Swimming Pool Earthing

[markythesparky]

Happy New Year guys!



I have a situation at a pool installation.



A pool is being built in a separate building from a house. It has (I have been told but not checked) a new three phase supply from the street going down the garden to the new pool building. The electrician has terminated into a three phase distribution board. There is no meter in the new building so it must be either in the house which is nearer the street or in a cabinet nearer the street. The building contains the pool, a kitchen, gym and bathroom. There is no earth spike around this building and the earth is carried on the SWA feeding the building from presumably the meter area although I don’t know at this stage where that is. Until recently there was no bonding to the incoming water or gas services to this building and no bonding to the structural steel RSJ’s which are exposed in the pool room.



1. The electrician is now going to bond the water, gas, RSJ’s but has also broken up the concrete floor to find the structural Rebar and will bond that too. This is not exposed unlike the water, gas and RSJ’s and is not, in my view an earth mat as described for TN-C-S systems. Does this need doing?

2. If the incoming system is a TN-C-S wouldn’t it need to be changed to a TT? If not where would the bonding need to run to?

3. If the system is a TN-S wouldn’t the bonding have to be taken to the MET which would be near the meter? If not where would the bonding need to run to?

4. If the system was changed to a TT, could the bonding be done at the new MET which would be at the Distribution Board?

5. If the system is TN-C-S then as far as I know, an electrode or mat can be installed and the Extraneous and exposed parts bonded to this but where would this electrode be installed? I'm thinking in the ground outside the building? If this is right, then it would reduce a PD within the pool room but would creat another PME.

 

[markythesparky]

I should add that I am an interested party as we are doing the pool plant.

 

[Wilko]

For your pool building I reckon (4) TT is logical as the bonding can be connected to a local earthing system and the possibility of tingles reduced. FWIW, I think GN8 section 5 has some good info on multi building design challenges.

 

[markythesparky]

For your pool building I reckon (4) TT is logical as the bonding can be connected to a local earthing system and the possibility of tingles reduced. FWIW, I think GN8 section 5 has some good info on multi building design challenges.

So I'm correct that anything other than TT and the bonding needs to go to the MET back at the meter?

 

[Wilko]

... anything other than TT and the bonding needs to go to the MET back at the meter?

Yep

 

[westward10]

1. The grid will require bonding.
2. TN-C-S is permitted. Doubtful the SWA supply is adequate to support bonding, would need to be 50.0, 4 core to support the minimum size of 10.0.
3. Same would apply for TN-S.

 

[markythesparky]

1. The grid will require bonding.
2. TN-C-S is permitted. Doubtful the SWA supply is adequate to support bonding, would need to be 50.0, 4 core to support the minimum size of 10.0.
3. Same would apply for TN-S.

1. Which grid? if you mean the rebar, why? its not accessible. and presumably only if the system is TN-C-S?
2. sorry I think you misunderstand. if the system is TN-C-S or TN-S the sparks will have to run new cables up to the MET for the bonding. not use the SWA! or are you thinking of the sheath? In any event this is not what the concern is.

 

[westward10]

If a solid floor incorporates reinforcing bars/rods/grids they should be bonded, accessible or not.
You are not running the bonds back to the source of supply (MET) then the armour of the cable must be adequate to support the bonding.
What is the concern if I am misreading you.

 

[markythesparky]

So the rebar should be bonded but only if a TNCS?

Ive not heard of running bonding via the SWA sheath before. In this building there is water gas, RSJ's and now rebar. So can he take them all back to the dis board in the new building and then from there use the Sheath as the bonds?

if so how did you work that size out? I'm learning tonight!! ;-)

 

[westward10]

It needs bonding regardless of the system.
Steel has a higher resistance than copper and hence you need to find the csa of the armour and divide it by a factor of 8 to find its copper "equivalent" size. Or times the size of the required bonding by 8 to find the what csa of armour is required. A copy of GN8 has all the info. To support 10.0 bonding it would have to be at least 50.0 4 core. The alternative is to put in place a TT earthing system and isolate the armour of the cable.

 

[markythesparky]

Westward, thank you so much for your replies. I must admit I hadn't known about using the armour as a bonding conductor.

 

[benji]

Only done 1 pool 25mtr at leisure centre and electrical consultants showed 2 earth bonds to re-bar under the pool taken to earth bar in pool plantroom also all sockets that were sunk int floor along sides of pool for handrails to fit into had to be bonded back to earth bar

 

[Bobster]

Read up on ufer earthing, might shed some light on the matter.

 

[Shaz]

Happy New Year guys!



I have a situation at a pool installation.



A pool is being built in a separate building from a house. It has (I have been told but not checked) a new three phase supply from the street going down the garden to the new pool building. The electrician has terminated into a three phase distribution board. There is no meter in the new building so it must be either in the house which is nearer the street or in a cabinet nearer the street. The building contains the pool, a kitchen, gym and bathroom. There is no earth spike around this building and the earth is carried on the SWA feeding the building from presumably the meter area although I don’t know at this stage where that is. Until recently there was no bonding to the incoming water or gas services to this building and no bonding to the structural steel RSJ’s which are exposed in the pool room.



1. The electrician is now going to bond the water, gas, RSJ’s but has also broken up the concrete floor to find the structural Rebar and will bond that too. This is not exposed unlike the water, gas and RSJ’s and is not, in my view an earth mat as described for TN-C-S systems. Does this need doing?

2. If the incoming system is a TN-C-S wouldn’t it need to be changed to a TT? If not where would the bonding need to run to?

3. If the system is a TN-S wouldn’t the bonding have to be taken to the MET which would be near the meter? If not where would the bonding need to run to?

4. If the system was changed to a TT, could the bonding be done at the new MET which would be at the Distribution Board?

5. If the system is TN-C-S then as far as I know, an electrode or mat can be installed and the Extraneous and exposed parts bonded to this but where would this electrode be installed? I'm thinking in the ground outside the building? If this is right, then it would reduce a PD within the pool room but would creat another PME.