Swa install to hot tub

[Sparksfly2]

Hi, looking for some advice,
6mm swa allready installed to a hot tub
Client now wants additions and my calcs say the original swa is allready too small.
26a but its120m run, im advising 16mm 2core.

However the swa installed is 4 core so was thinking of doubling cores together to save on time/ costs and putting rod in.

Any thoughts or potential issues with this?

 

[buzzlightyear]

6mm swa allready installed to a hot tub
Client now wants additions and my calcs say the original swa is allready too small.

what are the additional works regarding the up grade of wiring .

 

[buzzlightyear]

26a but its120m run, im advising 16mm 2core

what is the loading of the hot tube .

 

[buzzlightyear]

Multicore 90°C Armoured Thermosetting Insulated Cables​

Tables Apply to: H6942XL, H6943XL, H6944XL, H6945XL, Tuff Sheath,

Voltage:230V

Load:5.98kW / 26A

Length:120m

Method of Installationirect in ground or in ducting in ground

Cable Size:16mm²

 

[Sparksfly2]

Hot tub is 6.5Kw 26a.
Addition is few general sockets and light in shed/ summer house.

 

[loz2754]

My calculations also indicate 16 mm² for the hot tub alone. Doubling up using the other 2 cores of the 4 core would result in the equivalent of 12mm² at best.
A new cable run is the only option I can see.

 

[Sparksfly2]

Feel bit sorry for bloke and doubt he will pay for upgrade, and im not planning on doing works.
Was just thinking if in theory by doubling the existing cores would improve the current installation.

 

[davesparks]

Hot tub is 6.5Kw 26a.
Addition is few general sockets and light in shed/ summer house.

Surely you'd want a seperate circuit for general use sockets and a light?

 

[davesparks]

My calculations also indicate 16 mm² for the hot tub alone. Doubling up using the other 2 cores of the 4 core would result in the equivalent of 12mm² at best.
A new cable run is the only option I can see.

Odd, I get 10mm for the hot tub.

What voltage are you basing your calculation on? The load is stated as 6.5kW 26A which only makes sense if that rating is at 250V.
Based on 250V I get 10mm

But if you adjust the load for a 230V supply (assuming the majority of that load is heating and so resistive) it will be running at 5.5kW and 24A and again I get 10mm as being suitable.

 

[Sparksfly2]

My initial plan was a submain to a DB in summerhouse on TT feed hot tub from there utilising the existing swa until I realised it was undersized.

 

[davesparks]

Feel bit sorry for bloke and doubt he will pay for upgrade, and im not planning on doing works.
Was just thinking if in theory by doubling the existing cores would improve the current installation.

Yes doubling up the 4 core will improve the situation, it may not make it perfect but it will improve it.

But does the hot-tub work currently? If it does then it suggests that the volt drop is not currently so excessive that it will cause a functional issue.
Does the hot tub have a minimum supply voltage rating? (rememeber the percentages given in the regs are intended for use when the voltage tolerance of a load is unknown, not necessarily a hard limit for every circuit)

Obviously the fact that something works in its current states doesn't guarantee safety, but it does indicate that the supply may be functionally adequate.

Have you measured the voltage drop on the hot tub circuit?

 

[loz2754]

Odd, I get 10mm for the hot tub.

What voltage are you basing your calculation on? The load is stated as 6.5kW 26A which only makes sense if that rating is at 250V.
Based on 250V I get 10mm

But if you adjust the load for a 230V supply (assuming the majority of that load is heating and so resistive) it will be running at 5.5kW and 24A and again I get 10mm as being suitable.

Let me do it again. I think I may have used 32 amps as the load...

Edit:
Recalculated using 26 amps, still get 16mm² due to volt drop.

Edit 2:
I used installation method D1 assuming an underground cable run.

 

[Sparksfly2]

220v 6.4KW 29a at closer inspection of label

 

[davesparks]

Let me do it again. I think I may have used 32 amps as the load...

Edit:
Recalculated using 26 amps, still get 16mm² due to volt drop.

What voltage are you using at 26A?

 

[loz2754]

What voltage are you using at 26A?

230

Volt drop calculation:

For 6mm²
7.9 X 26 X 120 /1000= 24.648 Volts

For 10mm²
4.7 X 26 120 /1000= 14.664 Volts