We purchased a high end printing machine. The print machine vendor told us to provide electrical outlets with less than 3 V between earth and neutral else the machine might get damaged. Since the earth to neutral Voltage was above 10 V in our premises he suggested us to go in for an online UPS (uninturreupted power supply) with a built-in isolation transformer. we bought an online UPS with a built-in Isolation transformer as he said. After installation, we tested the neutral to earth voltage and it is still the same (10~11 volts). The UPS technician says that you will get the earth volt which already exists. Is this correct or was the Print machine vendor was correct? We are confused. Someone please advice.

 

A couple of things don't seem right.

There should be 0V between earth and neutral.

There ought to be no damage to the equipment if there is a small voltage difference between earth and neutral.

 

hi d14,
Welcome to AAC.
I had bought or intended to buy a machine that could be damaged by Earth to Neutral potential greater than 3V, I would ask why is a machine being sold with such a serious design flaw.?
E

BTW: there is about 25v between E and N on my domestic system, which is not unusual for this area and causes no problems.

 

I remember many moons ago an electronics magazine suggesting that you could free light by connecting low voltage bulbs between E and N.
Presumably now this would trip an ELCB?

 

In my residence, if there were potential difference between E and N the GFCI would trip.
I had to go and measure the voltage and got 0V reading on 200VAC range.

 

Earthing arrangements are different in different countries, and probably different areas and different circumstances.

If you accept that the printer requires less then 3V E-N (which sounds like unfit for purpose to me) then why buy a UPS?
Isolation transformer sounds sensible, but I don't see what an UPS gets you.

All very odd....

 

Earthing arrangements are different in different countries, and probably different areas and different circumstances.

If you accept that the printer requires less then 3V E-N (which sounds like unfit for purpose to me) then why buy a UPS?
Isolation transformer sounds sensible, but I don't see what an UPS gets you.

All very odd....

Thanks Hex. The purpose of an Online UPS is to give backup when there is a power outage as the print job will end abruptly and we will have to start over again (time, resource and money loss).

But the purpose of Isolation Transformer has not solved my earth to neutral problem.

 

The purpose of an Online UPS is to give backup when there is a power outage

Ah... that makes sense now, thanks.

 

A couple of things don't seem right.

There should be 0V between earth and neutral.

There ought to be no damage to the equipment if there is a small voltage difference between earth and neutral.

Thanks for the reply. But when I checked the earth to neutral voltages at random on many occasions over the past week and a half, I have seen variation like 17~18 v during morning time. 10~12 v during noon and less then 5 v during evenings. I am not able to understand this variation. Yesterday when I had checked in the evening it showed 18v.

 

Thanks for the reply.

As

I remember many moons ago an electronics magazine suggesting that you could free light by connecting low voltage bulbs between E and N.
Presumably now this would trip an ELCB?

Thanks for the reply.

As such I dont have an ELCB installed to my mains, which I am intending to do tomorrow, as it will trip it there is a residual or earth leak.

But will this correct my earthing problem? Please suggest.

Thanks.

 

Ah... that makes sense now, thanks.

Thanks for the reply.

But I am wondering why the Isolation Transformer which was built in in my UPS didn't bring my earth to neutral Voltage down as expected, or were I mislead?

Please suggest.

 

hi d14,
Welcome to AAC.
I had bought or intended to buy a machine that could be damaged by Earth to Neutral potential greater than 3V, I would ask why is a machine being sold with such a serious design flaw.?
E

BTW: there is about 25v between E and N on my domestic system, which is not unusual for this area and causes no problems.

Thanks for the reply.

I never thought from this angle.

But my printer vendor is not ready to start installation without me showing him the required <3 V diff between neutral and earth.

BTW : THIS IS A HP LATEX BASED LARGE FORMAT PRINTER 330 SERIES. FOR REFERENCE PURPOSES.

 

MAYBE an isolation transformer could have one output leg connected to building earth, but that would be highly dangerous if done wrong, and might well violate local safety laws. You need a qualified and licenced installer to certify any installation, or you could end up liable for any injuries caused.

Don't envy you the job of sorting it. It all sounds pretty dodgy.

... and don't believe anything said on this forum (especially my words). The advice may or may not be good, but useless in a court of law.

Does the Printer vendor provide an installation service? That might (or might not) shift liability to them. Be sure to get an installation safety certificate. EDIT: ah, I see they won't

Wonder what country you are in?

EDIT2: Hard to believe that HP are selling a machine that has such strange earthing limitations. I will just have to settle for not understanding. I am no expert anyway.

 

But will this correct my earthing problem?

I don't see how it could. As stated above, earthing arrangements vary from one country to another. It's my understanding, for example, that in the US the N and E are bonded at the consumer unit, whereas in the UK they are bonded at the sub-station and hence the wiring between the sub-station and consumer unit can develop a voltage difference between N and E which varies with load currents drawn from the substation.

 

We purchased a high end printing machine. The print machine vendor told us to provide electrical outlets with less than 3 V between earth and neutral else the machine might get damaged. Since the earth to neutral Voltage was above 10 V in our premises he suggested us to go in for an online UPS (uninturreupted power supply) with a built-in isolation transformer. we bought an online UPS with a built-in Isolation transformer as he said. After installation, we tested the neutral to earth voltage and it is still the same (10~11 volts). The UPS technician says that you will get the earth volt which already exists. Is this correct or was the Print machine vendor was correct? We are confused. Someone please advice.

Neutral to earth;
At the power plant the Neutral is connected to earth.
A long cable will run between the plant and your home with all types of loads connected to it.
Most of the time not symmetrical resulting in a shift of neutral to earth.
A earth lead is placed in the ground near your house but NOT connected to the Neutral.
When one phase, in the circuit, is running 50% more load than the other two phases an uplift will occur. I did measured 73V at a certain point in time.
System 3 x 240V 400 Amps 16 houses and one metal welding company.
A few houses where connected to one phase.
This is not a problem all grounds are elevated.

Your system does comply to the standard if it can't handle this uplift.

Picbuster

 

Earth ground methods often vary by country as @hexreader mentioned, For example, in the UK at one time the ground conductor could not come in contact with the N Anywhere in an installation, even the service panel, as it does in N.A.
Max.

 

1) Advice from experience: You need a professional with a good knowledge of the codes in your country.
2) I have observed N->E voltages in commercial laboratories, even virtually new ones, of up to 10V. A value of 3V was common. I routinely put instruments that need to be connected in any way electrically to each other (e.g., a recorder/printer to an analytic instrument) on the same outlet or outlet circuit (e.g., with 220 + neutral or 3-phase + neutral). That solved a lot of the problems.

These references may help:
https://electrical-engineering-portal.com/6-wiring-grounding-problems (See: Fig. 7)

NEC 250-26
http://www.psihq.com/iread/grounding.pdf (definition of Separately Derived Systems)

(d) Separately Derived Systems. A premises wiring system whose power is derived from generator, transformer, or converter windings and has no direct electrical connection, including a solidly connected grounded circuit conductor (neutral), to supply conductors originating in another system, if required to be grounded in (b) above, shall be grounded as specified in Section 250-26.

It appears that a transformer will allow you to use a separate ground connection.

 

It appears that a transformer will allow you to use a separate ground connection.

That has been common practice in many Industrial systems per NFPA79, especially where the supply is 3ph and a 1ph control transformer is used, one side of the secondary is taken to the service earth ground and becomes the neutral.
See TFmr connection X2.
Max.

 

www.powervar.com (they were called One AC) has some very good youtube videos on power conditioning.

I believe their conditioners basically allow you to remake the neutral to ground connection after the isolation.

In the building where I worked we had two issues that are related to your problem:

1. A broken ground in an outlet strip
2. Up to 470 possible defective duplex outlets that one of them would loose their ground depending on the mechanical positioning of the plug.

This is a 120 V system and a laboratory. N-G voltages were around 60 V. I know why it's about 60.

If you say take a computer and a parallel printer and plug them into outlets with this difference. One of both devices will get hurt.

Under my watch, I requested that we use a oneac power conditioner and an ISOBAR surge suppressor for a soon to be obsolete computer (PDP-11/2). I did self-mainenence to the module level, but that would do away with DEC going under. All computer problems were power supply, floppies and fans.

We replaced that system with a MAC computer. It ran 17 years before replaced. Only issues were dust, the fan and the floppy drive.

Since the success rate was so good, we budgeted in the upgrade power conditioning for a portable backup system (computer and electronics) and another system. UPS wasn;t necessary, but it needed to work nearly every work day.

The building ground needs to be looked into.

Ground currents need to be looked into. Some idiots grab ground a draw power from it. Unfortunately, I found about 5 home made systems that did, but the powers that be said, it worked for 25 years and still is, so don't fix.

If the difference does not exist from where you "could pull power from". An independent ground may help. Your protective ground can be conduit or Bx, but the Ground reference goes back to the panel.

If this printer communicates with anything that uses ground as reference and they are at different potentials, you have a problem. If the printer mfr uses surge suppression and suppresses ground to N voltage above some value them you will break that.

 

But I am wondering why the Isolation Transformer which was built in in my UPS didn't bring my earth to neutral Voltage down as expected

Earth to neutral voltage can be caused by the neutral current (which the earth line doesn't carry) causing a voltage drop due the line/contact resistance.
The isolation transformer would have no effect on the neutral current, thus no effect on the voltage difference.