Max Length Of Mains Tails ?

[Matt Thornton]

Can someone tell me the maximum length of mains tails please, I think its either 2 metres if cut-out indoors or 3 metres if cut-out outdoors, then to extend the supply further you will need a switched fuse(kmf800), also, will from the kmf need rcd protection ? cheers for any help.

 

[Guest123]

Hi Matt.

Spot on with the lengths mate.

As for the KMF needing an RCD, that would depend on how the sub-main was installed and also what type of cableing used i.e T+E buried in a wall somewhere with not earthed metallic conduit for protection or SWA or surface run etc.

Cheers.

​

 

[Matt Thornton]

Thanks Lenny, that was what I thought, but I still can't find any regulation in the wiring regs that cover this, any thoughts ??

 

[Mac]

Thanks Lenny, that was what I thought, but I still can't find any regulation in the wiring regs that cover this, any thoughts ??

Wiring Matters - magazine for electrical installation contractors - The IET
Take a look mate and click on the link(cables concealed in walls and partitions)

 

[Matt Thornton]

Thanks, but I meant the max length of mains tails, I believe that the max length of these are stated by the supplier,

 

[Spudnik]

.... I meant the max length of mains tails, I believe that the max length of these are stated by the supplier,

They are, so you will need to contact them

 

[Matt Thornton]

Thanks for that, just what I've allways believed, perhaps my fellow workers might now belive me when I tell them.

 

[tomasi]

As I understand it the mains tails can be as long as you like as long as the following applies:
The supply company agrees
You will probably have to fit a separate protective device at the origin to protect
the cables.
The cables will have to be rated for the protective device and other considerations such as method
of installation etc.

If connecting direct to service cut out seem to remember being quoted by local supplier that 3mtrs was max.

 

[holte end74]

alright lads, do you still need a KMF if the suppler has supplied a cut out, im doing a rewire and the cu is about 10 metres from the meter, there is a 100 amp switch on the digital meter looks pretty new and its marked up a contractors switch

 

[Des 56]

Safety wise I would say no,the suppliers stipulate max distance that they will permit tails as a protection against damage to their equipment
If they are allowing it ,then no need to fit the Kmf
Having said that,if there was a future problem,do you think they would admit to permitting the ommision
For anything over 3meters I would fit one come what may

 

[holte end74]

cheers for the advice