16mm tails with 100A fuse ???

[Toneyz]

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

Tin hat still on!

Take the tin hat off if you've got the fuse out de-rate the fuse to 60A there are millions of houses with 60A fuses that have had additional loads installed .

 

[Octopus]

Take the tin hat off if you've got the fuse out de-rate the fuse to 60A there are millions of houses with 60A fuses that have had additional loads installed .

Precisely.

Got a client near me, 5 bed house, separate annex, loads of external lighting, pool, tennis court, ..... 60A fuse

People get so hung up about needing a 100A fuse ................... unless you are doing space heating, cooking and water heating and live in a big house you won't get anywhere near 100A.

Just imagine the lecky bill if you were running these loads on a regular basis.............

 

[Wilko]

Ok - with k=115, S=16 and Ze 0.19 measured today, I get ... wait for it ...

Take the tin hat off if you've got the fuse out de-rate the fuse to 60A there are millions of houses with 60A fuses that have had additional loads installed .

Mine included ... that's why I'm pretty comfortable with 60A fuse .
Question is, do it myself (at least it's done) or ask DNO who may do it, or may not?

 

[telectrix]

hmmm. tails inside the CU are basically in free air, but with a slight derating due to be in the enclosure, although with plenty of airspace around. IMHO methed C can be applied without losing any sleep over it. if i doubt, replace the cut-out fuse with 80A. 16mm only gets lukewarm @ 110A. BS7671 figures are more pessimistic than me giving up beer.

 

[Octopus]

Ok - with k=115, S=16 and Ze 0.19 measured today, I get ... wait for it ...

Mine included ... that's why I'm pretty comfortable with 60A fuse .
Question is, do it myself (at least it's done) or ask DNO who will never do it

Edited that for you.............

 

[Wilko]

Using 230 x 0.95, I get 1,150A pssc and plugging that into 434.5.2, I get 2.56 seconds. The melting time for BS88-3 100A at 1050A is 0.4sec.

So for short circuit situation this 100A fuse will not damage the 16mm tails, if I've done that correctly

 

[telectrix]

my old man's house, built 1926 has a 30A rewireable DNO fuse. it blew in 1988, but only when we;d added a 12kW cooker, 8kW shower,washing machine, and tumble dryer. all were going when the fuse let go.

 

[westward10]

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

Just fit correctly sized conductors.

 

[Ian1981]

Just fit correctly sized conductors.

I guess you must C2 every domestic installation that has 16mm tails and a 100 amp fuse arrangement without consideration other than 'it's not the right size'

 

[Ian1981]

Ok - with k=115, S=16 and Ze 0.19 measured today, I get ... wait for it ...

Mine included ... that's why I'm pretty comfortable with 60A fuse .
Question is, do it myself (at least it's done) or ask DNO who may do it, or may not?

K would be 143 as the earthing conductor is not incorporated as part of a cable
S= I2t square root /k
So I is 1210 amps
t I'd have to look up a bs 1361 or is it bs 88?
K is 143

Edit for some reason I'm working out the earthing conductor size so ignore me

 

[westward10]

I guess you must C2 every domestic installation that has 16mm tails and a 100 amp fuse arrangement without consideration other than 'it's not the right size'

This wasn't the argument, the argument was the rating of said cable and my proposition that being partially contained should reduce the ccc. You have yet to give a flaw to this argument.

 

[Ian1981]

This wasn't the argument, the argument was the rating of said cable and my proposition that being partially contained should reduce the ccc. You have yet to give a flaw to this argument.

You've yet to confirm yours.
Show me evidence that cables need derating and to what method?
Then I'll come around.
Don't recall bs 7671 requiring us to derate cables entering a consumer unit or an enclosure in the appendicies with the list of reference methods it gives.

 

[Wilko]

Just ordered a couple of 60A fatboy fuses. Not saying where one might go

Edit : ok, just stop right there, you lot are just hopeless

 

[Dave OCD]

They must be around a fiver a go now ?

 

[Wilko]

They must be around a fiver a go now ?

Yes Dave, £3.83 from Discount Electrical.

 

[Deleted member 9648]

As has already been stated if there was a requirement to de-rate a cable entering an enclosure for termination clipped direct and free air installation methods would not be possible and would not be in the BYB.

 

[Dave OCD]

That's not too bad mate, worth it for peace of mind and not being criticised to death by W10.

Edit -reply to Wilko's post.

 

[westward10]

As has already been stated if there was a requirement to de-rate a cable entering an enclosure for termination clipped direct and free air installation methods would not be possible and would not be in the BYB.

Clipped direct would apply between service heads and meters etc. Once contained at its termination to a CU alternative ccc applies. Really quite simple.

 

[telectrix]

so what factor would apply to the cable rating just because it's inside a box? where in BS7671 does it say that a rating factor needs applying.

 

[Karin]

just for the craic, tne or other cables are usually stripped back to single insulated conductors inside an enclosure (so may closer reflect singles in trunking for that part), meter tails are usually sheathed right to the termination point. would this (how much?) affect the argument?
i've had a couple, there's no BYB in sight, i just wanted to get involved.. !