rcbo and zs

[frankie310581]

Ze = 0.21

zdb = 0.27

r1+r2 = 0.31 COOKER

zs = 22.3

this was just one of the 18 circuits giving the same very high zs this i have been told by elecsa tec line is down to the rcbos

dont you think rcbos should come with a resistance value

our would a resistance test from one side of the line to the other side of line on the rcbo give you the right value to subtract from zs to give the right zs

 

[Manator]

I am having trouble understanding your readings, have you taken measurements with another tester to confirm these? The Zs can be effected by rcd and rcbo's but never to the extent that you have recorded. Measured Zs will always be lower than calculated, what was the x1 and x5 rcbo disconnection times?

 

[Revved Up Sparky]

Have you tried inserting an MCB for testing purposes ?

 

[frankie310581]

X1= 28.3 x5= 8.5

no other tester has been used but all circuits are the same

thay are dormen smith rcbos never used these before teaster is ok as teasted mcbs and had the right results

this one has got me

---------- Post Auto-Merged at 21:38 ---------- Previous post was made at 21:36 ----------

NOT GOT ONE IN MY BOX TRICS TO FIT

 

[Bane]

X1= 28.3 x5= 8.5no other tester has been used but all circuits are the same

thay are dormen smith rcbos never used these before teaster is ok as teasted mcbs and had the right results

this one has got me

So does this mean, "IT CAN NOT BE DONE"?

 

[frankie310581]

Lol in a way yes lol

but as above post elecsa said its ok and down to rcbos

do you have any ideas

 

[Manator]

It is a strange one this, the disconnection times would suggest a healthy route for faults to earth, which would suggest a much lower Zs than those you recorded, I would expect a lower resistance through any rcd or rcbo than that. If all the readings on the eight circuits are the same I would suspect the culprits to be the dormen smiths. Let us know if you solve this, looks very interesting.

 

[Megaohm7]

I've fitted Wylex rcbo's and never had a high Zs reading from them and the trip times were well in too both 1* and 5*. Your trip times are fine . Could be a problem with the rcbo itself ?

 

[frankie310581]

I WILL LET YOU NOW IT IS A STRANGE ONE

---------- Post Auto-Merged at 21:58 ---------- Previous post was made at 21:54 ----------

That is what i was thinking at first but all 11 circuits were the same all being rcbos very high zs readings

 

[Megaohm7]

Please do! It would be interesting to know when you get to the bottom of it. Good luck in the meantime..

 

[ADS]

Hi,

You could take the Zs reading across the RCBO.

If the reading you get is more realistic, then you could subtract this from your initial reading and find out exactly how much the RCBO is adding to the measurement.

It would also confirm, without doubt, that it is the RCBOs causing the problem and you could possibly take it up with the manufacturer.

---------- Post Auto-Merged at 22:16 ---------- Previous post was made at 22:11 ----------

our would a resistance test from one side of the line to the other side of line on the rcbo give you the right value to subtract from zs to give the right zs

The 'right Zs' is what you measure, mate.

You can't go deducting the impedance of items that form part of the circuit just to get your measurement down.

If there was an earth fault, then the RCBO would be in the circuit.....so the Zs is what it is.

 

[frankie310581]

I understand that but just trying to find out if there is a bad earth path our is the circuit if fine and it just the rcbo (pice of mind ) hope you get where we are coming from

 

[ADS]

I understand that but just trying to find out if there is a bad earth path our is the circuit if fine and it just the rcbo (pice of mind ) hope you get where we are coming from

Do what I suggest then -

Link out 'Line' and 'CPC' at furtherest point on circuit.

Main Switch 'closed', all RCBOs/MCBs 'open'.

Take Zs reading - one probe on incomming 'line' of circuit RCBO, the other probe on outgoing 'line' of circuit RCBO.

Deduct the reading that you get from your initial reading - this will tell you what impedance the RCBO is adding to the Zs.

 

[tom1]

lose connection, i was at a job the other day where the main switch was not clamped on the buss bar, the screw was fully open.

you could measure the resistance between the incoming and out going side of the rcbo.

 

[sellers]

+1

check connections to the busbar!

 

[Glospark]

Had the loose connection brfore too. I have also had higher readings on when testing Zs on a circuit with CPN RCDs fitted.

Never with decent makes though, tells us something about cheaper component maybe???