VIRTUAL ELEX SHOW IET PRESENTATION

How about this to cover both subjects...


Say I'm asked to install an EV charge point on a private rented property - so the landlord has asked that my design has to comply with BS 7671:2018 to comply with the requirements of the The Electrical Safety Standards in the Private Rented Sector (England) Regulations 2020 . Is it permitted to use the PME earth and one of the latest charge points that attempts to detect a broken PEN by monitoring L-N voltage rather than an electrode (option iv of 722.411.4.1) as that option was only introduced BS 7671:2018+AMD1:2020?


  - Andy.

I’m not sure that’s a fair question to be asking the IET, AJ. They can’t be responsible for how legal documents are framed.

However, your question does raise a point about accepting the safety of using 722.411.4.1 (iv) as a stand-alone measure to counter open pen conditions. I am unsure as to how or when the IET arrived at the conclusion that voltage measurement could be regarded as acceptable. A wide ranging test commissioned by Myenergi showed that out of 10000 open pen situations 10% resulted in dangerous voltages from car to ground that would not have been detected by voltage measurement only. 

I will endeavour to dig up the reference.

edit to add the obvious: should 722.411.4.1(iv) be reviewed in light of this test.

No testing is required to achieve the 10 % figure - in fact, a slightly "worse" figure of 10.3 % can be obtained from phasor-space geometry ... the question to answer, is "Is that the whole story?"?


Perhaps also worth pointing out that a number of other organisations are involved in BS 7671, the IET representation is a small portion of the committee involved in BS 7671.

I’m not sure that’s a fair question to be asking the IET, AJ. They can’t be responsible for how legal documents are framed.

But given the existance of regulation 114 (and possibly 115) I don't think it's unreasonable for the IET to be able to provide us with some proper guidance.

 

A wide ranging test commissioned by Myenergi showed that out of 10000 open pen situations 10% resulted in dangerous voltages from car to ground that would not have been detected by voltage measurement only.

To play devil's advocate, I might obsever that only a little worse than the 7% failure rate for RCDs (including those in TT systems that are totally relied upon for ADS).

 

"Is that the whole story?"

Is that a suggestion that the N voltage during a broken PEN event isn't likely to stable - rather than just being a single voltage for the duration it's more likely to be bouncing all over the place - so quite likely to be outside of that "10%" sooner or later, and as long as the device latches off and requires a manual reset, is likely to detect most events, if with a small extra delay.


   - Andy.

Andy, the question about the version of standards reference in legislation and guidance has been asked - and answered - time and again.


The latest version of the standard is used.


It's no different to ESQCR referencing "British Standard requirements" in Regulations 21 and 22, where in the same legislation defines that term as meaning (according to the last Amendment in 2012) is BS 7671:2008 ? ... yet all of the industry guidance, including DCode documents which are effectively "requirements" are happily hoofing along with the 18th Edition ...


BS 5839-6 now has Amendment 1:2020. I'm sure no-one will worry that AD-B refers to BS 5839-6:2019, and no-one will rush to update it.

AJJewsbury:

 

A wide ranging test commissioned by Myenergi showed that out of 10000 open pen situations 10% resulted in dangerous voltages from car to ground that would not have been detected by voltage measurement only.

To play devil's advocate, I might obsever that only a little worse than the 7% failure rate for RCDs (including those in TT systems that are totally relied upon for ADS).

 

And when viewed with the 5 s disconnection time permissible in some cases, or 2 s for TT, and the fact that protection against electric shock isn't guaranteed for a percentage of adults anyway ....

"Is that the whole story?"

Is that a suggestion that the N voltage during a broken PEN event isn't likely to stable - rather than just being a single voltage for the duration it's more likely to be bouncing all over the place - so quite likely to be outside of that "10%" sooner or later, and as long as the device latches off and requires a manual reset, is likely to detect most events, if with a small extra delay.


   - Andy.

Yes, very perceptive. That's definitely part of the story.

I thought I would bump this to the top just in case anyone else had any burning questions they would like to ask?


JP

I got one John. Considering that in urban areas, in what may appear to be TNS installations,  external network connections may combine the earth and neutral. Would it make sense to err on the safe side and install as if it was PME? Unless of course it could be guaranteed by the DNO that the system was TNS and would stay that way.

Given the above, are the IET planning to update their guidance?

How about guidance on testing the different types of RCDs? 


How

when it’s important

what readings to expect on DC and AC earth leakage; do these produce different expected trip times and what are the limits fit the DC part?

"The downside is no free bacon roll I am sorry to say!"   ??? 100 free pens??? .


Oh well I guess it`s still a good day out though. Can`t wait for the real thing!