Measuring mains voltage

[king.oslo]

Hello there,

I am trying to measure if my cold water pipes are good grounding points for ESD. I tried to measure the voltage between the mains outlet and the pipe. I live in Scandinavia. Here our mains voltage is 230VAC 50Hz. I tried to measure between one pin on the outlet and the pipe. The reading on the first pin was 142VAC. The reading on the other pin was 148VAC. The voltage between the two pins (not via the cold water pipe) was 226VAC.

This surprises me. I expected to see 230VAC between one pin and the pipe, and 0V between the other pin and the pipe. My flat doesn't have earth ground on any outlets.

Does what does these readings tell you? Do they mean that the cold water pipe a sound ESD-grounding point? Or is something wrong?

Thank you for your time.

Kind regards,
Marius

 

[BrownOut]

I don't now how things are where you are, but in the US, we have 230V measured from phase to phase, and 120V measured from phase to neutral. What that means is if we are trying to measure 230V, we are measuring from phase to phase, no neutral wire is connected. So, each phase would measure ~= 120V to neutral or ground. My guess is you're looking at something similar, and the measurements from each pin on the outlet to your cold water pipe is correct.

 

[king.oslo]

Thanks. You think my multimeter is playing up? Do you think thats causing a measurement of 142V, and not 120 or 115, or thereabout? Thanks!M

 

[BrownOut]

Maybe so.

 

[Reloadron]

My take and this is guesswork is that Norway uses a non-polarized electrical distribution system. There is no reference to ground with a system like this. The mains voltage is pin to pin so what you read is what you get and sounds correct. Even a grounded plug may be plugged into the socket either way as the plug has ground clips.

That said as to ESD grounding you should be fine using a cold water pipe. The object being to dissipate the static charge which may be present.

Ron

 

[squishy36]

Another thing to be aware of is that you could be measuring phantom voltages, assuming you were using the typical 10 Mohm input impedance DMM. This is where a device with a lower input impedance is useful (like a 20 kohm/volt VOM).

Personally, I'd want to know my water pipes were actually grounded. There are only two ways that I know of doing this -- dig them up (probably something most of us won't do ) or pound a metal rod in the ground outside and measure a low resistance between this rod and your pipes. I've used this in measuring the resistance of my home's grounding rod (look up the fall of potential method for details). Of course, only an anal retentive would do this. But, you only have to do it once. I used this to verify that my electrical service was properly grounded.

I'm curious to know if, as reloadron suggested, whether Norway's electrical service is such that neither line's voltage is referenced to ground.

 

[king.oslo]

Yes, the plug can be plugged in either way. There are clips for ground on either side of the plug.

What does that mean? Does it mean that my water pipe, perhaps doesnt remove static potential?

Thanks! M

 

[RCinFLA]

My guess if your power pole transformer is center tapped 230vac secondary. The center tap is grounded below transformer so there is only earth between transformer center tap ground and your ground. You may be impacted by other ground currents in your voltage measurement. Try putting a progressively larger load from you hot plugs lines and ground starting with a few mA's and increasing load to see if your voltage readings change with loading to your ground.

Most of Europe uses a 460/230 split-phase transformer secondary with center tap of transformer as neutral connection which is also grounded at transformer. Neutral and a single side hot line is brought to residence. Your neighbor may get neutral to other hot end of transformer. In this configuration there should be no voltage between residential ground and neutral. For medium size users, like commercial stores and restaurants get both hots and neutral for full 460v/230v service, like U.S. but at twice the voltages.

Rural, out of the way country locations get some wierd configurations. There are even some setups still around that the transformer HV primaries (25kV) have only one wire feed, relying on earth ground for the transformer primary return current. If you do the math the primary is only carrying less then 2 amps but earth resistance can still cause a lot of voltage fluxuations at the user end.

 

[Nigel Goodwin]

Most of Europe uses a 460/230 split-phase transformer secondary with center tap of transformer as neutral connection which is also grounded at transformer. Neutral and a single side hot line is brought to residence. Your neighbor may get neutral to other hot end of transformer. In this configuration there should be no voltage between residential ground and neutral. For medium size users, like commercial stores and restaurants get both hots and neutral for full 460v/230v service, like U.S. but at twice the voltages.

You're getting confused by the peculiar American system - Europe (and most of the world) use three phase mains, not the American split-phase system.

So there are three lives and one neutral from the mains, and for domestic premises neutral and one live is provided, with alternate properties connected to alternate phases, to spread the load evenly, allowing a much thinner neutral cable then the lives. Commercial premises commonly have all three phases, required for large industrial machines (our small goods lift at work if three phase).

Certainly in the UK, and as far as I'm aware most countries?, the neutral is connected to earth at the transformer that drops the mains to 220/240 (depending on country, and nominally 230 in the EU) - and this is the basis of any kind of 'safety' from earthing appliances.

It sounds like the OP's pipes might not be earthed? - I would suggest checking from where the pipe (which obviously must be metal) actally enters the building - as there may be plastic piping inside, insulating where he tested to.

UK regulations require that ALL metal pipes are earth bonded using suitably thick wire, but this only applies to new builds, or when upgrading (there's no requirement to modify old buildings).

Edit: A quick google shows that most of Norway has a floating mains supply, see IT Network here:

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

Nasty!

 

[Reloadron]

Hi Nigel

Yes, as I mentioned earlier Norway is floated. That is why the OP saw the strange voltages.

This is off topic but anyway...

As to US mains and split phase. US mains are configured much like UK mains. Power distribution is 3 phase. The load in residential areas is divided over the three phases. For example in my more congested area we have three phase running down the road. Let's say L1, L2 and L3. Typically about 7 KV. A single transformer may feed three to five residences with each transformer alternating from phases for load balance. Moving out towards the rural areas only a single phase of the three is run. Much like the UK, in industrial areas frequently 3 phase is delivered to the end user. Anyway, in my area a single phase of the 3 available is run through a step down transformer delivering 240 volts center tapped with the CT grounded. Thus the US 240 / 120 split phase delivered to residences.

Ron

 

[king.oslo]

Alright. You guys are gods! So what is the verdict? Can I ESD-grond to the pipe or not?

Thanks! M

 

[Reloadron]

The pipe has my vote as to dissipating ESD.

Ron

 

[Nigel Goodwin]

The pipe has my vote as to dissipating ESD.

I would agree - assuming it's a metal pipe?

 

[Reloadron]

I would agree - assuming it's a metal pipe?

Uh yeah, metal pipe, as in conductive metal pipe.

Ron

 

[king.oslo]

Yes. I have now connected my ESD equipment on the conductive metal pipe M

 

[BrownOut]

Man, am I glad that's settled

 

[kiriakos-gr]

Most underground water pipes this days are plastic. PVC

You can always made your own ground triangle if you have soft soil next to your home.

 

[king.oslo]

@ everyone helping me to settle this: Thank you!! You are all very knowledgeable.

@*kiriakos-gr: I do. Where is the tutorial to make a grounding triangle? M

 

[Zerotolerance]

It all depends on what part of norway you live in and how old your house is.

New Construction in Norway uses a TN earthing system.
Old Construction uses a IT Earthing system

A TN Earthing System uses a ground at the mains (distribution) transformer.

An IT Earthing System has no connection to the earth at all. The House is the only thing connected to ground.

If you have metal (cast iron) pipe then I can almost guarantee you are on the IT earthing system.

Oops Oslo, sry I thought you were talking about the drainage pipes rather than the copper supply pipes. I had to go re-read your post. I apologize

 

[king.oslo]

My mains outlets don't have earth ground output. Perhaps it would be a good idea to implement one?

The cold water pipe is made of copper.M