MCCB Zs TO HIGH

[albi]

HI AGAIN
I HAVE 2 MCCB,s (moulded case circuit breakers ) RATED AT 120A AND 250A THE MAX Zs FOR THE DEVICES ARE 0.12 AND 0.09 MY PROBLEM IS THE Ze IS 0.24 AT THE DB. SO THERE IS MY PROBLEM AMY SUGGESTIONS WILL BE WELCOME

 

[Sparky Ninja]

Have you tried measuring the Zs? To see what effect any parallel paths may have on your readings.
Also, where did you obtain your max Zs info from?

 

[albi]

Yes tried parallel paths and at the main incomer Zs for MCCB was of the manufacturer

 

[ezzzekiel]

earthing arrangement is?

 

[albi]

the earthing arrangement is TNS

 

[DurhamSparky]

had this problem in a sheltered housing about 1 year ago when working with 3 Rivers housing!!

we changed 3 phase tails to 50mm and it dropped by 0.2ohm...!! end result was to remove the MCCB and insert a 250a tp&N isolator and we then changed all the MCB covering Socket outlets to 30Ma RCBO's big job and very costly but that was the way forward..!

 

[lamb]

Are you sure those Max Zs values are for 5secs disconnection? I commissioned a panel board today of Eaton MEM MCCBs 100A 25kA and the max Zs was 0.4something from manufacturers data