new garage installation

[comms]

in answer to flameports reply i used 3 core swa to take both phase conductors and an earth to the garages own cu unit which consists of a 40A,30ma rcd 1no 32Amcb for a 6 outlet ring main and a 6Amcb for the lighting does this not class as overcurrent protection.the isolator has been put in place just to cut the power to the garage consumer unit.

You need overcurrent protection for the swa from the house to the garage , which the isolator doesnt give.
Out of interest what csa are the P/N/E tails from the supply into your 63amp mainswitch & how have you gone about connecting it?

I tend to split the meter tails with henleys, take a set of 25mm tails into an enclosure containing dp 100A mainswitch & a correctly rated mcb these then supply the sub to outbuilding.

in answer to desl question the (r1 + r2) test in the garage was 0.17ohms for the ring circuit and 0.56 ohms for the lighting circuit and the Ze at the electrode at the front of the house is 76.3ohms

And what was the Zdb / R1+R2 / IR of the submain ?
If you've installed it, you need to test & cert it.

A little birdie told me that the electrode may not be conducting because of it being too dry in it's hole and to soak the patch in which it resides with water,anyone heard of this

Correct it's call soil conditioning, but adding another rod is the better method.

upgraded his main earthing conductor to 16mm

Doesnt need to be 16mm, could be as small as 2.5mm.........dont they teach this on the 7 day course?

my course was 7 days in total and i'm planning on the 17th edition exam early in the new year.

Get you money back 7 days aint long enough & be prepared to pay for a re-assessment.
It's not your fault it's these colleges & such places that give the impression that after 7 days reading about it you will be free to call yourself an electrician & do the work associated with being one.

and the only test we done on the part p course was on a tn-s system.

And there you have it.......grab your cash then teach the bare minimum.

 

[nozspark]

Also I've done a rough working out of your volt drop - your cable is undersized!!!!

6mm SWA at 30A will not even get you past 39m

 

[comms]

It's gonna be a fail on the assessment.........if not my niceic membership needs cancelling.

 

[ricicle]

Ladies and Gentlemen.....I thank you.

 

[DESL]

Op did'nt mention max demand for garage just the usual 32A ring final and 6 A light cct

So as yet 6mm2 may be sufficient

For me a garage would be 16A radial and 6A lights

I think design and specifying is maybe something that is amiss on the the so called part P courses

 

[nozspark]

So lets add a 20A MCB to supply the sub-main to the garage!!

 

[djjd21]

may i thank you all again for all your comments and critisiscm i shall endeavour to rectify all my installation with the appropriate devices and certainly do a lot more reading up on this forum as it is already proving to be a valuable source of information.

I would like to add that these courses for part p have opened my eyes to the fact that it is not all just about putting the right coloured wires in the back of a socket outlet as so many untrained and unqualified people do.I have done this course for the simple reason i have stated above, as i have done countless times, before i decided to do it properly and to be able to provide an honest service to people.A lot of things i have learned already since doing the course have been from hands on people like yourselves and which they do not go through with people on these courses.I do plan on getting more qualifications under my belt so that i am deemed a proffesional tradesman and maybe sometime soon i'll be more in a position like yourselves offering advice to newbie individuals like myself and pointing them in the right direction.

going back to my main problem which i see now from the comments i have had, would i be right in saying that if i split the meter tails which are 25mm in 2,run 1 to the main cu and the other to say a 60A switch fuse and do away with the isolator, which then would supply the swa to the garage cu with which i could keep the rcd in the garage cu would this be ok.the demand in the garage is 206w for the lighting and approx 5kw for the ring to which if i am doing the calculation right gives me a volt drop of 7.76v for which the 6.0mm would be suffice for the loading?
one of the things i don't understand about 1 of your comments is that of not linking the earth which could be at different potentials.surely just by using the extra core in the swa fed directly from the main earthing terminal in the house to the garage would be ok?

 

[djjd21]

i have just looked in the iee electricians guide to the building regulations,table 3.3.2b on page 36 denotes the csa of the protective conductor in relation to the csa of the phase conductor for tn-s systems and tt systems.the meter tails at the origin are 25mm so therefore as the earth conductor is not buried,has corrosion protection but not mechanical protection the csa should be 16mm,and yet on page 163 in the on-site guide table 10c denotes that it should be 4mm which one of these is correct?

 

[bongos]

incidentally does anyone know if the SWA between a house and garage has to be protected by a 30 mA RCD at the house end or can it be protected by a 100mA TD one (as long as there is a 30 mA one in the garage).

Also would you use 3 core SWA to the garage if this were a TN-S system or just have a separate rod for the garage.?

 

[comms]

incidentally does anyone know if the SWA between a house and garage has to be protected by a 30 mA RCD at the house end or can it be protected by a 100mA TD one (as long as there is a 30 mA one in the garage).

Also would you use 3 core SWA to the garage if this were a TN-S system or just have a separate rod for the garage.?

No need for rcd on a submain (unless the submain is supplying a metal clad cu), but one is required at the cu (the submain is supplying ) for any socket circuits

I tend to use an rod at the garage end (TT system), but use one of the 3 core swa as an earth from the TN-s supply but terminate into a insulated enclosure at the garage end.

But others will do it differently.

 

[nozspark]

Use an RCD for the sub-main aswell. Say for instance you had a L-e fault near the sub db with a Zdb (back to origin) of say 100 ohms and a 20A MCB, how long would you have to wait for the MCB to disconnect the circuit?????