Discuss Supply to Greenhouse in the Electrical Forum area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

To be honest I’d go for a separate feed from the CU, be it RCBO or a RCD in a housing.
Just going from experience with the father in laws GH it did trip on a regular basis. Fed from the bedroom FRC I can see you being late for work when the ring RCD trips and you’re happily in the land of nod with no alarm clock.

Hi Tony - RCBO - hadn't thought of that and like the idea. Despite it being a nearly impossible cabling job I am coming around to the idea of putting it on it's own circuit.

Although I do have a nice old wind up alarm clock with bells on the top which would wake up Rip Van Winkle !
 
Rick,
I cross posted with you, see post #20.

I would definitely consider putting it on it's own supply, with a small extra CU in the house and henly off the tails, use a small shower type CU and consider a 20A or 32A MCB and RCD or RCBO, with a seperate 6A and 16A MCB in another small IP rated CU in the GH.
 
hi again spark68

Why do you suggest a separate CU and not RCBO off main CU (there is room for it)

TBH I don't really understand fully the TT route as it is not something I have much experience of - in particular why not stick a spike in at the GH end and connect it to both CPC from house and armour of SWA?
 
hi again spark68

TBH I don't really understand fully the TT route as it is not something I have much experience of - in particular why not stick a spike in at the GH end and connect it to both CPC from house and armour of SWA?

Rick have a look at this, this is for a caravan pitch, but the idea is the same only you would have your RCD/RCBO at the supply end
 

Attachments

  • Caravan pitch 03.pdf
    1.2 MB · Views: 32
Many thanks to all who have commented so far… I said I would post again as I don’t like abandoned threads. Of course any comments / discussion are more than welcome…

In terms of supply

The most elegant solution: split the incomer to a Henley block, main switch then to SWA. Take SWA to greenhouse and terminate in IP rated CU with RCD, 16A MCB for Socket and 6A MCB for light (or better still two RCBOs)

The next best solution: 16A RCBO in existing CU, from here inside house in T&E to exit point, through wall into adaptable box and convert to SWA. Terminate in socket and provide further power to light by means of switched FCU fused down to 5A.

The least best but simplest to install solution: Spur off power circuit with FCU fused to 13A. Through wall and into SWA as per second solution.

I don’t see the merit in having a separate IP rated CU in the GH except in case of solution 1 as any RCD tripping could trip either RCD as there would be no discrimination (the house CU end having to be 30mA for the T&E run)

However the earthing and bonding arrangements were the original point of this thread, separate post below.

- - - Updated - - -

Earthing arrangements

(note that house earthing arrangements are TN-S – for TN-C-S this may well be different and TT the only way to go)

1. Put earth rod in at GH end. GH electrics (irrespective of supply type as above post) earthed via rod solely i.e. not connected to house earth. Armour of SWA connected to house earth at house end only. GH bonded to earth rod.

2. Export the house earth. For the purposes of earthing, this would be the third core of the SWA (not the armour). The armour would be connected to earth at the house end only. For the purposes of bonding, run G/Y 10mm cable back to the MET at the house supply.

The more I think about it the better I like idea 1. The floor of the GH will be earthy, and I think it’s better that the frame is closer to that earth than the MET earth, which could be at a different potential.

So why should one not export the house earth AND put in an earth rod and connect them together, as suggested by strima and somersetsparks? If so, should we connect the rod to the house exported CPC and/or the armour of the SWA or both?

If we connect the GH frame to the earth rod, and also to the house earth, surely the frame becomes an extraneous-conductive-part (as it would be connected to the house earth and also be well below 22KOhm to MET) and would therefore also require bonding back to the MET. So let’s suggest we do that – but then we have parallel paths to earth which could potentially induce eddy currents in the CPC…?

So I think the best solution is to TT the greenhouse and leave it separate from the house earth. But I am interested to hear opinions on this – if we TT the greenhouse, is it better to separate this from the house earth or not?

A further thought

1. The base of the GH is steel, the frame aluminium, and the bonding copper. Bonding between the three might degrade the quality of the connection over time?

Well, if you’ve made it this far thanks and I look forward to any further discussion.
 
Hi Rick,

As I said in an earlier Post,

If I was TT ing it, I would segregate the earthing system, the reasons for this are:

No 10mm copper equivalent back to the house Met required, if bonding is required.

If bonding is required, then this can be carried out locally at the GH end, and is much simplified.

You could use 2 core armoured.

I don't really see much point in combining the two systems, as your rod at the GH would need a very low Ra to be of any use, the TNS Ze max is 0.8 ohms, so an Ra much above 1 ohm is going to have very little effect overall, and you are still going to have all the conditions required of continuing the house TNS system anyway.

I would keep it as one system or the other at the GH, both have advantages and disadvantages.
By combining it you are going to make it more complicated than it need be.
 

Reply to Supply to Greenhouse in the Electrical Forum area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

Electrical Forum

Welcome to the Electrical Forum at ElectriciansForums.net. The friendliest electrical forum online. General electrical questions and answers can be found in the electrical forum.
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock