stuck on a question :(

[Jamie1990]

if anyone could help with this question i would greatly appreciate it...

explain why the following info is needed at the design stage of the installation on the extension;

a) the value of external impedance
b) new assumed current demand for the installation
c) disconnection time of the external bulkhead type luminaire

thanks in advance for any help

 

[telectrix]

that's not a complete question, surely. extension to what?

 

[malcolmsanford]

1 Value of external impedance (Ze) to prove an external earth fault loop and also to ascertain your Zs value or the internal earth fault loop as in Zs = Ze + (R1+R2)

2. To ensure that the new loads from the additrion will not be detrimental to the existing installation.

3. To ensure that during the event of a fault the operation of the protective device is achieved

 

[1shortcircuit]

Jamie, Probably worth keeping your questions to your week 4 TMA in one thread

I am also at this stage and have been working my way through the answers.

 

[Jamie1990]

thank for the advice guys

 

[Jamie1990]

also, another question im stuck on is...

when carrying out an insulation resistance test on an installation, state one reason for each of the following;

a) circuits under test to be de-energised

d) using an insulation resisteance tester capable of producing a minimum test current of 1mA at a minimum of 500V

e) operation or linking of two way and intermediate light switches


again any help or advice would be GREAT, thanks in advance

 

[Steve01_609]

I'm also stuck on this question.

 

[telectrix]

a. & b. you are measuring the insulation resistance between conductors. this relies on applying a voltage at least twice the operating voltage of the circuit. all IR testing is done with the circuit under test isolated from the supply.

c. you operate or link switches so as to include switch wire and strappers in the test.