In relation to cable voltage drop;

(a) explain how allowance is made for conductor operating temperature when the cables are carrying less than their maximum full load current where;

(i) the conductors of the circuit are less than 16mm²

(ii) the conductors of the circuit are more than 16mm²

(5 marks)

(b) explain how allowance is made for load power factor where;

(i) the conductors of the circuit are less than 16mm²

(ii) the conductors of the circuit are more than 16mm²

(5 marks)

A 400v three-phase load has a design current of 57A with a power factor of 0.75.

The load is supplied via a 16mm² three-phase multicore 70°C thermoplastic insulated and thermoplastic sheathed, non-armoured cable which is clipped direct (method C). No circuit rating factors apply.

What is the maximum length of the circuit considering the operating temperature and the load power factor in the assessment to ensure that the voltage drop does not exceed 2.5%?

(10 marks)

In relation to cable voltage drop;

(a) explain how allowance is made for conductor operating temperature when the cables are carrying less than their maximum full load current where;

(i) the conductors of the circuit are less than 16mm²

(ii) the conductors of the circuit are more than 16mm²

(5 marks)

(b) explain how allowance is made for load power factor where;

(i) the conductors of the circuit are less than 16mm²

(ii) the conductors of the circuit are more than 16mm²

(5 marks)

A 400v three-phase load has a design current of 57A with a power factor of 0.75.

The load is supplied via a 16mm² three-phase multicore 70°C thermoplastic insulated and thermoplastic sheathed, non-armoured cable which is clipped direct (method C). No circuit rating factors apply.

What is the maximum length of the circuit considering the operating temperature and the load power factor in the assessment to ensure that the voltage drop does not exceed 2.5%?

(10 marks)

I think that I shall pass on Level 4, though it could be interesting. Could one do 2396 without a portfolio of practical experience?

Now Lyle, that question is somewhat ambiguous, and therefore with a number of traps. I would love to see the examiners ideal answer and the marking scheme.

David, unless you have a cat suit and a swag bag and are prepared to sneak into the ivory towers at Giltspur Street London where the secrets of the Universe are stored, or you sign up for assessing scripts, you have no chance of getting any idea what are acceptable answers. 

So this is my attempt so you can assign me marks as you feel appropriate.

Glad to see you back, by the way!

By the way, the candidate has 18 minutes to make a response. It took me about 24 minutes to do above with no time for checking. This would be only one question out of 10. So any one with a 2396 deserves a pat on the back, sympathy for those who have tried and failed! 

Hi Lyle

Yes that looks like a very good answer. However I expect it took you a bit longer because of the neat (!) typed equations etc! In an exam neat writing is usually secondary, in my experience. For anyone not entirely familliar with the reasons why the volt drop varies with power factor, it is because the peak current no longer corresponds to the peak voltage, so the peak may well be somewhat unaffected by the current caused volt drop. A good question would probably what is the actual RMS calculated effect, with what the waveform might be, but that would be really quite hard. 2396 is notoriously hard, but getting a pass on the written paper is not the killer, it is the project which takes an awful ot of correct work to turn in a good file. It might be rare that real designs are as good as the projects, but who am I to say that