Maximum tail length

[johnad]

I am looking to have a consumer unit moved when it is replaced shortly
It's in a small alcove and I want it across the opposite side .
So the meter will be on the left hand side and the tails would need to run across an exposed beam to the right hand side to the the new consumer unit so they would face each other with a distance of about 1.5m.
Is ther a maximum length for tails ?
How far can the consumer unit be from the meter ?

 

[westie101]

DNO's prefer tails to be shorter than 3m, bear in mind that they may be protected by a 100A fuse.

 

[riveralt]

DNO's prefer tails to be shorter than 3m, bear in mind that they may be protected by a 100A fuse.

Don't take this the wrong way westie, but what has the meter tail length got to do with the DNO. The 100A fuse is protect their cable after the fuse - surely anything after the meter on the consumer side is the responsibility of the consumer and its length, size and voltage drop should be determined by themselves or their electrician - or are DNO's now going to provide free meter tails?

Reason I raise this is because I fitted a new consumer unit to a flat on the top (third) floor of a block of six flats. The main incoming supply and associated meters where all in a cupboard on the ground floor and there was at least 15 metres of what looked like 16mm cable from the meter up to this flat. There was an 80Amp fuse so 16mm just about covered it.
I spoke to the DNO about this and they said the usual mantra that anything after the meter on the consumer side is the consumers repsonsibility.

 

[RF Lighting]

I agree with the rule wether it is an actual rule or not.

Just put a switchfuse in at the meter position and then you cn do what you like and any fault with or damage to the tails is not going to blow the cutout fuse, and any repairs / alteration can be made without DNO involvement.

 

[dingodeano]

Any long run or where the tails ran in celling voids and through the building fabric i think I would use some 25mm armoured and switch fuse rather than risk tails getting nails.

 

[westie101]

Riveralt, but I'm sure you may just agree that having a long length of cable within a property protected only by a 100A fuse is a higher degree of risk than one protected, as would be the case in a modern installation, by an RCD and a lower value MCB.
In fact I wonder as it is part of the customer's installation how compliance with BS7671 would be obtained.

Oh and I said prefer not that it is a requirement.

Certainly going back some years we would not connect a new supply if the tails were over 3m and this was included in the spec for new supplies at the time.

 

[RF Lighting]

For tails contained within the fabric of the building, even if the cable is big enough to be on a 100A fuse, which means at least 25.0mm² tails or cable, and it does not require RCD protection (ie it's not concealed with in a wall) it will still be non compliant with BS7671 unless it is connected to a DP isolator at the source of the installation.

If all the above criteria are met then I think it would technically be compliant, but certainly not good practice.

I don't have a problem with a couple of meters of tails from the meter straight to the CU as long as there is no risk of mechanical damage, such as if it's run on the surface in trunking for example.

 

[ericmark]

433.2.2 and 434.2.1 is the regulation where it refers to 3 meters but this does not really apply to meter tails. It's more to do with when you can't fit the fuse at point where cross sectional area changes.

Personally I don't like long tails mainly as if damaged one can easy have exposed live parts without opening the protective device.

If we consider something like a scaffolding pole hitting cables where the line neutral and earth are together it is very likely it will open some safety device. But where run independent all to easy for it not to trip anything.

I though I had read somewhere how the circuit cables should be run together but looking now I can't find the reference.

 

[patrick122]

as already stated i would personally use an swa. from the meter position to the cu.no problem with length as long as cable size is ok for length of run.normal in any block of flats where the meters are positioned in a communal cupboard

 

[johnad]

Thanks for all your comments
The reson I was thinking about moving the location of the unit is that the new one will be longer and will have to be fitted lower than the old one meaning that all the existing cables will be to short so do I extend all the existing cables or move the unit and have longer tails (2m longer ???)
I will try and post a pic later tonight.....