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Topic Title: December 2013 C&G 2396 Exam Help Please!!!
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Created On: 06 December 2013 02:33 PM
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 06 December 2013 02:33 PM
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stebiggy

Posts: 5
Joined: 23 January 2008

Hi Everyone,

I am looking for someone set my head straight for me! Perhaps someone with experience of lecturing or even marking the design course exam.

I sat the 2396 exam last night. I felt I had done quite well, breezed through all the calculations without getting stuck on anything, then managed to answer most of the regulation related questions that make up the rest of the exam. Only issue I had was the time was too tight.

That was until the end of the exam when I was speaking to a few of the other lads. The scenario reffered to the installation of 36x 150w High Bay discharge lights split over 3 phases. So I worked out the Design Current, Cable Size, Protective Device, Volt Drop etc. Problem I discovered was that most of the other lads multiplied the design current by 1.8, which I though was a factor only for fluorescent fittings, not High Bay.

So although I got all my calcs right in a way, infact they were all wrong as all the calcs are based on design current. So my protective device was wrong, cable size wrong, volt drop wrong and so on.

What I am wondering if anyone knows is would you say its curtains for me? I wrote it all out and showed all calcs perfectly, will that still get me some marks that might get me over the line or has simply not putting the 1.8 factor in cost me the whole section?

Any help would be hugely appreciated. I am drving myself mad at the minute!

Thanks
 06 December 2013 02:45 PM
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stevechrry

Posts: 4
Joined: 24 May 2013

Hi stebiqqy.
Did mine also last night @Isle Of Wight College.
Will get back to you shortly.
 06 December 2013 03:26 PM
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OMS

Posts: 19628
Joined: 23 March 2004

OK - I would say that not recognising the fact that a high bay discharge lamp needs control gear and that control gear has losses that needs to be added to the lamp wattage is a pretty fundamental bit of knowledge to anyone acting in a design capacity - particularly as you have the knowledge regarding fluorescent lamps in your head

That said, it's not the done thing as i understand it to continue penalising a candidate for the same error when the results rest on an accumulation of data and results of an initial calculation form the basis of the next - unlike real life of course.

I'm not involved with C&G in any way, but I would be suprised if the error was compounded through the marking such that all your methodology etc was correct but you lost all the marks. I suspect you'll lose a couple but that's it.

At least I would hope that's the case - this is after all an exam not real life - and it will be a harsh lesson for you if true.

Perhaps JP or Marc might be able to comment further - they are both involved in academia with C&G I think

I hope it comes right for you anyway - best of luck

Regards

OMS

-------------------------
Failure is always an option
 06 December 2013 03:31 PM
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Parsley

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I don't think anyone uses the 1.8 factor anymore in the real world,
not sure about C&G land though. last time I asked a manufacturer the lad on the tech phone line didn't have a clue what the 1.8 factor was.

I would have thought if everything else was correct you shouldn't lose to many marks. JP might be able to help.


Regards
 06 December 2013 04:08 PM
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stebiggy

Posts: 5
Joined: 23 January 2008

Thanks for the info so far everyone.

Hopefully JP and Marc will see my plea and give their comments!!
 06 December 2013 04:20 PM
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OMS

Posts: 19628
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Do they not ?

Take a look at an example of a 400W HPS lamp

Nominal lamp wattage of 400W, running current at 230V of 2.20A and at 240V of 2.1A

calculated lamp current at 230V = 400/230 = 1.74A

I make that a factor of about 1.3

That's before you consider any harmonics etc, and the effect of limiting the number of luminaires on a circuit by increasing the lamp running current due to the impact of inrush current by using the higher factor.

I'd be very suprised if any design engineer isn't using a factor exceeding 1.5, if not the full 1.8.


Regards

OMS

-------------------------
Failure is always an option
 06 December 2013 05:20 PM
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Parsley

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http://www.thornlighting.co.uk...-flood-optic/96255682

I was referring to modern control gear with specific data rather than just lamp watts and magnetic ballasts.

What ratio do you make for the data sheet above?

I make it 1.1 but if I'm wrong I would like to understand why.

Thanks
 06 December 2013 05:57 PM
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OMS

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From the data sheet

1 x 100W HIT-CE lamp with electronic control gear.


and

Total power: 110 W


and

Connected Load: 110 W Lambda = 0.96


So whichever way you look at it that's a factor of 1.1 to start with

and that's before you consider harmonics, power factors (although lambda = 0.96 is actually very good in this case), inrush current adjustments etc, etc

If you calculate the current to be 110/240 = 0.46A, then you could get 20 fittings on a 10A MCB protected circuit.

You most probably wouldn't be able to switch them on though

Uing a factor of 1.8 would drop the number of fittings to say 10 or 12 - and a Type C might just survive the inrush.

As a house standard, we tend to allow no more than 40% of the MCB rating as connected lamp wattage expressed as current in early stage design to de risk the inrush component on yet to be selected luminaires.

Regards

OMS

-------------------------
Failure is always an option
 06 December 2013 06:37 PM
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John Peckham

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Stebiggy

I understand the question described sodium lighting. One of my students did not recognise that as discharge lighting as he new about SON and SOX etc. He and you should have used a multiplier of 1.8 for discharge lighting to work out your Ib. If you did not do this that would have compromised the cable calc. as you would have used the wrong In and again in the volt drop question. I don't know how this is reflected in the C&G marking scheme as a single error would impact on the following questions. Hopefully the C&G would award some marks for the formulas and working out albeit arriving at the wrong answers.

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John Peckham

http://www.astutetechnicalservices.co.uk/
 06 December 2013 10:05 PM
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Zs

Posts: 2863
Joined: 20 July 2006

Exam help please it says. That's done and gone so relax.

I know exactly what you are going through right now chaps. I wrote some carp on those pages. I spent days analysing how I had done. I did not finish the paper and my diagrams were worthy of Tate Modern. I know of at least 10 marks that I dropped because I had not written anything.

You must stop going through it in your mind. You know that if you had sat at your desk with that question you would have come up with the correct outcome. Let me tell you from first hand experience that in design for real you are able to think things through rationally. In real life you would have spent some time finding out about a factor for your hibays and would probably have a correction figure, somewhat lower that 1.8 direct from your specified manufacturer, with email evidence. However, I think C&G are in the dark ages and 1.8 is their figure.

That's not actually my point though.

On your desk right now you have a project over which you can mull and into which you can put your own 'take'. That's design. Get it done while you still use the term adiabatic as a mantra to yourself. The written paper can be retaken and my college offered a re take for free well in advance of sitting the exam. The project is a pig but you will not submit it until you are satisfied with it......so get on and do part 2 of this life changing qualification because it still counts.

I know it's horrid. I have the T shirt. But don't sweat the small stuff .

I bet you did just fine. Users of this forum invariably know more than they know they know. Bet you picked up some other marks instinctively that others missed.

Good luck and do the cable runs and calculations of your project first of all. I chucked mine in the bin after 50 hours of work because I realised my containment and cable runs were poo and weren't working as calcs. Do some long ones and some short ones first and then the ones in the middle.

You will be fine.

Edit: 2396 but I still can't type. Edited shocking spelling.

Zs

Edited: 06 December 2013 at 10:15 PM by Zs
 08 December 2013 08:41 PM
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stebiggy

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Joined: 23 January 2008

That was a really great response Zs, thanks. And to the rest of you also.

You have pretty much answered my next question before I asked it, and that is what to do with the project. I am about half way through it but I didn't know if I had to carry on, if I do ultimately fail the exam will this project still count towards the qualification when I take the resit? I don't really want to sit the whole course and do another project just so I can sit the exam again!

Are the resits usually before the next exam or will I have to wait until the next exam is run by C&G? Also would the resit be the same paper or a different one?

Stupid 1.8 factor!!!
 09 December 2013 10:14 PM
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Zs

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Joined: 20 July 2006

Results take about ten weeks.

The project only changes once a year so it might be worth finding out when it runs out so to speak.

I think it lasts as the partner of the written paper for about a year too but you'd better check that.

Where I fell down, if it helps, was on the cable grouping. These days I think in terms of an absolute maximum of 9 circuits sharing a run so as to limit the grouping factor, which is a demon. Even at 9 it is still a big number though so keep to very few amps per circuit. That said, I don't know what the project is this year.

Zs
 27 December 2013 02:51 PM
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stewartrussell82

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Joined: 16 July 2013

Hi I did my exam on the 5th as well, can't remember much about it know, although 3 hours is not long enough.

you should deffinatly do your project, there was a guy on my exam who was on his 3rd attempt, but his original project still counts.

Good Luck.
 31 January 2014 04:45 PM
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stebiggy

Posts: 5
Joined: 23 January 2008

Hi Everyone,

I went to the training centre to hand my project today and the lecturer had just recieved the results from the December Exam. Thanks to all those who answered my initial post, I passed!!

So if anyone else is waiting on results they are imminent and have been sent to the training centres.

Chuffed with myself!

One thing this proves with exams is put everything and anything down on paper, because little things get you those precious extra few marks.

Thanks for all your advise everyone!!
 31 January 2014 06:29 PM
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OMS

Posts: 19628
Joined: 23 March 2004

Congratulations - and good luck with the project

Regards

OMS

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Failure is always an option
 06 May 2014 01:15 PM
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Alex-123

Posts: 42
Joined: 25 July 2008

Hi,
We all make mistakes and as one writer above said you dont usually get penalised TWICE, if you just wrote an answer, say 0.2A and somewhere in the early calcs forgot to multiply it by 10 giving a correct answer of 2A then you would land up with ZERO marks but if you have shown a logical pathway throughout and just omitted to use a multiplier then I would say an Examiner should only knock off a few points. Dont worry and good luck
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