Ring main , 50 meter length on an MCB , floor area 100m2

[robgil]

Is this right? or is 17th edition different?
Ive read it is 60 meters on a pull fuse , 50 meters on an mcb and a floor area of 100 square meters.
If this is true , when can it be deviated from?

 

[Zebra]

I've got the On-Site Guide, so I'll see if I can help. A ring circuit on a 32A B-type MCB using 2.5mm cable, you can have have max circuit length of....... 106 metres. On a 30 amp 3036 rewireable fuse you could have 111 metres, unless you're on a TN-S system with no RCD on the circuit, in which case it's max 49 metres.
These lengths also are dependent on the cables not being totally surrounded by thermal insulation, or covered by more than 100mm thermal insulation.
Floor area, on either fuses or MCBs, should not exceed 100 sq metres for a ring wired in 2.5mm, although if you've got a lot of connected load you should consider separate circuits. It does specifically say that circuit arrangements other than those detailed in the On Site Guide are not precluded when specified by a competent person so you could deviate, but then you'd have to calculate all cable sizes, areas, lengths etc from scratch...
What is it you're trying to achieve?

 

[robgil]

I'm not , geezer at work reckons he can have a ring circuit as long as he likes ,he thinks there is no limit. I told him I read it was 50m because I read it, here http://www.diydoctor.org.uk/projects/ringmain.htm amongst other places, but he wasnt having any of it. I then told him the cable may need to be thicker and he just laughed.

 

[agbagb]

Try asking the numpty at work, if length and thickness doesn't make any differance why aren't rings and radials on 1.5mm2.

Length and thickness makes all the difference :roll:

 

[MdB]

Cable length makes no difference to the amount of current that piece of cable can carry. However there are two reasons I know of for why there is a limit (there are probably more).

1) Voltage drop - The longer the cable, the greater the resistance and hence the greater the voltage drop from one end of the cable to the other. With large loads, this can be significant and can take the voltage out of spec.

2) Typical usage - The longer the cable and the larger the area covered by that circuit, the greater the typical load on the circuit. You only want a maximum of 2 x 3kW electric fires on your circuit so keeping the area down reduces the likelihood of overloads.

 

[FamilyWiggs]

Try asking the numpty at work, if length and thickness doesn't make any differance why aren't rings and radials on 1.5mm2.

Length and thickness makes all the difference :roll:

 

[Penners]

Damn! FW got there before me!

 

[Zebra]

And MdB got there before me!
(Indeed you can have a longer ring if you use 4mm instead of 2.5, but I won't go and look up the details if you're just winning an argument. )

 

[Flyfisher]

4mm2 might be an option from an electrical perspective but is it actually physically possible to fix two 4mm2 cables into a socket?

 

[FamilyWiggs]

Damn! FW got there before me!

Penners - the girls that have said that to me.... :roll:

Double

 

[Penners]

Damn! FW got there before me!

Penners - the girls that have said that to me....

Understandable I suppose. My problem has always been my shyness, you know.

 

[Zebra]

4mm2 might be an option from an electrical perspective but is it actually physically possible to fix two 4mm2 cables into a socket?

Hmmm, I reckon yeah, on new sockets, the holes are bigger than they used to be (cue the Kenneth Williams picture again?) but must admit I haven't tried as I virtually never use 4mm.

 

[Lime]

2x4mm² fits, just make sure the backbox is big enough to take the cable bend radii.

 

[robgil]

I think you only have problems when it comes to using 10mm, I read it on a Niam HiFi forum , apparently a dedicated spur to plug your Niam HiFi into removes electrical mains noise from your HiFi and 10mm cable is better than 2.5mm.
A load of old pants if you ask me though, just switch your fridge off when you put Bob Marley on if you decide to be that anal about sound quality from your speakers.

And before anybody else does,


He said anal.

 

[Penners]

10mm cable is better than 2.5mm.

10mm^2 cable to power a hi-fi??

Wouldn't it be better just to buy a hi-fi with its own built-in nuclear power plant?

 

[Flyfisher]

Welcome to the weird and wonderful world of hi-fi pseudo-science and snake oil inhabited by super-beings able to aurally detect if you have a gold-plated mains plug on your amplifier, or not. No-one inhabiting this bizarre parallel universe would think of using anything as crude as ordinary 10mm2 cable for their speaker connections when they could spend £16k on stuff like this: http://www.pcpro.co.uk/blogs/2011/02/08/the-most-expensive-cable-in-the-world/

Even digital signals can be enhanced by the use of the appropriate cable technology, as these Amazon reviews by satisfied customers attest:
http://www.amazon.com/Denon-AKDL1-Dedicated-Link-Cable/dp/B000I1X6PM/ref=cm_cr_pr_product_top

 

[Penners]

Oh - speaker cables! I read Rob's post as referring to the mains supply to the hi-fi!

Yes, I am aware that unless you have speaker cables made of 25mm^2 twisted kryptonite, insulated with dragon's umbilical cord skin, the 100 kHz frequencies on your AC/DC recording will be virtually inaudible.

:roll:

 

[robgil]

Nope , I was talking about mains supply to the socket. Apparently Niam reckon you need a dedicated spur to eliminate mains noise from anything else on the ring main , fridges , washing machines etc etc. Their amps are ever so sensative to such things. 10mm for some reason is best, lets not get into RF interferance or DC pollution as we all may have to seek help from a head doctor should we delve too deeply.
Russ Andrews has a lot to answer for.
http://www.russandrews.com/product-13A-fuses-DCT-treated-1019.htm

This makes for interesting reading , for anyone who may be interested.

http://www.vinylengine.com/turntable_forum/viewtopic.php?f=50&t=24446

 

[Flyfisher]

Yes, I am aware that unless you have speaker cables made of 25mm^2 twisted kryptonite, insulated with dragon's umbilical cord skin, the 100 kHz frequencies on your AC/DC recording will be virtually inaudible.

Indeed. It's that 100kHz roll-off that takes the edge off the cymbals for me and ruins otherwise perfectly acceptable recordings.

Hi-fi mains cables are far cheaper than speaker cables though. This one is just £8,795 for a 1.5m mains lead.
http://www.highendcable.co.uk/Nordost%20ODIN%20Power%20Cords.htm

And, of course, being a multi-purpose mains lead it can be used on almost any household equipment, so well worth the price. I imagine that when used with a kettle, the resulting cup of tea would be truly astonishing.
:lol:

 

[Flyfisher]

Nope , I was talking about mains supply to the socket. Apparently Niam reckon you need a dedicated spur to eliminate mains noise from anything else on the ring main , fridges , washing machines etc etc.

Surely no-one would contemplate listening to their precious hi-fi with a washing machine and fridge whirring away in the background? :lol: