Lighting Question

[green-hornet]

As andy has said c6 do provide better protection against some nuisance tripping on lighting circuits, he also mentioned the Zs, on type C breakers this is far less than a type B.

New installations will almost always take a type C but older installations and installations with only 1 lighting circuit may struggle.

Also the type c 6 amp is less common than the usual C type 10 amp.

 

[Andy™]

As andy has said c6 do provide better protection against some nuisance tripping on lighting circuits, he also mentioned the Zs, on type C breakers this is far less than a type B.New installations will almost always take a type C but older installations and installations with only 1 lighting circuit may struggle.

Also the type c 6 amp is less common than the usual C type 10 amp.

i dont have any problems getting C6 MCB's. there an off the shelf item, along with the DB and all the B breakers

 

[a1spark]

20 minutes to post?!

Reading other posts THEN posting.......Once again so sorry !! Blushing

 

[Evans Electric]

It would be better to split it but how easy would it be? If you'd have to make a mess of their decoration then there's not much you can do. By upgrading the CU you are making the installation safer than it was.

Deke will come along and say "get on with it"!

You know me too well , 'Patch . :|

 

[Andy™]

It would be better to split it but how easy would it be? If you'd have to make a mess of their decoration then there's not much you can do. By upgrading the CU you are making the installation safer than it was.

Deke will come along and say "get on with it"!

You know me too well , 'Patch . :|

what happened to 'get on with it!'?!

 

[SPECIAL LOCATION]

Going to look at a job tomorow, this guy phoned and asked me to give him a price to change a 8 way rewired cu to a new 17th cu in a two bed terraced house. He then said he thinks it only has one lighting circut to upstairs and down ?? should these not be split to comply with 17th edditon or leave as is on the one mcb.Thanks

Chas

I presume you are thinking about division of installation to take account of danger that may arise form the failure of a single circuit, eg. a lighting circuit?

e.g. 314.1 (iii), page 39

BUT this is only marginally altered with 17th!

the general concept was still there in 16th!

e.g. 314-01-01 (i) page 33 brown or page 29 yellow.

So really it would have been preferable to have it done a long time ago!

MORE importantly a 6a circuit is only 1380watts,

if there happened to be a 500W or 300W security light,

That leaves even less for the rest of the circuit.

 

[SPECIAL LOCATION]

there is no requirement to wire 2 light circuits it would be nice some people wire 1 circuit for upstairs sockets and one for down.but I wire 1 front and 1 back. or house on 1, kitchen on another.

other than 314.1

Every installation shall be divided into circuits as necessary toiii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit.

Thats what my red book says...

seems quite clear to me that More that one light circuit should be installed...

Or did they print me my very own personal red book with customised regs that no one else has got?

or is it that no one else actually reads or referrers to it? ?:|

but then again as we all know BS7671 is only guidance for good practice..

so there is no requirement for anything!

insulation, testing, bonding... etc.. etc...

]

 

[SPECIAL LOCATION]

great tip ..... box of c6 ordered lol.. we are like sheep . are we not

you may be if you go out buying a bunch of C6?

have you considerd a 10A type B?

 

[SPECIAL LOCATION]

there is nothing to say how you should split circuits. its down to the designer. in a new house, its very unlikely to have 1 light circuit, but just because its only got 1 doesnt mean its dangerous. if your changing the DB, you are improving things. but you should consider a C6 for lighting if Zs permits

I presume form this statement you haven't actually don't the calcs re cable lengths, Zs, etc with Type B vs Type C?

I think you will find a 10a type B will give greater flexibility of Zs than a 6a type C.

e.g. taking general figures from Pg 58 OSG

or Page 40 Of Guidance Note #1.

Type B trip 3x to 5x ln

Type C trip 5x to 10x ln

so the 6A type B is typically 18A - 30A

6A type C is 30A - 60A

10A type B is 30A - 50A

Type C more commonly used where daily in-rush currents..

e.g. switching on commercial lighting / motors etc.. may cause trips..

Occasional domestic bulbs blowing is NOT a regular repeated switch on in-rush current as described in table 7.5 O.S.G.

NOW max ZS

Type B 6a 7.67

Type C 6a 3.83

Type B 10a 4.6

Knock off your 80% rule of thumb..

Type B 6a 7.67x0.8=6.13

Type C 6a 3.83x0.8=3.06

Type B 10a 4.6x0.8=3.68

If you also went & took off a typical worst case Ze, TNS -0.8 TNCS -0.35,

Type B 6a 5.49 to 5.86

Type C 6a 2.42 to 2.78 to

Type B 10a 3.04 to 3.4

then use your R1+R2 vales from table 9A, pg 166..

typical lengths assuming 1.5mm T&E are

Type B 6a 182m - 194m

Type C 6a 80m - 92m

Type B 10a 101m - 113m

so overall with a typeC 6A you are loosing 100m potential length!

more than half of your capacity!

A typeB 10a still looses enough but you gain an extra 20m over a type C..

with a very similar "inrush current" capacity!

I don't use typeC for Domestic lighting but for commercial yes I would!

 

[Apache]

It's always nice when he does his sums

 

[Andy™]

I presume form this statement you haven't actually don't the calcs re cable lengths, Zs, etc with Type B vs Type C?<snip>

i use them when wiring a house. which is often small. not a mansion. so although you are correct with cable lengths etc, is mostly irrelevent to most situations. and there is also the fact there is an RCD...

 

[Power Ball]

Thanks for all your replies guys, went to look at the job today 2 bed mid terrace house. 1 Ring 1 lighting 1 cooker 1 shower 1 immersion heater.

Gas and water bonded with 6mm and 16mm tails on board.

All wiring looks like 3/029 and 7/029 6mm on cooker and 10mm on shower (all looks in good condition took some boards up and looked behind sockets etc

Going to upgrade CU and tails, 6mm and 10mm earth all new socket and switch face plates.

Chas

 

[batty]

Double check it is definatly on one circuit. The reason I say this is in my own house it only had one fuse for lighting, but had 2 cables going into it, one for upstairs and one for downstairs so easily split up.

Probably borrowed neutral thats what you usually find so cannot split them.

batty