R1 plus r2 reading

[snowplough]

Hi Guys,

Just looking at a mock exam paper as i am takinking the 2391 in 3 weeks.
Trying to find answer to the question of why cant you use Zs - Ze to get R1 + R2 ,
Is it something to do with the temperature diff because the Zs is taken when the installation is energised.

Many Thanks

locket 4241

 

[Deleted member 9648]

It's because satisfactory R1+R2 should be confirmed before the circuit is energised...the correct test sequence of dead tests before live tests is to ensure a faulty circuit is not energised.

 

[snowplough]

Many thanks for that wirepuller, one down loads more to go

Regards

locket 4241

 

[snowplough]

Hi Guys,
Another question i cant seem to get my head around, if you cn help me.

A ring final circuit continuity test revealed incorrect polarity on three socket outlets.The results were:

P TO N P TO CPC

Socket A Open circuit correct
Socket B Correct Open Circuit
Socket c Open circuit Open circuit

State which conductors have reversed polarity in each case.

Im not sure where to start guys ,hope you can help


Regards

locket

 

[Mark.W]

If you were testing continuity on a ring you would want continuity on p-p n-n & cpc-cpc and open circuit between p-n p-cpc & n-cpc. Looking at the options of socket A baring in mind you are testing continuity, p-n is open circuit, which is what you want & p-cpc is correct?! (does that suggest you're getting continuity???)

Question is a bit vague really!

Mark

 

[Mark.W]

Hi Guys,
Another question i cant seem to get my head around, if you cn help me.

A ring final circuit continuity test revealed incorrect polarity on three socket outlets.The results were:

P TO N P TO CPC

Socket A Open circuit correct
Socket B Correct Open Circuit
Socket c Open circuit Open circuit

State which conductors have reversed polarity in each case.

Im not sure where to start guys ,hope you can help


Regards

locket

Socket A : phase - cpc cross polarity.
Reason : If you tested btw phase & cpc you'd get a reading even if they were crossed with each other because you are actually still testing between the same 2 conductors, you then test phase to neutral and get open circuit which means you were actually testing cpc - neutral and not phase - neutral.

Socket B : phase - neutral cross polarity.
Reason : If you test btw phase & neutral you'd get a reading even if they were crossed, if you then test btw phase & cpc and get open circuit it's because your are actually testing btw neutral & cpc

Socket C : n-cpc cross polarity.
Reason : If you test btw phase & neutral and get open circuit, then test btw phase & cpc and also get open circuit, your phase is in the right place but your neutral & cpc is crossed, if you tested btw neutral & cpc, you would get a reading.

Hope this is clear enough

 

[snowplough]

Thanks for Replying,

Im still a little onfused thou,

When i drew this out on paper ,as you said i got anclosed circuit for cpc-line reversal when i looped them at c.u and tested cpc-line at the socket where they were reversed, Now when i tested line -neutral at the same socket with line-neutral looped at c.u i still got a closed circuit when you said it would be open circuit.

Did you mean keep line-cpc looped at c.u but test line to neutral at the socket above which would give open circuit but why would you do that?

Hope you can clear this up for me


Many Thanks again

Locket

 

[Mark.W]

Put it this way, if you tested btw p & cpc you would get a reading even if they were reversed! Now if they were reversed and you linked phase & neutral at cu, then went to socket and tested btw phase and neutral, because they are reversed you would actually be testing btw cpc and neutral!

 

[SPARTYKUS]

Hi Guys,

Just looking at a mock exam paper as i am takinking the 2391 in 3 weeks.
Trying to find answer to the question of why cant you use Zs - Ze to get R1 + R2 ,
Is it something to do with the temperature diff because the Zs is taken when the installation is energised.

Many Thanks

locket 4241

Hi locket 4241

The other reason I can think of (and the sequence is main one, this is just a by product) is that ... it wouldn't work anyway.

When you record a Zs reading, it is with all bonding in place (live test). Therefore there are (or rather, may be) parallel paths that will alter your theoretical reading and give you a different (should be lower!) reading.

 

[snowplough]

Cheers Mark w for reply,

So are you saying that you would get an open circuit ,hence no reading on the meter by testing phase -neut at the socket with the cpc -phase reversed with phase - neutral looped at c.u. If so i cant work out when i have drawn this out i seem to get a closed circuit.

What am i missing ?


Many Thanks

Locket

 

[Mark.W]

Think of it as a loop!

If you link L & N at the cu and go to the socket and test btw L & N, you will get continuity if the polarity is correct!
If the polarity at the socket was reversed btw L & E ( ie E in the L terminal and L in the E terminal) and the link still in btw L & N at the cu, if you tested btw the L terminal and the N terminal there would be no continuity! Because the E is in the L terminal!

 

[snowplough]

Thanks for the reply,

I still seem to get a loop when i draw it out even though i know your right,

im obviously doing something wrong,

regards

locket

 

[IQ Electrical]

Hi locket 4241

The other reason I can think of (and the sequence is main one, this is just a by product) is that ... it wouldn't work anyway.

When you record a Zs reading, it is with all bonding in place (live test). Therefore there are (or rather, may be) parallel paths that will alter your theoretical reading and give you a different (should be lower!) reading.

The parallel paths answer is what C & G are looking for on this question.

 

[Mark.W]

Thanks for the reply,

I still seem to get a loop when i draw it out even though i know your right,

im obviously doing something wrong,

regards

locket

I will draw it for you this evening!

 

[snowplough]

Many Thanks,
But in order to get the Zs in the first place other then by loop imp measurement, havnt you got to no what R1 + R2 is to add to Ze to get Zs?.

Im trying to think it through

So if the Ques is as asking why cant you deduct Ze from Zs to get Ri+R2 you got to already no what Zs and Ze are I think ?

Kind Regards

Locket