Garage Earthing system

[william7900]

Hi friends,

I have been reading threads concerning garage earthing arrangements. Advice was given to extend the earth from the house to the garage. Please may I comment that this is a dangerous practice because if by accident someone went through the SWA cable with the mower etc, the result would be catastrophic, due to the fact that in the garden you will be in contact with the earth and a perfect conductor for electricity and receive a severe shock. The earthing system for a garage should always be TT, using earth rods and trying to achieve a resistance of 200 ohms. You may have to use more that 1 earth rod to acheive this. The garage unit should always be RCD protected.

This is why on building sites all the equipment is supplied by transformers which gives a separated environment and no earth is used for safety. Hope this helps.

Regards,

Bill

 

[telectrix]

i fail to see why the type of earthing at the garage would have an effect here. either way, you are in contact with the earth when you cut the cable. the cable is earthed at the supply end anyway, no matter what earthing system you have at the garage.

 

[Knobhead]

What kind of mower do you use, a combined harvester?

This subject has been done to death, use the search engine to find past threads.

 

[SW1970]

Hi friends,

I have been reading threads concerning garage earthing arrangements. Advice was given to extend the earth from the house to the garage. Please may I comment that this is a dangerous practice because if by accident someone went through the SWA cable with the mower etc, the result would be catastrophic, due to the fact that in the garden you will be in contact with the earth and a perfect conductor for electricity and receive a severe shock. The earthing system for a garage should always be TT, using earth rods and trying to achieve a resistance of 200 ohms. You may have to use more that 1 earth rod to acheive this. The garage unit should always be RCD protected.

This is why on building sites all the equipment is supplied by transformers which gives a separated environment and no earth is used for safety. Hope this helps.

Regards,

Bill

You need to read this thread... http://www.electriciansforums.net/e...159-good-guide-exported-pme-outbuildings.html

 

[Silly Sausage]

...... if by accident someone went through the SWA cable with the mower.......

What, do you just lay your SWA across the lawn? :bobby:


:welcome:

 

[Hawk81]

Hi friends,

I have been reading threads concerning garage earthing arrangements. Advice was given to extend the earth from the house to the garage. Please may I comment that this is a dangerous practice because if by accident someone went through the SWA cable with the mower etc, the result would be catastrophic, due to the fact that in the garden you will be in contact with the earth and a perfect conductor for electricity and receive a severe shock. The earthing system for a garage should always be TT, using earth rods and trying to achieve a resistance of 200 ohms. You may have to use more that 1 earth rod to acheive this. The garage unit should always be RCD protected.

This is why on building sites all the equipment is supplied by transformers which gives a separated environment and no earth is used for safety. Hope this helps.

Regards,

Bill

You are talking rubish. What if someone is using and extension lead from their house and cut it with their mower? Surley the earth from the house is at the mower and they are standing on the earth. So it has moved on fom not exporting a PME earth to not exporting any earth.

 

[Knobhead]

I fear for the future of mankind!

 

[SW1970]

Come on then Bill, happy with the feedback you've received?

 

[Engineer54]

I fear for the future of mankind!

The trouble is Tony, all this scaremongery about PME, has been going on for a very long time now, and it's convinced an awful lot of electricians in the process.

The old Leccy boards spent years ridding 100s of 1000s of homes of TT systems by providing a fully functional PME earthing system to these old installations. Now we have plonkers trying there best to reinstate or creating new TT systems!! I can only put this down to ignorance of the real facts, in preference to all the old wife tales that are being banded about to this very day!!!! The OP of this thread being a perfect example...

 

[Knobhead]

E54 we’re from the same era and both singing from the same hymn sheet.

I’ll stick to my statement that exporting earths is beneficial.
Both you and I have installed earth nests.
For my part they have included steel framed building covering hectares. All linked together. I’ve run dozens of radial sub feeders and not one with a supplementary CPC. Why because they were earthed through the structure of the building! I would have received a sever battering around the head for suggesting running a 95 CPC along side a 185 SWA.

Just as an aside the last nest I had anything to do with testing the commissioning engineer came out with the statement “I don’t know why we bothered” as he looked up at 10,000 tons of steel. As a matter of course I’d bonded the incoming services. 3 X 8” steel water mains will beat anything you can knock in the ground.

 

[GLENNSPARK]

E54 we’re from the same era and both singing from the same hymn sheet.

I’ll stick to my statement that exporting earths is beneficial.
Both you and I have installed earth nests.
For my part they have included steel framed building covering hectares. All linked together. I’ve run dozens of radial sub feeders and not one with a supplementary CPC. Why because they were earthed through the structure of the building! I would have received a sever battering around the head for suggesting running a 95 CPC along side a 185 SWA.

Just as an aside the last nest I had anything to do with testing the commissioning engineer came out with the statement “I don’t know why we bothered” as he looked up at 10,000 tons of steel. As a matter of course I’d bonded the incoming services. 3 X 8” steel water mains will beat anything you can knock in the ground.

Well BS7671 states that the metalic structure of a building CAN be used as a reliable means of earthing doesn`t it...
542.2.1 (p 127) states:
1...earth rods or pipes
2...earth tapes or wires
3...earth plates
4...underground structural metalwork embedded in foundations
5...welded metal reinforcement of concrete (exept pre-stressed concrete) embedded in the earth
6...lead sheaths and other metal coverings of cables, where not precluded by regulation 542.2.5
7...other suitable underground metalwork

 

[Deleted member 9648]

Hi friends,

I have been reading threads concerning garage earthing arrangements. Advice was given to extend the earth from the house to the garage. Please may I comment that this is a dangerous practice because if by accident someone went through the SWA cable with the mower etc, the result would be catastrophic, due to the fact that in the garden you will be in contact with the earth and a perfect conductor for electricity and receive a severe shock. The earthing system for a garage should always be TT, using earth rods and trying to achieve a resistance of 200 ohms. You may have to use more that 1 earth rod to acheive this. The garage unit should always be RCD protected.

This is why on building sites all the equipment is supplied by transformers which gives a separated environment and no earth is used for safety. Hope this helps.

Regards,

Bill

A wind up methinks.

 

[telectrix]

what, the thread or his mower is a wind up?

 

[william7900]

Hello guys,

You must understand that for TNCS systems the earth and neutral are the same conductors. Now if the neutral were disconnected due to a supply fault, the live conductor will now look for another path to complete the circuit which will be the bonded conductors on your gas and water pipes. Now just suppose at the same time you were digging your garden with your kango and made contact with the earth that you had run to your garage, you will form another low resistance path to earth and receive a severe shock. This is why electrical suppliers forbid the exporting of the PME earth.

Now for TNS systems you won't get this problem as the neutral and and earth conductors are separate. However the bonding to the garage from your house must be at least 10mm. For most installations this means running 2 cables as most garages use 4 - 6mm conductors. So again I would use a TT system because it is expensive to run a feed to the garage in 10mm swa unless it is a short run.

Hope this clears up the confusion.

Regards,

Bill

 

[Deleted member 26818]

No it doesn't, as it is you that is confused.
You don't need a cable in the garden for a loss of supplier's neutral to be a problem.
Any exposed or extraneous-conductive-part connected to the earthing will become live.
Your washing machine, your central heating even your crittle windows (if they're bonded).
This is one of the reasons, why in most other countries an earth electrode is installed at the origin of each installation.
However the loss of the supplier's neutral is not something that is seen as a problem in the UK, as there are measures in place to guard against this.
As for the cable in the ground, it should be at a depth so as to not be damaged when digging the garden.