Extending a circuit

Hi,

I'm planning to run a twin and earth 6mm cable (for an outside insulated structure) The first part of the circuit is intended to be in T&E internally for ease of run and the second part in armoured, externally.  At the point of joining them both up, I had figured on using a large metal junction box in order to correctly gland off/affix the armoured. This would then be joined to twin & earth with suitable sized wago type connectors. In regards inaccessible location: Ideally I wish to site the JB under the floor boards securely fixed to timber batons between the joists, sited very close to where the armoured cable enters the house.  Is this possible in a non wago JB ? (I wish to use metal as this will allow afford better gland fixing)   

Sorry .. pressed enter in error. So to continue....

I don't believe Wago do a metal JB ?  Any advice welcome, particularly as I wish the JB to be sited under the floorboard. I am aware that this is notifiable

I would use a 4x4 plastic box, neweys ones are quite robust , dont forget to use the earthing ring on the gland to connect the steel armouring. 6mm insulated crimps if you can't get wagos that big.

I would use. Piranha/earth nut on the SWA , as a locknut against plastic is frowned upon due to creep ( not the jmmy savil type of creep)

revjames said:

I would use a 4x4 plastic box, neweys ones are quite robust , dont forget to use the earthing ring on the gland to connect the steel armouring. 6mm insulated crimps if you can't get wagos that big.

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Wago do do a bigger version for 6mm and above cable. 

binky said:

Wago do do a bigger version for 6mm and above cable. 

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isn’t it just for 4 & 6mm cable?

not sure about siting the connections under floor boards either

Murdoch said:

isn’t it just for 4 & 6mm cable?

not sure about siting the connections under floor boards either

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Probably - I haven't used any of those for ages.

Wagos are maintenece free, so under floorboards is acceptable. 

binky said:

Wagos are maintenance free, so under floorboards is acceptable. 

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not 100% sure I agree with you

 Screwfix part No 25805.

6.0mm Wago push connector..

(link didn't work for some reason?)

Murdoch said:

not 100% sure I agree with you

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it's a spring loaded contact, same as the Hager maintenance free boxes. Personally I still prefer not to bury anything, but sometime it's unavoidable. 

revjames said:

I would use a 4x4 plastic box, neweys ones are quite robust , dont forget to use the earthing ring on the gland to connect the steel armouring. 6mm insulated crimps if you can't get wagos that big.

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Thank you revjames. I've expanded my thoughts on this now. I'm going with Wiska box on outside wall with suitable earth clamp which interacts with the JB.....anyways here goes: (I will likely get slated !)   

Hi, anyone willing to help with calcs and advice, from the onsite guide/regs themselves for a circuit to feed insulated cabin?

Thinking thus far:

I have an isolator just after the meter, so can kill all power and intend to split tails via Henley and add new switch fuse (16mm2 tails) for cabin. No spare ways in current CU. From there...

....7LM of 6mm twin & earth internally, terminated to external wiska box then continuing on for around another 13LM in 6mm 3 core SWA to cabin. (exporting the earth obviously)

Is it worth substituting the t&e for either 6mm2 Hi-tuff, or 3 no. 6mm2 single core, double insulated's, in order to increase the earth size and hence improve the earth loop impedance of the earth itself (t&e earth only 2.5mm2 csa) Thoughts please ? (the run inside doesn't really lend itself for conduit with singles, which I did think about doing. It looks challenging, but not impossible)

The initial intention is a simple ring or radial in the cabin (say 6/8 sockets and one outside cabin) and a central light or two. Two external lights from FCU's via ring/radial. I will very likely want more power there in the future, which is why I'm looking at the 6mm2 and over engineering this now.

In regards the switchfuse at head end (fed from the Henley) Am I better with an HRC fuse in an MCB type holder (I've read its better for discrimination and allows a larger variety of amperage ratings to be selected) thoughts please... whilst on this, what size MCB or HRC fuse size to use (the calcs I guess deduce this)

At the cabin. I intended fit a medium size split CU, where I would have the ring/radial on the RCD side and the internal lighting on the non RCD side (would then have a couple spare ways each side for the probable future additional circuits in the not too distant future)

I'm unsure if the incoming is TN-S or TN-CS, so would welcome any thoughts here, I.e. how to fully identify. I am aware that in the absence of actually testing that the max. permitted impedance of each is different, 0.8 and 0.35 respectively.

Also in regards above I also know that with TN-CS that the equipotential bonding is vital, but can confirm that there is no pipes or radiators, or anything else that I can thinks of in regards extraneous items now, or in the future that will be applicable in the cabin.....thoughts here please....

I used to be an electrician years ago and am currently a handyman, doing a fair amount of electrics (not the Part P stuff) My work is competent and I want this to be belt and braces. I am aware this is B.C. / Part P requirement and would add this is a job for myself. Not that makes any difference, but would not do this for anyone else.

Sorry about the long post, but I want this 100% Any helpful comments much welcomed.

Thank you in advance...

I did something similar a couple of years ago when I built my garage. I wanted a 32a supply so I ran 6mm t&e under the floor to the point where I wanted to connect my SWA for the short underground run to the garage. As you say the earth is only 2.5 on 6mm so I also ran some 6mm single earth cable with the T&E. terminated it in a neweys 4x4 box under the floor and made off the SWA with earth continuity ring, frying pan or whatever you call them. So 3 core SWA with 6mm earth conductor and SWA connected to earth from T&E as well as the 6mm singles. I crimped the phase and neutral with 6mm yellow insulated crimps and due to the larger size of the earths combined used a 10mm crimp for them with a heatshrink over the connection. all secured inside 4x4 box screwed to the side of a joist under my lounge floor. Ran it back to main consumer unit and fed from a 32A mcb which in turn is RCD protected. Fitted a schneider board in garage with  a 6a lighting circuit and a 20a socket radial and a 16a supply going to another outbuilding. 

Just my way of doing it and complying with the regs as I see it. As the buildings are very close to the house (2m) I didnt put a rod down and simply exported the earth.

if the incomer is underground paper lead or even concentric its likely to be TNS, overhead cables tend to be TNC-S

Hi. Many thanks for your detailed reply. Appreciated. I'm pretty sold on the hi-tuff in liue of the t&e as I'm guaranteed the 6mm on the earth. Given total run is around 20lm I want to be sure I have low resistance on the exported earth. There is minimal bends on the route and indeed there is a long straight run which I don't think I will have a problem running the hi-tuff. What is your thoughts please on the MCD/fuse size at the head end (I have no spare ways on cu, so I'm putting in a dedicated supply from a Henley. Cheers

FWIW why mess around with 2 types of cables - just run it all in SWA

MARK MCCANN said:

Hi. Many thanks for your detailed reply. Appreciated. I'm pretty sold on the hi-tuff in liue of the t&e as I'm guaranteed the 6mm on the earth. Given total run is around 20lm I want to be sure I have low resistance on the exported earth. There is minimal bends on the route and indeed there is a long straight run which I don't think I will have a problem running the hi-tuff. What is your thoughts please on the MCD/fuse size at the head end (I have no spare ways on cu, so I'm putting in a dedicated supply from a Henley. Cheers

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Hum ........... total load? distance? volt drop? max CCC?

Yes. I need to do the maths on that and wondered if the info would be in the on-site guide as opposed to having to obtain complete regs? 

Murdoch said:

FWIW why mess around with 2 types of cables - just run it all in SWA

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I have thought about this, but the internal part I just know would be difficult. Only a few slight ish bends to consider, but Ive used SWA before and with its weight and relative inflexibility vs Hi-tuff means I go with this on int. The majority of the ext run, bar a very short section (underground) is on a large brick wall.  

6mm 3 core is easy to handle, providing it is warm, can be a bit of a pig if it has been stored outside in freezing conditions and you go to use it straight away,  but if you know you are going to use it in the morning bring it indoors overnight, into a nice centrally heated house right next to the radiator and it will practically go in itself.

If it was my job I would be trying to do the whole lot in SWA if at all possible, the less joints the better.

Murdoch said:

FWIW why mess around with 2 types of cables - just run it all in SWA

Click to expand...

MARK MCCANN said:

I have thought about this, but the internal part I just know would be difficult. Only a few slight ish bends to consider, but Ive used SWA before and with its weight and relative inflexibility vs Hi-tuff means I go with this on int. The majority of the ext run, bar a very short section (underground) is on a large brick wall.  

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I have exactly the same thought as Murdoch... 6m of 6mm SWA under floor boards will be easy... I've run much worse for a much longer run by myself, as I'm sure most of the others on here have

Murdoch said:

FWIW why mess around with 2 types of cables - just run it all in SWA

Click to expand...

MARK MCCANN said:

I have thought about this, but the internal part I just know would be difficult. Only a few slight ish bends to consider, but Ive used SWA before and with its weight and relative inflexibility vs Hi-tuff means I go with this on int. The majority of the ext run, bar a very short section (underground) is on a large brick wall.  

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I have exactly the same thought as Murdoch... 6m of 6mm SWA under floor boards will be easy... I've run much worse for a much longer run by myself, as I'm sure most of the others on here have

Aslo.... I would rather use a RCBO board than a RCD one

NozSpark said:

I have exactly the same thought as Murdoch... 6m of 6mm SWA under floor boards will be easy... I've run much worse for a much longer run by myself, as I'm sure most of the others on here have

Aslo.... I would rather use a RCBO board than a RCD one

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Why introduce an unnecessary connection

why use cable which animals can chew through

SWA is the correct design, when considering the installation properly