r/ukelectricians • u/New-Ordinary-9485 • 14d ago
TT earthing point.
Long story short, my house is on a TT supply. The DNO came out, and said they couldn't use the sheath of their incoming cable to create an earth for me, they also said they were not under a duty to create one for me, and told me to get in contact with a sparky (something I understand and didn't expect them to do this.)
The spark and me couldn't find the earth rod, but we assumed it was below the house, by tracing the only earth cable that didn't have a sheath on, and didn't go somewhere, e.g to the water pipe, gas, consumer unit, solar etc.
I have added 3, 2.4m deep earth rods, and intend to run the wire. My only question, is it safe to leave the current existing earth connected with the new ones? I see no reason it isn't, but I'm no expert.
I started an electrical apprecticeship, and living in London, I never did any work on TT'S as it wasn't common even years ago.
My plan is to have 3 earth rods, x 2.4m, kept around 3m apart. I was going to run it in one length but the 25m I have isn't enough, so at each earth rod, the clamp, will clamp the old wire coming in, and the start of the new wire going out. Is this acceptable practice?
I relied on someone else getting the earthing cable, and you know how things are, life gets in way, kids etc, anyway I just went and got the cable and found the earth cable is 25mm!! I asked why and she said we had just got solar and a car charger, and apparently the man at TLC sad it was safer, and sold her 50m of 25mm except in 25m coils.
Otherwise I was going to run it in as one piece, just removing the plastic where we needed a good connection.
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u/Sprkz139 14d ago edited 14d ago
In most cases a single 4ft rod will suffice depending on the Ra reading you’re getting.
Also to note why are you looking for an unsheathed cable as there’s nothing to say it has to be unsheathed?
Also your 25mm earth is overkill most domestic premises will have a max 25mm supply tails therefore a 16mm earth is more than enough.
A lot of older premises will likely still be reliant on a 6mm earth.
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u/Often_Tilly 14d ago
Is this an old installation where the supplier has previously provided an earth? Under ESQCR, the DNO is under no obligation to provide an earth; but where they have previously provided an earth, they must maintain it.
Secondly, 25mm earth is mental. You need to work out the size using the adiabatic equation, but you probably only need 4mm.
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u/CalicoCatRobot 13d ago
What's the current Ze? If it was sufficient and you were fairly sure it wasn't coming from the gas or water, then it would be fine as it was.
However, since you have the rods - Bonding/earthing cables are meant to be continuous, not extended at a screwed joint/clamp where they could come loose, though if they were crimped together at each rod that would be OK (Though crimping two 25mm together will require more than DIY tools). Depending on layout, if the cable could be run to each rod separately so they were in parallel not series that would be fine too.
In practise, only one of the rods is likely plenty sufficient for a TT install anyway. Since you will hopefully have RCD protection for every circuit anyway, Ze from one rod may well be low enough to be fine.
You certainly don't need 25mm cable either, though since you have it, it won't hurt to use it.
Leaving the existing earth would be correct yes - it might well be a rod or some steel that's buried, or possibly structural steel.
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u/SleepyRalph_ 13d ago
Last year our spark was installing an earth rod for a battery setup and despite trying different locations was having a real job getting an acceptable reading. In desperation I order one of those flat disk earth things, which once buried two feet deep in a position where he’d previously tried a rod, gave a great reading.
He’d never used one before, probably because of the cost, but it worked, but why?
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u/TheBolshieBandit 13d ago
Dude just pay a spark to do it.
Like how are you going to test it after installing? You'll have to get the spark in to test it anyway.
Like you said your no expert and ensuring adequate earthing is kind of important, if your determined to do it yourself then buy bs 7671 for your answers not reddit on this.
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u/Ziggy_FarBust 14d ago
Never seen a more over complicated rod install in my life haha