Bi directional rcd testing

Newfutile said:

I have not fitted many type B and have only done the required test in BS7671 (testing as an AC type).

Testing at ½I_Δn and I_Δn (0° and 180°) as a type AC is all that you are required to do.

GN3 (pp 96 and 97) explains that further tests are intended, "for fault-finding and similar purposes only". This is because, "RCDs are only rated for a finite number of operations".

Im aware of what GN3 advises on (RCD) Residual Current Device testing ,though i would make the point that hager rate the CDA 240T rcd at a minimum of 2000 electrical operations.

the data sheet says:

Endurance

Electric endurance in number of cycles 2000

Number of mechanical operations 4000

even if the test button is pressed every 6 months and 2 more operations via rcd testing every 5 years in our rental properties it will take a while to wear out.

in any case my point is about the rcd that will trip on the supply side as the article states, i can see how this would work especially with neutral and earth joined  at the service head.

Newfutile said:

the data sheet says:

Endurance

Electric endurance in number of cycles 2000

Number of mechanical operations 4000

That is twice the minimum specified in BS EN 61008.

I agree that GN3 is perhaps being a bit pessimistic. Even if an RCCB is operated 20 times per year, it would still take at least 100 years to wear out.

Chris Pearson said:

That is twice the minimum specified in BS EN 61008.

Is it? I don't think the actual number of cycles the RCD has to meet in service is specified, only the numbers of cycles that are tested during type tests.

In BS 61008-1:2012+A12:2017, the current UK designated standard, the total number of cycles tested during type test is 4000 mechanical and 2000 electrical for devices with nominal (load) current rating up to 25 A, and 3000 mechanical and 1000 electrical for devices with nominal (load) current rating exceeding 25 A?

Chris Pearson said:

I agree that GN3 is perhaps being a bit pessimistic. Even if an RCCB is operated 20 times per year, it would still take at least 100 years to wear out.

Some RCDs are used in installations that have more frequent inspection and test periods than one year. The shortest periods between formal inspection and testing quoted in Table 3.2 of IET Guidance Note 3: Inspection and Testing are, effectively:

• 3 months for construction sites, although it's reasonable to expect a "test button" check before each use if an RCBO is used for each socket-outlet on a site distro board (which could be multiple times per day, but to be pragmatic, say 20 times per week). For a Type A, if we do full tests, that would be a minimum of 4x4=16 operations per for formal I&T, 50x20=1000 operations per year for routine check before use (assuming a 2-week shutdown) ... might just bring this in at under 4 years usage. For devices rated above 25 A nominal current, this drops to under 3 years. C
  Pragmatically, these periods of a small number of years might be OK for some sites, but site distro boxes to get reused, and no-one keeps a log of exactly how many trips have been made in the mean-time. 
  
  
• 'Each hire' for mobile and transportable units. this could be weekly ... certainly multiple times per year. Again, falls far short of 100 years.

In a workshop environment, where SRCDs are used, they might well be manually tested each day... so similarly, we're looking at 4 years of mechanical operations for devices with nominal current rating not exceeding 25 A, similar to a construction site, without any additional tests for periodic inspection and testing.

gkenyon said:

Is it? I don't think the actual number of cycles the RCD has to meet in service is specified, only the numbers of cycles that are tested during type tests.

Fair point. Some RCCBs might last well beyond the type test.

gkenyon said:

In BS 61008-1:2012+A12:2017, the current UK designated standard, the total number of cycles tested during type test is 4000 mechanical and 2000 electrical for devices with nominal (load) current rating up to 25 A, and 3000 mechanical and 1000 electrical for devices with nominal (load) current rating exceeding 25 A?

Not sure how you get that. For the 40 A device which Newfutile mentioned, there are 1000 mechanical operations; 500 each for test button and test rig = 1000 (presumably these count as electrical cycles); and a further 1000 mechanical. So 2000 mechanical + 1000 electrical.

Chris Pearson said:

Not sure how you get that. For the 40 A device which Newfutile mentioned, there are 1000 mechanical operations; 500 each for test button and test rig = 1000 (presumably these count as electrical cycles); and a further 1000 mechanical. So 2000 mechanical + 1000 electrical.

Surely the electrical tests are also mechanical tests, as they require manual opening and closing, or manual closing plus test button opening ... still exercises the mechanics.

So, I get first part of the test (under load), 2000 electrical+mechanical plus second part of the test (mechanical only) 1000 mechanical, totalling 3000 mechanical + 2000 electrical. (apologies for the typo 1000 should have been 2000):

In BS 61008-1:2012+A12:2017, the current UK designated standard, the total number of cycles tested during type test is 4000 mechanical and 2000 electrical for devices with nominal (load) current rating up to 25 A, and 3000 mechanical and 2000 electrical for devices with nominal (load) current rating exceeding 25 A?

Chris Pearson said:

Not sure how you get that. For the 40 A device which Newfutile mentioned, there are 1000 mechanical operations; 500 each for test button and test rig = 1000 (presumably these count as electrical cycles); and a further 1000 mechanical. So 2000 mechanical + 1000 electrical.

Surely the electrical tests are also mechanical tests, as they require manual opening and closing, or manual closing plus test button opening ... still exercises the mechanics.

So, I get first part of the test (under load), 2000 electrical+mechanical plus second part of the test (mechanical only) 1000 mechanical, totalling 3000 mechanical + 2000 electrical. (apologies for the typo 1000 should have been 2000):

In BS 61008-1:2012+A12:2017, the current UK designated standard, the total number of cycles tested during type test is 4000 mechanical and 2000 electrical for devices with nominal (load) current rating up to 25 A, and 3000 mechanical and 2000 electrical for devices with nominal (load) current rating exceeding 25 A?