RCD Test Failing

[deejay]

RCD test failing on a single outdoor double socket radial circuit (55.8ms on X5). All other tests ok (IR, R1+R2, ZS). Functional test of RCBO ok. Tried circuit on another RCBO and test still fails so not the RCBO.

Am I missing something obvious? Thanks

 

[James]

Is there something in the installation that may be injecting dc into the supply?

 

[Pretty Mouth]

RCD test failing on a single outdoor double socket radial circuit (55.8ms on X5). All other tests ok (IR, R1+R2, ZS). Functional test of RCBO ok. Tried circuit on another RCBO and test still fails so not the RCBO.

Am I missing something obvious? Thanks

Have you tried testing with the circuit conductors disconnected from the RCBO?

 

[deejay]

Have you tried testing with the circuit conductors disconnected from the RCBO?

Yes, it still fails the test with conductors removed. In fact, the issue is with 2 RCBOs on the same board now. Seems odd as they are brand new.

 

[Strima]

What make and type of RCBO? A/AC/B???

 

[davidjtown]

What make and type of RCBO? A/AC/B???

Hager Type A

 

[Sintra]

Hager recommend testing at the device not at the end of the circuit see this link https://hager.com/uk/support/regulations-18th-edition/updated-rccb-testing

 

[davidjtown]

Hager recommend testing at the device not at the end of the circuit see this link https://hager.com/uk/support/regulations-18th-edition/updated-rccb-testing

Thanks for that. The link seems to indicate RCCBs prior to July 2019?

 

[nicebutdim]

Thanks for that. The link seems to indicate RCCBs prior to July 2019?

Stock can take some time to filter through the supply chain.

 

[davidjtown]

Replaced the RCBOs with new ones and still having the same problem. Tried it at the socket (outdoor), and at the DB with the conductors disconnected. RCBO still failing for additional protection at 5X In (56ms).

Any ideas what could be causing this? Cheers

 

[Strima]

What do Hagar say about testing their RCDs?

 

[newfutile]

are you testing at more than 250 ma we have had hagar rcd’s that don’t meet the required 40ms at 150

 

[davidjtown]

are you testing at more than 250 ma we have had hagar rcd’s that don’t meet the required 40ms at 150

I’ve tested at 250ma and 300ma. Still having the same issue. The RCBOs pass the test when MFT is set to AC.

 

[timhoward]

This seems to explain the problem fairly well:

Are you already using 5 x 50ma ?

 

[Deleted account]

So when a product is faulty we alter the test parameters to ensure it passes?

not sure on the legalities of this.

the excuse is manufacturers instructions say to do this.

what takes priority b.s.7671 or manufacturers instructions?

if the manufacturers instructions are requiring a greater degree of protection or better disconnection time this is fine, but in this case it is not.

very naughty!

 

[Pretty Mouth]

So when a product is faulty we alter the test parameters to ensure it passes?

not sure on the legalities of this.

the excuse is manufacturers instructions say to do this.

what takes priority b.s.7671 or manufacturers instructions?

if the manufacturers instructions are requiring a greater degree of protection or better disconnection time this is fine, but in this case it is not.

very naughty!

Bizarrely, BS7671 seems to be telling us to do exactly this:

643.8
NOTE: Effectiveness is deemed to have been verified where an RCD meeting the requirements of Regulation 415.1.1 disconnects within 40 ms when tested at a current equal to or higher than five times its rated residual operating current.

That's 'or', not 'and'. Poorly written reg, or deliberate?

 

[Deleted account]

@Pretty Mouth well spotted.

I stand corrected, but am quite surprised at that.

 

[Pretty Mouth]

@Pretty Mouth well spotted.

I stand corrected, but am quite surprised at that.

It baffles me too. It seems that so long as it trips at any current => 150mA, all's well, but no need for it to trip at all at 30mA?

 

[westward10]

I believe Hager have addressed this but the Regulation quoted in #16 takes into the requirements of EN61008 which allows for ×5 and above.

 

[Julie.]

The issue isn't BS7671 nor the manufacturer's instructions, it's actually in bsen61008 and 61009 - the standards for the devices themselves, basically it has to operate above the set current (say 30mA), but does not have to do so within 40ms.

In addition, it must operate at 5x - OR at a figure declared by the manufacturer within 40ms.

BS7671 reflects this info poorly however.

So you must test to ensure an rcd or rcbo trips at its setting (typically 30mA), and in addition operates within 40ms at the figure declared by the manufacturer (typically 5x setting).

If it trips at 30mA within 40ms, actually there is no need to do a 5x - it's already passed!

Unfortunately those manufacturers who chose a different value than 5x as the trip time test current are finding loads of people claiming failures because they automatically test at 5x, of course the rcd is compliant (assuming it does trip in time at the correct test current), so it's becoming easier to change the product rather than deal with all the "false failures"

Normally instead of 150mA (5x) most chose 200mA as their test current for trip time.

I have a megger mft1731 which only does 5x so if I have to test a rcd/rcbo which has this 200mA value, I use the 30mA setting for trip operation, then the 40mA (operator set) setting at 5x for the trip time (unless it happens to pass at 150mA)

Hagar are 250mA.