Socket Zs High

[AdieB]

I have a supply in a log cabin, in the cabin is 6 double sockets and a couple of lights. Cables are in PVC conduit and are 2.5mm singles sockets and 1.5mm lights.

Sockets

L-L = 0.15 ohms
N-N = 0.15 ohms
E-E = 0.18 ohms
L1 with E2 & L2 with E1 = 0.07 ohms

L to E = >1000+ MG Ohms
N to E = >1000+ MG Ohms
L to N = >1000+ MG Ohms

Ze at board is 0.28 ohms 843 Amps.

Tested at socket Uc Rl 20 Amp 60898 type B

Socket 1 1.62 ohms 50V 0.04 V
Socket 2 1.29 ohms 50V 0.03 V
Socket 3 1.65 ohms 50V 0.05 V
Socket 4 1.62 ohms 50V 0.04 V
Socket 5 1.52 ohms 50V 0.04 V
Socket 6 2.12 ohms 50V 0.04 V Zs value to high.

This socket is approximately 300mm through a wall away from another socket. Only difference is that it is a waterproof socket with a neon indication. I have tried inserting the plug in and out numerous times in case of bad contact. I have taken the reading from the rear of the socket across the terminals and still the same problem. I am trying to come up with a reason for this.

Could change the mcb for 16A, but still can’t find the reason why it should be different than the others.

Any ideas?

Adie

 

[telectrix]

take a reading at the outgoing side of the MCB. the difference between the reading you get and the Ze is internal res. of MCB.

 

[i=p/u]

get cabin to -267 degrees then youl have a super conductor and should disconnect in time

 

[JUD]

What makes you think it's too high.

Max Zs on a B20 60898 is 2.3Ω

 

[spark 68]

I make it max 1.84

0.8 *2.3 , for temperature correction

 

[JUD]

I make it max 1.84

0.8 *2.3 , for temperature correction

Just realized that. :13:

**NOTE TO SELF** Think before you post

 

[spark 68]

Could it be due to tarnished connections on the outside socket ?

Is the outside socket part of the ring, or a spur ?

The other readings in your post look to be correct.

Sockets

L-L = 0.15 ohms
N-N = 0.15 ohms
E-E = 0.18 ohms
L1 with E2 & L2 with E1 = 0.07 ohms

Are you using the no trip setting (live test), or (R1+R2) (dead test) at the S/O's ?

 

[yellowvanman]

As its a socket should be on a RCD anyway, in which case Zs up to 1667ohms.

 

[AdieB]

Reading taken from green on site guide table B6 page 119

 

[spark 68]

As its a socket should be on a RCD anyway, in which case Zs up to 1667ohms.

I had thought about that too, but it should still be investigated for the higher reading, as you should not use the RCD as an 'excuse' for poor readings, I agree though it will mitigate an expected higher reading.

 

[i=p/u]

could be a spur, rcd , bigger cable, change mcb

 

[i=p/u]

could be A TT

 

[telectrix]

i tend to disagree with the osg figures. why? because that 0.8 factor assumes that the cable will be loaded enough to run at it's rated operating temp. of 70deg. that situation, in a domestic environment is as rare as rocking horse poo.

 

[JUD]

I have a supply in a log cabin, in the cabin is 6 double sockets and a couple of lights. Cables are in PVC conduit and are 2.5mm singles sockets and 1.5mm lights.

Sockets

L-L = 0.15 ohms
N-N = 0.15 ohms
E-E = 0.18 ohms
L1 with E2 & L2 with E1 = 0.07 ohms

L to E = >1000+ MG Ohms
N to E = >1000+ MG Ohms
L to N = >1000+ MG Ohms

Ze at board is 0.28 ohms 843 Amps.

Tested at socket Uc Rl 20 Amp 60898 type B

Socket 1 1.62 ohms 50V 0.04 V
Socket 2 1.29 ohms 50V 0.03 V
Socket 3 1.65 ohms 50V 0.05 V
Socket 4 1.62 ohms 50V 0.04 V
Socket 5 1.52 ohms 50V 0.04 V
Socket 6 2.12 ohms 50V 0.04 V Zs value to high.

This socket is approximately 300mm through a wall away from another socket. Only difference is that it is a waterproof socket with a neon indication. I have tried inserting the plug in and out numerous times in case of bad contact. I have taken the reading from the rear of the socket across the terminals and still the same problem. I am trying to come up with a reason for this.

Could change the mcb for 16A, but still can’t find the reason why it should be different than the others.

Any ideas?

Adie

Are you getting this reading at each socket or is that just what you get at the connections at the DB??

 

[i=p/u]

ther is a a sum to work it out as tel said its on the side of safety

 

[AdieB]

Sorry tried to edit my last post but it did not appear.

The socket is part of the ring circuit. The cabling is exactly the same on all sockets. It is a TNC-s system, I pushed the plug of the tester in and out numerious times so hopefully no tarnished connections. I also took reading from rear of socket. The DB is a MCG fuseboard with a 2P6330 RCD and 2 x 60898 mcb’s 1x 20Amp 1 x 6Amp. What is the table or reg that says about rcd controlled socket can be 1667 ohms.

 

[Geoffsd]

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)

 

[telectrix]

table 41.5, p50 in the red book. not sure where in bgb.

 

[spark 68]

pushed the plug of the tester in and out numerious times so hopefully no tarnished connections

I meant where the cables terminate in the back of the SO too, as your end to end readings were ok.

What is the table or reg that says about rcd controlled socket can be 1667 ohms.

Table 41.5 (BGB) p57.

It actually says anything above 200 may be unstable wrt Earth rods.

Edit: Tel beat me to it, again! lol

 

[johnboy6083]

the 1667Ω figure is for earth faults, and not for live-n faults. I would carry out a Zp-n, which means that you test between live and neutral, not live and earth. If your using a fluke, its just a case of swapping the leads over, but if its a megger, then youll have to use the probes. If this comes up ok, then youve identified that it is indeed a problem with the earth path, and not the live. If it comes up bad, then it means that you have problems wiuth either your live or neutral.