Swimming Pool Installation

[gselectrical]

Evening all.

We are currently involved in the installation of a small indoor swimming pool on a project we have been working on for over a year now.

The earthing system is TNC-S. The pool control equipment will be supplied by a 32A Type C RCBO with a rotary isolator next to the control panel.

My question is. Concidering the earthing system in use, are we required to install an earth rod and/or mat with a resistance <20ohms & connect to the MET, as the installation involves a swimming pool?

As I am currently having no co-peration from the M&E engineer or achitects, I thaught i would try to resolve the issue myself.

Cheers guys/gals.

GS

 

[Andy™]

the rod is only a note for wiring in zone 2, so unless you have wiring in zone 2, then the rod isnt required

 

[gselectrical]

Thanks Andy. When you say wiring, do you mean accessories?

The only wiring we have within 2.5m of the pool, is a 6mm SWA below floor screed supplying the pool.

Its more of a very big bath than a swimming pool!

GS

 

[gselectrical]

So I'm assuming the rod is not required? GS

 

[Sidewinder]

Is it PME?

 

[gselectrical]

Is it PME?

Yes it is.

GS

 

[Sidewinder]

OK, so it is TN-C-S & PME then yes?

 

[SLIPSHOD & SLAPDASH]

What about lighting ?

 

[gselectrical]

OK, so it is TN-C-S & PME then yes?

Yes mate. GS

 

[gselectrical]

What about lighting ?

Hacel ip led's specified on walls around pool. 3m from pool.

GS

 

[Sidewinder]

OK,

702.410.3.4.3 Zone 2

One or more of the following protective measures shall be employed:

(i) SELV (Section 414), the source for SELV being installed outside zones 0, 1 and 2. However, it is permitted to install the source for SELV in zone 2 if its supply circuit is protected by an RCD having the characteristics specified in Regulation 415.1.1

(ii) Automatic disconnection of supply (Section 411). using an RCD having the characteristics specitied in Reg lation 415.1.1

NOTE: Where a PME earthing facility is used as the means of earthing for the electrical installation of a swimming pool or other basin, it is recommended that an earth mat or earth electrode of suitably low resistance, e.g. 20 ohms or less. be installed and connected to the protective equipotential bonding.

Whilst this reg is specific to zone 2, in it's location, it is not specific in it's wording.

However, if, you have nothing in zones 1 & 2, then you could possibly omit the rod.

The reason for the rod is to control/limit step/touch voltages.

The pool water will be a conductor as it is an electrolyte due to the chemicals.

Do you have any earthed metalwork within zones 1 & 2?

If you do then rod it if you don't then it's your shout.

Who is signing for the design?

Is it on it's own 11kV transformer or on a public transformer with multiple consumers?

Is the incomer overhead or underground?

What are the chances of the incomer being damaged, does it cross farmland for example?

What is the state of the origin kit, & db's like, good?

What is the submain like?

Can it get damaged?

What are the earthing arrangements for the site distribution?

Is the SWA armour reliably earthed at the source end?

What are the chances of the outer sheath being damaged during the install & life of the installation?

Have you included a CPU core internal to the SWA?

 

[gselectrical]

OK,

702.410.3.4.3 Zone 2

One or more of the following protective measures shall be employed:

(i) SELV (Section 414), the source for SELV being installed outside zones 0, 1 and 2. However, it is permitted to install the source for SELV in zone 2 if its supply circuit is protected by an RCD having the characteristics specified in Regulation 415.1.1

(ii) Automatic disconnection of supply (Section 411). using an RCD having the characteristics specitied in Reg lation 415.1.1

NOTE: Where a PME earthing facility is used as the means of earthing for the electrical installation of a swimming pool or other basin, it is recommended that an earth mat or earth electrode of suitably low resistance, e.g. 20 ohms or less. be installed and connected to the protective equipotential bonding.

Whilst this reg is specific to zone 2, in it's location, it is not specific in it's wording.

However, if, you have nothing in zones 1 & 2, then you could possibly omit the rod.

The reason for the rod is to control/limit step/touch voltages.

The pool water will be a conductor as it is an electrolyte due to the chemicals.

Do you have any earthed metalwork within zones 1 & 2? No

If you do then rod it if you don't then it's your shout.

Who is signing for the design? M&E engineer, we are singing for the construction & T&I.

Is it on it's own 11kV transformer or on a public transformer with multiple consumers? It is on its own transformer.

Is the incomer overhead or underground? Underground

What are the chances of the incomer being damaged, does it cross farmland for example? Very low

What is the state of the origin kit, & db's like, good? New

What is the submain like? New

Can it get damaged? No

What are the earthing arrangements for the site distributio n? TNC-S

Is the SWA armour reliably earthed at the source end? Yes

What are the chances of the outer sheath being damaged during the install & life of the installation? Low

Have you included a CPU core internal to the SWA? Yes

Thanks Sidey. I'm red. GS

 

[Sidewinder]

OK,

It's going to get messy if I try to re-quote your message, trust me!

Who is the M&E consultant? (PM if you want, may be better?)

The DNO head is fed directly from a dedicated DNO 11kV transformer via an underground Waveform?

It is the only consumer off the Tx?

You are distributing power around the site after the DNO head via TN-C-S? Please confirm as this requires special permission?

You have the SWA reliably earthed at the source end & a cpc within the cable?

Sizes please, CSA & Length, also the OCPD at the origin of the sub main.

Have you checked the cable calcs?

Also size of incoming supply & other supply details etc. please.

 

[gselectrical]

OK,

It's going to get messy if I try to re-quote your message, trust me!

Who is the M&E consultant? (PM if you want, may be better?)

The DNO head is fed directly from a dedicated DNO 11kV transformer via an underground Waveform?

It is the only consumer off the Tx?

You are distributing power around the site after the DNO head via TN-C-S? Please confirm as this requires special permission?

You have the SWA reliably earthed at the source end & a cpc within the cable?

Sizes please, CSA & Length, also the OCPD at the origin of the sub main.

Have you checked the cable calcs?

Also size of incoming supply & other supply details etc. please.

-I will PM you about the M&E consulatant.

-Regarding power distribution around the site, its a small site & builders are currently using 110v trannies to supply power & lighting, Trannies plugged intol clinets existing sockets (30mA RCD protected)

-6mm SWA cable feeding pool, glanded & earthed at isolator.

-Pool requires a 32A supply, 6mm 3C SWA cable as recommended by manufacturers. 15m length. 32A Type C RCBO.

-Small site, so 100A Single phase supply. (Have had various discussions with M&E engineer to upgrade to 3ph, but he's not having it.)

Cheers

GS

 

[Sidewinder]

GS,

You may have misunderstood.

I'm not interested in the construction phase TBH!

Where is the incoming DNO cable fed from, is it a dedicated 11kV/400V transformer, or is the supply from a "pole in the street"?

What is the total load excluding diversity and what are these loads?

i.e. what is the likely N volt rise between the transformer earth connection & the consumers origin?

You will need the size of the DNO cable to work this out.

 

[gselectrical]

GS,

You may have misunderstood.

I'm not interested in the construction phase TBH!

Where is the incoming DNO cable fed from, is it a dedicated 11kV/400V transformer, or is the supply from a "pole in the street"?

What is the total load excluding diversity and what are these loads?

i.e. what is the likely N volt rise between the transformer earth connection & the consumers origin?

You will need the size of the DNO cable to work this out.

Sorry. (Very tired)

DNO cable is fed from a transformer on a pole (25m away), in a field next to the site. New transformer, only house supplied from this particular transformer. 16mm single concentric cable feeds the cut out of the property. 100A main fuse as requested by M&E engineer.

Total load, basically a very large house. Last time I spoke to the engineer his maximum demand calculation was 285A excluding diversity. 95A including diversity. Electric underfloor heating (approx 40A), Pool (32A) Oven, outbuildings etc etc.

My area engineer took a look at the plans during my last assesment and he didn't seem to have a problem with the maximum demand, even though I was unsure!

Cheers

GS

 

[Sidewinder]

No need to apologise!

OK, I'd not be concerned about the MD either TBH.

So you are likely to see 25m worth of volt rise at your end wrt the transformer earth rod, & true earth at MD in the earth provided by the DNO, which you are connected to.

Is the DNO cable 16mm, sounds small, it's not waveform then?

Is it split con?

If we know the real size of the line conductor then the CNE size can be derived from that.

Then you can calc the voltage rise wrt true earth and risk assess that against the possible shock risk and the risk of the CNE becoming compromised.

 

[Chr!s]

Two thing to consider with TNC-S PME

1, Are there any Exposed/Extaneous conductive parts within any of the Zones? If so ther may be a perception of an electric shock, this depends upon the voltage dropped accros the Neutral. Cure = TT

2, Broken Pen,Potential between Exposed/Extraneous Conductive Parts and True earth maybe as high as Uo. Cure = TT, A low impedance Electode connected to MET.

So what are the risks In your installation?

 

[gselectrical]

My mistake.

Its 25mm single concentric.

No there are no exposed / extraneous parts within zone 2.

Cheers.

GS

 

[Sidewinder]

OK, GS,

I would be tempted to "PME" the site!

I would drop a rod at the origin & connect to the BEMT with a 16mm.

At the end of the sub main to the pool area I would drop another rod & again connect to this BEMT with a 16mm.

I would in this case connect the SWA at BOTH ends to the relevant BEMT's & the internal cpc in the SWA the same.

Don't stress too much about getting the rods below 20 Ohms, but, I would get the Ra to a level such that there would be no discernible touch voltage between any, "parts" & true earth.

Don't stress about the csa of the sub main vs the csa of the armour vs the PME bonding requirements, because IF the install is the ONLY supply from the 11kV/400V Pole mount Tx, then it is NOT PME!

It "may" be TN-C-S, but I am in heated debates with other significant parties wrt the situation of it being PME, how can it be?

Also there can be NO diverted N currents from outside the install as there is nothing supplied from the Tx that is outside the install to get back to the Tx.