The neutral is the return path which completes
the light bulb circuit.
An open neutral on the light bulb is analogous
to a bird sitting on a high voltage overhead wire.
The bird is not harmed (nor would a light bulb be) because
there is no complete circuit.
In greater detail; a light bulb supplied with line voltage
will rise to line voltage with a current flow equal to it's
capacitance (perhaps 10^-15 Farads). However, without
the potential difference across the filament supplied
by the neutral (return), no current will flow.
I have your additional details.
Switching neutral leaves the fixture at line voltage
with the switch off. The socket, wiring, and fixture will
present a hazard when re-lamping or servicing.
I welcome your new details regarding a traffic light.
In theory, a fixture with three bulbs should have three
plugs and not four. Each cord carrying active should have it's
own return.
If I understand your device; your neutral plug is internally common
for three lamps.
Firstly, this would put three times the load on a single conductor.
Second, if any one of the active lines is plugged in when neutral
is not; the other two exposed active plug blades will rise to active
voltage.
The arrangement might appear satisfactory, but it is not fail-safe,
does not meet any standard of electrical practice, it is not worth
the risk for whatever novelty value the device might possess.
Lee26loo could handle your traffic light safely and you might as well,
but bare in mind that children and pets do in fact stick their fingers
in empty light sockets as well as conductive foreign objects into outlets.
Do you assume wide spread good judgement, and common sense?
The response about a switched neutral is correct. The circuit will be completed but the shock hazard is present at the object when the circuit is not complete.
A simplified way to look at this is. The active wire has a pressure of electrons(voltage). These electrons will flow to neutral/ground(amperage)if there is a path. If the path goes through the light (resistance) the light will glow.
I am not sure what the object breaking has to do with this. It can happen if the pressure of electrons (voltage) is higher than the light can withstand.
The answer is NO ! Nothing will break and nothing happen and of course lamp would not light up because it is an OPEN CIRCUIT.
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As for your last additional question....
"Occasionally a light fixture is mis-wired and the neutral is switched.
The circuit works the same, but is not safe, due to shock hazards."
ANSWER:
It is still safe because all wires, junctions and lamp socket are sealed and nobody will do such a stupid act to touch the bare metal lamp socket by insert finger into it.
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" I plug all 4 plugs in the wall. The green yellow and red gets all plugged on. If I take out only the red and yellow actives, green will only be on (with the neutral/earth plug plugged in).
So this is safe or not safe? Just want to be sure. "
ANSWER:
SURE IT IS SAFE !
You should settle to the previous good answer even if he was "born yesterday".
Ok, here is a light bulb.
I know if you connect earth and neutral wires but not connect the active wire to the house. The light will not lit up. The object will not break.
If you connect the active wire without the neutral and Earth wires plugged in. Will the object break? Or will it simply not light up?
The object is the light bulb (lamp).
