I want to clarify some theoretical concepts related to electricity. I am just asking I am not doing it practically because working on this main supply is so dangerous so want to understand first principle for better knowledge



Can it be found with a screw driver tester which is line and which is neutral ? As far as I understand I think yes it can be used to detect line and neutral of main supply. just want to confirm from experience person.

Can a multimeter measure the voltage and current of a power supply?

As far as i know yes supply voltage and current can be measured with multimeter but need confirmation to doubt

 

Generally yes.

There are also fuses or circuit breakers in the system, and these days a ground wire.

 

A screwdriver tester (normally a resistor in series with a neon bulb), will illuminate with the blade in contact with a live (mains) voltage; but not when the blade is in contact with the neutral. It will not illuminate if the live circuit is not energised – so they have limitations.

 

Generally yes.

There are also fuses or circuit breakers in the system, and these days a ground wire.

Look at this picture



When the tester's red light is on does it mean it is a line cable and if the light is off it is a neutral wire cable

 

Look at this picture

View attachment 265720

When the tester's red light is on does it mean it is a line cable and if the light is off it is a neutral wire cable

Neon off, means there is no . or low voltage
could be its the neutral, or could be that its the live with no power connected

And to confuse things,
Some neutrals are not that low a voltage
I have seen neon drivers glow on neutrals if Im on a good earth
Not as bright as the Live but still a voltage,

 

When the light is on, it is in contact with a live (mains) voltage.
When the light is off, it is not in contact with a live (mains) voltage – it could be touching neutral, earth, a floating circuit or nothing.

 

I know that fuse is always connected in series. I do not understand where the fuse is connected, is it connected between the meter and the MCB or it is connected after MCB ?

 

Usually the fuses or circuit breakers for individual circuits are after the main circuit breaker. In my house the main circuit breaker is in the distribution panel that also contains the breakers for all of the circuit in the house. But then again where you live the electrical code is probably different from what it is here.

 

Hi Dadu@,

1. A screwdriver neon tester may be used to identify the 'line'. It follows that the other one is the 'neutral'.
2. The supply voltage may be conveniently measured using a multimeter.
3. It would neither be safe nor convenient to measure line current, using a multimeter, in the absence of terminals to connect it at a break in the line. The right way would be to use an ammeter which would have terminals, unlike a multimeter with test prods.



Nandu.

 

Wrong connection can cause damage to home appliance. Homes can have fans coolers, TVs and so on, so do they need to be checked for polarity to connect to the supply?

 

One of these
https://www.lowes.com/pd/Southwire-Digital-100-to-600-Volt-Test-Meter/1000095087
and you can test for voltages from 100VAC to 600VAC.

A green light means the No Contact Voltage Tester (NCVT) is active. The red light means it's sensing a voltage above 100VAC and is accompanied with an audible alert.

 

Wrong connection can cause damage to home appliance. Homes can have fans coolers, TVs and so on, so do they need to be checked for polarity to connect to the supply?

If you're connecting between Line and Neutral the chances of damage are minimal. A two wire appliance isn't going to be bothered by polarity that much. Mostly polarity is for safety reasons (I believe - but not certain). In a three wire system where you have Hot, Neutral and Ground - yes polarity is critical. The NCVT will only light and beep when close to the live line. Neutral and ground won't trigger it.

[edit] A friend plugged a computer into one outlet and a printer into a different outlet. A previous owner crossed hot and neutral AND they wired the ground pins of the plugs to the neutral line. With the reversed polarity - the computer was case hot (the frame was live) and the printer was properly grounded (for the sake of argument, the neutral acted like ground). When he plugged the printer cable into the computer there was all kinds of excitement and cursing. And an expenditure of money to find where the lines were crossed AND to properly ground all the outlets.

 

In N.A. Red & Blk is L1 & L2 both fused/breaker, there is also a white, a grounded neutral.
The system is a 120v-0(N)-120v.
The Neutral is earth grounded.
Other jurisdictions vary, UK, EU has 1 phase and a neutral of a 3ph system. 230v-240v etc.
In your diagram, you do not show the grounded neutral.
The neutral is not normally fused or broken.

 

In N.A. Red & Blk is L1 & L2 both fused/breaker, there is also a white, a grounded neutral.
The system is a 120v-0(N)-120v.
The Neutral is earth grounded.
Other jurisdictions vary, UK, EU has 1 phase and a neutral of a 3ph system. 230v-240v etc.
In your diagram, you do not show the grounded neutral.
The neutral is not normally fused or broken.

Maxis correct in that what he has stated is how things SHOULD be. But not all home wiring is correct. I have had to deal with variations, I have been knocked of an aluminum ladder once by a hot wire that was supposed to be a neutral. Only fell three feet, but it was really startling.
A screwdriver-light checker can be useful for an experienced person, it can lead an inexperienced person to belive that the power is off when it is not off.