Extra low voltage pump ?

[aldm]

Hi,

I've installed a 24v ac pond pump in the garden. I didn't want to install a 240v ac pump as the supply work would be notifiable, but I think I am confusing myself on what is and isn't required.

I have had to extend the original cable to the pump, so have fitted a plastic JB and used a length of 0.75mm 2 core cable to run the extra distance in to the garage. The JB is only IP44 and the cover removable without the need for tools but as the system is selv, is this is ok.

View media item 81321
The supply is from a isolating transformer inside the garage, I was a bit surprised to see the output rated at 1A, could this cause harm even at low voltage?

View media item 81322
In the first pic I have protected the cable with metal covering and wondered if this should be earthed, but then reading up on selv, came across this "2. - there must be no connection whatever between the live parts of the SELV system and earth or the protective system of low voltage circuits. The danger here is that the earthed metalwork of another system may rise to a high potential under fault conditions and be imported into the SELV system."

so is what I've done ok?

(sorry the pics are sideways)[/img]

 

[Taylortwocities]

so is what I've done ok?

From a connection point of view it is OK, but why didn't you just use one of these? http://www.tlc-direct.co.uk/Products/BRH65Z.html

Yuk yuk using garden hose. The box may have been IP44 but not with the hose in one side and the flex in the other.
You should have used proper conduit and fixings, and/or stuffing glands.
Please drill a hole in the bottom of the box so that the water, that WILL get in there, can drain out before it floods your connections.

And, no you do not need to earth that metal capping.
And, it doesnt matter that the power supply is capable of delivering 1amp, it could be rated at 1,000,000,000amps. The pump will only pull a miniscule amount of the PSU's capability.
And, you could have used a 230v pump. This work is not notifiable.

 

[aldm]

thanks for the reply. I used the jb as I already had it. The pump manufacturer sell there own extension cables for £10, which is basically a length of 0.5mm 2core with a plug on one end and a socket the other, this is then connected between the trany and pump, no instruction to protect it or keep it dry, the connection at the pump end would in theory be in free air.

The hose is just to give the pump wire a bit of extra protection, it will be covered in gravel around the pond edge. I didn't think I needed any extra protection with the circuit being selv, but wasn't sure of what I did/didn't need to do hence the post. I can pick up a couple of 20mm glands, but the pump cable is only 0.5mm 2 core, so I am not sure the gland would compress small enough. If the box did get full of water, is there any electrical risk or will it just pop the trany. I understand that the device draws as much current as it needs, but a fault current would be a lot higher.

Also if I was to use a 240v pump, it would have needed a socket outlet near to the pond as the pump cable would not have reached the garage. It was my understanding that any electrical work outside is notifiable, this is why I chose the lower voltage model.

 

[ericmark]

And, you could have used a 230v pump. This work is not notifiable.

That would depend where the poster lives in the UK.
It is notifiable in Wales.
I note Part P covers extra low voltage as well as low voltage so except with telephone and like using ELV would not change any requirement to notify.

Not that I would bother but as far as law goes using extra low voltage does not make it exempt as far as I can see.

As to the job personally I would have used heaver cable and provided some drain hole. But nothing really wrong with the job.

As to current it can only flow when there is some voltage to push it so there is no danger.

 

[Taylortwocities]

Fair enough, but do put a drain hole in the bottom.

re

It was my understanding that any electrical work outside is notifiable, this is why I chose the lower voltage model.

The notification rules were IMO stupidly revised (watered down) last year. So generally its only new circuits, consumer units and work in bathrooms that require notification.

 

[ericmark]

Fair enough, but do put a drain hole in the bottom.

re

It was my understanding that any electrical work outside is notifiable, this is why I chose the lower voltage model.

The notification rules were IMO stupidly revised (watered down) last year. So generally its only new circuits, consumer units and work in bathrooms that require notification.

Only in England

 

[aldm]

I am in Wales and that is interesting about selv wiring being notifiable, as these pumps are clearly aimed at the DIY installer.

View media item 81358
Why would you have use bigger cable?, would it be for mechanical protection? The wiring on the pump supplied is only 0.5mm, I have extended it using 0.75mm.

Also the extension cable you can buy has the same connections as the pump/transformer

View media item 81359
Even the IP44 enclosure I have used gives more protection that this!

I just want to know that if the kids go "exploring" or the cable were to get damaged, there is no risk of electric shock, isn't this the idea of selv. Can you put my mind at rest.

thanks.

 

[JohnW2]

I am in Wales and that is interesting about selv wiring being notifiable, as these pumps are clearly aimed at the DIY installer.

Yes, if you are in Wales then even SELV 'fixed' wiring outdoors is, strictly speaking, notifiable, no matter you daft you/we might regard that. It is for you to decide what attitude to that to take.

Why would you have use bigger cable?, would it be for mechanical protection? The wiring on the pump supplied is only 0.5mm, I have extended it using 0.75mm.

The only real reason for using bigger cable would be if voltage drop along the cable was a problem - which I very much doubt it would be in your case. In terms of current-carrying capacity, 0.5mm² is clearly more than adequate.

I just want to know that if the kids go "exploring" or the cable were to get damaged, there is no risk of electric shock, isn't this the idea of selv. Can you put my mind at rest.

Yes. For all practical purposes, 24V is not itself going to harm anyone. I suppose that, theoretically, it could make them 'jump' and fall (into the pond or damaging their head) - but the same could be said of an unexpected clap of thunder!

Kind Regards, John

 

[bernardgreen]

I just want to know that if the kids go "exploring" or the cable were to get damaged, there is no risk of electric shock, isn't this the idea of selv. Can you put my mind at rest.

Yes. For all practical purposes, 24V is not itself going to harm anyone. I suppose that, theoretically, it could make them 'jump' and fall (into the pond or damaging their head) -

SELV relies on the insulation / isolation between the 230 volt and ELV circuits to ensure there is no hazardous potential on the ELV circuits. A fault in the transformer could make the ELV circuits become live and yet still supply to ELV supply to the items. Everything seems OK as the items work but touching any of the "SELV" wiring could result in a 230 volt shock.

If one side of the ELV is earthed then when the isolation fails the RCD will operate.

That said SELV supply transformers from reputable sources are unlikely to suffer a breakdown of insulation due to the way they are designed and built.

 

[JohnW2]

SELV relies on the insulation / isolation between the 230 volt and ELV circuits to ensure there is no hazardous potential on the ELV circuits. A fault in the transformer could make the ELV circuits become live and yet still supply to ELV supply to the items. Everything seems OK as the items work but touching any of the "SELV" wiring could result in a 230 volt shock.

That is, of course, possible, but the risk to which you refer applies to vast numbers of everyday ELV sources (from phone/camera/whatever chargers upwards), and if one is going to 'lose sleep' over that, I think one would have to live in a 'padded cell'! As you go on to say:

That said SELV supply transformers from reputable sources are unlikely to suffer a breakdown of insulation due to the way they are designed and built.

Quite. There are innumerable examples of things we encounter and use every day which, if they fail to function as they were 'designed and built' could represent a hazard, but there is a limit to how 'worried/cautious' one sensibly can be ... as always, going up a ladder or having a bath (let alone travelling in cars or crossing roads!) are, statistically speaking, much greater risks to life and limb!

Kind Regards, John