The difference between safety grounding and power grounding

Please see the Wikipedia article on earthing systems.

Emc²,

I am sorry to feel a need to give a negative vote. Lifting grounding or grounded (neutral) wires, although a theoretical practice, is generally unsafe and strongly discouraged. I believe the OP was asking a different question than your answer. When working on circuits that have been disconnected from the mains or supply, it is often desirable or even required to install a safety grounding conductor from the de-energized wires to ground. This is to bleed to ground the induced voltages that can still be lethal as well as to provide a short-circuiting ground path in case the conductors accidentally become energized. Power grounding is done whenever an application requires a limit to the voltage between the energized conductor and the ground potential. It is done via transformers for systems that are not designed with a grounding point or at the source of supply for systems that have a commong grounding point available.

Regards--JMM

Or try this.

A "grounded" conductor normally carries current.

A "grounding" conductor does not normally carry current.

All power "grounding" conductors are used for safety.

i suggest a reading of two papers here . . .

http://www.schneider-electric.com/documents/technical-publications/en/shared/electrical-engineering/dependability-availability-safety/low-voltage-minus-1kv/ect173.pdf

http://www.schneider-electric.com/documents/technical-publications/en/shared/electrical-engineering/dependability-availability-safety/low-voltage-minus-1kv/ect172.pdf

Consider a transformer with a center tap.From the center to either leg is one half the voltage from leg to leg.If you relate this to a pole transformer, the same applies.The supply voltage (in the USA) for residential, is 240/120 volts at 60 cylcles.The center tap is the neutral, which is bonded to ground at the pole, to a #6 copper wire that runs down the pole to a coil of wire on the bottom of the pole.This is called the MGN, or Multi Grounded Neutral. All power poles in the USA are connected to each other in this manner.This is also connected to the uninsulated neutral wire that goes from the pole to your house.

If all loads are 240 volts, and you have no 120 volt loads, the neutral (center tap) will carry zero current.This condition rarely exists, so the neutral carries the unbalance load return.If you have all 120 volt loads, and they are balanced across both phases equally,there will be no current on the neutral wire.This is also a very rare condition.So it is safe to say that in residential apppilcations, the neutral always carries some current.

The equipment grounding conductor, however is always green, and the terminal screws must be green where it attaches to the equipment.

At the main panel it is required for the neutral and equipment ground to be bonded together, along with the ground rod, and the metal plumbing piping, however ,in a subfed panel, they must be separated.The idea is to prevent a difference in potential between the two systems by providing a single ground point.The green provides a safety route if a short develops on an appliance or tool.This will cause the breaker to trip or the fuse to blow, thereby protecting the user from a dangerous shock.

Since the neutral and equipment ground are going to the same place on the main panel, one may ask "what's the difference, whether I use a ground or neutral?" The green wire is an emergency-use only lane, whereas the neutral is a busy interstate highway.There will always be sufficient current carrying capacity in time of need on the green wire.

Hope this helps.

HTRN

which country?

dear

safety grounding - the grounding done for the safety of human and equipment

power grounding- the grounding done for the fault protection