hot water tap on ring

[mo2]

So I have a 32A ring final wired in 2.5mm T+E, could somebody point me in the right direction as to how to calculate if it could take 3 or 5kW(as an extension of the ring)?

I've found this:
http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html
,but this seems to be for radials?


Also, if I did have to have a dedicated cct, how is the mcb size calculated
thanks in advance, mo2

 

[RF Lighting]

What is it you are actually trying to acheive?

 

[electronicsuk]

So I have a 32A ring final wired in 2.5mm T+E, could somebody point me in the right direction as to how to calculate if it could take 3 or 5kW(as an extension of the ring)?

As per RF, what are you trying to do? You certainly can't have a 5kW point load (or 'spur') from the ring. You can have 3kW, and it will most likely need to be via a 13A Fused Connection Unit, but fixed loads >2kW should be on their own circuit rather than be part of a ring final.

 

[mo2]

for a 3kw heater I've decided...

So, what I mean is an FCU (13A or 20A?) not spurred, but with two cables going to it.

The run, is through the eaves(?) and under capping on the wall. I'll give measurements, if anyone fancies doing the calcs. The MCB is a type B 32A, and there 3 other sockets on the cct. So with the FCU it'd be 4 points if ya know what I mean

 

[mo2]

gawd, i forgot to mention i mean A 3kw water heater thingee mabobbee

 

[electronicsuk]

for a 3kw heater I've decided...

So, what I mean is an FCU (13A or 20A?) not spurred, but with two cables going to it.

Where have you seen these 20A FCUs? Seen as FCUs generally accept BS1362 fuses, and BS1362 fuses go to 13A, how do you plan on connecting a 20A load?

Besides, it's still a spur if you take a feed off the ring via an FCU, but the important difference is that it's a fused spur.

Just so there's no confusion, you can't have a fused spur greater than 13A from a ring final, and unfused spurs in 2.5mmsq are only permitted to feed ONE standard BS1363 single or twin 13A socket, or a similar electrical accessory such as a fused connection unit. You cannot use an unfused spur to take a 20A supply from the ring.

The run, is through the eaves(?) and under capping on the wall. I'll give measurements, if anyone fancies doing the calcs. The MCB is a type B 32A, and there 3 other sockets on the cct. So with the FCU it'd be 4 points if ya know what I mean

Irrelevant.

 

[Steve]

gawd, i forgot to mention i mean A 3kw water heater thingee mabobbee

erm actually . . .

for a 3kw heater I've decided...

 

[mo2]

gawd, i forgot to mention i mean A 3kw water heater thingee mabobbee

erm actually . . .

for a 3kw heater I've decided...

im tired

and errr, so fused spurring 3kw would not be clever as 3kw will blow the 13A fuse. OK, i think my brain is computing that.

So dedicated cct then.

erm,,,how does one work out what wire/breaker to use then.
That TLC thing tells me:

Required Cable Size 2.5 mm
Voltage Drop 2.35 Volts.
Percentage Drop 1.0%
Current Load 13.0 Amps
Max Cable Load* 15.6 Amp

So a 2.5mm or 4.0 just to be sure and a 20A type B!? breaker.

Sorry about my confusion i really am ker-nackerd

 

[mo2]

also wouldn't the 3kw be less than 13A, as I'd use a short amount of flex from the FCu to the heater, or would thte fuse be popping all the time?

 

[electronicsuk]

and errr, so fused spurring 3kw would not be clever as 3kw will blow the 13A fuse. OK, i think my brain is computing that.

What? Who ever said that? 3kw = 3000w. 3000w/230v = 13.04A. It would be fine on a 13A fuse, but read on...

So dedicated cct then.

That would be preferable, as BS7671 now asks us to put loads >2kW on their own dedicated radial circuit.

erm,,,how does one work out what wire/breaker to use then.
That TLC thing tells me:

Required Cable Size 2.5 mm
Voltage Drop 2.35 Volts.
Percentage Drop 1.0%
Current Load 13.0 Amps
Max Cable Load* 15.6 Amp

So a 2.5mm or 4.0 just to be sure and a 20A type B!? breaker.

Sorry about my confusion i really am ker-nackerd

Sorry, but not even going to attempt to answer that, as (no offence intended) it's quite clear that you don't have the knowledge or experience to be undertaking this sort of work.

 

[mo2]

well i'll be running the cable for sure, and I can do basic bits and pieces, but if someone were to explain what I need to consider in this new situation which I am not familiar with, I would most definitely go and figure the rest out for myself and do it it safely

 

[electronicsuk]

well i'll be running the cable for sure, and I can do basic bits and pieces, but if someone were to explain what I need to consider in this new situation which I am not familiar with, I would most definitely go and figure the rest out for myself and do it it safely

Obviously the cable run can't be that long if the TLC calculator is giving you 1% drop. Other than that, all usual rules apply - cable to be run in safe zones and RCD protected unless buried >50mm in wall or run in earthed metal conduit/SWA/similar. You will need to be sure that ELI will be low enough to break the circuit in the required time, which will be affected by factors such as your choice of protective device, conductor size, cable length, and the earthing arrangements and Ze already existing within the installation. And much, much more besides. You wont be able to determine Ze or perform many of the other tests required on this installation without expensive test kit, which will cost more than getting a spark to do the job.

My point is, you can't possibly expect anyone to teach you how to do all this via a forum, which is why you should be employing the services of a good electrician who is a member of a self certification scheme. They will be more than likely happy for you to do most of the legwork (chasing, clipping cables, etc) as long as they can see it for first fix inspection, and you clear everything upfront before starting the job!

 

[mo2]

Thanks very much for the answer, I'll have to rethink then

 

[ban-all-sheds]

I'm not a bully.

I just don't like pathetic losers telling lies here for a laugh.

 

[ColJack]

well i'll be running the cable for sure, and I can do basic bits and pieces, but if someone were to explain what I need to consider in this new situation which I am not familiar with, I would most definitely go and figure the rest out for myself and do it it safely

since none of the Part P police have shown up it's up to me I guess..

you must notify the LABC ( and pay a fee ) in advance of commencing any electrical work in a kitchen, bathroom, shower room, outdoors and for any work involving the provision of new fixed cabling, a new circuit, and altering of the OCPD.

you can use a registered electrician who will do the notifying for you, or as above, DIY and pay the fee..

as this is titled "Hot water tap" then it's a safe bet that it's for work in a kitchen or bathroom...

look up part P in the wiki at the top of the page.

for your circuit you want 2.5mm² cable and a 16A B type breaker, a 20A DP switch