2391 Past Exam Paper

[Spazz]

Im doing a past 2391 Paper now, a question has come up - dont think it applies to 17th regs but want to check

State the correct title of the protective conductor that is connected between two extraneous conductive parts


Am I right in saying this is the bonding between the water pipes and radiator - therefore not covered under the 17th regs?

 

[Spazz]

Also another one - I don't do an 3 phase work hardly

Am I right in saying the test voltage of an IR test on 400V three-phase kiln is 500v DC?

 

[Silly Sausage]

Im doing a past 2391 Paper now, a question has come up - dont think it applies to 17th regs but want to check

State the correct title of the protective conductor that is connected between two extraneous conductive parts


Am I right in saying this is the bonding between the water pipes and radiator - therefore not covered under the 17th regs?

I would say 'Supplementary Bonding Conductor' 544.2.3 in BRB

Also another one - I don't do an 3 phase work hardly

Am I right in saying the test voltage of an IR test on 400V three-phase kiln is 500v DC?

Yes.

 

[Spazz]

still not sure about the top one - my tutor expects us to know what is not covered in the regs as well - if I put this answer in and its not covered in 17th Regs he will mark it wrong even though it may have been right when this paper was issued - hes a T***

 

[spark 68]

still not sure about the top one - my tutor expects us to know what is not covered in the regs as well - if I put this answer in and its not covered in 17th Regs he will mark it wrong even though it may have been right when this paper was issued - hes a T***

Why are you still not sure ?, supplementary bonding is still used in the 17th ed. particularly in some special locations, agricultural locations used for livestock for one (sec. 705 BGB), it is still one valid method of additional protection.

 

[Spazz]

ok thanks spark68

 

[Spazz]

Doing some more past papers now - Question:

If the temperature at the time of the test was 20 C (no factor) and the cable is 70C pvc (factor 1.2), determine by calculation wether the measured vales are acceptable (Ze = 0.4 ohms)

32A Circuit 1.07 - Max Zs 0.83 Measured Zs

Can someone confirm the way to do this one please and I can do the rest - Am I right in saying that its not 1.07 x 0.8 = 0.83?

 

[trev]

What's the 1.07 Nicholas?
I'm not sure if I'm reading your question correctly but you take the tabulated values from 7671 and apply the 0.8 rule of thumb to that then compare it to the measured value to see if it complies

 

[Spazz]

Sorry should of posted it like this:

32A - Circuit - MCB
1.07 - Max Zs
0.83 - Measured Zs

 

[trev]

I get .856 for the adjusted tabulated 7671 value so you're just inside of that

 

[trev]

Good grief looking at your question again it's clear what you meant, sorry Nicholas must be that auldtimers disease catching up with me

 

[Spazz]

the Question

a)If the temperature at the time of the test was 20 C (no factor) and the cable is 70C pvc (factor 1.2), determine by calculation wether the measured vales are acceptable (Ze = 0.4 ohms)
b) If correction factors were unavailable, which method would be used to make a valid comparison of measured and tabulated values? - Rule of thumb?
c) Using this method indicate whether the results would be acceptable. - Max Zs x 0.8 = acceptable or not

 

[Spazz]

The values:

32A Circuit
1.07 Max Zs
0.83 Measured Zs

10A Circuit
3.43 Max Zs
2.4 Measured Zs

6A Circuit
5.71 Max Zs
4.4 Measured Zs

 

[trev]

The Ze is a bit of a red herring as you'll be getting that included when you measure ZS because Zs =(Ze+(R1+R2)) as you know
So using the same values as a minute ago this time, because your max allowed is 0.8 ohms you're going to be outside it.
0.8X0.8=0.64< your 0.83 measured.
Assuming all your values are the same

 

[trev]

So the logic is if Max allowed Zs from 7671 x 0.8> measured Zs you're ok and the circuit complies

 

[Spazz]

so where does this cable factor come into it?

 

[Spazz]

I was thinking because we have the cable factor do I:

0.83 x 1.2 = 0.996
1.07 Max = Acceptable

 

[trev]

I'll have to go and dig my 2391 notes out

 

[Spazz]

Here is the whole question - might make more sense

 

[trev]

Ok I'll put my hands up here, I'm drawing a complete blank on this cable factor. It can't be a derating factor as they are considered at the design stage and an up rating factor makes no sense