No, never use the neutral conductor for anything but a neutral. If the house has no grounding system then there is no need to connect the fan ground wire to anything. Just keep in mind that the wiring in the house could be 70 plus years old and the insulation on this wire will be starting to break down if handled too much. Just cap the wire off and install the fan. Old two wire knob and tube systems were used in the 20's and they never used a ground with them. In the 40's NMD cable was used but it also never had a ground wire. It was in the early 60's that the third wire was added to NMD cable, it was a bare copper wire that was used for grounding equipment. Now the new wiring code states that there must be a grounding system in place for new installations.
Ground and neutral are only supposed to be bonded at a single location at main panel. If you do this at an outlet and plug in a grounded device you could create what is known as a ground loop and create a possible shock hazard.
In a properly balanced three phase system, there is negligible current on neutral. If there is substantial current on neutral, then the system is not balanced and/or something is wrong.
If the motor is operated from a three phase three wire distribution system the motor will not need a neutral wire.
The current carried by the neutral of a three phase four wire system is the un balanced current. If the three phase system was completely balanced on all three phases there would be no need for a neutral, eg a three phase motor. This neutral current will be less that the phase current so a reduction in the neutral size is allowed.
A reversal of the hot and neutral wires in a wall outlet may not cause a fire, since there is no electrical connection between them. There is a potential for a fire when a device, equipped with a three prong plug, is inserted into this improperly wired outlet. The use of outlet status plugs with luminous indicators help identify improperly wired outlets.
The limit or range of the neutral current in an unbalanced three phase system is the third harmonic in single phase non-linear load current is the major contributor to neutral current.
No a 208 volt outlet does not need a neutral. 208 volts is the line voltage between any two legs of a three phase 208 volt system.
the bare copper is always a ground
A delta-connected system is described as being a three-phase, three-wire, system, and doesn't have a neutral. But a balanced star (wye) connected load (e.g. a three-phase induction motor) doesn't actually require a neutral.
This can be tricky. You can only place a receptacle from the location of the box where the three way circuit is fed from. The wires from the three way to three way boxes only carry the "hot' traveller wires. There is no neutral carried from box to box even though there might be a white wire in the three wire group. So you have to locate where in the three way system the hot and neutral wires are located. From this location you can extend new black and white wires to your new receptacle outlet.
In a properly balanced three phase system, there is negligible current on neutral. If there is substantial current on neutral, then the system is not balanced and/or something is wrong.
If the motor is operated from a three phase three wire distribution system the motor will not need a neutral wire.
Nominally 120 Volts.
Zero, or very close to it. If there is a large neutral current flowing, voltage drop on the neutral leg could cause a volt or so to read between the two. If you read full line voltage, the outlet is wired wrong!
Earthing point is where conductor is directly connected to ground and its potential is always zero. Neutral is a return path in single phase system and in three phase system Neutral point will have zero potential if all the loads are balanced in the system. In un balanced three phase system even neutral point will have some potential
TPN Load break switch: Is basically a main switch used in three phase system and know as Three pole neutral or Three phase neutral having four connectors for three phases and one neutral.
If all three legs of the system are balanced then zero amps will flow all the way up to 100 amps if only one leg of the three phase system is used. The neutral in a wye three phase system carries only the unbalanced current. This is why in services for a three phase four wire system you are allowed to reduce the size of the neutral conductor.
The current carried by the neutral of a three phase four wire system is the un balanced current. If the three phase system was completely balanced on all three phases there would be no need for a neutral, eg a three phase motor. This neutral current will be less that the phase current so a reduction in the neutral size is allowed.