Just been to job today to add 2 sockets into attick conversion tested socket in bedroom which was to supply spur with 13A fuse the zs was 312 ohms and ze was 320ohms the owner said last electricians said it was a bit high and knocked in earth rod(outside front door earth seems damp enough) a bit more and it was ok which from the readings i have this seems they didn't get reading down the system is protected by a 30ma rcd not time delayed 100ma, do you think i need to fit new earth rod :|
high zs and ze on tt
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green-hornet
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I would try to bring down the earth fault loop Ze for the earth rod to below 200, preferably to 100. This can be done by driving the rod deeper into the soil if possible by use of extentions, or put another rod in and connect in series.
Maximum zs for a TT system is 1667ohms for a 30mA rcd( 50/1 delta).
Maximum zs on all tables are for TN installations and not TT.
Maximum zs for a TT system is 1667ohms for a 30mA rcd( 50/1 delta).
Maximum zs on all tables are for TN installations and not TT.
Thanks just found this on table41.5 not had much to do with tt systems in my area mostly tn also on this job was aked to change kitchen socket as it wouldn't switch off when i removed it it was black and cables burnt from loose connections
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I did one the other day when tested the loop was 940ohm . Customer said earth rod was under concrete so I put new 5/8 earth rod in new position reading was then 45ohm. I usually use 5/8 rods as they are threaded and if ground is not to hard you can push another rod in on top. There was a post the other day about using an sds drill to knock it in seemed like a good plan.
But if ground is chalk you probably won't get a good reading no matter how far you go down and certain other ground is not good also ie rock but I don't think you would be able to knock a rod in rock anyway. I am waffling on I hope this helps.
Batty
But if ground is chalk you probably won't get a good reading no matter how far you go down and certain other ground is not good also ie rock but I don't think you would be able to knock a rod in rock anyway. I am waffling on I hope this helps.
Batty
remember if you do decide to put another rod in series to keep it far enough away from the first one,
as a minimum the same distance away as the rod is deep is a good rule of thumb without working anything out.
HTH,
as a minimum the same distance away as the rod is deep is a good rule of thumb without working anything out.
HTH,
green-hornet
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Just one more question on this because i am adding to circuits does the main 30mma rcd cover this as the 17thed says less than 50mm deep,i thought this would be ok and in the remarks columb to say that cicuits not segragated only one rcd consumer unit is old wilex with retrofit mcb's with rcd before unit.
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Any socket under 20 amps needs 30mA Rcd protection in 17th you cannot have Rcd as main switch on 17th so note that on cert ie does not comply.
Batty
Batty
Thats what i thought advise not correct just to cover myself cant see that my work is making it any worse,at the end of the day were are not here to just bang in new circuits as our builder friends would like but we follow correct guidelines thanks daryl.
green-hornet
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Marcanite whilst does improve ground resistance requires a bore hole of at least 100mm.
The marcanite is then poured into the hole and semi sets around the earth rod.
Good for some industrial uses but not practical for most domestic or small commercial.
The marcanite is then poured into the hole and semi sets around the earth rod.
Good for some industrial uses but not practical for most domestic or small commercial.
Yep that chalky ground is a right royal pain in the backside, job I'm on at the moment I cant get the Ze down below 198ohm , have got 2x rod deep + one in series (1 rods length away). Still 198ohms is better than the 500+ohm I did have.
And Dewalt do a earth rod driver for sds
http://www.transtools.co.uk/store/prod_5632/power-tool-accessories/sds-max-concrete-chisels/dewalt-dt8093qz-sds-max-earth-rod-driver-chisel.html
And Dewalt do a earth rod driver for sds
http://www.transtools.co.uk/store/prod_5632/power-tool-accessories/sds-max-concrete-chisels/dewalt-dt8093qz-sds-max-earth-rod-driver-chisel.html
at that price, its cheaper to get a chasing bit, cut in half and drill a hole for fit over rod! something ive been going to do for a long time now!
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wouldn't the rod fit in the chuck without a bit..............
depends on rod - you wouldnt get a 5/8 in there. never tried with 3/8, but it may fit
green-hornet
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Some rods have a threaded end on for extentions, when you try to hammer these in the end of the rods can mushroom and the thread becomes un usable.
If i need it I have a socket that just fits the end and does not cause too much damage.
If i need it I have a socket that just fits the end and does not cause too much damage.
Thats why the driving stud is handy to have, I then use the sds with a chisel thats been ground down to fit in the top of the stud.
See I'm not that mean as to make the hired hand struggle.......after all time is money.
should really be a minimum of 2X away then, there is a very good reason for this, just for the life of me cant think of the proper way to explain it and how to put it in writing at this hour,
still, I doubt it would help that much in getting it down a lot more if the ground is just rubbish.
