M
MDJ
again true 612.9 loop impedance can be determined by an alternative method other than measurement, still worth doing and a grey area when verification is required IMO
Discuss Zs on TT in the UK Electrical Forum area at ElectriciansForums.net
What is the point in carrying out zs on TT system other than verifying a loop.
We got an Ra of 14.8 but when all bonding is in place it comes down to 1.9 ohms for most circuits zs results. I just don't see the point if rcd protected .
So what is the point or significance of carring out a Zs test on final circuits within a TT install when the Ra has been measured and the R1+R2 (presumably) has also been measured and an RCD is used for earth fault protection........still the same point???
Sorry Im not trying to be arguementitive, Im just interested to know what other electricians think about this.
Ahhh Hawkmoon the eternal champion....the old "you might of damaged or pulled out a conductor" argument. But what if it was a radial with a FCU on the end? Wouldn't you have to take it off the wall to measure Zs?
I know Zs is the whole circuit or loop impedance path, read post No 58..oh here it is
"Agreed, I like to test it myself too, but an Ra plus R1+R2 of each final circuit will give a more accurate/stable assessment of the earth fault loop impedance and would not include parallel paths which may be removed at some point.
I've had Zs values on TT installs that fall easily within the TN bracket and would suggest that an RCD would not be required to meet disconnection times, but if these parallel paths were to be removed then obviously the tiny earth fault currents would not disconnect at any time. So how significant is a measured Zs in this instance?
Remembering Im talking about RCD protected TT install here
you had them sharpened ready to savage the next Electrical Trainee that asks a stupid question?A good answer By Sintra and a proper way to verify, Sorry I have been away, just got back from the Dentist
You still need to consider overcurrent protection as well as an RCD M8, which is something I think you mentioned somewhere. To be honest we are so far off the original question now I may even be wrong about that HAHAWe are getting there slowly. But I think you see what I mean now all ---
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