than not.......

We don't know ... You may be right. I don't have the knowledge to evaluate it.

[Jack 0009]

6 minutes ago, bankruatsteve said:

Is that reversed maybe?  IE:  L-N at 156V and L-E at 238V is not what I would expect in any condition of earth.

that is the correct measurement

I am not at his house now

the suggestion to measure N to E with the mains off I did not do but a good suggestion

[PMK]

>> Is that green/yellow on the ground bus making good contact (is that the rod wire)?

That is just a ground to a nearby electric oven.

[Jack 0009]

2 minutes ago, PMK said:

We don't know ... You may be right. I don't have the knowledge to evaluate it.

I did see two white wires on the ground bus. that was a head scratcher.

refer to the picture of his box

[Crossy]

You absolutely need a KNOWN reference, you cannot rely on ANYTHING in the box for now. Bang that big driver into the lawn and water it if it's a bit dry.