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Topic Title: 4mm radial
Topic Summary: Safe cabling?
Created On: 20 April 2017 06:46 PM
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 20 April 2017 06:46 PM
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RGiant

Posts: 4
Joined: 17 April 2017

Guys, I have found a 4mm radial in place as follows - 4mm twin and earth from a 32a mcb on a RCD - cable runs to a maintenance free junction box where it splits into two 4m lengths of 4mm to two single gang sockets.

Opinions welcome - safe - unsafe - resolutions?
 20 April 2017 07:00 PM
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OMS

Posts: 22312
Joined: 23 March 2004

Well what do you think is wrong with it

Find out the current carrying capacity of 4.0mm T&E for the installed conditions and ascertain the maximum theoretical connected load on 2No 13A single sockets before you reply

Regards

OMS

-------------------------
Let the wind blow you, across a big floor.
 20 April 2017 07:05 PM
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weirdbeard

Posts: 3078
Joined: 26 September 2011

Welcome to the forum, sounds like it does not meet the regs that require all accessible joints to be maintainable.

-------------------------
:beer)
 20 April 2017 07:07 PM
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AJJewsbury

Posts: 15632
Joined: 13 August 2003

And check Fig 15B on page 454 of the current regulations.
- Andy.
 20 April 2017 07:08 PM
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OMS

Posts: 22312
Joined: 23 March 2004

Originally posted by: weirdbeard

Welcome to the forum, sounds like it does not meet the regs that require all accessible joints to be maintainable.


Maintenance Free (or MF) joint box ?

Regards

OMS

-------------------------
Let the wind blow you, across a big floor.
 20 April 2017 08:21 PM
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weirdbeard

Posts: 3078
Joined: 26 September 2011

Originally posted by: OMS

Originally posted by: weirdbeard

Welcome to the forum, sounds like it does not meet the regs that require all accessible joints to be maintainable.



Maintenance Free (or MF) joint box ?




If a joint is accessible then it is available for inspection and thus maintenance, only in-accessible joints are excused inspection and maintenance, depending on limitations of course

-------------------------
:beer)
 20 April 2017 08:43 PM
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OMS

Posts: 22312
Joined: 23 March 2004

Send again in clear - it makes no sense to me

OMS

-------------------------
Let the wind blow you, across a big floor.
 20 April 2017 09:31 PM
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Zs

Posts: 3792
Joined: 20 July 2006

Hello RGiant, Welcome.

I don't see a problem with that , provided that the connector block used is suitable for the current carrying capacity of the cable and given some thought about the circuit use. I am assuming that by 'maintenance free' you mean wago or similar? The normal ones are 24A I think. I'd make a call on that by looking at how the circuit is used or likely to be used. If it is the big red wagos I'd be quite satisfied.

What do you think is wrong with it? Or do you?

Zs
 20 April 2017 10:03 PM
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Alcomax

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Joined: 12 November 2009

Ashley J803 is 32 amp and MF
 20 April 2017 10:09 PM
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mapj1

Posts: 9107
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Sounds to me like its a very minimal 4mm christmas tree radial circuit, just with only one branch.
Unless the cable is routed through unusual insulation, or grouped in a way that means it is not up to 32A, then there is nothing to see than a standard circuit.



With acknowledgement to John Ward of the Flameport website whose drawings are far better than many official ones.

-------------------------
regards Mike


Edited: 20 April 2017 at 10:18 PM by mapj1
 20 April 2017 10:29 PM
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AJJewsbury

Posts: 15632
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If a joint is accessible then it is available for inspection and thus maintenance, only in-accessible joints are excused inspection and maintenance, depending on limitations of course

I think your copy of BS 7671 must be a a counterfeit or you have a copy that's fallen through a wormhole from a parallel universe - in my copy at least it's the requirement for accessibility that's excused when using MF joint boxes (reg 526.3).
- Andy.
 20 April 2017 11:33 PM
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mapj1

Posts: 9107
Joined: 22 July 2004

Good heavens, I never realised some of us had copies of the regs from a parallel universe.
That may explain some of weirder the discussion we get on here.

-------------------------
regards Mike
 21 April 2017 10:39 AM
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ebee

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Joined: 02 December 2004

From the information given, and all other things being equal , I do not see a problem.

Mmm parallel universe regs? That explains some posts on here!

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 21 April 2017 05:47 PM
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RGiant

Posts: 4
Joined: 17 April 2017

Thank you all for your responses. Perhaps I did not ask a clearer question.

Its a 4mm t& e radial split into two separate three metre long cables serving two single gang 13 amp sockets. It is protected by a 32amp MCB - MK systems. The MCB is in the range on the CCU protected by an RCD.

The sockets are protected ie waterproof outdoor sockets. The cables run to them separately in 22mm round conduit.

The radial is split at a Hager J803 maintenance free junction box which is accessible.

I would welcome your comments on whether this is safe to use, or should alterations be made.

As far as I am aware the single sockets can only be loaded to 13amps - 3kw max. With the cable in conduit outside, the capacity of the cable is 35amps. I'm not sure if the 32a MCB should be downgraded - also the split into two legs concerns me as a radial should be daisy chained not turned into spurs?

Many Thanks

Edited: 21 April 2017 at 05:56 PM by RGiant
 21 April 2017 05:54 PM
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geoffsd

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What do you think might not be safe about it or what do you think might need altering?
 21 April 2017 05:57 PM
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RGiant

Posts: 4
Joined: 17 April 2017

Thanks Geoff - please see my edited reply above
 21 April 2017 05:59 PM
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ebee

Posts: 6298
Joined: 02 December 2004

If you go thru all the reasons you are doubting it and the reasons why then we will talk them thru one at a time

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 21 April 2017 06:23 PM
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sparkingchip

Posts: 9836
Joined: 18 January 2003

Originally posted by: RGiant

Guys, I have found a 4mm radial in place as follows - 4mm twin and earth from a 32a mcb on a RCD - cable runs to a maintenance free junction box where it splits into two 4m lengths of 4mm to two single gang sockets.



Opinions welcome - safe - unsafe - resolutions?


From your description it sounds perfect, you will have to tell us precisely what you think the issues are.

Andy B.
 21 April 2017 10:22 PM
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mapj1

Posts: 9107
Joined: 22 July 2004

A daisy chain is the simplest example of a radial circuit, but there are many others.

Can you see the picture of the tree layout in my post above ?

That is also an example of a valid radial configuration, and so would be a centre fed version with the CU part way up the tree.

-------------------------
regards Mike
 23 April 2017 09:22 PM
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antric2

Posts: 1262
Joined: 20 October 2006

Originally posted by: mapj1





With acknowledgement to John Ward of the Flameport website whose drawings are far better than many official ones.


Evening Mike,that John Ward bloke does some very good videos of his charts and I personnally think he is a must see for most up coming and experienced sparkies.

Regards
Antric
IET » Wiring and the regulations » 4mm radial

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