Does this make sense ? What do you think.

[Pat Tester]

I have a job to connect up a shed and greenhouse (socket in each) from a detached garage. House is TT and garage is fed via swa up garden.
I am unsure of the correct procedure re bonding in the greenhouse or not. I spent some time looking and could only find conflicting advice
and nothing specific within the regs.

I have already upgraded c/u with rcbo's on all circuits during loft conversion work.

So as I pay a considerable sum per annum to one of those scheme providers (no names but I like their biscuits) I contacted tech dept and asked should I seperate earth from house, put a rod in for the garage with a small c/u and 30ma rcd and then bond greenhouse, only 5M away from garage ?

I was told they would like to see greenhouse treated as a seperate zone, with its own rod and c/u and rcd within the greenhouse ! leaving the shed and garge with the house earth.

Has anyone put a consumer unit within an 10' x 6' aluminium greenhouse ?

I would appreciate some input from respected members who will know a great deal more than I..

 

[GLENNSPARK]

Well how would you fix it for a start? Glass screws...lol.............

 

[GLENNSPARK]

caus its a metallic structure that greenhouse is....thats why they want you to TT it....

 

[Deleted member 19807]

also what about the enviroment, could get a bit humid in there,

 

[ackbarthestar]

I wonder whether your enquiry will be logged with the assessor for him to check when you come up for your next assessment?


You would certainly have to use an IP rated DB and cover the greenhouse circuits with an RCD.

 

[Pat Tester]

Yes I am aware it's conductive, humid and glazed; what I was questioning is actually fitting the c/u within the greenhouse, not the fact it should have its own rod. I asked why not fit it within the shed 6" away but was told they would prefere it in the greenhouse. Has this ever been done before or as I suspect would I be breaking new ground
on the domestic front ?

 

[Engineer54]

The advice you received makes no sense at all on a TT system, The more rods you install the better will be the Ra when all are connected together!!

Use a 3 core SWA cable from green house to garage, and connect any rod or service bond (water pipe) to that 3rd core, and use the SWA as your CPC. No real need for a CU in the greenhouse either, if all that is wanted is a socket or two in there.

 

[yellowvanman]

Can't see why you need to stake the greenhouse. Couldn't you just supplementary bond the socket outlet to the framework for protection.

 

[Engineer54]

Can't see why you need to stake the greenhouse. Couldn't you just supplementary bond the socket outlet to the framework for protection.

Yes, no problem with that either!!

 

[Pat Tester]

The advice you received makes no sense at all on a TT system, The more rods you install the better will be the Ra when all are connected together!!

Use a 3 core SWA cable from green house to garage, and connect any rod or service bond (water pipe) to that 3rd core, and use the SWA as your CPC. No real need for a CU in the greenhouse either, if all that is wanted is a socket or two in there.

So you are suggesting putting in a rod for the garage - shed - greenhouse and connecting this new rod via swa & cpc back to met and house rod ? and then supplementary bond to framework.

This makes more sense to me, but how come I received the advice I did ?????

Many thanks for your help 54 & yellowvanman

 

[Engineer54]

Pat Tester,

What i'm saying is that with a TT system, the more rod's you drive into the ground the better the Final Ra is going to be. If you connect the rods for the garage shed and greenhouse via a 3rd core of a SWA cable to the EMT at the garage CU the 3rd core of the supply SWA cable will take those Rod installations back to the MET. Use the SWA armouring as your CPC for the supply and distribution cables.

Personally, the shed and the greenhouse can both be supplied from the Garage CU on one or two radial circuits. As stated earlier nothing to stop you supplementary bonding the greenhouse metalwork to one of the sockets....

 

[ackbarthestar]

Yes I am aware it's conductive, humid and glazed; what I was questioning is actually fitting the c/u within the greenhouse, not the fact it should have its own rod. I asked why not fit it within the shed 6" away but was told they would prefere it in the greenhouse. Has this ever been done before or as I suspect would I be breaking new ground
on the domestic front ?

There are several ways you could achieve a safe installation in a greenhouse. bonding the greenhouse structure to the electrical earth. Here's a couple but there are variants and hybrids of these. Its really up to you.

1/ Use the RCD in the shed and use the armour or 3rd core of the swa, IP rated SFCU from the IP rated socket outlet

2/ Separate the earthing and apply earth rod to the shed with either the above or an IP rated DB with RCD and then out to final circuits.

Just a couple of points
1/ will your assessor be signing this work off for you?
2/ This not new ground, maybe for you and the greenhouse, but domestic/horticultural systems have been around since plants needed heat and light to grow and, I was forgetting, electricity was available.

 

[Engineer54]

2/ Separate the earthing and apply earth rod to the shed with either the above or an IP rated DB with RCD and then out to final circuit.

Please explain to me why on earth you would separate a TT system earthing arrangement?? Just exactly what are you going to achieve, by this TT from TT separation??

 

[Des 56]

House is TT and garage is fed via swa up garden.
put a rod in for the garage with a small c/u and 30ma rcd and then bond greenhouse,

Why have an rcd in the shed ?

I assume the house has an rcd (but not s type) protection,so the both will trip whether you split earthing systems or no

 

[ackbarthestar]

Please explain to me why on earth you would separate a TT system earthing arrangement?? Just exactly what are you going to achieve, by this TT from TT separation??

As I said, there are various ways of providing an earthing system to an installation. Separation by the use of an earth rod is one way.
The greenhouse earth electrode will provide a separate earth and make the greenhouse an independent entity. The problem, of course, is the extra complexity of separating out the interaction between the two separate electrodes. 5m between electrode is probably not enough. But that is for our horticultural novice to experience.