UK 3 phase testing

[Asjad]

Dear All,

I have recently been told to to test the presence of voltages on a 3 phase supply,
i.e to find if a fuse has blown on a phase.

I am familiar with working with a normal single phase UK supply.
Can anyone tell me how to test UK 3 phase supply.

Using a multimeter (connections, readings to expect?), neon indicators circuit?


CHeers

 

[rigdoctor99]

I have one suggestion, If you dont know how to test 3 phase systems leave them alone...........
If this is for your job, then ask a suppervisor to explane it to you....... You will get badly hurt or even killed if you dont know what you are doing.........

3 phase systems have greater voltage and current than a domestic supply...

LEAVE IT ALONE

 

[JimB]

I second the warnings which RigDoctor has given.

Now lets try and give a little bit of insight into a 3 phase supply.

There are three phases, they are named Red, Yellow and Blue. If you are lucky the cable cores will be identified with those colours.
There is usually a neutral connection, but depending on the application it may not be used.

Measuring between any two of the phase wires you should measure 415volts, so:
R to Y = 415v
Y to B = 415v
B to R = 415v

Measuring between the phase wires and neutral you should see 240 volts. So:
R to N = 240v
Y to N = 240v
B to N = 240v

The power supply to a street of houses is three phase, the first house is connected to red and neutral, the second to yellow and neutral, the third to blue and neutral and so on down the street to balance the load on the three phases.

A three phase motor has three windings, and there are two ways of connecting those windings. The two ways are referred to as Star and Delta.

The star connection has the three windings with one end connected to a common point (the Star Point) which can be connected to the neutral line of the supply. The neutral connection is not necessary as no current flows in the neutral on a balance 3 phase system.

The delta connection has the three windings connected end to end in the form of a Greek letter delta. With the delta connection there is nowhere to connect the neutral, it is not required.


I think that is enough for now, it only just gives the minimum of information.
Be carefull there is no reset button on reality. Death is permanent.


JimB

 

[Nigel Goodwin]

Measuring between the phase wires and neutral you should see 240 volts. So:
R to N = 240v
Y to N = 240v
B to N = 240v

Just a little update - the nominal mains voltage in the UK has been 230V for many years now, it was standardised as such across all the EU (we were 240, the rest were 220).

However, we use a different tolerance to the rest of the EU, so 240V comes within it's acceptable limits.

 

[Hero999]

However, we use a different tolerance to the rest of the EU, so 240V comes within it's acceptable limits.

I thought we all use the same tollerance, both 240V and 220V are within the tollerance.

 

[Nigel Goodwin]

I thought we all use the same tollerance, both 240V and 220V are within the tollerance.

No, I can't remember the actual figures, but it's something like 230V +/-5%, and the UK is 230V -3%/+7% - you get the idea!.

 

[Hero999]

https://en.wikipedia.org/wiki/Mains_electricity
Interestingly the UK is +10/-6% while the EU is +/-10%.

 

[Nigel Goodwin]

https://en.wikipedia.org/wiki/Mains_electricity
Interestingly the UK is +10/-6% while the EU is +/-10%.

I wonder if that's correct or not?, it seems a bit pointless doesn't it? - it would make more sense +14/-6% - otherwise why bother been different?.