rcbo on ring circuit

[coxy84]

iv got a 32 type b rcbo covering a socket ring circuit with 12 points on it. its a tns system.
it on a run of about 45metres

my problem is i cant seem to get it trip within the acceptable time.

1x 198ms 5x way above 40ms

iv replace it with another unit thinking the rcbo was faulty but im getting pretty much the same results.

any idea's?

 

[nick611]

the length of circuit will make no differance.test from the top of the rcbo at the board.try on a rcbo you know is ok to check your tester

 

[coxy84]

yeh iv done both still seem to get the same readings

 

[IQ Electrical]

yeh iv done both still seem to get the same readings

Got to be a faulty batch then?

 

[telectrix]

so the next move is to test with a different tester. it's got to be one or the other, RCBO or the tester.

 

[Deleted member 9648]

Make sure all loads are disconnected from the circuit and it will trip within the limits.

 

[Paul.M]

Could it be time to change the batter in your tester? Think I saw a post last month just like this one.

 

[coxy84]

thanks guys.
the same rcbo tested fine on another circuit.
my new fluke 1653b will be here tommorrow so will see if that makes a difference, ill also disconnect the loads.

 

[Deleted member 9648]

If there were loads on when you tested that'll almost cerytainly be the reason....anything with a capacitor..(fridge...fluorescent light etc) will hold a charge when the power is interrupted,your meter is fooled into giving a higher trip time.....Disconnect all loads and it'll be ok.

 

[coxy84]

If there were loads on when you tested that'll almost cerytainly be the reason....anything with a capacitor..(fridge...fluorescent light etc) will hold a charge when the power is interrupted,your meter is fooled into giving a higher trip time.....Disconnect all loads and it'll be ok.

cheers!
there might have been a fridge pluged in i will check tommorrow!

 

[GONK43]

I had the same results with my Fluke 1652 on a smoke detector circuit, but no loads were on the circuit, just the base plates and the wiring. Used a different tester and got same results, so changed RCBO and got the same results again.

x1 310
x5 50m/s

Disconnected wiring at board, tightened screws on load outlets and re tested. Times were OK. Reconnected wiring, and hey presto, the same bad results as above. Checked wiring, only 2 detectors on circuit, all OK.

I have no idea what to do next!

Did not see any magic wands in the wholesaler! Going to change batteries in tester and see what happens.

Gonk43

 

[tony mc]

Trying to get my head round this but no matter what load is on the cct its the RCBO tripping time thats being tested ,if ramp tested yes the leakage would bring it down the mA reading so I would go with faulty RCBOS or something stupid like a damaged earth fly lead.

Try connecting the RCBO to another cct and do a series of tests not just a couple and see if there are any big variations with the results.

If when loads are connected to the cct and the tripping time does not come within the regs then its got to be a fail as its not doing the job its their for IMO.

 

[Gordon]

I usually test rcd's & rcbo's at the board, remove the live conductor from the rcbo, connect to live terminal at the rcbo & test, it guarantees no load when testing, Test rcd's the same way switch off all but 1 mcb then test sdame way as rcbo. I use a megger 1552 as it will do 2 lead RCD testing.

 

[Deleted member 9648]

Trying to get my head round this but no matter what load is on the cct its the RCBO tripping time thats being tested ,if ramp tested yes the leakage would bring it down the mA reading so I would go with faulty RCBOS or something stupid like a damaged earth fly lead.

Try connecting the RCBO to another cct and do a series of tests not just a couple and see if there are any big variations with the results.

If when loads are connected to the cct and the tripping time does not come within the regs then its got to be a fail as its not doing the job its their for IMO.

Not the case,although I can see where you are coming from.....a load is likely to increase the tripping time,so the RCd has to be tested with no load. The usual reason is a load with a capacitor,this holds a charge for a split second after the tester trips the RCD,the tester may pick up this charge and be fooled into giving a higher trip time. On my tester you can actually see the display figures rolling for a fraction of a second after you've heard the click of the rcd tripping.

 

[tony mc]

Thanks wirepuller understand what your saying.

He states the loads on the cct were disconected so would a couple of smokes give false readings.