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?

 

[Sparksfly2]

Im getting 16mm for both calculations, borderline 10mm

 

[davesparks]

230

Ah, that'll be the difference.

We have been given a load of 6.5kW and 26A which only makes sense if that is at a rated voltage of 250V.

So you either need to calculate at the rated voltage or adjust the load value for the voltage you are going to do the calculation at.
Adjusting the load for a voltage of 230V (assuming the load is resistive, or mostly resistive, heaters) it becomes 5.5kW and 24A at 230V.

 

[Markyd]

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.

Dont worry....he will get Dave from down the pub to do it

 

[loz2754]

Ah, that'll be the difference.

We have been given a load of 6.5kW and 26A which only makes sense if that is at a rated voltage of 250V.

So you either need to calculate at the rated voltage or adjust the load value for the voltage you are going to do the calculation at.
Adjusting the load for a voltage of 230V (assuming the load is resistive, or mostly resistive, heaters) it becomes 5.5kW and 24A at 230V.

Thanks for pointing this out, however I believe I fully understand the nature of resistive loads in this context.

However, whichever way I calculate it, even with a design current as low as 24 amps, it doesn't reduce the volt drop enough for a 10mm² cable to comply with maximum 5% volt drop.

I just noticed the OP has given new figures from the rating plate of 220 V, 29 amps.
Using these figures, volt drop is still the limiting factor, according to my reckoning.

 

[Sparksfly2]

Yes I can see the existing just being added to and him ending up with underfloor heated garden

 

[Sparksfly2]

I agree as ive tried various alterations to current voltage also just based on the hot tub without any additions but the length of run is the limiting factor.

 

[brianmoooore]

Hot tub will be far from a resistive load. There's likely to be a couple of 2hp motors, plus a smaller air pump, as well as the resistive load of the heater.

 

[littlespark]

120m away from the sounds like a big garden…. Will be freezing before you get back to the house.

 

[Sparksfly2]

Yeah its quite a run, long way to go for a top up, previous install looks pretty good

 

[buzzlightyear]

120m away from the sounds like a big garden…. Will be freezing before you get back to the house

a squrials nuts off.

 

[Spoon]

Just a reminder people, if you are using 90°C cable for the calcs, you have to make sure the equipment the cable is connected to is also rated for 90°C.

 

[brianmoooore]

If anything is going to run anywhere near 90 degrees in a hot tub install, then that thing needs to be immersed in the tub water. Tubs are expensive enough to run, without heating soil.
At the distance involved, voltage drop considerations will dwarf the current rating of the cable, so cable temp. is not likely to be a concern.