SWA cable calculation.

[5544]

sorry if I'm dwelling on this but have to supply 230v to a hot tub on PME.

load 32amps.
separate RCD back at the house, 54 mtrs away.
exporting PME through third core and armoured sheath.
no extraneous conductive parts at the tub.
MCB 40amp type C ZS - 0.57ohms
Cable is going to be clipped direct all the way down.

after calculating volt drop and ZS the only one i can fit is 10mm three core. 6mm will do the V drop but not the Ze.

has anyone got one of these quick apps they can check this.

only asking as this is the first hot tub i have done at this distance.

thanks

 

[Plonker 3]

Why use a app. Use pencil and paper wrote down all your calcs and double check it then check it again.

 

[telectrix]

do you really need a C type MCB?

 

[DNO]

"separate RCD back at the house"---why are you concerned with the Ze?

 

[Plonker 3]

"separate RCD back at the house"---why are you concerned with the Ze?

The RCD has no influence on the Ze

 

[telectrix]

think OP meant Zs. a better value might be obtained by using a 32A MCB. and why the RCD at supply end?

 

[Richard Burns]

6mm would not comply with the volt drop requirements for a 32A load at 54m circuit length (12.6V).
10mm would at 7.6V

The only way 10mm 3 core, using the armour as an earth as well, would comply (theoretically) with Zs for a C type 40A breaker would be if the Ze was less than 0.23.

 

[Engineer54]

sorry if I'm dwelling on this but have to supply 230v to a hot tub on PME.

load 32amps.
separate RCD back at the house, 54 mtrs away.
exporting PME through third core and armoured sheath.
no extraneous conductive parts at the tub.
MCB 40amp type C ZS - 0.57ohms
Cable is going to be clipped direct all the way down.

after calculating volt drop and ZS the only one i can fit is 10mm three core. 6mm will do the V drop but not the Ze.

has anyone got one of these quick apps they can check this.

only asking as this is the first hot tub i have done at this distance.

thanks

If you are supplying a Hot Tub with a PME supply i suggest you read your BGB/OSG for additional requirements....

 

[telectrix]

and move the hot tub closer to the house. :6:

 

[rytech]

If you are supplying a Hot Tub with a PME supply i suggest you read your BGB/OSG for additional requirements....

OSG & BGB give no mention of hot tub installs on PME, only special locations swimming pools and basins has a note regards PME advising the use of an earth rod or grid with a resistance of 20 ohms or less to be connected to the protective bonding. My interpretation of this would be as the OP said there are no extraneous conductive parts it is not required, unless the water within the hot tub is classed as the extraneous conductive part due to connection with submersed heaters etc...

also with an upfront RCD in the form of RCBO or seperate 1 way board the RCD would cover the disconnection times negating the need to have a sufficiently low enough ZS.

regards

 

[Engineer54]

Then you're interpretation as well as the OP's would be WRONG!! Hot tubs,Jacuzzi's, Swimming Pools supplied from a PME/TNC-S supply will need a supplementary rod being provided. Now tell us why do you think that would be the case??

 

[rytech]

Ok but your statement saying check the OSG/BGB for additional requirements is WRONG as the only mention of a PME supply to swimming pools and basins is if there is extraneous conductive parts which the OP said there is none, I do however agree it's sensible to install such measures or convert to TT to reduce risks associated with PME supplying a swimming pool such as a loss of neutral on the suppliers side and the potential between bonded parts and true earth.

 

[Engineer54]

Class/treat Jacuzzi, Hot Tub's, Basins as you would swimming pools, where a PME/TNC-S supply is provided, that i would have thought, would be common sense.

The only time i would consider to relax the supplementary earth rod on an external hot tub etc,would be where the hot tub/jacuzzi, is located on a wooden or other insulating floor material for at least 2 or 3 metres all round the tub....

 

[ian.settle1]

How big's the bloody garden if the hot tub is 54 metres away?