High reading on TT System

[Power Ball]

Got a call today from customer who has just had her gas fire serviced,the engineer has told her that the earth TT is over 200 ohms and can exploded at any time so needs to have it sorted, she is in her 70's and now worried sick, so before I go and test it for myself what can be done to bring it down, I was thinking along the lines of putting in another rod and link it to the first one. Any advise would be greatly welcome

Thanks

Chas

 

[initforthemoney]

I expect you will find that its earthed through the water pipe still.

Just take a new rod and some 10mm earth and bang it in.

Just get it as close to 100 as you can.

Good luck.

 

[NozSpark]

If it was a BG service they use the socket & see tester which has lights that give an indication of Zs.. they will have an idea of TNS and TNC-S, but not TT.

When you do your Ra test you may find that it's perfectly OK

 

[initforthemoney]

Or worse due to p/paths, assuming they exist.

 

[NozSpark]

Could be...

like you said, still worth a rod & some 10mm

 

[paul b b]

remember if you do put 2 rods in it needs to be 1 unbroken cable

 

[paul b b]

not sure why it would explode though?

 

[M107]

Extra rods in parralell is the way forward.

 

[vince]

if you can't get the reading down low enough the regs say use a rcd to meet disconnection times

 

[vince]

oh and why on earth would it explode??????? if the impedance is high your don't meet the required disconnection times it would still trip eventually

 

[NozSpark]

oh and why on earth would it explode??????? if the impedance is high your don't meet the required disconnection times it would still trip eventually

Not necessarily..

say you have a Zs of 100ohms (no RCD) and an earth fault at that point.. the earth current would be 2.3A and it'll never trip an MCB or blow a fuse

that's why TT installations must have RCD protection on all circuits

 

[vince]

your right of course,but there would still be no 'explosion' i think rcd is the way to go as well as reducing impedance as much as poss

 

[sparkytim]

If its TT then it may have RCD already, if 30 m A then 1666.66 ohm is max Zs

200 ohm Max RECOMMENDED to indicate stable earth connection only

See BRB Pg 50 Table 41.5 and note 2

I have had this before with B Gas they are equipped with A Martindale that indicates ranges of Zs with > 200 ohm as top range and condem anything above with no knowledge of Regs and TT systems. headbang

As has been said to reduce Ra install Parrellel Rod(s) keep more then depth of Rod apart and it should half the reading.

 

[initforthemoney]

e 2I have had this before with B Gas they are equipped with A Martindale that indicates ranges of Zs with > 200 ohm as top range and condem anything above with no knowledge of Regs and TT systems. headbang

BG are just a bunch of cowboys.

They should stick to ripping people off for new boilers and pointless maintenance contracts.

mr forthemoney

i have asked previousy for you to avoid using such language in your posts

if you continue the moderators will be forced to issue infractions

thankyou

mr smith

 

[NozSpark]

BG are just a bunch of cowboys.They should stick to ripping people off for new boilers and pointless maintenance contracts.

+1

 

[initforthemoney]

BG are just a bunch of cowboys.They should stick to ripping people off for new boilers and pointless maintenance contracts.

mr forthemoney

i have asked previousy for you to avoid using such language in your posts

if you continue the moderators will be forced to issue infractions

thankyou

mr smith

I think the swear filter worked perfectly well, as that is what it is there for.

And, im not the only one using swear words, and i dont see anyone else getting told off with red pen?

I will try to be good.

 

[Mr Smith]

mr forthemoney

and others whom it may concern

there are indeed swear filters

although in some cases the starred word is obvious to all

this does not mean you must test them at every oportunity

as regards other people

if they are seen to be using such language

by myself

or another moderator

they would recieve the same warning

thankyou for trying to be good

mr smith

 

[Power Ball]

Thanks for all your imput on this one I hope to get a look at this job on friday and go for 2 rods with a continuous earth. as far as I know it is an old wylex box with re-wired fuses coverd by one rcd on the full installation. They will not go for a new 17th box due to the cost headbang

Chas

 

[steptoe]

If its TT then it may have RCD already, if 30 m A then 1666.66 ohm is max Zs 200 ohm Max RECOMMENDED to indicate stable earth connection only

See BRB Pg 50 Table 41.5 and note 2

I have had this before with B Gas they are equipped with A Martindale that indicates ranges of Zs with > 200 ohm as top range and condem anything above with no knowledge of Regs and TT systems. headbang

As has been said to reduce Ra install Parrellel Rod(s) keep more then depth of Rod apart and it should half the reading.

+1

I also advocate the use of galv conduit for the underground run to the rod and bond this to the rod also, usually helps.

TT can be a funny old spud sometimes if you are not used to it.

 

[green-hornet]

+1I also advocate the use of galv conduit for the underground run to the rod and bond this to the rod also, usually helps.

TT can be a funny old spud sometimes if you are not used to it.

I have seen this done before, it was rotten with rust but still lowered the Za.

When I was young and tender one of the old guys I worked with used bare copper underground for the same reason.

I doubt it would pass any PIR these days, but it did last for as long as the safety of the installation did.