Garage earthing

[SparkJ]

Customer has a house with and old consumer unit with semi enclosed wire fuses. Earthing is TT with a 100ma RCD. One way from CU connected to 30A fuse is connected to 2.5mm three core SWA cable to garage 20m away. There is bonding to gas/water in place.

In the garage is and old style metal CU with four ways also with wired fuses (each of 5A rating) one way is connected to the garage internal lighting circuit, another for some sort of security camera, another for a bunch of PIRs/security lights on the outside of the garage and another for some garden floodlights. The customer would like to keep each of these circuits separately fused for some reason.

There is no extraneous metalwork /water pipes etc that I can see in the garage. As far as I can see earth return for the garage is via one of the cores of the SWA and possibly the armouring.

He wants me to add a new radial circuit in the garage to serve one double socket for a freezer and for the odd power tool.

I

 

[Gforce]

I was led to believe a tt system had to be fully rcd protected-so a new cu would be the case wouldnt it. Then as for bonding-from earth stake to cu and then I would think the earth from the swa is fine for a garage as there are no water pipes or extra stuff there are there?

 

[Apache]

I knows I'm only a vet but 16mm on a TT? You could seperate the earthing or wack another rod in? Exporting it not really an issue with a TT as it's only your own fault current you need to worry about.

As far as I know

 

[Andy™]

the SWA can be used as the earth back to the house and to the rod there. before considering any work in the garage, you should be changing either the cable to a bigger size, or the fuse down to 20 at the most. you will also need to use 30mA RCD's (which would be covered with a new board)

16mm is OTT for a rod, i normally wire them in 10mm, but thats because i dont have 6mm or 2.5mm earth in the van

 

[SparkJ]

Points taken re the 20A fiuse and 10mm for earth cable to rod. What is the concensus regarding the earthing to a rod at the garage or using the earth core of the SWA.

Does it matter which method is used and if I use a rod at the garage should I disconnect the earth core and the armouring at the garage end?

 

[Andy™]

if the house is TT on TN-S, then no problem using the SWA as an earth. normally only install a rod at far end if house is TNC-S. you may be able to export PME in certain circumstances, but id rather TT it

 

[Apache]

if the house is TT on TN-S, then no problem using the SWA as an earth. normally only install a rod at far end if house is TNC-S. you may be able to export PME in certain circumstances, but id rather TT it

It's TT!

 

[Andy™]

It's TT!

i know, simply stating the other options

 

[Janice]

If the main system is on TT, then you can bang in as many rods as you like and join the whole lot together. The more the merrier.

To my mind, TT (or TNS because of its' lead sheath) is the safest of all. Your connection to earth is looking after your system ONLY.

The only time you have to worry about separating your earth paths is when you are on TN-C-S (PME)

 

[steptoe]

Im starting to like this place,

 

[batty]

Me to.

 

[Apache]

It is fun

 

[avinalarf]

If the main system is on TT, then you can bang in as many rods as you like and join the whole lot together. The more the merrier.To my mind, TT (or TNS because of its' lead sheath) is the safest of all. Your connection to earth is looking after your system ONLY.

The only time you have to worry about separating your earth paths is when you are on TN-C-S (PME)

Sorry to hi-jack the thread, but...

If one has a TN-C-S system, is it possible to convert it to TT by removing the earth shared with the supply neutral and connect it to your own supplied rod.

Sorry if it's a really dumb question, but I was just wondering Blushing

 

[binky]

Sorry to hi-jack the thread, but...If one has a TN-C-S system, is it possible to convert it to TT by removing the earth shared with the supply neutral and connect it to your own supplied rod.

Sorry if it's a really dumb question, but I was just wondering Blushing

Yes you could do that , but why would you want to?

 

[Andy™]

Sorry to hi-jack the thread, but...If one has a TN-C-S system, is it possible to convert it to TT by removing the earth shared with the supply neutral and connect it to your own supplied rod.

Sorry if it's a really dumb question, but I was just wondering Blushing

yes, just ditch their earth and connect to your rod. but dont connect their earth and your rod together!

 

[Andy™]

Yes you could do that , but why would you want to?

to supply an outhouse as TT?

 

[avinalarf]

Yes you could do that , but why would you want to?

It's just that it was stated that TT & TN-S were safer - not sure exactly why this is thought though.

 

[Andy™]

It's just that it was stated that TT & TN-S were safer - not sure exactly why this is thought though.

TNC-S can have voltage above earth on it. if your in a house, no big problem - all pipework etc will be the same voltage, so not potential difference between anything. but if you export it out of the house, then you could get a shock between a class I appliance and ground. TT and TNS dont have this problem since TT you have your own earth at ground voltage, and TN-S doesnt share neutral back to substation so wont get higher than ground voltage at service head

 

[steptoe]

It's just that it was stated that TT & TN-S were safer - not sure exactly why this is thought though.

disconnect your incoming Neutral and Earth at your CU (this will replicate a dropped Neutral fault at the transformer) and see how much metalwork in the house goes live!!!!

this is just one of the many faults possible on TNCS, cant really be bothered going over the multitude of reasons again why IMHO PME should be banned.

 

[avinalarf]

disconnect your incoming Neutral and Earth at your CU (this will replicate a dropped Neutral fault at the transformer) and see how much metalwork in the house goes live!!!!

Mmm - I think I'd be too nervous to try that one ; \

this is just one of the many faults possible on TNCS, cant really be bothered going over the multitude of reasons again why IMHO PME should be banned.

I'll have to look for them in some other thread Steps. Why is PME so popular then, if it's not as safe?