RCBO Testing

[a1spark]

Hi ! I wonder if anyone has any ideas on this one.................When testing for x1 and x5 trip times on RCBOs I have on more than one occasion [ in fact several ] obtained exactly the same readings for both tests [even on the 180 degree test ]....I have never had this problem with D.P RCDs.....Do RCBOs trip in the same time span regardless of whether it is 30Ma or 150Ma test current ???

...I Dont think it was down to faulty RCBOs. and My test Meters are Spot On !

...Am I missing something Here. ......Help would be greatly appreciated !

a1spark

 

[Andy™]

just because they trip in the same time doesnt mean its a problem. as long as readings are within limits, there OK

 

[a1spark]

just because they trip in the same time doesnt mean its a problem. as long as readings are within limits, there OK

Yes I realise what your saying , but whats puzzelling me is why they trip in exactly the same time and why it never happens on D.P RCDs?????

..Any clues ?

 

[wozz]

Im sure this was discussed recently, i think it was concluded that RCBOs work slightly differently than RCDs if i remember correctly?

I often find RCBOs that trip faster on 1I than 5I.

 

[a1spark]

I didnt catch that discussion Wozz..ive only just rejoined the forum after a short time away from it.

I Know the RCBO uses the flying lead as a reference point,but I would be interested in knowing their tripping characteristics in relation to x1 and x5 test currents...I suppose I could always contact the manufactures Technical Department for guidance...Ha ! Ha!

a1spark

 

[Andy™]

Yes I realise what your saying , but whats puzzelling me is why they trip in exactly the same time and why it never happens on D.P RCDs?????..Any clues ?

i have no idea why its like this, it just is. one of those strange things in life you will never get the answer to. until patch arrives, that is!

 

[Revved Up Sparky]

I've resurrected this thread as I am a little puzzled after testing some RCBO's in two domestic properties yesterday. They were both TT earthing systems, one with a good low Ze (17.8 ohms) and the other with a high Ze (430 ohms.)

Both the RCBO's were 60A 30mA and protected the whole installation.

They passed on the x1 (30mA) test with 21ms and 35ms respectively but when I did the x5 (150mA) test, the RCBO tripped off but my multi-tester gave an error report.

I have been racking my brains as to why the RCBO successfully tripped within the correct tripping time on x1 but failed on x5.

For years I have been inspecting and testing and if I got a faulty RCBO it usually failed on x1 but sometimes tripped on x5.

Any thoughts on what could be causing this to happen gratefully appreciated.

Best Regards

Tim

 

[Andy™]

what was the error it gave? and what test kit are you using?

 

[a1spark]

Hi Tim,

I posted the original thread you refer to.. .ive since been advised [hopefully correctly] ,that rcbos use Electronics to derive their means of actuator tripping from the incoming supply as opposed to an RCD deriving it directly from the Earth Fault imbalance path......this results in the rcbo tripping the same on x1 and x5 tests......hope this makes sense

In reply to your point about your meter displaying an error report on the x5 test.......what does your meter manual describe this as being an indicator of ?

...Have you checked all connections at the supply...the earthing points and your meter ?

One further point is that you state the installations are TT and the rcbos protect the whole installations...is there a D.P. main switch upstream of them or are they D.P...cos Neutral conductors require breaking for effective Isolation on a TT system.

hope that helps.

a1spark

 

[Revved Up Sparky]

Thanks for your input guys, I really appreciate it and sorry I've been away for a while- I've been busy lol.

My multi-tester is a Megger MFT1052 and seems quite a nice piece of kit.

I cannot remember the exact error message but it was something simple like 'error' or 'fail'.

With regard to the property with the 430 ohm Ze, I went back to that house and hammered in two more rods reducing the Ze to 60 ohms. After doing this I did another RCD test which gave me 40 ms for x1 and 45 ms for x5. 45ms is still a fail for x5 of course but at least I got a reading this time ! B-)

Thanks again

Best regards

Tim

 

[Evans Electric]

I know this doesn't help but I dislike RCBOs (a) Because they fill up the board and (B) Both my impedence testers trip the bloody things out and I am not prepared to buy a third one!!! I was told it is because RCBOs are single pole , never followed it up , just fit regular RCDs now.

The electronic explanation is interesting though.

Suggest A1 asks the Tech . Dept. at his Scam provider.

 

[a1spark]

Hi Evvo .

Thats a strange one about your loop tester tripping the RCBOs out...cant say ive ever had that problem apart from the usual 6A B type

loop trip issue.

As for asking the NICEIC for some Tech info on RCBOs...lifes too short to waist it hanging on the line waiting for them to pick the phone up !

:z I Will try and make enquiries elswhere and let you know if I come across any further info...

 

[batty]

Hi Evvo .Thats a strange one about your loop tester tripping the RCBOs out...cant say ive ever had that problem apart from the usual 6A B type

loop trip issue.

As for asking the NICEIC for some Tech info on RCBOs...lifes too short to waist it hanging on the line waiting for them to pick the phone up !

:z I Will try and make enquiries elswhere and let you know if I come across any further info...

It will be because they put a 25 amp current down line when loop testing. Most mft now only put a small current down line when testing but they are not as accurate as the old testers but they don't trip Rcbo's.

Batty