big red book

[atm]

definition of "clipped direct"?

does this mean clipped to wall outside and not buried, in insulated wall, in ground etc?

if so what is "in free air"?

many thanks.

also the difference between magnetic and non magnetic armoured please?

just asking because i am calculating cable size and VD.

many thanks
atm

 

[mikethesparky]

the difference between magnetic and non magnetic armoured is the armourings, non magnetic is aluminium and magnetic is steel. Aluminium Wire Armour (AWA) is used in single core cable because it is non-magnetic. When an electric current passes through a cable it produces a magnetic field (the higher the voltage the bigger the field). The magnetic field will induce an electric current in steel armour (eddy currents), which can cause overheating in AC systems. The non-magnetic aluminium armour prevents this from happening.

 

[mikethesparky]

sorry missed off the first question. clipped direct would be for example a clipped cable accross a joist in the roof or down a wall, not inside a wall. but i can see your point about free in air as this would suggest hanging a cable between two locations not supported by anything i.e between house and garage lol. but a cable suspended on a catinery wire would be free in air. cant think of any other ways a cable could be in free air....

 

[atm]

thanks mike,

so for my cable size calcs and then my VD calcs what should i use..

my SWA will run through 9 inch brick work and then will be clipped to an outside wall and not run underground.

clipped direct?
free air?

 

[mikethesparky]

for VD you need to refer to table 6D2 in the 17th editon it will depend on your cable size for refernce method C,F (clipped direct,on tray of free to air) the common values for guidance are

1.0 44mV/A/m
1.5 29mV/A/m
2.5 18mV/A/m
4.0 11mV/A/m

as for cable calcs, havent got my red bible with me but this is a rough guide cable calcs are in appendix 6 of the 17th on site guide for your reference.

1.5 -- 18A
2.5 -- 24A
6.0 -- 41A

however this does not allow for any thermal effects which the cable may be subject to this value is free to air but by the sounds of it thats what you doing anyway.

 

[atm]

thanks mike.

will use the clipped direct method to be on the safe side.

as for the VD. i am hooking up a 5.5kw hot tub so it will draw 24amp.

will be using 32amp breaker. cable length is 15m.

iam meant to use 24amp (ie prospective current draw) in my calcs not beaker size correct?

if this is the case then i will use 4mm 3 core,, so 11x24x15 = 3.9v which is a 1.7% VD over the 230v which is well within limits.

is there any reason i should use 4 core.. should i double earth plus earth my armour?

many thanks for your help.

 

[mikethesparky]

i would use the three core swa for L,N & E and use glands to pick up the armourings as well, i've been trying to find a document i read on hot tubs someone mentioned using the armourings as a second earth, but cant find it and i dont remember why they suggested it, as long as the circuit is rcd protected i cant see any point to the double earth, i dont know if anyone on here installs hot tubs regularly enough to confirm my advice.

 

[atm]

thanks again mike...

so when calcing the VD do i use the prospective draw of hot tub ie 24amps or the breaker amps ie 32amp?

 

[Pensdown]

When calculating volt drop use Ib which is the design current for the circuit, in your case 24amps.

 

[scousespark]

atm, don't take this the wrong way, but I'd suggest you should look locally to get some experience working with an electrician.

On your assessment, you will be expected to answer questions about the job to prove YOUR competence. Your posts are asking very basic questions and the NAPIT guy would not have to ask much before you'd struggle.

If you do want to go for it, then I'd say you should look at another job to show. This is a complicated job for somebody just starting out.

 

[atm]

thanks scouse, i must sound like a d!ck. did have a job for a week with a firm however they went under recently and everyone in my yellow pages doesn't seem to be employing at the mo.

I have past my EAL Domestic Installers course and reading my big red book everyday and have been trying to pick up extra knowledge on the way. i am competent in putting the physical stuff together and my basic testing is ok however i do lack a MASSIVE amount of experience hence my basic questions. (however i must say i have learnt loads off you guys thanks)

The reason behind my getting Napit involved on this job is that the bigger job they sign me of on the bigger jobs that i can sign off on going forward. The "defined scope" is what i am looking for, and i don't want that "defined scope" to be fitting a shower (plumber) or wiring in a cooker circuit (kitchen fitter). like you said i need a job getting my experience however i need some income as i am a mature new wanna be spark who was made redundant at the beginning of the year. I am not a bodger and will always seek expert advice when i am even slightly unsure of the situation and safety elements.

The chances of me doing a board change again very soon is very slim (it will be more outside lights, spurs, light in a shed etc) so along the way i can improve my testing and gain a bit of extra knowledge.

I just need this board change so i can get more leeway with Napit for the future.

Or do i just knock it on the head. I feel depressed now.

 

[Dartlec]

Stick with it. I went the EAL route, but rather like driving, you don't really start learning until after you've passed the test!

I don't have knowledge of Napit's procedures, but in my experience the main thing for assessments is that you know the testing procedure inside out to prove that your work has been installed safely.

This forum is a great place to learn and pick up techniques from the more experienced, but you should never feel bad about asking questions - much better than assuming you know the answer and doing the wrong thing...

Gavin

 

[atm]

Stick with it. I went the EAL route, but rather like driving, you don't really start learning until after you've passed the test!

I don't have knowledge of Napit's procedures, but in my experience the main thing for assessments is that you know the testing procedure inside out to prove that your work has been installed safely.

This forum is a great place to learn and pick up techniques from the more experienced, but you should never feel bad about asking questions - much better than assuming you know the answer and doing the wrong thing...

Gavin

Gavin you legend!!!!!!!! don't feel like topping myself now ta.

Anyone out there thats had a first visit from Napit?

thanks

 

[scousespark]

I wasn't trying to make you depressed atm. Just pointing out that you need to know your stuff. I'm with NIC so have no knowledge of what the NAPIT assessor will be looking for in your case. The assessor should check your work, but the chat he has is designed to check your knowledge. You should cram as much as you can beforehand.

Oharaf has another thread regarding a NAPIT assessment on Friday.
I'd check with him afterwards.

One thing to bear in mind is that the assessors are not out to get you, just check you are competent.