2394 exam question

[N6rul]

how can the polarity of a single phase supply be confirmed?
I'm looking at t his question and thinking are they asking me to confirm polarity at circuits or the supply at db. Confused, they just don't make it clear. Someone please.

 

[lauriehurman]

Test voltage relative to earth.

If you mean the dead test for polarity then that's just a continuity test of the line conductor.
Otherwise;
If you have a cable with 3 conductors and you test Line to earth you will get 230v, if you test line to neutral you get 230v, if you test neutral to earth you will get zero. So even without the insulation colours you should be able to tell in most circumstances the polarity.

Beware - this won't come up in your exam but you should understand that just because you have 230v to earth on a conductor doesn't mean it's not a neutral.


Laurie

 

[MDJ]

how can the polarity of a single phase supply be confirmed?
I'm looking at t his question and thinking are they asking me to confirm polarity at circuits or the supply at db. Confused, they just don't make it clear. Someone please.

Have you got an exam coming up then fella?

 

[N6rul]

2394

MDJ
Yes mate, in december. I'm trying to get much info as possible from experienced electricians, I have been doing it for 10 years, with a company now they decide to send me on all these courses. Lol!

 

[Poorle]

Re: 2394

10 years and you don't know the answer to that question?

 

[stuartcourt]

Mate I think you need to chill and not worry about it so much, if you have been doing it for 10 years I am sure it will be alright on the night, as I have said a few times keep doing your homework and remember they are not trying to trick you it will be reasonable questions

 

[stuartcourt]

And if you can stand the initial abuse on this friendly forum log in each day for an hour and you will learn that I promise

 

[Engineer54]

Mate I think you need to chill and not worry about it so much, if you have been doing it for 10 years I am sure it will be alright on the night, as I have said a few times keep doing your homework and remember they are not trying to trick you it will be reasonable questions

Things must have changed a hell of a lot since my day's of exam questions then!! lol!!

The knack was reading the question at least 3 times, to understand what is actually being asked!!

 

[stuartcourt]

True I was trying to be nice

 

[SirKit Breaker]

how can the polarity of a single phase supply be confirmed?
I'm looking at t his question and thinking are they asking me to confirm polarity at circuits or the supply at db. Confused, they just don't make it clear. Someone please.

They want the polarity of the supply. Think about how the supply is supplied to the property (TN or TT), and look at the circuit the supplier supplies, and i guarantee you that the penny will drop if you have 10 years experience. GN3 also covers it, so i would buy one and revise it.

Cheers.............Howard

Cheers............Howard

 

[iamelectric]

i am doing the 2394 course and this question has come up , if u read a few of the examiners reports they say students did not understand that initial verification was before the installation was energized , then another says when asked how to confirm polarity of a supply students were say use a low resistance ohm meter which i would say was correct as the installation is not energized but they said its incorrect so they dont even make sense and these are the people who are marking them

 

[Adam W]

Presumably they want to know what tests you would do to confirm polarity.
Remember polarity is the test you carry out as part of the dead testing and the live testing; dead testing you would confirm the polarity of the switching with an R1+R2, but I think they're really after the polarity of the incoming supply.
After dead testing you'd test Ze; before you press the test button your meter will give you the supply voltage and tell you if it's OK to proceed, ie if the polarity is OK.
Remember the first thing you do before any of that?
Safe isolation. Measure L-N and you should get 230v. L-E 230v. N-E a lot less than 230v.

 

[SteveEmartin]

Remember if they are talking about testing they will be following the sequence of test from guidance notes 3. Polarity is classed as a dead test so they will be looking for an explanation on how to verify polarity whilst it is not energized...

 

[iamelectric]

yes but as stated in the first post supply of what they should make the question more clear , i sat the written exam last week and one of the questions was list 6 items to be inspected on a pvc conduit system before the wiring is installed , then the next question was list what you would inspect for the 6 items above , wtfs that all about , a tip for anyone who is doing the course know your on site guide inside out because most of the questions are from that , i spent months reading over GN3 and doing 2391 mock exams and only 2 or 3 questions from them where in it

 

[Adam W]

If it's anything like the old 2391 it really helps to know what's actually written on the forms, ie what's written next to the boxes which you tick.