16mm tails with 100A fuse ???

[Wilko]

Job today to change out old fusebox and I'd noted the 16mm tails but on pulling the fuse this morning it was 100A which I wasn't expecting. Fairly recent new smart meter installed by XYZ who are also the DNO ... Shouldn't the fuse be limited to 60A in this case? Thoughts and advice appreciated

 

[westward10]

Could you not change them to 25.0

 

[Ian1981]

As it's existing are you expecting that your total demand is going to be higher than the rated CCC of the tails ?
16mm tails are good for 87amps clipped direct

 

[westward10]

What are they rated at once you enclose them in CU as they are no longer clipped direct and should be derated.

 

[Ian1981]

WEve had this argument before.
Then by definition nothing can be classed as clipped direct as it ultimately terminates into an enclosure

 

[westward10]

Between meters and service terminal blocks they are, as soon as you contain them they are no longer clipped direct throughout and that rating will not apply.

 

[Ian1981]

Rubbish!

 

[westward10]

Is it, justify clipped direct when it is partially contained.

 

[Rpa07]

What are they rated at once you enclose them in CU as they are no longer clipped direct and should be derated.

Do you really think that Westy, really or is there some pedantry going on- you've brought it up in the past?

 

[Ian1981]

Its all about how the cable is installed and it's ability to dissipate heat.
Sorry but that's just another post meant quite frankly to annoy people

 

[Octopus]

Back on track - how difficult would it be to change the tails?

What do you estimate the maximum load to be for the property? If its well under 87 amps you could reasonably leave the 16mm in place ....

tin hat is on!

 

[westward10]

Its all about how the cable is installed and it's ability to dissipate heat.
Sorry but that's just another post meant quite frankly to annoy people

Quite the opposite it is a reasoned argument using as you say, how the cable is installed and it's ability to dissipate heat whereby this ability is lowered once contained.

 

[Des 56]

If a cable passed directly through a insulation packed 4x2 stud partition so that those few inches were all that was not clipped direct,how many of you would de rate the cable?
Getting rid of that heat is what the ccc are all about as Ian mentioned previously

 

[Rpa07]

Maybe we shouldn't be IP rating the CUs then - let the wind flow free! Or fit a permanently running CPU fan!

 

[Wilko]

Well, I did try to move the tails but only got the 20cm I needed for the new CU and they won't budge any more, although there is slack at the meter. So changing the tails will be mission messy. Tails leave the external chest high meterbox in a cavity brick wall, go up and over the front door and drop down from the ceiling. CU mounted high up next to ceiling behind front door. New CU is in the location of the original fuse unit, at Customer's request. But somewhere in that lot the tails go through a beam I reckon and are jamming up. Nothing I can't sort if I rip into the plaster ceiling she's just had done .

In terms of load, I am sure a 60A fuse would be fine. 2BR mid terrace, newish combi for CH and HW. Biggest drain will be an induction hob she's got on order.

There's no insulation anywhere near the tails that I can see looking from both ends. The tails will be less than 3m long.

 

[Octopus]

Pop a 60A fuse in .............. nobody will ever know

Tin hat still on!

 

[Ian1981]

Well, I did try to move the tails but only got the 20cm I needed for the new CU and they won't budge any more, although there is slack at the meter. So changing the tails will be mission messy. Tails leave the external meterbox in a cavity brick wall, go up and over the front door and drop down from the ceiling. CU mounted high up next to ceiling behind front door. New CU is in the location of the original fuse unit, at Customer's request. But somewhere in that lot the tails go through a beam I reckon and are jamming up. Nothing I can't sort if I rip into the plaster ceiling she's just had done .

In terms of load, I am sure a 60A fuse would be fine. 2BR mid terrace, newish combi for CH and HW. Biggest drain will be an induction hob she's got on order.

There's no insulation anywhere near the tails that I can see looking from both ends. The tails will be less than 3m long.

As long as regulation 434.5.2 is met for protection of the tails for fault current and your total load profile taking into account diversity is not going to overload the CCC of the tails you will be fine.

 

[Ian1981]

Of course the DNO may stipulate a maximum CSA of bigger than 16mm tails if connecting directly into their equipment.
Of course we all ring them all the time to enquire don't we?

 

[Wilko]

Of course the DNO may stipulate a maximum CSA of bigger than 16mm tails if connecting directly into their equipment.
Of course we all ring them all the time to enquire don't we?

Yes, what was the DNO thinking putting 100A fuse in and saying nothing to owner (she's lived there forever) about the 16mm tails... and the DNOs smart meter guy ...

 

[Wilko]

As long as regulation 434.5.2 is met for protection of the tails for fault current and your total load profile taking into account diversity is not going to overload the CCC of the tails you will be fine.

Got the books out, calculator valves just warming up.