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tt system

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  1. B

    RCBO's on TT system

    Excuse my ignorance,can someone explain to me the problems of using RCBO's on a TT system,and whether and why its unsafe
  2. P

    TT system cable size

    Hi all. Can anyone tell what size the earth cable should be from CCU to the earth rod. To clarify I am installing an TT system in a two bed regular house.
  3. R

    Earth Loop Impedance on a TT system

    Afternoon all, I did a standard Ze test on a TT installation yesterday, and got a value of 215 ohms. The ground is really wet at the moment and so I'm assuming its about as good as the rod is going to get. Would simply replacing the rod with a longer type improve the Ze result? and if not...
  4. Baker1988

    rcd on a tt system

    hi ya i have a home work question which is: What additional protection is required on a TT system, justify your answer, Stating what regulation from bs7671 requires additional protection. I am sure that answer is a rcd but i just cant fine the reg that states that you need a rcd the closest i...
  5. A

    rcd requirements on a tt system

    Hi all A new shower circuit has been installed into a town property that is a TT earthing set up. The shower is protected by a 60amp 30 ma rcd and a 40 amp breaker. The ZS is 9.8 ohms, the Ze is 9.7 oms. Should this circuit be protected by a further 100ma rcd before the 30ma rcd or is the 30ma...
  6. A

    TT System testing and results

    Hi Guys, I have been testing for about a year and have come across my first tt system yesterday. I disconnected the earth and tested for Ze and got 8.67 ohms which I believe to be a great reading as osg allows up to 200 ohms. I couldn't do a Ra reading as the rod is under the house and...
  7. B

    External earth fault loop tt system

    Evening all could anyone please tell me the the maximum ze for tt systems the jobs entail Rec cut out fuse bs88 16a to feed 1x 30 ma rcd fuse spur for feeding socket outlet what should the max ze be please
  8. M

    TT system sub main design

    Hi all, a little stuck with a couple of things. house on a TT system with a 16mm main earth and a 100A main cut-out. the board has a 30mA 2 pole RCD main switch and all the circuits are 60898 protected. One of the circuits supply's the garage with a 6mm 70 degree SWA. The garage, however is...
  9. N

    TT SYSTEM. Zs readings confusing me.

    Howdy all. A friend of mine has recently bought a house and asked me to pop round and do a few tests just for piece of mind everything's ok. It's a TT system with 30mA split DB Ze(Ra) - 10.59 with all bonding disconnected When I got some Zs readings they were all coming up at around the 15...
  10. W

    Protection on 2 garages with TT system

    Hello Guys, ive been looking through posts for a number of months now and thought its finall time to take the plunge and ask my own question. I have 2 garages which are supplied from a meter in the first garage. It is a TT system. The current protection is a 80A RCD on a Metelclad single 6 way...
  11. M

    TT system issues???

    Hi, I've had to change a TN-S over to a TT system. My first problem is that my earth rod resistance is too high. At the moment it's measures at 161ohms (taken it wet conditions). To satisfy NICEIC I need to get it below 100ohms in normally dry conditions. What is the most effective way of...
  12. D

    Time Delayed RCD Protection for a TT system

    Hello all I have a standard CU at present with 30mA RCD protection. As there was no decent earth in place, I'm in the process of installing TT and, so far, I've installed an Earth Rod, tested and found sufficiently low loop impedance. My next job is to get the necessary RCD protection in...
  13. R

    Ze of TT system and Zs value.

    Evening all. Iv come across a problem. I'm going to change a d.b. The earthing arrangement is TT system with a 10mm cpc. Water and gas bond is 10mm also. My Ze when the main earth Is disconnected is 59.1ohms which as we know is fine. When taking zs at socket outlets I'm getting a value if...
  14. 9

    tt system

    Customer has a tt system with a 30ma rcd as main switch on cu. would you upgrade this board and put type s in or..??
  15. D

    RCD for TT system

    Hi all, I have just read an old periodic report that has highlighted a TT system that has an RCD main switch mounted in a non insulated enclosure (metal) as a category 2. Does it state anywhere in the reg that the RCD should be in an insulated (plastic) enclosure. I've had a look but cant find...
  16. DaveyD

    100mA delayed RCD tripping before the 30mA at DB. TT System

    Hello Just not on the job at the moment but the builder called. He plugged his small angle grinder in to a new circuit and it took out the RCD at the supplying DB not the 30mA at local CU. Here's the set up: TT . 100A DNO fuse House CU old and full so split tails into small CU with...
  17. D

    Wiring a hot tub on a TT system

    Just a quick one I'm wiring up a hot tub tomorrow (yes, on a Sunday !) know I shouldn't transport a PME earth to the installation. The house is out in the sticks and on a TT ................ my query is, would you still put an earth electrode locally to the hot tub or would you rely on the...
  18. La Poste

    Mini TT system

    Greetings. I've got a friend who lives in Thailand in a house with no earthing. It's a two wire system with a RCD/ELCB at the point of entry to the house. They seem to do this in Thailand, put an RCD at the main incomer even though they have no earth circuit. I guess something is better than...
  19. D

    Exporting Earth on TT system

    Working on supplying three phase power to a new shed in a farmyard. Running armoured underground. I was going to connect the armour to the earth rod at the Main DB then use the armour at the other end in the new shed as the earth in the new shed, bonding all extraneous metalwork to it. Is this...
  20. N

    TT System - Earth Rods

    Just abit of advice needed please. Off to do a job next week on a TT system the Ze was 463Ohms so I plan to install a new rod and main earth cable, But I know it's going to be a pain to get it low enough. If there any rules on having a link from my new rod to the old one? Thanks

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