Whenever the National Electic Code says to do so.
Or, when the inspector tells you to.
If you mean where, there is a neutral busbar in your breaker panel, from which goes a wire to a ground rod outside your building.
As Lewish says, in the U.S. you must comply with the NEC. Connection of the neutral to ground is called "bonding" and it is covered in Article 250. This is generally done where the utility service enters a building (at service entrance equipment) or at the source of a separately-derived system (transformer).
In general, the neutral is connected to ground at only one place.
As dpc say, you must "bond" the neutral to ground. If you have a metallic piped water supply in the building (house) you must also bond to that with a separate wire other than the one which must go to a ground rod outside. In the state of Washington, you must run ground wires to two separate ground rods which are located more than 10 feet apart.
Here in Ireland there is no such requirement. However, the supply authority will usually provide a separate ground facility or connect the installation ground to their neutral. Do supply authorities in the states generally provide grounding facilities for their consumers?
I take it that all metal parts in the electrical installation are connected in some way back to this grounded neutral? Regards,
if you are referring to a control transformer...say 240V/120VAC...one leg of the secondary 120VAC is hot...and the other leg is the "NEUTRAL"... you use a ground wire from the transformer termination point to the chassis ground...normally just beside the control transformer..then that is the time you run the neutral wire to the designated terminals...
keep in mind that the neutral wire is being picked up from the "transformer" not the chassis ground...
dydt, help me to understand. You call the connections to the secondary side of a control panel as hot and "NEUTRAL". If the "NEUTRAL" is not grounded at the transformer, will this "NEUTRAL" be a neutral at all and will it "float" with respect to ground. If so, would this cause problems?
RE: If the "NEUTRAL" is not grounded at the transformer, will this "NEUTRAL" be a neutral at all and will it "float" with respect to ground -- Yes, but this would be illegal. It's required to be grounded.
RE: If so, would this cause problems? -- Yes, it would be considered a safety hazard.
No electric genious here, all that I read was correct.
Would like to add however that it would be best if the designer always considered how a neutral was functioning.
In the US - Because neutral is used to make a circuit, if it is bonded anywhere beyond the service it causes the ground system to become part of a circuit, not a great idea. If neutral is bonded after the service, and either the ground or the neutral develp a high resistance then the ground circuit becomes energized.
NEC code allows the shell of the conduit to be the "equipment ground", the non-current ground it must be bonded full length on the conduit run.Bonding means there is no metal breaks in this conduit.Some local codes require a green insulation colored wire to be used for the "Equipment ground" instead of the conduit, but the conduit still need to be grounded and bonded.
The conductor everyone call the neutral is called the "grounded conductor" in the NEC.
The neutral and "equipment ground" need to be grounded at the service to a water pipe and usually a ground rod or ufer ground "concrete encased wire that is in contact with the soil". The metal frame of the building must also be grounded to the same water pipe and ground rod.
Every transformer secondary (Certain exceptions) must be grounded to the soil too, using the various methods stated.
The control transfomer is a little different it can be grounded from the equipment grounded conductor. Only if you have a good equipment ground that is solidly bonded and if your local building department/inspector allows it.
If you can run a insulated green colored cu wire form the service grounding bus it would be best, but if it is rework sometimes it is hard to do.
Post this question with EC&M web site for more answers. They address these types of questions all the time with some really great NEC code experts. Code interpretations vary with different people and areas.
You may ground the Neutral on a 120 VAC single phase circuit at different places. For instance, there will be one ground wire from the Neutral bus bar to the Ground bus bar in a breaker box for power coming into a house. The power company's Neutral is grounded separately. You DO NOT want to USE THE POWER COMPANY'S GROUND.
It's important to remember that the Neutral is connected to
Ground in ONE PLACE ONLY within a "system".
Sometimes a ground grid is used, with multiple ground rods. This is still typically connected in ONE place to the Neutral.
