Board change on 16mm tails

[DNO1981]

Hello all

Just some input needed

I have 16mm meter tails & earth looks undersized coming unto the board also. I want the consumer unit changed, I understand that the tails need to be 25mm & earth 10mm I spoke with my electricity supplier who is going to get the technical department to call next Friday about changing these. Seems like it's going to take a while.

Can I get the board changed with the existing set up first, new rcbo board installed on the 16mm tails & current earth, then after upgrade the meter tails?

 

[MJPD29]

They don't nessecarily need changed to 25mm, have you confirmed the size of the fuse?

 

[DNO1981]

They don't nessecarily need changed to 25mm, have you confirmed the size of the fuse?

The fuse is 60amp
UK power networks won't upgrade this until tails are 25mm

 

[MJPD29]

Can't understand that, 16mm tails are absolutely fine with a 60a fuse. How did they come to that decision?

 

[DNO1981]

Can't understand that, 16mm tails are absolutely fine with a 60a fuse. How did they come to that decision?

We're having some outdoor heaters fitted & a board for a jacuzzi. We were told to speak with someone & noted the 60amp fuse & tails should be changed.

 

[MJPD29]

I'd love to know how they calculated that, 16mm tails are fine on a 80a fuse also. Is the board located beside the meter or further away?

 

[Dave OCD]

Outdoor heaters ? I can't speak my mind here....

 

[DNO1981]

I'd love to know how they calculated that, 16mm tails are fine on a 80a fuse also. Is the board located beside the meter or further away?

The board is just behind the meter. So I don't need to wait for any tail or earth upgrade. Its ok to go ahead with the 16mm tails, I think the tails to the Meter from the consumer will be changed anyway by the electrician. It'll just be the 16mm coming from the fuse to the meter which be 16mm. I'll get on this now o know I don't have to wait

 

[i=p/u]

they wont put 100A fuse in unless 25mm tails. As for the upgrade I'd check your bonding if you say has small earthing conductor.

 

[pc1966]

If it is, or soon will be, on a PME system (i.e. TN-C-S) then 10mm is the minimum extraneous bond size (Table 54.8) , and obviously that also applies to any incoming earth...

Also from the simple guide (Table 54.7, not adiabatic computation) for CPC size then for 16mm tails your main earth should also be 16mm, as it would be for 25mm tails.

For an existing installation without signs of thermal stress then often you would simply let it be, but if you are looking for a supply upgrade to 80A or 100A then it makes sense to check and impose the current regulations of cable sizing.

 

[Dartlec]

Hello all

Just some input needed

I have 16mm meter tails & earth looks undersized coming unto the board also. I want the consumer unit changed, I understand that the tails need to be 25mm & earth 10mm I spoke with my electricity supplier who is going to get the technical department to call next Friday about changing these. Seems like it's going to take a while.

Can I get the board changed with the existing set up first, new rcbo board installed on the 16mm tails & current earth, then after upgrade the meter tails?

Yes, it's fine to get the board changed now. The best option would be to get a Henley block installed with the existing 16mm tails from the meter going in, then 25mm tails to the new board. That way, if you get the fuse upgraded the DNO/meter supplier can easily change their tails with no inconvenience to the existing installation...

Note you may need to get the meter tails changed separately by your electrical supplier - they own the meter, and the DNO look after the main head (in some areas they will liaise, but in others you may need to get both involved...)

Whoever you get to install the board should be able to give guidance on earth sizing and whether any upgrade to existing bonding will be needed.

 

[HappyHippyDad]

I would class 16mm tails as acceptable with a 100A fuse if max demand is not going to exceed the current carrying capacity of a 16mm conductor, also it would have to meet regulation 434.5.2. I.e Any fault occurring shall be interrupted before the permitted limiting temperature of the conductor is reached. You calculate this by using the given equation within the regulation.

The above advice can be seen in Best practise Guide 6, point 6.1 note 4.

 

[dodger421]

The above advice can be seen in Best practise Guide 6, point 6.1 note 4.

Just to note this is now Best Practice Guide 1 (Issue 4) Point 5.1, Note 4.

BPG 1 Replacing a consumer unit in domestic premises.

BPG 6 is now portable and stationary appliance testing in private rented accommodation.

Up to date BPG’s here.

 

[pc1966]

I would class 16mm tails as acceptable with a 100A fuse if max demand is not going to exceed the current carrying capacity of a 16mm conductor

Certainly for tails in open air. While they stop at 25mm for that case, a look at Table 4D1A columns 11 & 12 shows 25mm rated at 130-146A and scaling that by the sort of ratios seen for, say, clipped direct (column 6) gives ratings of at least 100A for 16mm.

But often DNOs complain if it is not 25mm so if installing new than it is easier to go with that. If you use the Doncaster easy-fit 19-standed version they are not too difficult to wrangle.

 

[hasel5]

Will also depend on your supply from the DNO if they will let you upgrade. Your supply may be looped