Discuss BG RCBO ramp test on one of them shows trip at 15ma every other one is 24 ma in the UK Electrical Forum area at ElectriciansForums.net

T

The Ghost

So just did an EICR few problems mostly rectified. Customer wanted new CU so put in BG with RCBO just five circuits. Tests on EICR were fine except for high ohms on Zs for lighting first floor so tracking that down. All RCBO are fine except this one 32a ring final circuit. RFC tests all fine IR around 400 + Mohms. 10ma leakage with clamp on tails. So it was the end of a long day. Said I will replace the 32 rfc RCBO.
What really made me wonder is when the downstairs ring is used i.e. kettle on, the upstairs ring trips. I just can't right now formulate an approach to it. And I do seem to remember BG RCBO being quite often defective, is that true in your experience. My first thoughts were that there is some cross connection between the RFC, not that I picked that up on testing. Now I can assure you that I have not mixed up the RFC neutrals I triple wipple checked on that.
 
A little more info. The upstairs RCBO tripped when certain items were plugged in. With the ramp test showing the RCBO for up trips at 15ma which is very low, then plugging a newish tv in or lamp trips the RCBO. If I take them downstairs the RCBO for down does not trip. So I take that as the RCBO for up is defective. So replace it... But as I say what throws me is why would a separate circuit trip when an appliance is plugged into another circuit. Now there is one socket that is downstairs at the back of the house on an extension that comes from the upstairs RFC. I am thinking considering the lighting wiring that I had to re-do in the shower room (really bad wiring)
 
Tel has covered it really, if there is already a NE fault on the upstairs ring the RCBO is tripping when the leakage current and test current reach (say) 24mA but the leakage of (say) 9mA causes the test current to only read 15mA.
Previously posted diagram of NE fault causing RCD to trip, the fault is on the circuit that trips even if the load is on another circuit.
RCD Trip due to other side loading.jpg
 
The ramp test at which most are tripping at, 24ma is low. Manufacturers do not design a device to trip at 30ma and allow some leeway normally around 27ma.
 
Agree there's likely a cabling fault. Also, if rcbo is isolated from the circuit it should not trip at 50% of rated current, just saying :)
 
Wylex told me once, a 30mA RCD tripping at 21mA, was within design tolerances (circuits disconnected).
In fairness you don't need Wylex to tell you that the standard permits anything above half the rated residual operating current and not greater than the rated residual operating current. So I wouldn't have questioned it tripping at 21mA. In fact I never ramp test RCDs as the standard test sequence tells me what I need to know. (Other than perhaps to ascertain what leakage is being caused by connected appliances or something like that.)
 
In fairness you don't need Wylex to tell you that the standard permits anything above half the rated residual operating current and not greater than the rated residual operating current. So I wouldn't have questioned it tripping at 21mA. In fact I never ramp test RCDs as the standard test sequence tells me what I need to know. (Other than perhaps to ascertain what leakage is being caused by connected appliances or something like that.)

Twas contradicting a previous post :p
 
15mA with circuits connected or dissed
Hi just got back from work. Errm... circuit disconnected, I am not sure I understand what you are asking? Anyway nipped in to change the RCBO no change to the situation. So looks like get in and break the circuit down bit by bit. Needle in a haystack it seems like at the moment but anyway it's the weekend so maybe come Monday I'll have a vastly good idea. Sometimes works like that for me. Still stewing over @Richard Burns' post. I meant to phone kewtech to ask how the RCD function works exactly. i.e. does it discount existing leakage then give you an answer and so on. It may be the leakage of 10ma on the tails is all on the upstairs sockets. Will know more Monday anyway. Now for a rest.
 
Last edited by a moderator:
This is where you need an old style rcd tester so you skip the 1/2 × test, can't remember the last time I did this test:D
 

Reply to BG RCBO ramp test on one of them shows trip at 15ma every other one is 24 ma in the UK Electrical Forum area at ElectriciansForums.net

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