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### Ground to Neutral Voltage

04/11/2012 2:11 PM

we are having 230 vac.we have made grounding for the system. but we still have ground to neutral voltage of 0.6v. our desired value is 0.2v.how we can reduce the ground to neutral volatge below 0.2v.

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#1

### Re: Ground to Neutral Voltage

04/11/2012 2:50 PM

It's kind of arbitrary to set a minimum value for a "system" without knowing what the "system" consists of.

If you are running 10 or more three phase motors of varying capacites and loads...then things get complicated.

Just throwing those numbers out there doesn't mean much to me.

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#12

### Re: Ground to Neutral Voltage

04/26/2012 3:25 AM

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#2

### Re: Ground to Neutral Voltage

04/11/2012 7:10 PM

The reason you have any voltage difference between neutral and ground is because you have current flowing on the neutral. Why did you choose 0.2 volts. 0.6 is not much.

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#3

### Re: Ground to Neutral Voltage

04/11/2012 10:28 PM

Thanks for the reply.we have cep stabilised laser system.for properfuntioning of the laser system we need less than 0.2 volts.if it is more then the system does not work properly.

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#4

### Re: Ground to Neutral Voltage

04/11/2012 10:46 PM

VEry strange, what kind of equipment are designed to work within voltage range of Neutral and Earth !! Are you sure?

Some imbalance in 3 phase system is perfectly normal, you cant get perfect balance.

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#9

### Re: Ground to Neutral Voltage

04/12/2012 2:44 PM

Oh...now that sounds like a good reason!

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#13

### Re: Ground to Neutral Voltage

04/26/2012 3:26 AM

according to comany specs its should be less than o.2volts.

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#5

### Re: Ground to Neutral Voltage

04/12/2012 12:37 AM

The voltage between the Neutral and Ground depends on the distance (Resistance) of the nearest Grounding point. (Normally at the switchboard/ Fuse box).

IF the voltage (between Ground and Neutral) is too high, there may be some faulty appliance (creating a fault current to ground) causing an imbalance.

Also: the position of the 'Grounding Rod' needs to be checked.

Permissible Resistance varies in different countries/ states (check local regulations).

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#6

### Re: Ground to Neutral Voltage

04/12/2012 2:45 AM

At some point in your system, the neutral and ground circuits are tied together. This connection is called the X/O bond, and is usually at the service entrance. It may be simply a long screw that goes through the neutral bar, through the insulator, and into a threaded hole in the back of the breaker box. That screw may be missing, or loose, or stripped, or corroded. At that, good, bonding point, there is no voltage difference between the ground and neutral. From there the neutral and ground circuits take separate paths. In theory, there will be no current through the ground circuit, it is only there to protect you if there is a short from the hot wire to the case of the equipment you have plugged in. However, there is current through the neutral circuit. The voltage difference from one end of this wire to the other end, is a function of the current and the resistance of the circuit. Ohm's law says that E=I*R, voltage = current(amps) times the resistance (ohms). All sizes of wire have resistance, it is dependent on the size of the wire and the length. Larger diameter wires have a lower resistance for the same length. The resistance of wire of any given size can be looked up. It is given as a value per distance, for instance 2.5 ohms per 100'. If you research the size of the neutral wire in your installation, measure the current through the wire under normal operating conditions, and multiply these together, you should get the voltage drop from one end of the wire to the other. If the value you get is higher than that, you may have a loose or corroded connection somewhere that is introducing more resistance, and therefore more voltage drop. If the math checks out, and the drop is still unacceptably high, then the only two choices you have are, 1 reduce the current in the neutral circuit by turning things off, or 2 increase the size of the neutral wire.

This is assuming, (and we all know what that means), that you are measuring the voltage difference from a ground wire that is connected to the ground at the service entrance, to a neutral wire that is tied to the neutral bus in the same service entrance and that they are properly bonded together at that point. Beware, there are sometimes shortcuts that are allowed, which may make this a little more complicated. Sometimes, one neutral wire will be used for more than one outlet or circuit, and the two or more other connections may be at any point from the outlet to the service entrance. This could lead to more current flowing in portions of the neutral path than you would measure at the outlet you are working at. Another shortcut that I have seen is the use of metal conduit as the ground circuit. I have seen a metal conduit separate above a drop ceiling, (because the screws on the coupling were never tightened) causing the outlet at the other end to not have a functioning ground. Personally, I don't trust anything except an unbroken wire that goes directly from the outlet to the service entrance for critical circuits.

Good luck.

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#8

### Re: Ground to Neutral Voltage

04/12/2012 4:53 AM

Thanks for the good suggestion.i will try to check this points.

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#10

### Re: Ground to Neutral Voltage

04/12/2012 2:56 PM

Damn dude...why not just have him read the Green book and be done with it? Sounds good.

I would also suggest an isolation transformer dedicated to the input of the "laser".

Keep it close and the runs short. Utilize a single point ground and maintain it for the entire space which the equipment is housed in. Balance the panel and keep the PF as close to unity as possible.

Regardless of what anybody says...it is possible to get to a PF of 1.00 for sensitive electronics loads. They are not usually incredibly reactive by their nature.

It's more expensive to keep the critical and support loads separate, but it makes the mission much easier to accomplish (and can deliver neutral levels less than the .2 "requirement").

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#11

### Re: Ground to Neutral Voltage

04/12/2012 6:01 PM

The use of an isolation transformer is a good idea. That may solve all his issues by itself, but this seems to be very sensitive equipment that he is hooking up.

In broadcast facilities, I have designed and installed separate critical load, generator, and main distribution panels. They can be a pain to set up but are well worth the effort. Along the way, I have been taught some hard lessons that may be of use to anyone setting up sensitive equipment.

The generator is never big enough to run everything, so it's loads must be separated from the main building. Included should be the critical loads plus hallways, bathrooms, exit lights, security systems, and some lighting in critical equipment rooms and studios. If possible, the break room refrigerator and water coolers are welcome during a long outage due to, say, a hurricane. Radio and TV stations need to stay on the air during outages. And don't forget to include the engineering workbench and shop. Where else are you going to fix the broken stuff during the storm?

Air conditioners can be a real problem for a generator. The start-up current can be a real deal breaker. This problem can even sneak up on you. I was doing an extended test of our emergency circuits one weekend. I killed the main disconnect to the building, and everything seemed to be fine. We stayed on the air, and I started working on a project in my workshop. Suddenly the lights blinked out, and I heard a sound that I can only describe as a cross between a scream, and the wail of a tortured demonic spirit. This lasted for only a few seconds, then everything was back to normal. I started looking around, but couldn't find anything wrong. Then about ten minutes later it happened again. It turned out that a five ton air conditioner was trying to start it's compressor. It overloaded the generator, and caused the voltage to drop so low that everything went off. The HVAC unit had a time delay relay installed that prevented the compressor from starting for ten minutes after a power outage. This protects the compressor from trying to start up against a full head of pressure after a short power glitch. Our earlier system tests, had all lasted for less than the ten minutes of the "delay before make" time delay relay.

The sound I heard was the 30 KW generator. It was a direct drive generator connected to a natural gas fueled engine. It was inside of it's environmental enclosure, 50' outside of the brick building, on the other side of our on air studio from me. The studio had one modestly sized, double pane 1/4" thick glass, sound trap designed window set in double walls built with two isolated frames, triple layered sheetrock, and with 12" of sound absorbing insulation between them. This building and studio were so sound proof that we never heard any airplanes, even though we were in the main glide path for one of the runways of Houston Intercontinental Airport, and planes were only a few hundred feet high when they went directly over us. I still don't have any idea how that generator made that much noise.

The critical circuits must be generator backed up, but further, they must be better protected from surges, over and under voltages, and outages. That protection can include multiple and better surge protectors, ferroresonant transformers, full time uninteruptable power supplies, enhanced chemical grounding systems, and dedicated distribution panels.

One last thing for my soap box for today, when installing surge suppressors, keep in mind that surges caused by lightning happen very, very fast. These surges are so fast that in some ways they act like radio frequency signals. This means that they don't like to make sharp turns, don't make neat 90 degree angles in the wires. They also happen so fast and the voltage is rising so fast that the length of the wires between the suppressor and the protected circuit becomes critical. It takes time for the spike to travel along the wire and because the plot of the voltage rise is almost vertical, the difference of a few inches can make a great difference in the voltage passed on to the protected circuits.

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#7

### Re: Ground to Neutral Voltage

04/12/2012 3:11 AM

This particular issue has been covered in CR4 many times. To describe a repetition of it as tiresome would be an understatement.

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#14

### Re: Ground to Neutral Voltage

05/15/2012 2:48 AM

hello rodney , to reduce that neutral / ground voltage to have a 6meters ground rod that if you are in wet ground but if you are in a dry or desert location you need 12 meters deep hole and to make a good grounding result you need to cut bronce plate littlebit the size of your hole and put it insde the hole flat position and next your ground rod and get 3 bucket of chacoal pulborized it ang then mix in two bucket of salt then pour on the grounding hole get two bucket of water pour it together then next the soil that way you can si the good result of your grounding system. this we are using in high voltage transmossion line grounding system,

hope this will make your jod done !!!!

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