RCD trip curve

Humm. I presume the 2nd "Maximum operating times" in table 6E.2 should read "Minimum operating times". (so it's not just JPEL/64 that lacks a proof reader?)

I am interested on your take on verifying the stated requirements by  using alternate points on the curve

I guess in a way we're reliant on that theory anyway - a real earth fault current or actual shock through a person is highly unlikely to be exactly 1x I_Δn or 5x I_Δn (or 250mA if it's Hagar). Just because an RCD checks out OK at 30mA and 150mA what guarantee is there that it'll disconnect within 0.2s at several amps of earth fault? or within something sensible at 148mA? Unless we're going to undertake an almost infinite number of tests across the range from zero to perhaps several kA we've ultimately got to resort to reasonable interpolation - hopefully based on knowledge of the underlying design principles (e.g. there being nothing in mechanism design that should result in a longer delay for a larger residual current) - which I think boils down to trusting the manufacturer's specification and carrying out a few 'sanity checks' just to make sure the thing isn't completely wrecked.


   - Andy.

We had a long discussion about this in a thread just over 12 months ago: https://communities.theiet.org/discussions/viewtopic/1037/23532


I had a similar observation regarding some RCDs not always passing the 5x test after getting 1x well below 40 ms, and put together a table comparing the tests to the Initial Verification objectives in the 18th Ed:


 

RCD Residual current Rating

Tests, results and notes

10 mA

Conduct both 1x and 5x tests Record the 5x result. Verifies both additional protection to 643.7 and ADS to 643.7.1 b) for 0.2 s and 1 s disconnection. I would be able to demonstrate compliance with Regulation 411.3.2.4 and 411.3.2.1.

30 mA

Conduct both 1x and 5x tests. Requires loop impedance less than 1364 Ω if you take into account full volt drop Record the 5x result. Verifies both additional protection to 643.7 and ADS to 643.7.1 b) for 0.2 s and 1 s disconnection. I would be able to demonstrate compliance with Regulation 411.3.2.4 and 411.3.2.1. Whilst the full Zs of 1667 Ω presented in Table 41.5 wouldn't provide sufficient current for a 5x test with lower voltages, earth electrode resistance should be limited to 200 Ω so no issues anticipated

100 mA

Conduct both 1x and 5x tests. requires loop impedance less than 409 Ω if you take into account full volt drop Record the 5x result. Verifies ADS to 643.7.1 b) for 0.2 s and 1 s disconnection. I would be able to demonstrate compliance with Regulation 411.3.2.4 and 411.3.2.1. Whilst the full Zs of 500 Ω presented in Table 41.5 wouldn't provide sufficient current for a 5x test with lower voltages, earth electrode resistance should be limited to 200 Ω so no issues anticipated If you are asserting it's unsafe to test the RCD at 5x in domestic, then do and record the 1x, but now you only have verified disconnection at 1 s and compliance with 411.3.2.4, and therefore in domestic this RCD can only provide ADS for distribution circuits, and final circuits not covered by 411.3.2.2.

300 mA

Not practicable (or perhaps safe) to test at 5x, so we are limited here to testing at 1x. Record the 1x result. Verifies ADS to 643.7.1 b) for 1 s disconnection. I would be able to demonstrate compliance with Regulation 411.3.2.4, but not 411.3.2.1. This leads me to assert that the 300 mA RCD may only provide ADS for distribution circuits, and final circuits not covered by 411.3.2.2

500 mA

Not practicable (or perhaps safe) to test at 5x, so we are limited here to testing at 1x. Record the 1x result Verifies ADS to 643.7.1 b) for 1 s disconnection. I would be able to demonstrate compliance with Regulation 411.3.2.4, but not 411.3.2.1. This leads me to assert that the 500 mA RCD may only provide ADS for distribution circuits, and final circuits not covered by 411.3.2.2

100 mA Type S

Conduct both 1x and 5x tests. requires loop impedance less than 409 Ω if you take into account full volt drop Record the 5x result. Verifies ADS to 643.7.1 b) for 0.2 s and 1 s disconnection. I would be able to demonstrate compliance with Regulation 411.3.2.4 and 411.3.2.1. If you are asserting it's unsafe to test the RCD at 5x in domestic, then do and record the 1x, but now you only have verified disconnection at 1 s and compliance with 411.3.2.4, and therefore in domestic this RCD can only provide ADS for distribution circuits, and final circuits not covered by 411.3.2.2

300 mA Type S

Not practicable (or perhaps safe) to test at 5x, so we are limited here to testing at 1x. Record the 1x result. Verifies ADS to 643.7.1 b) for 1 s disconnection. I would be able to demonstrate compliance with Regulation 411.3.2.4, but not 411.3.2.1. This leads me to assert that the 300 mA Type S RCD may only provide ADS for distribution circuits, and final circuits not covered by 411.3.2.2

500 mA Type S

Not practicable (or perhaps safe) to test at 5x, so we are limited here to testing at 1x. Record the 1x result. Verifies ADS to 643.7.1 b) for 1 s disconnection. I would be able to demonstrate compliance with Regulation 411.3.2.4, but not 411.3.2.1. This leads me to assert that the 500 mA Type S RCD may only provide ADS for distribution circuits, and final circuits not covered by 411.3.2.2