- #36
Averagesupernova
Science Advisor
Gold Member
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Lenny, I'm just curious about the practices in the UK.
Here in the USA we commonly have 200 amp 240 volt residential services. What size do you have in the UK? You say there is no transformer. Just how far away is it from the residence to the first transformer?
lennybogzy said:well, in series with earth
Studiot said:If the centre tap were not grounded a condition could arise where the centre to one line voltage was 130 , 140, 160 or whatever.
I_am_learning said:Can you please elaborate on how that could occur?
I am still unclear here. Suppose the transformer is 11KV/240V (with center taps).Studiot said:AS, you are not understanding.
It is a statutory requirement for the power company to deliver 230volts (within tolerances) to the supplier/consumer interface at the property meter.
The capacity of the three phase supply running past not only one property but the perhaps hundreds in that road, has to be sufficient to supply all the property spurs.
Yes the consumer may suffer voltage drop if his own wiring runs are too long - there are standard formulae to determine this.
You effectively stated this by saying 'relocate the transformer' ie it is the power companies responsibility to size the feed cable/voltage to the transformer primary to achieve the desired secondary output.
IAL,
Take a transformer with a centre tap.
The voltages between each end and the centre are equal in magnitude (and of opposite phase)
Now short out one or more turns.
The voltage between one end of the transformer and the tap is now different from the voltage between the other end and the tap, as it is no longer exactly half way along the winding.
Or, as I said, the tap has shifted its voltage position from the centre.
Although the end to end voltage will have reduced it is now unevenly distributed betwen the two outputs so the bigger 'half' will be greater than 120.
go well
Is it safe to touch the neutral conductor standing on ground.
I'm sure you don't mean "short out one or more turns". That would lead to a lot of current flowing in those shorted turns and would either burn out the transformer or get it very hot and waste a lot of energy. Far better to subtract some turns from the end of one secondary ('tap down', as they say).Studiot said:AS,
Take a transformer with a centre tap.
The voltages between each end and the centre are equal in magnitude (and of opposite phase)
Now short out one or more turns.
Studiot said:Further there is a definite danger in the british system of unwittingly grabbing the wrong wire.
This is because the wiring colour for neutral is also used for line voltage in certain circumstances (light switches).
So a wire carrying the neutral colour will be either at line voltage or disconnected if part of the light switch circuit.
This is very annoying, bad practice and there is no excuse why a professional electrical installer shouldn't use a different pair of colours in the cable that runs from the ceiling rose to the light switch. A different cable with yellow down to the switch and a brown up to the lamp would avoid any problem. But this cannot be a problem, only with the UK system. It will happen anywhere where they are too stingy to use a different cable colours for light switch cirtcuits.
I_am_learning said:"Why don't we connect the neutral itself to the equipment body and totally eliminate the use of ground wire?"
Perhaps a Diagram would help.Evil Bunny said:Because we don't normally want current flowing through our equipment bodies. We would rather keep it in the wires.
I_am_learning said:So, I was asking what are the bad things about the protection scheme of the Upper Diagram?
yes iam pretty sure they are conductors so can the fifth wire be the 'protective conductor' because in two phase supply someone said that there are three wires and the third wire is 'protective conductor' so can in three phase fifth wire is protective conductor?Studiot said:Difficult to comment on your local wiring system as I know nothing about it.
Are you sure they are all conductor wires, not supports?
What about the size of grounding wire? Are they also selected more thicker to increase factor of safety? But, I don't think that will be necessary because the current flows only for very short time.
Studiot said:AS, you are not understanding.
It is a statutory requirement for the power company to deliver 230volts (within tolerances) to the supplier/consumer interface at the property meter.
The capacity of the three phase supply running past not only one property but the perhaps hundreds in that road, has to be sufficient to supply all the property spurs.
Yes the consumer may suffer voltage drop if his own wiring runs are too long - there are standard formulae to determine this.
You effectively stated this by saying 'relocate the transformer' ie it is the power companies responsibility to size the feed cable/voltage to the transformer primary to achieve the desired secondary output.
...in no case shall
they (equipment grounding conductors) be required to be larger than the circuit conductors supplying
the equipment.
It just seems to me that it more impractical to run low voltage (by this I mean 240 volts) the long distances you tell me they are run in the UK compared to the shorter distances we run here in the USA.
So, the answer is no... The "ground wire" doesn't need to be any bigger than the line and neutral wires.
The neutral wire is a current-carrying conductor that completes the electrical circuit, while the earth wire is a safety measure that provides a low-resistance path for current to flow to the ground in the event of a fault.
Having both a neutral wire and an earth wire ensures that the electrical circuit is complete and that any excess current is safely directed to the ground. This helps prevent electrical shocks and fires.
No, the neutral wire and earth wire have different functions and should not be used interchangeably. The neutral wire is intended to carry current, while the earth wire is only meant to be used in the event of a fault.
The neutral wire and earth wire work together to create a safe and reliable electrical system. The neutral wire carries the return current from the electrical load, while the earth wire provides a low-resistance path for any excess current to flow to the ground.
If the neutral wire is damaged or missing, it can cause an imbalance in the electrical circuit, leading to potential hazards such as electrical shocks and fires. If the earth wire is damaged or missing, it can result in a lack of protection from electrical faults, increasing the risk of electrical shocks and fires.