Hot Tub shock

[aaronstuart]

Hot Tub shock
Been to look at a customers hot tub today to assure him it was protected by an RCD which it was.

This installation was done a couple of years ago, with a dedicated 20 amp supply, and ran in armoured.
Its a PME supply.
No earth to water which will be sorted asap.

He has informed me that on 2 occasions he has had a nasty shock while testing the temperature of the water, as he was standing on the ground. ( the tub is outside ).
I couldn't see anything wrong with the circuit wiring visually, but i was unable to test it.

When he phoned up the manufactures, they said it could be a bad earth connection resulting in feedback? Could this be caused by there being no earth on the incoming water pipe?

Any advice would be much appreciated on how to deal wtih this.

Obviously i told him not to use it.

Many thanks

 

[Graeme Harrold]

Hot Tub shock
Been to look at a customers hot tub today to assure him it was protected by an RCD which it was.

This installation was done a couple of years ago, with a dedicated 20 amp supply, and ran in armoured.
Its a PME supply.
No earth to water which will be sorted asap.

He has informed me that on 2 occasions he has had a nasty shock while testing the temperature of the water, as he was standing on the ground. ( the tub is outside ).
I couldn't see anything wrong with the circuit wiring visually, but i was unable to test it.

When he phoned up the manufactures, they said it could be a bad earth connection resulting in feedback? Could this be caused by there being no earth on the incoming water pipe?

Any advice would be much appreciated on how to deal wtih this.

Obviously i told him not to use it.

Many thanks

Remove the PME earth from the Tub, but leave the CU side intact for cable protection. Then spike the tub to make it a mini TT system thus removing the local earth potential..........By having the earth from the house extended you run the risk of creating an earth PD between the tub and the PME earth. Keep it local.

 

[The Truth]

have you tested the RCD? sounds to me like to need to check the earthing at the house end...especially if there is no water bond.. it could be an earth fault in the house back-feeding to the hot tub CPC and then to the tub pipework. It could also be the immesion heater in the tub breaking down and livening up the tub. make sure the RCD is protecting the armoured cable and not just the tub end.. as again an earth fault on the armor could carry to the tub and not be picked up by the RCD

 

[thepurple1]

Disconnect the heater and do an insulation resistance test on the heater

 

[Graeme Harrold]

Disconnect the heater and do an insulation resistance test on the heater

Not all hot tubs have heaters, and some rely on the pump warming the water due to the mechanical effort of pumping................just in case you go looking for a heater that might not be there........

 

[hotXbun]

Remove the PME earth from the Tub, but leave the CU side intact for cable protection. Then spike the tub to make it a mini TT system thus removing the local earth potential..........By having the earth from the house extended you run the risk of creating an earth PD between the tub and the PME earth. Keep it local.

Hi Graeme, I thought the same thing (and I still like the idea of a mini TT system) but could you please explain this bit ... By having the earth from the house extended you run the risk of creating an earth PD between the tub and the PME earth ............... the reasoning in my mind, if the whole thing protected by an rcd wouldn't any extraneous path, potential, trip the rcd? ...

Also, please point me in direction of understanding why there should/might occur an earth PD between the tub and PME earth .. many thanks

Stewart

 

[Graeme Harrold]

Hi Graeme, I thought the same thing (and I still like the idea of a mini TT system) but could you please explain this bit ... By having the earth from the house extended you run the risk of creating an earth PD between the tub and the PME earth ............... the reasoning in my mind, if the whole thing protected by an rcd wouldn't any extraneous path, potential, trip the rcd? ...

Also, please point me in direction of understanding why there should/might occur an earth PD between the tub and PME earth .. many thanks

Stewart

Connect the armour sheath to the house, but cut it back before getting to the Tub junction box. That way the armour protection is still intact due to the earth connection in the house, but is not affecting the tubs earthing, then make a mini TT system for the tub arrangement. RCD discrimination will need concideration if already in place.

 

[sparks1234]

Seems you have posted this twice.
I had this problem that could only be felt by people getting in and out of the pool as they had no shoes on, I fixed it by installing a stake next to the pool to give you no PD between the earth at the incomer and the mass of earth

 

[aaronstuart]

yeah sorry, posted it first in the wrong section.

 

[The Truth]

surely there are could be no PD as both pieces equipment are at earth potential under normal circumstances.. UNLESS there is an earth fault at the house end and the PD is caused simply by the impedance of the cable...which is even more unlikely if its only a 10 metre run.. RCD may not trip under this condition. recommend checking house wiring as this voltage cannot magically appear from nowhere. The sympton was 'a nasty shock' so i think there is something wrong here...Disconnect the earth conductor check out the PD between the main earth conductor and the MET while installaltion is 'live' and that will tell you if there is a lurking earth fault somewhere in the house.

 

[sparks1234]

surely there are could be no PD as both pieces equipment are at earth potential under normal circumstances.. UNLESS there is an earth fault at the house end and the PD is caused simply by the impedance of the cable...which is even more unlikely if its only a 10 metre run.. RCD may not trip under this condition. recommend checking house wiring as this voltage cannot magically appear from nowhere. The sympton was 'a nasty shock' so i think there is something wrong here...Disconnect the earth conductor check out the PD between the main earth conductor and the MET while installaltion is 'live' and that will tell you if there is a lurking earth fault somewhere in the house.

Mine was a long run so is fairly irrelevent to this problem

 

[aaronstuart]

forgive me for being thick but how do I do that?

 

[Graeme Harrold]

forgive me for being thick but how do I do that?

Disconnect Earth at MET and test voltage across the OPEN connection. Beware, there is a risk of shock if there is a problem, so treat as live until you know otherwise