2391-10 Written Exam - 01/12/11

[cr0ft]

Just sat this tonight. What does everyone that sat it tonight think of the paper?

 

[pfjt]

There wasn't a question on earth electrode resistance was there

 

[brav]

Wot about the Supply Transformer to MET for tt, tns, tncs? Did u start at Transformer i.e. transformer, supplies Line conductor.. etc, or start at MET i.e. MET, installations Earthing Conductor...?

 

[leonard]

Yes Banjo that's what i did the only supply characteristics that you cant measure.

 

[pfjt]

I don't remember this question how was it asked

 

[Danm1877]

The volt drop answer was 0.38x30Ax1.2=13.68v. Which is over 11.5v and exceeds the maximum volt drop. But I couldn't work out if the roller shutter was in a private or public installation as it was in a retail outlet but not part of the shop??????! This would change the max volt drop.

 

[cr0ft]

Our tutor told us the day before the exam that you no longer multiply by 1.2 now. Hope he was right or I am wrong on that one!

 

[Marnik]

Votage drop calculation formula= R1 + Rn x 1.2 x Ib
So in this case = 0.38 x 1.2 x 30
Voltage drop = 13.68v = 5.95 % DOES NOT COMPLY!!

 

[leonard]

hi marnik have you maid it up because the formula for calculating the volt drop is Vd=(R1+Rn)xId
and on GN-3 said that on circuits supplying motors with high inrush starting current is allowed higher voltage drop and 1.2 factor is not mentioned.

 

[i=p/u]

well im getting taught at present and last year level 2 they didnt mention that 1.2 factor for voltage drop

 

[malcolmsanford]

The volt drop answer was 0.38x30Ax1.2=13.68v. Which is over 11.5v and exceeds the maximum volt drop. But I couldn't work out if the roller shutter was in a private or public installation as it was in a retail outlet but not part of the shop??????! This would change the max volt drop.

???????????

 

[Danm1877]

There is different % of allowed voltdrop from a electrical installation that is in a public area than one it is a private area. Hope this solves your ???????????

Sounds like we are all being taught something different!

 

[pfjt]

It's not areas it's distribution networks there are public distribution and private distribution ie if a factory has its own transformer in its own substation or public is if you are off a standard substation

 

[malcolmsanford]

There is different % of allowed voltdrop from a electrical installation that is in a public area than one it is a private area. Hope this solves your ???????????

Sounds like we are all being taught something different!

I suggest you have another think about that.

As far as I was aware the only deviation in the volt drop values allowed in the BS 7671-2008 concerns motors and is regulation 525.4 in the BRB. Now as the C&G 2391 based on the BS 7671 perhaps that is what you mean when referring to a roller shutter.

 

[NMc]

Q1 was something like this - an inspection of an installationis being done as part of an intial verification. What 3 conditions must be verified?

Q4 purpose of initial verifcation as per GN3

 

[NMc]

In a way you are both right App 12 has two for a public (DNO) system and two for a private supply. 525.4 is as stated in quote

The question as I remember was something like - a single phase motor is running slow and gets hot and it is believed it is a volt drop issue
1. calc vd if L1 & LN is 0.38 and motor load is 30A
2. does vd above meet regs
3. one course of action to be taken if vd is too high and why

I suggest you have another think about that.

As far as I was aware the only deviation in the volt drop values allowed in the BS 7671-2008 concerns motors and is regulation 525.4 in the BRB. Now as the C&G 2391 based on the BS 7671 perhaps that is what you mean when referring to a roller shutter.