Shower circuit 10mm

[ultinator]

Was reading an older thread and dont have any books to hand, but basically.

If a cable for a 10kw shower is to be run, the current drawn would be 43.4 A.

So if 6mm cable was appropriate for say 70% of the run that was clipped direct, but not suitable for 30% of the run due to de-rating factors, as it would be covered by insulation . Could you size up to a 10mm cable just before the cable hit the insulation part of the run, the drop back to 6mm after the insulation where it may be clipped direct again.

I would like to note that this a hypothetical question, and the thought behind it was that if you had a long run then being able to buy only 30% of the run in 10mm would save you monies on cables.

Also (on a separate note) with gu10 firerated lights is there a recommended clearance of insulation from around them i.e. in a loft where the lights come up from ceiling below, as I presume you would want as much insulation to remain as possible.

Hope that all makes sense, thanks.

 

[Guitarist]

Stepping up, or down, depends on which way you are looking at it
Personally, I wouldn't change cable size to allow for derating through a small section. Remember, a cable should be selected appropriately for all factors that affect it. If you take this hypothesis to the nth degree you could end up with several connections in one length.

 

[ipf]

Stepping up, or down, depends on which way you are looking at it
Personally, I wouldn't change cable size to allow for derating through a small section. Remember, a cable should be selected appropriately for all factors that affect it. If you take this hypothesis to the nth degree you could end up with several connections in one length.

Maybe on an outside lighting circuit, for example, wired in, say, 6.00mm because of volt drop, some of the further points could be wired in smaller...?

 

[imago]

As already mentioned it could be done, but could doesn't equate to should. The only time I would do something like that would be the run to and from the isolator. So you may have 6mm to the isolator and 10mm from the isolator to the shower as it runs through an insulated stud wall. Doing it that way though is more about convenience for running the cable and making it off than the cost of cable.

 

[Engineer54]

Maybe on an outside lighting circuit, for example, wired in, say, 6.00mm because of volt drop, some of the further points could be wired in smaller...?

Virtually every street/road lighting arrangement is installed this way. as the load get's lighter the supply cable size is reduced. Lucy and other street lighting protection equipment suppliers, have standard post equipment that facilitates this arrangement....

 

[ipf]

Virtually every street/road lighting arrangement is installed this way. as the load get's lighter the supply cable size is reduced. Lucy and other street lighting protection equipment suppliers, have standard post equipment that facilitates this arrangement....

Exactly my point.

 

[silverfox]

50m 10mm T+E £170

10m 10mm T+E £35
50m 6mm T+E £ 75

This is just a question i wondered to myself, and so the length of runs could vary but as long as it conformed to 7671 and the joint in cable was necessary due to derating, then on a '50m' run you can save £60 or 1/3 of the cost of cable by this method. I would again like to stress I am not contemplating this as an installation I was just wondering and thought someone may be able to satisfy my curiosity.

Its not that simple. Are we pricing for a junction box as well. How long would it take you to mount the box and make it off.

 

[Guitarist]

Virtually every street/road lighting arrangement is installed this way. as the load get's lighter the supply cable size is reduced. Lucy and other street lighting protection equipment suppliers, have standard post equipment that facilitates this arrangement....

My apologies. I thought we were hypothesising about a standard domestic situation.
I will get my coat... :waving:

 

[telectrix]

cheaper to rip out and bin a couple of yards of fibreglass, and use 6mm throughout.

 

[ipf]

My apologies. I thought we were hypothesising about a standard domestic situation.
I will get my coat... :waving:

What's the size of hypos got to do with it ?

 

[sparks1973]

Think your referring to stepping down a cable size!! The bigger the cable the better, except for your, or your clients bank balance!! lol!!!

Getting back to the topic, yes you can do it this way, but no self respecting spark would do so, your just adding unnecessary joints and weakness into a circuit. On top of that, it's going to probably work out cheaper to run the circuit as it should be done, in the lager cable size, when considering the overall costs...

quite right eng...the voice of sense....

 

[sparks1973]

cheaper to rip out and bin a couple of yards of fibreglass, and use 6mm throughout.

then `Mr insulation man` just comes in and lays a load more....straight over said cable....

 

[telectrix]

not on my jobs he don't. amazing the reaction to a handfull of fibreglass down the back of his y fronts.

 

[sparks1973]

not on my jobs he don't. amazing the reaction to a handfull of fibreglass down the back of his y fronts.

itchy or scratchy Tel?...lol....

 

[Strima]

amazing the reaction to a handfull of fibreglass down the back of his y fronts.

Oi, non of that talk on here kinky, what you get up to in your own loft is your business, not mine... :lol:

 

[ultinator]

Ok, so basically you could, but whether you should or would is different. That is fine, as this isnt a real situation there is no need to panic.
Also with regards to the junction box costing extra money and time, surely pulling a 10mm cable over a '50m' run (with v.d excluded and not being taken into account) would be more tedious than pulling a 6mm cable...

Nonetheless my question has been answered and thanks for that !

.....one more thing ha, if you were to design a circuit with all things considered and no insulation around any cable, then mr ecosulation man comes and dumps a crap load of insulation on your cable thereby severely underrating it and a fire starts would he be solely liable and responsible?