r1/r2 and ze dont measure up?

[jam2020]

ive just tested a 16a radial socket circuit. r1+r2 was 0.14 ze was 0.2 but measured zs was 0.74. am i right in thinking this is to high? why would i get this figure?

 

[johnboy6083]

bad connection in the board?

 

[jam2020]

sound connections through out,even with bonding/parralell paths involved the reading should only be 0.16 or slighty more?

 

[Jimmy Boy]

Did you IR the cables ?

 

[jam2020]

all greater than 299 on my brand new megger. what value zs would you accept if you were testing?

 

[Jimmy Boy]

I take it you did the Zs using plug top method at last point at radial ? Check connections at board and back of socket(s) or measure it with probes on the back of socket see if the same (Don't forget your safety specs)..
0h and was this a hard test or a soft test ?

 

[jam2020]

yes measured zs with plug adaptor, what reading would you be looking for steve? also why will ze=r1+r2 never really give an accurate reading? thanks for all your help im quite new to the testing side of things and classroom learning and on the job situations are a bit different!!

 

[SimpleSimon]

Any substantial part of the cable going through any insulation or temperature change?

 

[telectrix]

reading is well below max. allowed for 32A MCB. acceptable. if you test on no trip for Zs and high current for Ze, that could be the reason. still poss poor connection. terminal screw thru insulation? try other sockets. if you get big difference between 2 sockets, that,s where to look for bad connection

 

[jam2020]

no its a 6m run clipped to joists under floor,no insulation anywhere near it, im going to go back and retest it as its playing on my mind now and i want to sleep tonight!

 

[keniff]

I wouldn't worry about this at all, u will never get a calculated answer bang on when u use your megger, especially if it's on no trip, u can be up to 2.87 ohms on a 16 amp mcb so u have a good reading, also just make sure u zero ur leads out?

 

[nickblake]

As keith says 2.87 is Max Zs , what could be causing the high reading is a worn socket outlet you may never get the perfect readings

 

[beaver74]

I have just today had this
tested ZE live side of RCD then load side and there was a differance of .40 ohms
this would explain it

 

[tomxhug]

possibly bad connection with your plug top adapter, either the leads on the Socket outlet?

 

[jam2020]

cheers lads, im planning on using it for an niceic assessment so probably being a bit over cautious,as i say megger is brand new so perhaps it is the no trip/high settings. ill have a play with it tommorow on another installation and see where i go. thanks again