Tt earthing conductor max length

[Engineer54]

Can't say you have ever pointed anyone to any such publications on the why and where the 200 ohm max comes from!! I for one would love to see such a paper!! I dare say though, it'll be totally based on a 30mA RCD protection, ...right??
Absolutely amazes me why you would accept and defend such a high value?? No-one else seems to think it's acceptable, certainly none of the International Regulatory Bodies that i know of, nor a growing number of UK bodies/faculties!!

In the past, the Ra value that was aimed for as the max, was 10 ohms, which is a far cry from your magical and perfectly adequate 200 ohm Ra. No RCD's around in those days either, all they had was the services bonding conductor(s) but then they didn't have short rods, they were approx 2.5 to 3m 5/8'' and 3/4'' and more often than not doubled them... Another far cry from your 1.2m rods

Why on earth would i need to convince anyone with half an once of commonsense that Low Ra values are always going to be better than a numbty 200 ohms Ra?? Are you being serious here?? lol!!

I personally would always advocate at least ''Trying'' for near TN values, certainly wouldn't advocate aiming for your magical 200 ohms that's for sure. As for your saying it's a ''Safe'' value, you've just got to be having a laugh now!!

I must have been missing something all these years installing TT systems!! I should have been taking notice of BS 7671 and reading publications with statistics (always reliable data) that says 200 ohm Ra s is a perfectly adequate and safe value. ...Yeah Right!!!

You stick to your BS 7671 Poo IQ, ...I'll stick to basic electrical technology, It's seen me through 40 odd years with no problems so far...lol!!

 

[rich.250]

Can't say you have ever pointed anyone to any such publications on the why and where the 200 ohm max comes from!! I for one would love to see such a paper!! I dare say though, it'll be totally based on a 30mA RCD protection, ...right??
Absolutely amazes me why you would accept and defend such a high value?? No-one else seems to think it's acceptable, certainly none of the International Regulatory Bodies that i know of, nor a growing number of UK bodies/faculties!!

In the past, the Ra value that was aimed for as the max, was 10 ohms, which is a far cry from your magical and perfectly adequate 200 ohm Ra. No RCD's around in those days either, all they had was the services bonding conductor(s) but then they didn't have short rods, they were approx 2.5 to 3m 5/8'' and 3/4'' and more often than not doubled them... Another far cry from your 1.2m rods

Why on earth would i need to convince anyone with half an once of commonsense that Low Ra values are always going to be better than a numbty 200 ohms Ra?? Are you being serious here?? lol!!

I personally would always advocate at least ''Trying'' for near TN values, certainly wouldn't advocate aiming for your magical 200 ohms that's for sure. As for your saying it's a ''Safe'' value, you've just got to be having a laugh now!!

I must have been missing something all these years installing TT systems!! I should have been taking notice of BS 7671 and reading publications with statistics (always reliable data) that says 200 ohm Ra s is a perfectly adequate and safe value. ...Yeah Right!!!

You stick to your BS 7671 Poo IQ, ...I'll stick to basic electrical technology, It's seen me through 40 odd years with no problems so far...lol!!

I'm with you E54. Always aim for tn.
And if you can't get it that low, just calculate the max for your Rcd to operate.... Simples

 

[rich.250]

I think the problem is the 'on****e guide' lol.

 

[IQ Electrical]

I'm with you E54. Always aim for tn.
And if you can't get it that low, just calculate the max for your Rcd to operate.... Simples

And what would be 'the max for your RCD to operate' ?
For 30mA it's 1667 Ohms simples

 

[rich.250]

Yes. If you can prove its stable. But the lower the better I say. Also if your using the 30ma for additional protection. I would say that it should be no more than 333 ohms.
50\.15= 333.33

 

[rich.250]

But the lower it is the less you rely on Rcd protection as a sole Means

 

[IQ Electrical]

Yes. If you can prove its stable. But the lower the better I say. Also if your using the 30ma for additional protection. I would say that it should be no more than 333 ohms.
50\.15= 333.33

Additional protection is 30mA, where on earth (no pun intended) do you get .15 from?

 

[rich.250]

5 x 30mA. Is 150mA or .15 A.
I only say this as the touch voltage may go over 50 volts when a x5 fault current occurs. Hence requiring a lower impedance earth path. I don't know if it says that in the regs. But I found that to be a problem whilst testing numerous high resistance TT systems

 

[needasparks]

I was not going to join in as i left my shin pads in the van but surely the whole point is to stop voltage being higher than 50 volts on the earth which is where the calc originates, in saying that we know that we should be able to do alot better than that. Is that where the confusion is ?

If you want me I'll be under the sofa !

 

[rich.250]

I was not going to join in as i left my shin pads in the van but surely the whole point is to stop voltage being higher than 50 volts on the earth which is where the calc originates, in saying that we know that we should be able to do alot better than that. Is that where the confusion is ?

If you want me I'll be under the sofa !

LOL.
I just don't like the that'll do attitude of a lot of people.
Not pointing fingers as I know people on here who join in these threads know what there talking about in general.
It's only the x5 test can throw up over 50v touch voltage if it's over 333. That's all I'm saying lol

 

[IQ Electrical]

5 x 30mA. Is 150mA or .15 A.
I only say this as the touch voltage may go over 50 volts when a x5 fault current occurs. Hence requiring a lower impedance earth path. I don't know if it says that in the regs. But I found that to be a problem whilst testing numerous high resistance TT systems

Rich, you're getting confused here and may be confusing others reading this:

No device (OPD or RCD) can limit touch voltage, only the duration that it is present.

Have a look at this thread: http://www.------.org/forums/forum/messageview.cfm?catid=205&threadid=35891

 

[rich.250]

Yeh sorry just realised how confusing my posts were lol.
I can't explain what I was trying to explain. Brain has given up helping me

 

[rich.250]

There method of explaining makes a lot more sense.
Need to improve this before I sit 2396 lol

 

[needasparks]

Rich, you're getting confused here and may be confusing others reading this:

No device (OPD or RCD) can limit touch voltage, only the duration that it is present.

Have a look at this thread: IET Forums - TT Supply RCD Disconnection Time

Thats where i was going IQ. There was so many triangles i thought i was listening to the new seekers.

 

[Pat Tester]

My last earth rod job I achieved a reading of 9.32 ohms with two 1M 5/8 rod coupled together.
The last meter was a right pig.
One thing I can't work out is why they would make a coupler that's a larger diameter than the rod, therefore
the second rod flaps around. I think the first rod should screw into the second larger diameter rod.