What load can this 2.5mm T&E take???

[Joe S]

As above, I have a plumber who's changed the water heater on a finished garage annex that we've been doing. The original one was 1.2kw in a bathroom undersink unit. There is an electric rointe 750w towel rail aswell so I put the two on the same circuit to save ways in the new board. He now wants to put a 3.5kw heater in as the first has popped a pipe off due to pressure problems. I'm not a plumber so not bothered except when the kw's are involved. The cable is 2.5mm T&E that runs about 8.5m to the S.F Spurs, 1 for each appliance. The majority of the cable is high up on a concrete wall in box trunking and then goes into the suspended floor, through joists with celotex between (approx 3.5m). I have been looking through the books and it says between 20 - 23a for this cable. I usually go on a rule of thumb of 5a to 1kw so the two together are nearly 20a without any diversity or correction.

I'm just after a second opinion as I usually don't like my installs running too close to their limits. Any advice appreciated

 

[trev]

The celotex is going to derate the cable mate

 

[Thomas123]

Well your load is 19.56a, put the 2.5 on 20a breaker and bobs your uncle

 

[telectrix]

bloody celotex. as if a few inches will save oodles of cash and save the planet. rip it out.

 

[Joe S]

It's on a 16a at the moment, I was just wondering by how much does celotex derate the cable as the books are still assuming fibreglass?

 

[telectrix]

asssume worst scenario. over 400mm in insulation, derate by 50%

 

[Joe S]

asssume worst scenario. over 400mm in insulation, derate by 50%

So my cable is only good for 9.8A??

 

[trev]

So my cable is only good for 9.8A??

Worst case scenario.

 

[Farmelectrics]

2.5 takes 27 amp but that's clipped direct if it goes insulation this can halve if you want to be certain and sleep at night run 4mm in its place

 

[telectrix]

a 2.5mm is rated at 27A. if enclosed in insulation > 400mm length, then it's down to 13.5A. just cut the bloody stuff away. a little bit of heat escaping from the over heated kitchen to the bedroom above, no big deal. this obsession with confining heat to a room is , IMO, nothing short of stupidity gone daft. it's like the current fad for dumping tungsten light bulbs. OK, they lose energy through heat loss. but it's not lost! the heat from tungsten lights warms the room, so less energy needed from the heating system.

 

[Farmelectrics]

Tel if you cut it away couldn't some one put it back at some stage would be happier pulling 4mm in but might be over the top

 

[kingeri]

Can't install everything thinking what someone may do in the future. otherwise we'd be running 6mm ring finals!

 

[Farmelectrics]

Think of worst case scenorio your covered then

 

[telectrix]

Tel if you cut it away couldn't some one put it back at some stage would be happier pulling 4mm in but might be over the top

there's only one place for insulation between rooms of the same abode. it's called a skip

 

[Joe S]

Tel if you cut it away couldn't some one put it back at some stage would be happier pulling 4mm in but might be over the top

That's what I was thinking. I'm sure that the celotex was under the cable but I'm not sure if the builder overlaid some more?! I did cut away what I needed to get the cables through and clear of what celotex was near.

 

[Farmelectrics]

Ok as tel said skip it haha