An Awful Feeling This

[Deleted member 26818]

on a side note page 76 gn3

motor circuits

loop impedance tests on motor circuits can only be carried out on the supply side of isolated motor controlgear. Continuity tests between the circuit protective conductor and motor are then necessary.


where would i connect to the motor? would this literally be just clamp on the main body? this is a test i have never done but i have never tested any motors before

You'd have to open up both the motor termination box, and the motor control gear box, and then perhaps with a wander lead test between each termination of each conductor.

 

[Deleted member 26818]

Do you mean phase sequence?

If so, why would you be interested in that before polarity?

No not phase sequence, I've never really bothered with that. If the motor runs backwards, I just swop over two of the conductors.
I'd check continuity of the phase conductors, because if one is broken, or not terminated, you can burn out the motor on energization.
As for polarity, does it apply? There's no neutral.

 

[gap30]

Areas i need to cover big time - ip codes, testing earth electrodes, factors that can affect conductor/insulation resistance, terminology

 

[gap30]

An installation has been seriously overloaded and requires investigation. State
a) the type of inspection and test that would be required. (1 mark)
b) two areas which require close inspection as a result of the overloading. (2 marks)

could this be any 2 from the scope ie SADCOW

Safety,ageing, deterioration, corrosion, excessive overloading, wear and tear

 

[Deleted member 26818]

Overloading of a conductor will cause insulation deteriation and increased resistance.

 

[IQ Electrical]

An installation has been seriously overloaded and requires investigation. State
a) the type of inspection and test that would be required. (1 mark)
b) two areas which require close inspection as a result of the overloading. (2 marks)

could this be any 2 from the scope ie SADCOW

Safety,ageing, deterioration, corrosion, excessive overloading, wear and tear

The SADCOW just leads you back to the question really, the areas for close inspection would be areas that might have sustained damage from the associated overheating:

Distribution equipment and as Spin suggests, conductor insulation properties.

I could make a good case for close inspection of overcurrent protection too, how did that installation become 'seriously overloaded'?

 

[gap30]

The SADCOW just leads you back to the question really, the areas for close inspection would be areas that might have sustained damage from the associated overheating:

Distribution equipment and as Spin suggests, conductor insulation properties.

I could make a good case for close inspection of overcurrent protection too, how did that installation become 'seriously overloaded'?

Thats the first thing i thought but thats not the question they are asking is it? they want to know the after affects

Thanks spin,iq in the real world the first thing you are gonna do is go straight to the mains

atm i am trying to look at the questions and the wording more closely - damage to main switch, damage to main incoming cables, damage to cables feeding circuits even possible damage to fixed electrical equipment?

 

[IQ Electrical]

[/B]

Thats the first thing i thought but thats not the question they are asking is it? they want to know the after affects

Thanks spin,iq in the real world the first thing you are gonna do is go straight to the mains

atm i am trying to look at the questions and the wording more closely - damage to main switch, damage to main incoming cables, damage to cables feeding circuits even possible damage to fixed electrical equipment?

Stay away from 'fixed equipment'.

The question asks for '2 areas which require close inspection' 2 of the 3 above would get you marks but you won't find much mention of fixed equipment in GN3 and even if it was covered, the INSTALLATION being overloaded would probably have little effect on fixed equipment but more on distribution and wiring.

 

[gap30]

17 State the
a) purpose of the IP coding system
b) level of protection provided by
i) IPXXB - finger contact only
ii) IP4X. - solid or foreign bodies up to 1mm

is this to verify the level of ingress protection to fixed electrical equipment?

 

[JUD]

17 State the
a) purpose of the IP coding system
b) level of protection provided by
i) IPXXB - finger contact only
ii) IP4X. - solid or foreign bodies up to 1mm

is this to verify the level of ingress protection to fixed electrical equipment?

a) Gives the level of ingress protection for electrical enlosures.
b)
i) IPXXB -- Solid foreign objects ≥ 12.5mm
ii) IP4X -- Solid foreign objects ≥ 1mm

 

[gap30]

R =1.83m/ohm/m at 20C for 10mm 45A load 80 metres length of circuit
R=m/ohm/m x Length / 1000
R=1.83 x 2 x 1.2 x 80 / 1000 = 0.35136
R= 292.8/1000
R=0.2928
R = rounded up to
0.3 ohms
vd = R X I
vd = 0.3 x 45
vd = 13.5v
max of 5% 11.5 v so 13.5v not acceptible as greater than max

this is from a post by brucelee, tbh i am struggling with getting my head around this one a little, i cannot get the sums to add up

 

[JUD]

Resistance of 10mm² at 20°C is 1.83mΩ/meter

Circuit load = 45A
Circuit length = 80m

Total resistance at 70°C = (mΩ/m x 2 x Ct x L) ÷ 1000
Total resistance at 70°C = (1.83 x 2 x 1.2 x 80) ÷ 1000
Total resistance at 70°C = 0.35Ω

VD = IR
VD = 0.35 x 45
VD = 15.75V
VD > 11.5V (5%) so not acceptable

The 292.8 figure is the resistance at 20°C (1.83 x 2 x 80 -- no correction for 70°C) and is not used when working out voltage drop.

 

[brucelee]

soory Gap this was the only one that threw a spanner in the works for me when i did the exam i only knew how to work volt drop from mv/A/m x Ib X L /1000

I knew it was to do with ohms law so worked it out best i could and endd up forgetting to use the 1.2 for increase in resistance due to operating temp

jud is correct the total resistance is 0.35136 rounded down to 0.35
Vd = IX R
Vd = 15.75v and is greater than the 5%value of 11.5v so is unacceptable
so you can either increase Csa of conductor shorten length which will be almost impossible lol

If you work it out without the 1.2 correction factor then you will come up with the answer i did

I spent ages on this in exam as really was stuck rest of the exam i had done in 1 hr 20 spent 20 to 30 mins on it then rest going over exam again and this again

mate you have brought it all bvack to me lol

Now I know how to do it correctly as i spent the next few days going over exam on forum until i was sure I had done enough

 

[rick.oshea]

Gap,

I'm not sure if this has been mentioned (as 27 pages of posts takes some time to read through.....I got to page 9!) but time management can play a major part in the exam and place unnecessary pressure on you. I remember the feeling well!! As a lot of the guys have said, getting you mind right is going to play a major part in getting this nailed this time around.

I remember last year when I did mine, the first 2 questions in section 1 fried my brain, which put me on the back foot straight away (I'm sure they do it on purpose, mind you). I ended up wasting time on questions in section 1 and rushed section 2 where the main marks are.

The scenarios in section 2 are more relative to the work we do day-in day-out I found, where marks in section 1 can sometime be down to getting the wording & terminology exactly right for C&G.

On the day of the exam, try starting with Section 2, getting that nailed and hitting the weighted part of the paper and tot up the marks and then do section 1. Unconventional, but is a good way to manage your time productively relative to the weighted marking. It was a tip that was given to me after the event and in hindsight, probably would have been a better approach.

I hope this exam tip helps & good luck mate...

 

[gap30]

i have hit a brick wall atm with my studying, still so much to absorb, still dont fully understand tt installations with resistances and rcds ie Ra, been looking at q.26 on march exam 100ohm therefore 50/100 = 0.5 - definately one area i need to brush up on

 

[Sparky Ninja]

Hows it going in here? I thought as IQ is on his 'hols' I'd pop in and lend a hand. You guys have done an awesome job so far. :clap:

 

[gap30]

Hows it going in here? I thought as IQ is on his 'hols' I'd pop in and lend a hand. You guys have done an awesome job so far. :clap:

as i said earlier for some reason i have hit a bit of a brick wall, one test paper i can fly through, others struggle like hell!

 

[Sparky Ninja]

as i said earlier for some reason i have hit a bit of a brick wall, one test paper i can fly through, others struggle like hell!

I've PM'ed you .

 

[gap30]

I've PM'ed you .

thanks

 

[brucelee]

Gap you will be ok mate you cant know everything but you can give it a go and as i have seen your doing enough mate

I put similar effort in and like you and was daunted at first.The more i read practised the more I started to understand, You think you wont know enough but I am sure you will.
I am sure you will find like I did because of all the study fly through it but take your time to read the quetions at least twice before rushing in
any your stuck on just move on and try to answer at the end
then read through it all if you have time until that cert drops on the floor you wont be 100% certain
But as you have put everything into it like me sure you will be OK

how long before the exam

 

[gap30]

Gap you will be ok mate you cant know everything but you can give it a go and as i have seen your doing enough mate

I put similar effort in and like you and was daunted at first.The more i read practised the more I started to understand, You think you wont know enough but I am sure you will.
I am sure you will find like I did because of all the study fly through it but take your time to read the quetions at least twice before rushing in
any your stuck on just move on and try to answer at the end
then read through it all if you have time until that cert drops on the floor you wont be 100% certain
But as you have put everything into it like me sure you will be OK

how long before the exam

11th August mate, brucelee can i run something past you mate

compile a list of 8 checks to be made during the inspection process that could apply to any type of electrical installation using any type of wiring system in any environment

now does this apply to 2.6.3 inspection checklist or,

2.6.2 comments on individual items to be inspected or,

the main headers on form 3

now after reading the question i am immediately thinking

connnection of conductors
identification of conductors
routing of cables within prescribed zones
basic protection
fault protection
selection of conductors for current-carrying capacity and voltage drop
presence of residual current devices
erection methods

but the ones i have listed are all from schedule of inspections, and the first two options i gave you are slightly different and go into more detail, i have almost memorised the schedule of inspections but am i right in thinking the question wants a bit more elaboration?

 

[Mark.W]

another one for you

state the purpose of an initial verification of a newly installed circuit

To conform that the circuit complies with the designers intentions
The circuit has been designed, installed and tested in accordance with the requirements of BS7671
It is not damaged so as to impair safety or otherwise defective

ok but guidance note 3 also says

initial verification shall be carried out to verify:

all installed electrical equipment and material is of the correct type and complies with applicable British Standards or acceptable equivalents
all parts of the fixed installation are correctly selected and erected
no part of the fixed installation is visibly damaged or otherwise defective

so which one is right?

The second part as per GN3 basically means that as part of an initial verification, these items should be inspected!

 

[brucelee]

mate your on the money as it asks for a list and for the first 20 questions its either a couple of wordsor a sentance at most

your answer is ok as its asking for a list like a shopping list so your on the mark and as long as applicable to any instalation then i reckon full marks for that answer
and from 2.6.2 these 19 items
and could be from also from pg 27 depending on situation and installation eg conduit then look down the general ist on pg27 see if any relevent then pg 30 for conduits

the 19 on pages 20 onwards are aplicable to all for initial verification
the ones from 27 depend on the installation either pir or initial

there is also a list for PIrs pg 66 3.9

the schedule ofinspections is the list from pages 20 - 26 they are the same and the C&G are testing your knowledge of the certs and GN3 also bs7671 so answer as per GN3 and your on the money


Iq or widdler may be able to explain better than me

 

[gap30]

mate your on the money as it asks for a list and for the first 20 questions its either a couple of wordsor a sentance at most

your answer is ok as its asking for a list like a shopping list so your on the mark and as long as applicable to any instalation then i reckon full marks for that answer
and from 2.6.2 these 19 items
and could be from also from pg 27 depending on situation and installation eg conduit then look down the general ist on pg27 see if any relevent then pg 30 for conduits

the 19 on pages 20 onwards are aplicable to all for initial verification
the ones from 27 depend on the installation either pir or initial

there is also a list for PIrs pg 66 3.9

the schedule ofinspections is the list from pages 20 - 26 they are the same and the C&G are testing your knowledge of the certs and GN3 also bs7671 so answer as per GN3 and your on the money


Iq or widdler may be able to explain better than me

yes mate i forgot about page 66 - so basically if i stick to schedule of inspections i am ok

 

[andybrock]

Gap you will be ok mate you cant know everything but you can give it a go and as i have seen your doing enough mate

I put similar effort in and like you and was daunted at first.The more i read practised the more I started to understand, You think you wont know enough but I am sure you will.
I am sure you will find like I did because of all the study fly through it but take your time to read the quetions at least twice before rushing in
any your stuck on just move on and try to answer at the end
then read through it all if you have time until that cert drops on the floor you wont be 100% certain
But as you have put everything into it like me sure you will be OK

how long before the exam

Excellent thread this guys.Taking my wriiten exam on the 11th Aug too so full into revision at the moment.
I'm on the course next week with my practical on Thurs.

 

[brucelee]

state the purpose of an initial verification of a newly installed circuit

To conform that the circuit complies with the designers intentions
The circuit has been designed, installed and tested in accordance with the requirements of BS7671
It is not damaged so as to impair safety or otherwise defective

ok but guidance note 3 also says

initial verification shall be carried out to verify:

all installed electrical equipment and material is of the correct type and complies with applicable British Standards or acceptable equivalents
all parts of the fixed installation are correctly selected and erected
no part of the fixed installation is visibly damaged or otherwise defective


as for this i was like you i thought eh 2 answers for same question but its not same

C&G will ask whats the purpose of initial verification according to Bs7671

Or initial verification carried out to confirm
M materialsof the correct type and comply with BS blah blah
E erected and selected properly
D damage and defects not present

I questioned out tutor on this and a few other things lol as we had a booklet they give us which had errors i spotted
he was a good tutor and always willing to help tried to add the answers he gave but cant sus out how to do it since the forum changed

 

[Sparky Ninja]

I'm halfway through looking at the paper Gap. I've checked part A and there is probably only 2 marks out of the 60 that I would consider knocking off. I'll finish going through it in the morning and then get back to you with the feedback.

 

[brucelee]

yeah mate but they may ask about a certain installor initial or pir installation eg conduit or trunking whatever then look at p20 onwards for initail and 27 onwards also if for pir pg 27 onwards and pg 66 etc

 

[gap30]

I'm halfway through looking at the paper Gap. I've checked part A and there is probably only 2 marks out of the 60 that I would consider knocking off. I'll finish going through it in the morning and then get back to you with the feedback.

cheers mate thats good to hear!

 

[gap30]

Excellent thread this guys.Taking my wriiten exam on the 11th Aug too so full into revision at the moment.
I'm on the course next week with my practical on Thurs.

you with me on the 11th pal, you stressed out as well lol

i had one of them days in work today lol, grafted all day just got in now, now i got to eat then more revision noooooo!

 

[andybrock]

Yep know what you mean.Had head in the books over the weekend lol.Loads of stuff buzzing around there now !!
Some superb advice on here.
Have some past papers,let us know if you need them:smiley2:

 

[gap30]

Yep know what you mean.Had head in the books over the weekend lol.Loads of stuff buzzing around there now !!
Some superb advice on here.
Have some past papers,let us know if you need them:smiley2:

hi just been to norway for a couple of days and drank a lot of beer, now i got to study hard for 10 days

Just been offered a new job £12.50 an hour - toying with the idea atm, as i said in my other thread i am on a week to week basis in work atm

 

[gap30]

Taken from the exam success book

Describe the test procedure to determine the resistance of the installation earth electrode

seek permission to isolate the installation
safely isolate supply and all circuit breakers
select an earth fault loop impedance tester
disconnect the earthing conductor
connect the instrument, earth lead to disconnected earthing conductor, neutral to outgoing neutral of main isolator and phase to outgoing phase of main isolator
close the main isolator
check the instrument set to 200 ohms and carry out the test
open the main isolator and disconnect instrument in the reverse order
reconnect the earthing conductor

page 50 of gn3 shows a picture which shows the main switch as open

is this absolutely necessary? does the main isolator have to be closed (turned on) i assume by this they mean the main switch on db 1 for example

 

[Graeme Harrold]

Did the book question tell you which method to describe? i.e. Method 1 with the probes, or method 2 as a loop test

 

[Graeme Harrold]

page 50 of gn3 shows a picture which shows the main switch as open

is this absolutely necessary? does the main isolator have to be closed (turned on) i assume by this they mean the main switch on db 1 for example

Access dependant, your enclosure should be IP2X, therfore finger safe in theory. Add the line check and cover/shield live accessable areas. You should also be able to get your L and N probes onto the incomming terminal screws of the main switch, which will be live, therfore no need to close and open the switch to perform the test, making it a bit safer.

 

[gap30]

Access dependant, your enclosure should be IP2X, therfore finger safe in theory. Add the line check and cover/shield live accessable areas. You should also be able to get your L and N probes onto the incomming terminal screws of the main switch, which will be live, therfore no need to close and open the switch to perform the test, making it a bit safer.

yes mate i have never done that i usually just open the main switch carry out the test and then reconnect earthing conductor and then close main switch

The question in full so you can get a better idea

a periodic inspection is to be carried out on a residence with gardens front and rear, which is to be used by a housing association for residential letting.

the original installation was carried out ten years ago, and a kitchen and bathroom extension was added five years later when mains gas was installed to the property. There are no forms of certification or circuit details available for the original installation or the additional work.

the installation forms part of a 230v, 50Hz TT system with a PFC of 1.3kA. A 100mA RCD which also serves as the main isolator, is installed in the consumer unit

 

[Graeme Harrold]

When answering the question, think safety, then BS, then technical, hence the shielding point I made earlier. This board may not have a busbar cover, so cover yourself in the answer by highlighting the safest method of working. The most valid point made when I did my 2391 3 years age was "you are not working live when testing, just in proximity of...."

 

[gap30]

bs 7671 requires fuses to placed in the line conductor only. State

a) two reasons why it is unacceptable to place fuses in the neutral conductor only
b) the test that would identify this error

had a look in the regs on this one and does not say why, just it cant be done - could anyone point me in the direction of the information relating to the answer of this question

the test i assume is polarity

 

[La Poste]

You just have to think what would happen in the event of an earth fault, the circuit breaker would not operate.
If a line and earth wire were to touch and cause a short circuit the fuse being in the neutral cable would not be part of this fault circuit and therefore would not operate, this could result in a fire.

Also if you had a short circuit line to neutral the fuse would blow but the line would still be at 230V so when you went to investigate you would probably get an electric shock.

Polarity is the correct test to use to ensure the fuse is in the line and not the neutral.

 

[gap30]

when working out cable resistance do i only add the 1.2 multiplier if told to do so ie 20C, i tend to add it all times and it can really change the final figures of Ze, Zs etc.

when working out questions in 2391 i often find myself second guessing on this

 

[La Poste]

Probably best to work out at 20C (R1+R2) and then compare to BS7671 but multiply BS7671 figures by 0.8. City and guilds seem to prefer it this way.
If they specifically ask for the 1.2 then use it.
City and Guilds tend to concentrate more on R1+R2 than Zs in my experience.
With this exam you really have to read the questions and figure out what they want to know.
That is why doing past papers is so important.

 

[gap30]

Probably best to work out at 20C (R1+R2) and then compare to BS7671 but multiply BS7671 figures by 0.8. City and guilds seem to prefer it this way.
If they specifically ask for the 1.2 then use it.
City and Guilds tend to concentrate more on R1+R2 than Zs in my experience.
With this exam you really have to read the questions and figure out what they want to know.
That is why doing past papers is so important.

i am more referencing if they want the zs and r1/2 for the circuit but no mention of cond temp that 1.2 can really be the diff on max zs

 

[La Poste]

i am more referencing if they want the zs and r1/2 for the circuit but no mention of cond temp that 1.2 can really be the diff on max zs

Post a question.
From an exam paper I mean.

 

[gap30]

using the information provided in the scenario, determine the PEFC at the origin of this installation

nominal voltage 400/230v TN-S System , Ze 0.3 ohms

now i have it in my head Ipf = Uo/Ze

but the sums dont add up to me 400/0.3 = 1333.3

plus i am right in thinking on 3 phase systems the prospective short-circuit current will always be higher anyway

right sod it i am going for 230/0.3 = 766 amps its the 400v thats knocking me

 

[brucelee]

Hi mate Uo is 230V U is 400v i think lol
Pfc will always be higher between the lines but you shouldnt measure that just measure the 3 lines to earth individually and multiply the highest by 2 this is the 3 phase pfc and this figure errs on the side of safety i think the real figure is 1.732 which is the square root of 3 but for 2391 multiply highest line to Neutral by 2 and record this

PSCC is always higher on 3 phase and for 2391 practical this was all we had to measure as it will always be higher than PEFC
L1 - N =516
L2- N = 505
L3 - N = 514
so L1 - N X 2 = 1032A or 1.032kA is the PFC

 

[electrician4u]

don't know what the statistics are but when i took the exam i was the only one not resitting out of 20-odd guys. i was surprised (and elated) i passed first time. i realised there were going to be no short cuts to success and read and re-read the regs, guidance notes and any other books i could find, especially the ones with pics-far more interesting! the regs make for an extremely boring read but if you're serious about passing, you've GOT to read them. you'll also need a good knowledge of them to register with Part P

 

[gap30]

using the information provided in the scenario, determine the PEFC at the origin of this installation

nominal voltage 400/230v TN-S System , Ze 0.3 ohms

now i have it in my head Ipf = Uo/Ze

but the sums dont add up to me 400/0.3 = 1333.3

plus i am right in thinking on 3 phase systems the prospective short-circuit current will always be higher anyway

right sod it i am going for 230/0.3 = 766 amps its the 400v thats knocking me

766 x 2 = 1532 so i assume it 1.53 ohms

 

[malcolmsanford]

No look at Bruce's post # 295

Do you actually read what posters write as an help to you ??

 

[tony mc]

Don't get the PSCC & PEFC mixed up.

The PEFC is what you are after so you do not multiply by x 2 or 1.73 as it is a single phase calculation between a phase and earth.

230/03 = 766A

So your PEFC is 766 Amps

I hope this makes sense.

 

[gap30]

No look at Bruce's post # 295

Do you actually read what posters write as an help to you ??

measure the 3 lines to earth individually and multiply the highest by 2

yes i try to but sometimes i get it wrong hence the original post i made