H07Rn-F Cable For Fixed Wiring/submain?

[Aragorn]

I'm about to replace the cable that feeds a small workshop/big shed in my garden.

Currently there is 2.5mm T&E from the CU, thru the house, out thru the wall and off along the ground completely unprotected before going up the wall and entering into the workshop. To top it off, its protected by a 40A MCB.

Proper cowboy job by the previous owner!

I'm going to replace the external run with 10mm SWA, but i dont particularly fancy trying to route that cable thru the tortuous route required to get it from the back of the house to the front where the consumer unit is, so i'm going to joint it onto something a bit more "interior friendly" at the external wall.

The cable isnt buried and doesnt need earthed protection once inside the house, and i'm wondering if i can use H07RN-F?

I was going to use split-con, but no-where local will sell me a section, only selling full rolls as they dont keep it in stock. I could use T&E, but that means running a seperate 10mm earth single alongside which isnt ideal. Its also not ideal for sealing into the external box due to its shape.

Been using a lot of H07RN-F at work for connecting big equipment and realised it might actually do the job just fine.

Cant figure out if its actually allowed or not though?

Any alternative ideas?

 

[Marvo]

Although the price may be prohibitive, from what I understand there's no regs against using trailing cables such as HO7 RNF ans installation cable in the UK but there can be issues with termination techniques.

 

[Andy™]

flex can be used for fixed wiring. some tables are in 7671 but for some you might need to get data from manufacturer

you dont always need a 10mm earth alongside T&E, the 4mm it has is perfectly adequate in many circumstances

 

[Aragorn]

Marvo: I could probably get some bootlace ferrules and crimper from work, if that would improve the termination issues?

Andy: Thanks. I'd hate to install it with the 4mm earth and find the Zs is above whats allowed for the Fuse protecting the submain. Theres also potential equipotential zone issues, so i'd prefer to just fit a 10mm earth!

 

[Marvo]

I'm not familiar with UK regs but I'm guessing ferruling the ends would be required for any fine stranded wiring terminated in an accessory like a socket/switch and in an MCB cage clamp.

 

[apprentice87]

Hi Aragorn.

I take it that you want the 10mm as you are taking TNCS out to your shed?? Anyway, leaving that aside, you say that you do not want to risk using something with a 4mm cpc in case of Zs issues, but if you did the cable calcs you would know for a fact what the resultant Zs was going to be.. 10mm 3 core HO7 is lovely flexible stuff and what's more, smells lush in a pervy sort of way!!!

Oh I ALWAYS use ferrules on the ends, Not to do so would be bodgy in the extreme....

john...

 

[Andy™]

Andy: Thanks. I'd hate to install it with the 4mm earth and find the Zs is above whats allowed for the Fuse protecting the submain. Theres also potential equipotential zone issues, so i'd prefer to just fit a 10mm earth!

and what if you install 10mm then find out Zs is too high?

you do cable calculations in advance so you know exactly what size you can use. its not take a guess, install it then test to see if it complies or not

 

[Aragorn]

The supply is currently TN-S. But its some nasty 6mm VIR cables in a conduit from next door, with the earth supplied by the conduit and a clamp.

I had the DNO out to look at it not long after moving in, and the guy agreed it was bad and needed replaced, but said it was a low priority job. (incidentally this reminds me i need to chase them up)

Theres always the possibility that the replacement supply might end up as TNCS/PME, which would cause me problems if i used the smaller earth.

I dont recall the numbers, but i did some quick calcs a while back when i'd measured the Ze and decided it was all a bit "close". I'd have to go re-measure the Ze and calculate everything out, will do this before i order anything!

Cheers

 

[kerching]

Why are the ferrules on the end of bootlaces not called bootlace ferrules?

Just wondering!

Agreed it does smell,nice! Probably why diving appeals to my inner perviness!

The flex is nice to work with as well....had to double check spelling there!

 

[NozSpark]

Because they're called Aglets

 

[Andy™]

maybe we should start calling them wire aglets?

 

[sprocketflup]

maybe we should start calling them wire aglets?

:slap

 

[binky]

never heard of aglets....

cable is manufactured with earth suitably sized for the current carrying capacity. I can't think of single incident where the standard cable earth has been undersized and failed to meet Zs requirements. I'm sure someone will correct that or have experience where by I'm wrong.

 

[Aragorn]

Not really sure thats correct? Sometimes you need to go up a cable size to meet Zs requirements, depending on the characteristics of the protective device...

Gets particularly tricky with big Type C and D breakers.

 

[Blue Duck]

never heard of aglets....

cable is manufactured with earth suitably sized for the current carrying capacity. I can't think of single incident where the standard cable earth has been undersized and failed to meet Zs requirements. I'm sure someone will correct that or have experience where by I'm wrong.

16mm t&e submains

 

[kerching]

AIGLETS!

Not Aglets....just remember how picky some folks are on here!

 

[Marvo]

I wouldn't mind if he actually had laces on his avatar. :maria:

 

[apprentice87]

You will very often need to have a much bigger CPC than is required for strictly "CPC" purposes, as it might be serving a dual purpose as a main equipotential bonding conductor....

john..

 

[Tony S]

maybe we should start calling them wire aglets?

Maybe not if you look up the 2nd definition.

 

[steptoe]

Remember,

If you do get TNCS,  then you will need to get permission from your DNO to export it,

They will most likely refuse,

So, just do it right, TT your shed. 

Only an idiot would take TNCS outside the EZ without taking other precautions, and I don't mean just a BIG earth.