powering a shed for horticultural lighting

[marteee]

Hi there

I'm after some advice, please (I'm by no means an electrician but I can follow advice/instruction). I want to power a small shed. It will be running horticultural lighting - maximum of 325w (two lamps) but mostly likely a single 200w lamp. There will also be a small fan (35w) and heater (120w), both of which will be thermostatically controlled. The fan will keep temps down when the lights are on, the heater will keep things warm at night (the shed's insulated) when the lights are off. Everything will run through a 3kw contactor relay.


I already have an outside socket, which is an RCD protected spur from the kitchen. Working backwards from the shed, i was thinking of putting a twin socket RCD in the shed, running 3 core, 2.5mm armoured cable from the socket back to a IP65 enclosure, and then having a short cable (with a plug attached) from the enclosure to the socket (as I'm assuming it's going to be a little fiddly to fit a plug to armoured cable). The total cable run from shed to socket will be around 13m, and with the exception of having to run the cable under one flagstone, all cabling will be above ground.


I'll only be running the system through the colder months - December through April, and as I'm living in rented accommodation I don't really want to have to go through the rigmarole (or expense) of running a new circuit from the main consumer unit.


Is this safe/sensible and will it work? So I guess my questions are:


- will this fit with legal requirements?
- do I need an RCD in the shed as well as the one in the kitchen?
- is 2.5mm cable heavy enough for my requirements or do I need something thicker?


advice appreciated, thanks.

 

[malcolmsanford]

Several questions as the shed is a horticultural site there are quite a few stringent regulations you have to abide by and these are outlined in a special location section of the regulations.

Unfortunately you may not be able to take a supply spurred from that socket at the house, apart from the fact you can not spur off a spur, if it is of a certain earth system, which is a TNC-S system, without taking or achieving certain conditions, you may have to TT your shed.

As for the 2.5mm SWA well as your load seems to be so low,less than a KW if both lamps are used, the size will be dependent on how far this is, but I would be suprised that unless it was in the next county, that the cable is unsuitable

Apart from the spur on a spur condition, if you have an RCD at the house then you have no need to also have an RCD at the shed, as unless you start redesigning you protection devices and your installation, then you will not achieve discrimination between them.

To be honest you have a few issue really, design of the installation, the regulations regarding special locations, and what can or can not be done. Honestly my advice would be to seek professional help. It's not a huge job perhaps a day or less for a sparks and they will design and install something that is safe and viable. I'm sure if you posted your general location a lad off here will be happy to advise you

 

[HandySparks]

- will this fit with legal requirements?
- do I need an RCD in the shed as well as the one in the kitchen?
- is 2.5mm cable heavy enough for my requirements or do I need something thicker?
advice appreciated, thanks.

If it's an ordinary wooden shed with no water, gas or other pipework to it, it should be OK.

Provided that the existing RCD has a 30mA trip rating, you don't need a second one.

As you're using a 13A fused plug to connect your new cabling, 2.5mm² cable will be just fine over the length you've stated.

If you're going to go down this route you need to make sure that the cover of the existing outside socket will close and seal round your cable (some don't). You also need to make sure that both cables are properly glanded into the junction box and into the socket at the shed end.

As Malcolm says, it's probably best to get an electrician in. You're best to get someone who is registered with one of the Part P Competent Person Schemes. He will be able to terminate the armoured cable correctly, advise on anything not aparent from your description, test the existing supply including the RCD, test the new installation (I don't mean just plug it in and see if it works) and register the work with the local building control.

By the way, what's the contactor relay for?

 

[NMc]

If you are not competent get an electrician as you may end up breaking H&S regulations

 

[JamesBrownLive]

Have a read of this and then decide if you're competant. If you'll still scratching your had after reading this, then I think you'll know the answer to that question :yes:

View attachment Garage-Shed Supplies.pdf

 

[High Tower]

Wonder what hes growing

 

[JamesBrownLive]

On my old mans side of the family, he had a rich relative that had a big place down on the south coast. The husband passed away and the wife decided to sell up. Whilst waiting for the place to sell, she let the gardener live there.
This all corresponded with one of our infrequent periods of snow, and unfortunately for the gardener the game was now up, as it was the only house around that did not have any snow on the roof.... The rozzers came a calling and found he had turned the attic into a wacky baccy farm :behead:

 

[marteee]

Thanks guys, that's really helpful. I need to check the existing load on the circuit (it is a ring final) and workout whether it can cope with the additional load (I think it should but I'll do the math) but it looks like option 2 on the shed supplies pdf will suit my purposes and I won't be breaking any regulations in the process. I can do the installation, I'll just then need to get it tested and certified.

And I know what you're referring to... yes, I am growing exotic, no, it's not illegal. I'm not sure that the heat signature from a 200w cfl will be cause for too much concern but it has occurred to me that i might get a knock on the door (at least I hope it's a knock and not a knockdown). They'll be a little disappointed if they do.

 

[Darkwood]

Can you smoke Cactus??? :hippy:

 

[telectrix]

i'll try anything once.

 

[marteee]

You don't smoke cactus. I believe the best way is to boil it in water and make tea. The Indigenous Americans have been doing it for centuries - it's called peyote, the active ingredient of which is mescaline. Try reading 'The Doors of Perception' by Aldous Huxley if you want to know what you can expect from the experience.

 

[Darkwood]

You don't smoke cactus. I believe the best way is to boil it in water and make tea. The Indigenous Americans have been doing it for centuries - it's called peyote, the active ingredient of which is mescaline. Try reading 'The Doors of Perception' by Aldous Huxley if you want to know what you can expect from the experience.

It was a rhetorical question with a hint of sarcasm but thankyou for the info'.

 

[marteee]

I had realised... and i replied with a completely straight face, obviously. I'm pleased to hear my indoor gardening is the cause of such mirth and speculation.