Slow rcbo times ??

[burntwire]

Hi,
Ive fitted a new fuse board, having RCBO's for some circuits (commercial) when I was doing the testing one of the RCBO's had a much higher disconnection time than all the rest, circuits all tested out fine, changed RCBO and still rubbish! Its MEM Eaton MCB with pod fitted. Any ideas why this is ?
TIA

 

[Spark123]

What were the times and at what current?
I have seen electronic RCDs take a bit longer than their mechanical counterparts at I. As long as they trip within 300mS at I (EN61009) and 40mS at 5I (30mA device max) then it is a pass (both + and - cycles).

 

[burntwire]

Its a 30ma, disconnection times are x5=40 and x1=125, when tested on old board was x1=146 and x5=22,

 

[Spark123]

They are still a pass, only just though
I take it that it was tested in isolation i.e. with the outgoing circuit disconnected?

 

[burntwire]

When I tried to test at the rcbo it would not trip, only when i plugged my tester in at the socket would it work, is this normal for RCBO's ?

 

[Spark123]

Nope, it should trip when you press the test button and when you connect a tester across the outgoing terminals and earth.

 

[burntwire]

mmm, I thought so but none of them tripped out this way and there are 5 fitted. Thought maybe it was due to being a pod set up.

 

[Spark123]

If none tripped when you pressed the test buttons then that is a fail
Was the Ze/Zs OK?

 

[burntwire]

Sorry, they all tripped when the test buttons were pressed but not when tested accross out-going, pfc = 0.23, ZE = 0.24

 

[rebuke]

I assume you definitely had a good earth connection at the board, as if for some reason whatever you clamped on to wasn't actually earthed, then your tester wouldn't be able to actually send any current away to test, which might explain the failure to trip (although I'd have thought most testers would tell you / refuse to test if this is the case)...

 

[burntwire]

ZS was 0.20, on old board was 0.55

 

[Spark123]

You were definately connected to both the L & N on the outgoing side of the RCBO and the earth rail in the CU?

 

[burntwire]

Yep earth connection was fine meter would have failed but double checked as well.

 

[burntwire]

100 %

 

[Spark123]

Outgoing wires disconnected?