TT earthing arangment

[Nedd]

Hi can any one help, I have a TT earthing arrangment I have a Ze reading of

28.1 ohms my ring main has a R1+R2 of 0.65 so Zs=Ze28.1+R1+R2 0.65=Zs 28.75

Bs7671 is asking for 1.44 up to 32A x.8=1.15ohms I'am getting 28.75 what am I not understand.

Regards Apprentice sparks

 

[Zeespark]

Remember that your circuit will be protected by either a 100mA or a 30mA RCD.

AndyGuinness

 

[m4tty]

You won't ever (is possible tho) meet disconnection times on a tt which is why all circuits must be covered by 30mA rcd which will be ok upto 1666 ohms hth

 

[Nedd]

Thanks Zeepark

 

[Doc Hudson]

Hi can any one help, I have a TT earthing arrangment I have a Ze reading of28.1 ohms my ring main has a R1+R2 of 0.65 so Zs=Ze28.1+R1+R2 0.65=Zs 28.75

Bs7671 is asking for 1.44 up to 32A x.8=1.15ohms I'am getting 28.75 what am I not understand.

Regards Apprentice sparks

I think you will find you are reading BS7671 wrong, the tables you are reading do not relate to TT installations. The max Zs for TT refer to the type of RCD used and they are in a different table. I shall move this thread to the student zone, where it is more appropriate.

Doc H.

 

[SLIPSHOD & SLAPDASH]

Where is Steptoe when hes needed for TT advice :Salute

He's diddling with his rods.

 

[steptoe]

didnt get home til gone 11,

but, there are a lot more learned than me here, and anyway, its not that hard, some of my learned friends are coping with the issue very admirably.

 

[NozSpark]

All work and no play won't make Steptoe a happy man

 

[Sharpend]

All work and no play won't make Steptoe a happy man

What you on? he's been down the pub!!

 

[steptoe]

according to the missus I moan anyway,!

but when was she last right?

anyhow, having a cracked one or two now,

 

[NozSpark]

What you on? he's been down the pub!!

If he'd benn down the pub he'd still be there

 

[steptoe]

What you on? he's been down the pub!!

I wish,

have you seen me rant yet? must mean Im still drunk from yesterday then,

when I start to sober up I go off on one and rant, not good,!

 

[Revved Up Sparky]

Did you test the Ze (which is in effect Ra on a TT circuit) with the incoming services still connected to the MET ?. Water and gas servcies run in copper pipe are notorious for giving a much better earth reading than the earth rod itself. I lost count of the number of times I measured the Ra minus the services and got a reading way over 200 ohms but with the services connected the 'Ze' would be a very low reading.

 

[batty]

Would you try to improve the rod reading though?

 

[ADS]

Did you test the Ze (which is in effect Ra on a TT circuit) with the incoming services still connected to the MET ?. Water and gas servcies run in copper pipe are notorious for giving a much better earth reading than the earth rod itself. I lost count of the number of times I measured the Ra minus the services and got a reading way over 200 ohms but with the services connected the 'Ze' would be a very low reading.

How do you manage that??........with the 'Earthing Conductor' disconnected from the MET, as it should be, for Ze or Ra, it wouldn't matter if the service 'Bonding' was still connected to the MET.

 

[steptoe]

cos you cant/shouldnt be doing a Ze on a TT system

 

[wicksy]

You could always pee on the rod

Sorry couldn't resist anyhoo that's not that bad for a TT

 

[Steve3948]

Well yesterday, installed a W/P FCU for electric gate supply, the fuseboard was in the gardeners garage store.

Started with a ZS on one of the sockets just to see what it was like and with the intention of do an RCD test also.

ZS came up at 384 ohms, not good, moved onto RCD test with the Megger 1730, would not test with a warning triangle and a >50V touch voltage reading.

Did a test on the rod +400 ohms.

I've not had a reading this high since having the 1730, and did not realise it will not continue with the test if a reading of >50V is measured.

Live and learn, going back next week to bang in a new rod away from the building, as the current one is up against the wall.

This is where I hate TT, rod going in ground but what's down there ??

 

[wicksy]

You might have to mat it

 

[Steve3948]

You might have to mat it

Hope not, I hate TT, too much hassle.