What is AC does it have a polarity.

[ericmark]

I know the BS7671 tells us to test polarity and it means test the voltage in respect to earth. But AC changes its polarity in step with the frequency. So this image:-

shows an alternating current zero to max without any change in polarity. But in the main I am sure we would call this DC. However the current is still alternating and if you connected the supply to a transformer it would still transform it although not very well.

So real question is if the polarity refers to positive or negative what word should be used to refer to relationship of the live wires in relation to earth? Polarity seems the wrong word.

 

[Gerrydelasel]

Potential might be a better choice of word, since what you're really checking for is which wires are not at earth potential, i.e. they're hazardous.

 

[ericmark]

I think you are spot on Potential seems right.

 

[Taylortwocities]

Looking at BS7671. The only reference to "polarity" is the para relating to making sure that a single pole switch is in the line conductor.
Otherwise it is not mentioned, or defined.

That is as far as my interest goes in this matter….

 

[winston1]

However the current is still alternating and if you connected the supply to a transformer it would still transform it although not very well.

If you connected that supply to a transformer the large DC component would soon burn out the transformer.

 

[JBR]

shows an alternating current zero to max without any change in polarity. But in the main I am sure we would call this DC. However the current is still alternating and if you connected the supply to a transformer it would still transform it although not very well.

I don't think I'd describe that graph as showing an alternating current. To me, 'alternating' suggests regular change of direction of the current. I suppose a better term for that graph might be 'pulsating DC'.

Mind you, I'm not an electrician, so what do I know?!

 

[ericmark]

I see your point it only alternates in magnitude not polarity. However Gerrydelasel has given the answer I was looking for Potential does better describe the neutral and line not being swapped.

 

[EFLImpudence]

Potential does better describe the neutral and line not being swapped.

And therefore you know which pole is which.