protect pool from light transformer electrical failure

[notrub]

I have 2 LED Emaux pool lights that are, I think, 12v.  The transformer is marked 20VA.  My friend has commented on my junction box joining the low power transformer to my pool lights.  It was not correctly installed but it all works fine.  The transformer itself is in a weatherproof box under the eves.  He said that even though I have low volts (harmless) from the transformer to my lights in the pool, a catastrophic failure of the transformer could send 240 volts down the wire.  This would certainly kill the lights but might conceivably harm someone nearby at the time.  What I plan to do is to put an in line fuse(s) on the light feed side of the transformer so any failure would just blow the fuse.  Here is the question.  What amperage fuse should I use?  Will a normal glass fuse work OK?  Would it be better to use the blade type commonly found in cars?  I would put the fuses on all wires going from the transformer to the light.   Thanks for any comments.

[carlyai]

I have 2 LED Emaux pool lights that are, I think, 12v.  The transformer is marked 20VA.  My friend has commented on my junction box joining the low power transformer to my pool lights.  It was not correctly installed but it all works fine.  The transformer itself is in a weatherproof box under the eves.  He said that even though I have low volts (harmless) from the transformer to my lights in the pool, a catastrophic failure of the transformer could send 240 volts down the wire.  This would certainly kill the lights but might conceivably harm someone nearby at the time.  What I plan to do is to put an in line fuse(s) on the light feed side of the transformer so any failure would just blow the fuse.  Here is the question.  What amperage fuse should I use?  Will a normal glass fuse work OK?  Would it be better to use the blade type commonly found in cars?  I would put the fuses on all wires going from the transformer to the light.   Thanks for any comments.

Sorry, I think this is the wrong approach.

The pool transformers the pool companies flog in Thailand are not correct. They have no individual fuses and no protection against transformer breakdown.

With the help of Crossy from the electrical forum I worked out that I needed to buy a specialised pool lights transformer (also maintaining the pool as a Farrada cage with no earth attached to the pool rebar).

You need to buy a specialised pool lights transformer, not from Thailand, but search Australia for one. I can't remember the name at the moment but the transformer comes in a complete water proof enclosure with all the protection needed.

I'll send a pic of mine tomorrow if you need it.

Throw that other crap away and buy the real deal.

I remember asking a sponser why they don't stock them and the answer was that they're too expensive and Farangs wouldn't buy them.

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[Crossy]

@carlyai is correct, the transformers sold here are not to Western SELV (Separated Extra Low Voltage) standards. Of course they work just fine until they don't.

 

As an absolute minimum you need to install a 10mA RCBO/RCD on the 220V side of the unit, that will ensure that should the transformer break down nobody will die.

 

Installing fuses will achieve nothing from a safety point of view.

[Naam]

5 hours ago, notrub said:

He said that even though I have low volts (harmless) from the transformer to my lights in the pool,

your friend possesses a wealth of no idea what is harmless and what not.

[carlyai]

Here's some pics of my setup. When you take the cover off, you can see the unit is well made.
With those transformers I've seen available for pool use, you wouldn't know if they have been made in someone's back yard or not.
In electronic power supplies I've only known 1 transformer to fail, so they don't fail that much, but, they do fail.

First pic is the pool transformer unit. Other pic is of the pool light switches which I initially had, but then added a remote controlled switch so the lights could be turned on from the house or internet.

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[Crossy]

If your transformer has these symbols then it's safe for powering your pool lights.

 

 

The symbols mean, left to right:-

• Double insulated
• Separated Extra Low Voltage
• Thermal fuse protected

This is as safe as you can get, and I would still include a 10mA RCBO on the input.

 

[notrub]

Thank you for your comments.  I have an RCBO and surge protector on my panel already.  My no name transformers are 20 VA and there is one per light (2).  My pool is cement blocks, tiled and not earthed.  My friend said I should earth the water in the pool by putting a copper wire into the water connected to a ground rod.  I don't have a pool ladder or any metal in the water and fixed to the tiles around the pool.  The wires coming from the transformer are connected to the pool lights in a junction box which is full of water (it is lower than the pool water level). 

 

I have looked and cannot find an Aqua Quip transformer nor any that are SELV certified on Ebay, Ebay Aus, Amazon or Lazada.  The transformers I have are in an exterior box in a sheltered location and the pool lights would not be switched on during an electrical storm anyway.

 

Further comments welcome, thanks.

[Crossy]

49 minutes ago, notrub said:

My friend said I should earth the water in the pool by putting a copper wire into the water connected to a ground rod.

 

At this point you should turn on "ignore".

 

Your pool water is actually already a pretty good ground, concrete actually conducts electricity (Google "Ufer ground").

 

If you already have an RCD in front of the transformer you are pretty safe although I would add a 10mA unit to the transformer itself to be doubly sure.

 

It's not an electrical storm you need to worry about, it's faulty design or manufacture of the transformer allowing 220V through to the lighting circuit.

[carlyai]

Correct pool transformer is/was hard to find, but if I remembèr correctly I bought mine from The Pool Man, a mob in Queensland Australia. Google them. If I'm wrong let me know and I'll find the info for you. Bloody expensive and courier freight on top.

I did a lot of research about the transformer and pool earthing, with a lot of advice and discussion with Crossy.

In some circumstances earths can have a dangerous voltage, so if you don't have an earth wire from the mains connected to your pool, your pool can never be live from the earth wire. And as mentioned, the cement and reo. of the pool construction, in the good soil, is a pretty good earth.

I know it's a worry, but the only other way you could get a dangerous voltage in the pool, is thru the transformer, as that's the only other thing that has a connection to the mains supply.

For me, I would only use the correct pool transformer and no earth wire.

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[Sealbash]

It is my understanding that the odds of a transformer failure allowing the higher voltage through to the low voltage side are about equivalent as being struck by lightning from a clear sky. Not impossible, but very highly unlikely.


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[carlyai]

It is my understanding that the odds of a transformer failure allowing the higher voltage through to the low voltage side are about equivalent as being struck by lightning from a clear sky. Not impossible, but very highly unlikely.


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I would agree, but have you looked at the pool transformers they are selling here?

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[carlyai]

I just checked and Mr Poolman from Aus. has the transformers, but TV won't let me post the pic.

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[Sealbash]

I would agree, but have you looked at the pool transformers they are selling here?

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Yes, I have. Which further reinforces the idea that they would most likely fail to an open circuit state, rather than passing through the higher voltage.


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[daveAustin]

On 5/12/2019 at 2:41 PM, carlyai said:

I know it's a worry, but the only other way you could get a dangerous voltage in the pool, is thru the transformer, as that's the only other thing that has a connection to the mains supply.

Though unlikely, you could also have PE propagating from a faulty pump that is not earthed correctly and/or protected by an RCD. 

As above, if unsure, bung an RCD/RCBO in front of your transformer. Fuses blow on overload and are relatively slow, while an RCD monitors current, is sensitive and fast.

Whoever said to put an earthing cable in a pool needs their head read... you wouldn't even do this to a lined pool. What if there's a fault to earth in the vicinity of that earthing rod?