# how to check AC electrical outlet using a digital multimeter:

Joined Feb 4, 2022
110
It is common to have power supply sockets installed in our homes.

I want to understand how it is measured whether it is 230 AC volt or not using multimeter.

AC supply has three terminals, Line, earth neutral. If I want to find the line in these three holes, then I can find out which line using tester. But if I don't have a tester and can't even see the wires, here's how to find out which are line, earth and neutral with a multimeter.

I don't not understand how to connect the multimeter black and red probe into the socket I know red should be connect to the line and black should be connect to either neutral or Earth. But by looking at the holes on socket, it is not known which is line, neutral and earth, so how will we identify?

Please explain the logic behind testing electrical outlets using a digital multimeter.

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#### Dodgydave

Joined Jun 22, 2012
10,238
Usually the right-hand hole is the Live and the Large hole at the top is the Earth.

Set the meter on AC voltage and put the red probe in the right hole and the black in the left , it will read the designed voltage.

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#### Alec_t

Joined Sep 17, 2013
12,733
There should be no voltage between the left and top pins, if neutral and earth are wired properly.
I don't know if that's true for the 'round-pin' plugs in all countries, but for the 'square-pin' type (BS1363) the left-hand connector position (as seen looking at the face of the socket) is Line..

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Joined Feb 4, 2022
110
I have a doubt which I want to clear as seen in the given image in which we are measuring voltage, for this we have put the probe of multimeter in the socket

I want to know that after interchanging the probes, will I get AC voltage, is it safe if I interchange the probes?

this is the basic question i want to understand about electricity

#### MrChips

Joined Oct 2, 2009
25,920
Since this is AC the colour of the probes make no difference.
Interchange the probes and you will still get 240VAC.

Joined Feb 4, 2022
110
Since this is AC the colour of the probes make no difference.
Interchange the probes and you will still get 240VAC.
Thanks a lot, I did both the tests successfully. I saw 250 VAC volts on the multimeter display.

Joined Feb 4, 2022
110
So if I put a probe in one of the down hole and the other probe in the upper hole, will there be a short circuit?

I am thinking because there will be one earth and other will be neutral connection

#### MrChips

Joined Oct 2, 2009
25,920
So if I put a probe in one of the down hole and the other probe in the upper hole, will there be a short circuit?

I am thinking because there will be one earth and other will be neutral connection
DMM typically have 10MΩ internal resistance when in voltage measurement mode. This is not normally considered a short circuit.

#### MisterBill2

Joined Jan 23, 2018
11,580
One consideration is mechanical, not electrical. A friend poked a probe too far into a poor quality USA style outlet, and the probe made contactwith both the line connection and the ground frame of the outlet. That is notpossible with a standard line plug, but the probe was quite a bit longer. There was a very impressive spark and a loud noise, and a portion of the probe was evaporated. All of us were rather startled.

With a high-input-resistance digital multimeter it is often possible to determine the "Line" terminal by holding one meter probe tip between my fingers and probing with the other probe. Ground and neutral circuits give no indication but a line circuit will show several volts. Do not try this with ananalog meter because the resistance ids MUCH lower and probably a shock be received.

#### Ramussons

Joined May 3, 2013
1,228
I have a doubt which I want to clear as seen in the given image in which we are measuring voltage, for this we have put the probe of multimeter in the socket

View attachment 267183

I want to know that after interchanging the probes, will I get AC voltage, is it safe if I interchange the probes?

this is the basic question i want to understand about electricity
You seem to be a beginner should not be playing around with mains voltages. Do not do these tests when alone.

#### MisterBill2

Joined Jan 23, 2018
11,580
OK, and that is an interesting electrical outlet that I am not familiar with.
Measuring voltage in an AC circuit in this manner, exchanging the connection positions will have no effect on safety or accuracy of the measurement. What is important is to avoid contact with the metal portions of the probes while doing the connections. When either probe is inserted the other probe is now energized to some extent. Thus making the connections to read the voltage demands caution to avoid contact with the active portions of the probes. Thus the arrangement in the photo is quite safe, and exchanging the positions of the red and black connections will also be quite safe.

I do suggest reading about ac power circuits so as to gain understanding of what is involved.

#### Ian0

Joined Aug 7, 2020
4,838
OK, and that is an interesting electrical outlet that I am not familiar with.
It was standardised in Britain in 1934, hence it found its way to the Indian subcontinent, Africa and some of the Caribbean (but not Austrialia and New Zealand). It was replaced in Britain by the 13A with rectangular pins and a built-in fuse from 1947, due to the introduction of the 30A ring-main to save on expensive copper after World War II. The 5A version is still in use in Britain for lighting circuits (usually in a drawing room where there are a number of table- and standard-lamps all controlled by one switch or dimmer. The 15A version is used in theatres for the outputs of dimmers so that dimmed circuits don't get confused with ordinary 230V circuits. It is being superseded by the 16A IEC-309 connector, as luminaires are being replaced by DMX-controlled luminaire and dimmed circuits are being phased out.

The socket in post #5 which appears to have 5 pins will take either a 5A or a 15A plug. That was never used in Britain, and I think is an Indian standard.

So now you know!

#### MisterBill2

Joined Jan 23, 2018
11,580
OK, and thanks.

#### MrAl

Joined Jun 17, 2014
8,864
It is common to have power supply sockets installed in our homes.

View attachment 267177
I want to understand how it is measured whether it is 230 AC volt or not using multimeter.

AC supply has three terminals, Line, earth neutral. If I want to find the line in these three holes, then I can find out which line using tester. But if I don't have a tester and can't even see the wires, here's how to find out which are line, earth and neutral with a multimeter.

I don't not understand how to connect the multimeter black and red probe into the socket I know red should be connect to the line and black should be connect to either neutral or Earth. But by looking at the holes on socket, it is not known which is line, neutral and earth, so how will we identify?

Please explain the logic behind testing electrical outlets using a digital multimeter.
Hi there,

I guess you made some progress with this already and found the pair that gives you 230vac or whatever you have in your location, but be aware that you should be able to measure that in two ways. First is hot to neutral, 230vac, then there is hot to ground, should also be 230vac. Neutral to ground should be zero or very low.

One funny thing about this though. With the advent of digital multmeters the input impedance went up by a huge amount over the older analog meters. This presents a problem for some measurements because even if there is a rather large resistance in the line you will still see 230vac. Load it with a 10k resistor however, and the voltage could drop significantly.
So when using a digital multimeter with high input impedance it is best to load the outlet with at least a 10k resistor, but if you dont have that then you can use a small table lamp. Plug it in then do the measurements as above.

This isnt always a problem but in once case it really is a problem and that is when looking for a leakage current such as in a bathroom (but really anywhere).
A bathroom is a little more critical because there is water around and when taking a bath or shower you are subject to having to stand or sit in water and so you dont want anything around that is 'live' that you can reach and touch. TO check to see if it is live, you can use a meter to measure from the case of the device (such as ceiling lamp) to the ground. Now in theory you should nto measure anything and with an older analog meter you will measure either zero or a small voltage. With a newer multimeter though you may measure a higher voltage that makes it look like the lamp fixture is not wire correctly when really it is. So to get a better idea what is what it is best to load the device with at least a 10k resistor, and for a leakage test or rather a reversed wireing situation you should use a 10k resistor that can handle the power of a 230vac line voltage.
It's important to get this right because you dont want someone in the shower reaching up to touch the case of the lamp fixture and getting a shock which could be very very bad.

You may also find this 'unloaded' problem with some light switches too. They will appear to be turned 'on' when really they are not. This is especially with older light switches that may have a little carbon buildup. Again, use a small load like 10k or something.

In all these tests you would put the 10k resistor across the two leads of the multimeter thus reducing the input impedance of the meter by a huge factor and thus it will not pick up and unusual leakage current which will mean you will get a better picture of the situation.
Unfortunately at 230vac you will need to use a 10k, 10 watt resistor and watch that it does not get too hot if you touch it. You can try a 50k resistor that may work also with 230vac. In that case a 5 watt resistor will be ok.

Ground fault interrupters are also great for the bathroom and kitchen.

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#### Ramussons

Joined May 3, 2013
1,228
It was standardised in Britain in 1934, hence it found its way to the Indian subcontinent, Africa and some of the Caribbean (but not Austrialia and New Zealand). It was replaced in Britain by the 13A with rectangular pins and a built-in fuse from 1947, due to the introduction of the 30A ring-main to save on expensive copper after World War II. The 5A version is still in use in Britain for lighting circuits (usually in a drawing room where there are a number of table- and standard-lamps all controlled by one switch or dimmer. The 15A version is used in theatres for the outputs of dimmers so that dimmed circuits don't get confused with ordinary 230V circuits. It is being superseded by the 16A IEC-309 connector, as luminaires are being replaced by DMX-controlled luminaire and dimmed circuits are being phased out.

The socket in post #5 which appears to have 5 pins will take either a 5A or a 15A plug. That was never used in Britain, and I think is an Indian standard.

So now you know!
It is a 2 pin / 3 pin 5 Amp combination socket. The difference is that the 2 pin 5A spacing is a little less than that in a 5A 3 pin socket.
Of course, you do get a 5 A and 15 A 3 pin combination socket, with and without a switch.