Help Level 3 Exam tom struggling

[Danelec73]

can anyone help please? Have an exam tom doing a few test papers at the moment could do with answers to a couple of questions.

Q1-If a resistance of 1.99Mohm is recorded on a final circuit,what action should i take?

Q2-If the Zs cannot be met,how might you get round the problem without installing bigger cables?

Q3- Why would PEFC and PSCC figure be the same in a TN-C-S install? and what does PScc stand for ?

And does anyone know which key on scientific calculator -6 -9 etc

 

[Deleted member 26818]

Q1, look for the break.
Q2 install supplementary bonding, ues a lower rated CPD, or use an RCD.
Q3 because TN-C-S uses a combined conductor for neutral and earth (PEN or CNE). Prospective Earth Fault Current, Prospective Short Circuit Current.

 

[firemanowl]

What exam have you got tomorrow?

 

[Sparky Ninja]

can anyone help please? Have an exam tom doing a few test papers at the moment could do with answers to a couple of questions.

Q1-If a resistance of 1.99Mohm is recorded on a final circuit,what action should i take?

Compare your reading with your assessment of the instalaltion to justify its value. Most likely, further investigation would be needed.

Q2-If the Zs cannot be met,how might you get round the problem without installing bigger cables?

Asess the existing earthing characteristics and determine if a change in protective device may be necessary.

Q3- Why would PEFC and PSCC figure be the same in a TN-C-S install? and what does PScc stand for ?

In a TNC-S system the earth fault return path uses the neutral in the suppliers installation (hence 'combined'). This reduction in impedance in the earth fault return path (that's why it's 0.35ohm maximum btw) will mean a similar fault current in the earthing conductor and neutral. In theory this would become more and more unlikely as you go further down an installation, as more resistance is introduced between the earth and neutral conductors individual return path tho the origin.
PSCC stands for prospective short circuit current.

And does anyone know which key on scientific calculator -6 -9 etc

Huh?

 

[Danelec73]

Apreciate it thank you very much going crazy.

 

[Danelec73]

1st Exam of city & Guilds 2330 level 3

 

[Deleted member 26818]

Similar sort of questions as for the 2391.

 

[Danelec73]

Dont know the Key that i need to press on the calculator so i can do the calculations of mega micro and nano 10-6,10-3 etc

 

[SMB]

I think the answer to question 1 is this......

if a circuit measures 2megohms, or less, then investigation is required.

A circuit passes an IR test at 1 Megohm (upto 500v, selv is 0.5 megohms i think?).

But if it measures 2 megohms, or less, then it needs to be looked into.

good luck.

 

[john25]

can anyone help please? Have an exam tom doing a few test papers at the moment could do with answers to a couple of questions.

Q1-If a resistance of 1.99Mohm is recorded on a final circuit,what action should i take?

Q2-If the Zs cannot be met,how might you get round the problem without installing bigger cables?

Q3- Why would PEFC and PSCC figure be the same in a TN-C-S install? and what does PScc stand for ?

And does anyone know which key on scientific calculator -6 -9 etc

1.) 1.99Mohm is an acceptable result So if you couldn't find any issues with the Circuit from further investigation then you can put down that result on the Schedule of Test results.

2.) As previosly Stated you could de-rated the protective device of the Circuit.

3) again as stated that the TN-C-S system uses a PEN conductor for it's Neutral and Earth which is then separated at the Installation side.

4) to use the -3 or -6 key you use the X10 button at the bottom of the Calculator and then to put the -3 option in you press the Little - button thats on the left side of the Calculator.

 

[j.mawer]

On some calculators its labelled exp so you would press exp 6 and then the +- key

 

[firemanowl]

Have a look on your calculator for the 10 with a small x button. E.g 3.75 10x button-6 ohms is the same as 0.00000375 ohms. Hope this makes sense.

 

[r10ley]

To get (to the power of) its normaly a button either displaying x10 (supersript x) or sometimes its called exp. The button is normaly left of the Ans button.

Good luck in exam : )

r10ley

 

[SMB]

1.) 1.99Mohm is an acceptable result So if you couldn't find any issues with the Circuit from further investigation then you can put down that result on the Schedule of Test results.

im not up me own butt or anything.....but....a reading of 1.99 Mohms requires investigation in my book.

 

[john25]

im not up me own butt or anything.....but....a reading of 1.99 Mohms requires investigation in my book.

Thats what I said lol I was just stating that 1.99Mohms is an acceptable test result and that if he could not find any issues from Further investigation then he could put that result down on the Schedule of Test results.