Should the ground and neutral wires be wired together?

Answer 1

The answer to that question depends on exactly where in the building's wiring is being asked about.

The only place the neutral and ground (or "earth") wires in a building should ever be tied (or "connected") together is at the incoming service main breaker panel "upstream" of all the fuses and/or circuit breakers which are there to protect the hot (or "live") wires for the various circuits installed in the building.

In the absence of an earth wire (= ground wire in US/Canadian English), if the appliance suffered some damage that caused a short circuit between the high voltage "hot" lead and the case of the appliance, the damage would make the case live and it would cause an electrical shock to anyone who touched it.

If the case is earthed by using a ground wire (= earth wire in British English), if that same damage occurred the hot lead would immediately be shorted to ground and in theory cause the fuse to blow or circuit breaker to open, thus eliminating the danger of a live case.

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In the USA I think we refer to what you are calling an "earth wire," as a GROUNDING CONDUCTOR, which in effect is a separate conductor which seems to be doing nothing but is in fact a protective wire. It is there, ready to take the current away to earth if it, or the body/frame of the electrical device it is connected-to, makes contact with any "hot" wire. [120 Volts mains power is carried in two current carrying conductors "hot" and "neutral".]

So, IF one of the "hot" conductors should contact the metal frame or housing - perhaps because the appliance got damaged by being dropped from a table, or similar accident - the third wire which is the "ground" or "earth" wire, which runs directly from the housing to the grounding [or earth bus] in the fuse or breaker panel, will in effect cause a short circuit which should blow the fuse or trip the breaker.

This third wire also guarantees a current path back to the load center where the fuse or circuit breaker protecting that circuit is located, in the event the hot wire should be in contact with the frame, but the other [neutral/return] conductor should happen to be cut, disconnected, or open.

The idea is to guarantee that if a part of the device should become "hot," which could be fatal to anyone who then came into contact with it, would trip/open the circuit protection device [fuse or breaker], turning off the flow of current to that circuit.

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All the neutral and ground (or "earth") wires in a building are tied or linked together at the incoming service main breaker panel. This is the only place they should ever be tied together because it is "upstream" of all the fuses and/or circuit breakers protecting the hot (or "live") wires for the various circuits installed in the building.

Warning: we must never assume that a neutral is safe to touch: it has to be checked with a voltmeter or a voltage indicator to be sure it is not "live". This is because a neutral wire is designed to carry current under normal circumstances.

So, if a neutral wire going back to the incoming main breaker panel has not been properly connected - or suffers a deliberate disconnection or some accidental damage which causes it to break - then it and any neutral wires connected to it further downstream will go live up to the break because of being connected to the downstream loads which still have hot feeds coming into them!

That is why we should never use a neutral as a substitute for a proper, separate, ground or "earth" wire.

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In addition to the above description it should also be mentioned that the presence of an earth wire allows a very sensitive safety device called a Ground Fault Circuit Interrupter (GFCI) to operate. It will cut off the power supply to the appliance even if a tiny current of a few thousandths of an Amp is detected flowing in the earth wire, which should normally carry no current at all.

In USA/Canada, and similar countries which use mains supplies running at 120 Volts 60 Hz to feed power sockets, it is probable that the latest designs of GFCIs which are fitted to all new wiring work actually operate in the same way as the RCDs described in the next paragraph, although they are still commonly called GFCIs.

In Europe, where 230 Volts, 50Hz mains supplies are standard in homes, offices, etc. such protective "trip" devices are called Residual Current Detectors (RCDs) because, in addition to being able to detect small earth leakage currents, they have the ability to detect very small differences between the currents flowing in the hot (or live) wire and the neutral wire. Such imbalances might be caused by minor damage to the appliance which allows a small current - known as a residual current - to leak to earth either via the user or via the earth wire (if one is connected) even though the appliance itself is still working. So using an RCD helps to prevent a serious shock hazard to users if ever the kind of minor damage occurs which, in the absence of an RCD, would cause the appliance's casing to become "hot" or live.

Thus RCDs give a very high level of safe operation even if no circuit breaker has tripped and no fuse has blown and the appliance appears to be working normally. (But it has really become unsafe!) Because of the enhanced protection they give to users of appliances the latest European wiring regulations (= wiring codes in US/Canada and elsewhere) make it compulsory to fit RCDs to all new power circuits.

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As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.

Before you do any work yourself,

on electrical circuits, equipment or appliances,

always use a test meter to ensure the circuit is, in fact, de-energized.

IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB

SAFELY AND COMPETENTLY

REFER THIS WORK TO QUALIFIED PROFESSIONALS.

Answer 2

A comment about your statements re: GFCI receptacles.

A GFCi does NOT trip because of current on the ground path. It trips because it senses an inbalance of current between the hot & neutral wires. That inbalance MAY be caused by current flowing on the ground due to some sort of issue in the circuit wiring or the load. But the inbalance may be caused by current flowing ANYWHERE that is not on the hot and neutral, for instance through your body to ground. A GFCI does NOT monitor current on the ground wire. It only monitors the current on the hot and neutral to be equal within 3-4 thousands of an amp, a difference greater than that it trips. That is why GFCIs will work just fine on a 2 wire circuit (no ground). The handy GFCI testers will not work when a GFCI is on a 2 wire circuit because those testers direct some current from the hot and neutral circuit onto ground to cause an inbalance tripping the GFCI. No ground, no inbalance, thus tester doesn't work. BUT if you get an inbalance on a 2 wire circuit, that GFCI will work just fine.

Answer 3

No, they should not be wired together.