voltage between neutral and ground

[etalaat]

I have supply source with 3-phase and neutral without ground to feed our telecommunication shelter through distribution panel.
we made seperate earth and connected to the panel, and when i measured tha voltage between neutral and earth bar in the panel using DMM i found that it reads 10 volt.what is the reason for this voltage difference. :?

 

[don_resqcapt19]

Is the neutral bonded to earth at any point?
Don

 

[mdshunk]

Sounds like "phantom voltage". Put your fingers on the DMM leads, and the votlage will likely go to -zero-.

 

[yanici]

"I have supply source with 3-phase and neutral without ground"

Neutral is not grounded? Is that correct?

 

[mdshunk]

Ahhh,.. they have a subpanel and they're trying to use the earth as the EGC. Oops... I missed that part. Yeah, that is certainly a potential difference. The voltage will go away when a N-G bonding is added or the 5th conductor run from the MDP.

 

[etalaat]

no connections between earth and neutral.

 

[don_resqcapt19]

If there are no connections between the electrical system and earth the system is floated and the voltage to ground can be any voltage between 0 and the system voltage.
Don

 

[etalaat]

The neutral is earthed from the supply side, but i measured voltage between it and my own earth at the panel.

 

[petersonra]

The neutral is earthed from the supply side, but i measured voltage between it and my own earth at the panel.

what are you refering to when you say "earth"? A rod you sunk in the ground at the new panel or the green wire you ran with the feeder?

 

[dereckbc]

Etallat, I am a telecom power engineer and from what you describe not only violates code but is extremely dangerous to personnel and likely to cuase a great deal of noise and equipment malfunction.

Sounds to me like you fell for the “MY EQUIPMENT NEEDS AN ISOLATED GROUND TRICK”. The panel used for your telecom panel has to have a ground (EGC) ran from the service panel. Sounds like you just added a rod which is floating and isolated from the building ground electrode system. That is why you are measuring a voltage. What you should see is something on the order of 1 or 2 volts between N-G at your telecom branch panel. That voltage of 1 or 2 volts is normal and is a result the I*R voltage drop developed on the neutral from load current.

If you are wanting to establish a new reference point for the telecom panel, you went about it the wrong way. To do this you would need to install a separately derived transformer in the telecom electrical room to establish a new N-G bond and reference point. However, even doing this still requires you to use the buildings ground electrode system and not a isolated ground rod.

 

[etalaat]

earth mean rod sung in the ground near panel

 

[etalaat]

Earthing mean rod sung in the ground near our panel

 

[poweringtech]

The voltage you have been measuring is the system capacitance. If the system is ungrounded, in your case the neutral is not grounded, There will still be line-to-ground voltage due to the system capacitance.

 

[lquadros]

voltage drop

voltage drop

dereckbc,
That voltage of 1 or 2 volts is normal and is a result the I*R voltage drop developed on the neutral from load current.
Can you elaborate please? Thank you.

 

[tallgirl]

dereckbc,
That voltage of 1 or 2 volts is normal and is a result the I*R voltage drop developed on the neutral from load current.
Can you elaborate please? Thank you.

Ohm's Law.

If neutral and ground are connected at the panel, and 10A flows on the neutral wire between the panel and wherever you measure, and the resistance of that wire is 0.1 ohms, the voltage drop is 1 volt because "volts = amps * resistance".

Makes sense?

 

[W6SJK]

If there are NO metallic connections between your telecom building and the building containing the power source then you can bond the neutral to ground and set the usual grounding electrodes. If there ARE or will be any future metallic connections between buildings, including shields of signal wiring, then you have to run an equipment grounding conductor with the feeder conductors to the sub panel.