I have had a hand me down external Hot tub installed and now need power to it. It is 20mtrs away (approx cable run) from a sound electical service. The Pump is rated @11a, the heater @ 3kw, what is the correct rated amoured cable I need to purchase to complement this load?
Correct Amoured cable
- Thread starter Davetc
- Start date
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Hi
The source is a Pool house with a current 60a feed (Local CU)) fed from the main house CU.
I guess heater and pump will occasionally work together.
I only wish to supply (and Lay/route) this cable for a Sparky to terminate (although I am capable) on a dedicated RCD
The source is a Pool house with a current 60a feed (Local CU)) fed from the main house CU.
I guess heater and pump will occasionally work together.
I only wish to supply (and Lay/route) this cable for a Sparky to terminate (although I am capable) on a dedicated RCD
Ask the spark you're going to get to terminate it what he wants you to use, and make sure you agree the route with him and depth to bury it to etc. While most sparks will be happy for you to do the donkey work of burying it, to sign off on it they need to be happy with the size, and the route/depth of the cable.
If you just lay a cable and then ask a spark to turn up and terminate two ends of a cable, with no proof of how it's run, they will probably (and certainly should) refuse to do it...
If you just lay a cable and then ask a spark to turn up and terminate two ends of a cable, with no proof of how it's run, they will probably (and certainly should) refuse to do it...
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8" (~200mm) is almost certainly not sufficient, I believe the regulations require it to be at a minimum of 450mm.
In terms of cable size, assuming your pump is 11A at 230V thats 2530W, plus the 3000 for the heater gives a total load of 5530W, so you'd need 2.5mm SWA (using the calculator here: http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html). This is very close to the limit of 2.5mm though, so if you're ever expecting to add any other circuits out there, might be worth putting in 4mm instead. Also, you'd need a 25A breaker on it, which I've never seen, 4mm would mean you could use a 32A breaker, which are readily available.
Basically though, as I've said get an electrician to agree the size etc before putting it in, otherwise you might end up with a cable that you can't get anybody to terminate...
In terms of cable size, assuming your pump is 11A at 230V thats 2530W, plus the 3000 for the heater gives a total load of 5530W, so you'd need 2.5mm SWA (using the calculator here: http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html). This is very close to the limit of 2.5mm though, so if you're ever expecting to add any other circuits out there, might be worth putting in 4mm instead. Also, you'd need a 25A breaker on it, which I've never seen, 4mm would mean you could use a 32A breaker, which are readily available.
Basically though, as I've said get an electrician to agree the size etc before putting it in, otherwise you might end up with a cable that you can't get anybody to terminate...
Thanks for that, I'm a bit wiser now 
So would a cable with a statement 'Conductor nominal cross sectional area mm2' of 4.0 be the recommended one. I assume it refers to each available conductor (in this case 3).
What VA (typically) does 4mm allow?
So would a cable with a statement 'Conductor nominal cross sectional area mm2' of 4.0 be the recommended one. I assume it refers to each available conductor (in this case 3).
What VA (typically) does 4mm allow?
Yes, the 4mm^2 refers to the individual conductors. The current carrying capacity of a cable is affected by the type of cable (i.e. SWA is different to T&E, and there are even multiple types of SWA depending on what insulation is used), and what route (properly termed installation method) is used (e.g. burying it underground will be different to clipping it to a wall).
Once you have the current carrying capacity (the TLC calculator will give you this), the maximum VA it can carry is obtained by simply multiplying the 'A' figure you've got, by the voltage (nominally 230V, in reality is normally 240V).
As well as the current carrying capacity, there is a limit based on voltage drop - the longer the cable, the more volts it will drop, so you sometimes have to put a bigger cable in to avoid the voltage drop being too high. The TLC calculator takes this in to account when you specify the length of cable...
Once you have the current carrying capacity (the TLC calculator will give you this), the maximum VA it can carry is obtained by simply multiplying the 'A' figure you've got, by the voltage (nominally 230V, in reality is normally 240V).
As well as the current carrying capacity, there is a limit based on voltage drop - the longer the cable, the more volts it will drop, so you sometimes have to put a bigger cable in to avoid the voltage drop being too high. The TLC calculator takes this in to account when you specify the length of cable...
The route has to be one which complies with the regulations, none of which end with "..unless the presence of a raised garden prevents this."
No you don't. Your electrician will have to sign an official document to say that she did the design, so she has to be the one to specify the cable size.
But you've already been advised that, and I get the impression you aren't listening...
it also doesn't cite 450mm as an exact minimal depth..
it does however say that they they shall "... be at a sufficient depth to avoid being damaged by any reasonably foreseeable disturbance of the ground"
while this is generally considered to be greater than a spade depth when crossing open ground, where it is a raised bed, it's unlikely that a spade will be used on it, more likely hand trowels etc.., but I suppose that depends on how raised is a "raised bed"..
it does however say that they they shall "... be at a sufficient depth to avoid being damaged by any reasonably foreseeable disturbance of the ground"
while this is generally considered to be greater than a spade depth when crossing open ground, where it is a raised bed, it's unlikely that a spade will be used on it, more likely hand trowels etc.., but I suppose that depends on how raised is a "raised bed"..
Not that this would matter if a spark is self certifying, as it would be up to his interpretation of the regs etc, but when I notified my LABC about the cable I'm going to be running out to my shed, they mentioned that they require it to be at least 500mm down...
Hi all
I am listening
The cable run is expected to fit against the back brick work of the raised wall. 8" was a guestimate as also running below this depth are the buried pipes to the swimming pool for both skimmer & cleaner feed services. It would make sense to utilise this 'don't dig here space' for both items to be hidden. The builder that made the Tub Gazeebo suggested it was common practice to also have an isolator installed near to Tub. Is this essential?
PS the raised garden borders next door, is about 3 feet wide and houses small Laurel trees, laylandii & shrubs. It rarely sees a spade, but frequently a trimmer!
I am listening
The cable run is expected to fit against the back brick work of the raised wall. 8" was a guestimate as also running below this depth are the buried pipes to the swimming pool for both skimmer & cleaner feed services. It would make sense to utilise this 'don't dig here space' for both items to be hidden. The builder that made the Tub Gazeebo suggested it was common practice to also have an isolator installed near to Tub. Is this essential?
PS the raised garden borders next door, is about 3 feet wide and houses small Laurel trees, laylandii & shrubs. It rarely sees a spade, but frequently a trimmer!
An isolator local to the tub is not only common practise, its essential!
As is a 30mA RCD.
As is a 30mA RCD.
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