Socket Zs High

[lister]

"I think you must agree, that if 6A a breaker will trip with a 7A fault current(CPC-L), then it surely will trip with a 8A current short circuit(L-N)."

Will it?????
ever???
in 0.4s ??

 

[Moses]

Check the cable terminals are nice and tight at both ends going to the suspect socket.

If cable long enough, re-strip and make new terminations.

Now measure Zs at both ends of the cable.

If the cable is only 300mm, replace cable and there should be un-measurable difference in Zs at both ends.

 

[JUD]

Am I missing something?

Shouldn't the reading be 0.35 (or even less with parallel paths) at all the sockets?


1666 ensures the RCD will disconnect before voltage rises above 50V.
It should not be used to ignore maximum Zs values - unless unavoidable (e.g. TT)

Totally agree, should be getting a Zs of around 0.35ohms at each socket outlet. Sounds like a loose connection at one of the sockets.....

Not true!!!

R1+R2 should be the same at each socket outlet. Zs will increase towards the middle of the ring and decrease back towards the DB therefore you will get a reading of around 0.35Ω near the middle of the ring.

 

[GLENNSPARK]

Thank god we r on the same page

I agree with your comment of a Hi z on the N wire.

But that's another reason why Zs is measured between L-CPC, it ensures the earth fault durations are limited.

high Z...well that`s changed then....a minure ago it was Zs....

 

[Jonny66]

Not true!!!

R1+R2 should be the same at each socket outlet. Zs will increase towards the middle of the ring and decrease back towards the DB therefore you will get a reading of around 0.35Ω near the middle of the ring.

Agreed to a point (Hence "around" 0.35ohms)
I believe the ring in question is fairly small and the figures the op states seem way off by 1 and a bit ohms....seems alot to me, especially as he states these sockets are all on the ring final and not spurs.

 

[Moses]

"I think you must agree, that if 6A a breaker will trip with a 7A fault current(CPC-L), then it surely will trip with a 8A current short circuit(L-N)."

Will it?????
ever???
in 0.4s ??

Geoff, my friend, Zs is the impedance of the circuit, and not a current.

Lister, my friend, a 6A type B CB will trip in 0.4Sec with a minimum of 30A current. 7A & 8A were given as examples.

There fore 230V/30A = 7.67 Ohms is the theoretical max Zs for a 6A type B CB.

 

[Moses]

Originally Posted by Moses
Thank god we r on the same page

I agree with your comment of a Hi z on the N wire.

But that's another reason why Zs is measured between L-CPC, it ensures the earth fault durations are limited.



high Z...well that`s changed then....a minure ago it was Zs....


Yes but no, but yes but no, but yes but no Glenn

That Hi Z on the N wire is a fault, faulty connection.!!!!!!!!

 

[Moses]

Agreed to a point (Hence "around" 0.35ohms)
I believe the ring in question is fairly small and the figures the op states seem way off by 1 and a bit ohms....seems alot to me, especially as he states these sockets are all on the ring final and not spurs.

Sipmles he has not zeeored

or

he has a low battery

or

He has a faulty meter

 

[Jonny66]

Points to something along those lines agreed....where is the OP????

 

[Moses]

Points to something along those lines agreed....where is the OP????

Well confused by now i bet!!!!!:laugh3::laugh3::laugh3:

 

[GLENNSPARK]

Sipmles he has not zeeored

or

he has a low battery

or

He has a faulty meter

so if he hasn`t `zeeored`...or the batterys are low....hmm, so its a faulty meter then is it Moses?....possibly...but rather than just condemn the meter..would you not check the leads first?....

 

[Guitarist]

I had to send my Megger 1730 back a couple of weeks ago because the EFLI test at a socket (using plug adaptor OR on the terminals) was way higher than I was expecting. As has been said, it can be the internal resistance of the MCB/RCD so that would have to be deducted.
All that said, once I got my new 1730 and did the same tests, they were very close to Ze+(R1+R2), so it was definitely a faulty tester in my case.

Edit... Forgot to add. I have to do a 3-wire no-trip test, as the 2-wire is always at least 0.5 ohms higher!

 

[GLENNSPARK]

but my point was you dont just condemn the meter....its only as good as the test leads you are using....

 

[Guitarist]

but my point was you dont just condemn the meter....its only as good as the test leads you are using....

Totally agree mate.

 

[Geoffsd]

Sorry for delay - something crashed.

Geoff, my friend, Zs is the impedance of the circuit, and not a current.

Yes, I'm sorry. I should have written -

But that's what Zs IS ​- a measured value to determine prospective earth fault cuurrent

The same test between L & N is to determine the prospective short circuit current.

The greater of these two is the prospective fault current.