Discuss Hot tub volt drop in the UK Electrical Forum area at ElectriciansForums.net
Yeah its not just the cost aspect, i already have a drum of 6mm and it would make the job easier as its running through the loft first (clipped up off the insulation).Checking e.g. Superlec cable prices, for 50m, the cost difference between 6 and 10mm2 SWA 3-core is less than £30, which in the overall cost of the install and tub must be small change. So I'd just use 10mm2.
Think of it as undersoil heating. So you can walk from the house to the hot tub in your bare feet.Customer would rather heat their hot tub than the soil between it and the house if explained to them, and 5% drop is the current 'fashion'. 2.5% for most om my career, and, for the sake of a few pounds, is what I still prefer to work to. Better for the pump motor starting performance, and the electronics might appreciate the reduced spikes.
70 deg PVC - Can you still get that?I ran it again for 70 degree as it's maybe more likely the OP has that
That is a good point, wonder what the cross-over point is when it pays for the bigger cable?Hot tubs run up a fair old electricity bill. In normal, non Covid times, I run two, so I should know.
I wouldn't want to spend 5% of that cost heating the ground, just to save a few pounds on installation.
Whether you can or not, unless the accessories etc to which it's connected are rated to run at 90°, 70° is all you can take it up to.70 deg PVC - Can you still get that?
But that will be a no for VD reasons, not because the current carrying capacity of 6mm² SWA is too low. And the VD will be calculated with the resistance of the cable at 70° or 90°.My software with a correction for being buried is a 'no' for 6mm, 32A at 50m. Are there any other derating factors to consider?
Depends on how many webcam customers you can get.Possible over a year or so, but I have no idea what the running cost of a stable heated sex pond is.
Without stating the obvious, yes of course??But that will be a no for VD reasons,
If you can regulate the temperature in an attic void and underground?If you can get the temperature down then the resistance comes down -
If you listen carefully you might hear a collective groan as this subject has been discussed a lot recently!I have seen lots of conflicting information regarding how this should be tackled and I believe there are 3 options (probably more)
- 32a Type c from split RCD board
Option 1 - use the PME earth for the entire job as this isn't a swimming pool but a "built to product standard" hot tub so doesn't fall under section 702 - no exposed parts etc
Option 2 - PME earth covers supply cable to isolator but then is stopped there (Plastic gland and heat shrink armourings), Earth spike local to isolator and then use a TT earth from the isolator tail to the hot tub
Option 3 - PME earth covers supply to an external enclosure and 30mA RCD, TT spike from this point to isolator and tail but then you have 2 RCD's covering the circuit.
Anyone have any input on this?
If you listen carefully you might hear a collective groan as this subject has been discussed a lot recently!
Brief comments:
Option 1 is compliant but has issues. I used to do this but wouldn't now. See recent thread on tingly feet when getting out if you want a long read. [Also IET Guidance Note 7 (Special Locations) does have stuff about hot tubs outside coming under Section 702, as a recommendation)
Option 2 - What I'd do.
Option 3 - Also Fine but I'm missing the gain over option 2 - complete pot luck which RCD would go? If you could avoid upstream RCD this would clinch option 2 for me.
What do your cable calcs tell you? if of course you have bothered doing any.Can i get away with 6mm SWA on a 50m run for a 32a supply to a hot tub? Cable will be burried.
I believe its very close to being over the 5% max Permitted?
Whats your thoughts, should i go up to 10mm?
Thanks
My cable calcs told me that the only limiting factor would be the VD (5.19%) at 50m using installation method 72 - D2 but as its only 45m it would come under the 5% for a power circuit.What do your cable calcs tell you? if of course you have bothered doing any.
Reply to Hot tub volt drop in the UK Electrical Forum area at ElectriciansForums.net
We get it, advertisements are annoying!
Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.