High ring test results at socket outlets

[maudy]

Hi, I was wondering if you guys can help with some errant test results.

I'm testing a ring and i get
L-L = 0.41
N-N = 0.40
E-E = 0.63

Great

Figure 8 L-E = 1.0 ohms.

Still good

Figure 8 at each socket varies from 0.8 ohms to 1.1 ohms (I was expecting much lower)>

Oddly Zs = 0.23 (which is what I was expecting for both this and my R1-R2 [at socket] tests.

Any ideas?? System is TNS / Ze of 0.09

Maudy

 

[Octopus]

Think parallel paths.

 

[telectrix]

your fig.8 R1+R2 should approximate (r1+r2)/4 so your 1.0 ohms looks high. are you sure you have nulled leads for the R1+R2 readings?

 

[truckster]

deleted brain fart!

 

[maudy]

deleted brain fart!

???

you what

 

[Farmelectrics]

make sure you null leads are you on right legs of ring your fig 8 should be aprox 0.26 given the values you have given the reason the readings might be different at various points is possible spurs

 

[telectrix]

or crappy sockets.

 

[Farmelectrics]

true tel spent many an hour searcing for fault on cable in past for it to be a bad socket face good shout

 

[SirKit Breaker]

Or crappy test leads!

 

[brucelee]

check at terminals of outlets as i installed a load of mk sockets and readings at fron varied wildly
N terminals were hard work to screw down plastic seemed to be restricting it

ended up removing them all and replacing with BG

also as you say your reading increased was this to the mid point of the ring as you could have incorrectly identified the legs and not carried out cross connection correctly
your R1 +RN should be more like 0.2 and your R1 +R2 should be around 0.26ohms or within 0.05 ohms of each other so 1.0ohms to high

 

[jumpin jax]

How are you measuring your figure of eight? It sounds asthough you are disconnecting the cables from the sockets and measuring 2 end to ends as the results are your L-l and E-E added together

 

[maudy]

How are you measuring your figure of eight? It sounds asthough you are disconnecting the cables from the sockets and measuring 2 end to ends as the results are your L-l and E-E added together

Mhahaha

Yea - its wired in T&E so I wouldn't make that mistake.

It not that the socket readings start off low and get higher - they're all too high. Or as I suspect the figure 8 end to end (measured at the board) is too low. WHich makes me think Murdoch is right.

 

[jumpin jax]

Why would you do a figure of eight end to end?

 

[maudy]

Why would you do a figure of eight end to end?

You don't

Those are two separate tests

 

[Octopus]

How old are your tester leads?

 

[maudy]

How old are your tester leads?

Hmmm

Its a Megger 1552 (one of the last ones). So at least a couple of years old now.

I do have slight issues nulling them - but then I always found Meggers difficult to zero reliably. However in every other way, I dont dispute the test results that I get.

Have you experienced problems with old leads

 

[brucelee]

to check leads set MFT to continuity setting connect 1 lead to both connections of instrument and if the resistance is all over the shop the probably lead or the socket tube of the tester as this was happening with my megger MFT
did you register online and get 3 yr warranty if so contact megger and they replaced all my leads even the 13A 3 pin plug adapter lead
gave me new detachable probe tips better than the plastic ones that came with instrument and they calibrated all for free
i even got a new extra set as the green new lead was damaged so they sent me a extra set