Some Special locations won't allow PME to be used.which I understand. However with EV charging points. We can overcome the PEN fault by automatic disconnection of supply is described in 722.411.4.1(iii).
So why can't we use the same logic in other locations. Where lost of supply doesn't in danager life or property.
Well, it is an interesting question, and one where pragmatism meets history and ideal engineering.
The only shock risk from a PEN fault is when metalwork connected to the PEN is simultaneously accessible as other metalwork at true earth (terra-firma) potential.
EVs greatly increase the no of locations where the PEN problem might arise, and is far less easy to control compared to the traditional prohibitions that are all fixed installation such as mobile telecom equipment, static caravan sites, farms and so forth, as those are very fixed and quite large with clear boundaries, whereas cars may be driven in at different angles,leads trailed into front gardens etc, making controlling access and accidental overlap with other earthing systems and things very tricky.
Until very recently the O-PEN sensing was not possible, and is very specific for the problems of the EV case.
For things where the aim is to keep the step voltage very low - e.g. dairy farms where cows are very sensitive, a far lower limit is desirable than that needed just for protection of life.
Also electrode-less PEN fault sensing relies on detecting the L-N voltage going wild during the fault. It is not perfect - there will be a range of conditions where the earth voltage rise may be dangerous without the LN voltage going far enough out of limits to guarantee the fault being detected.
It may well be that the same ideas could be extended into some areas of traditional prohibition, but it would need a bit of a sea change in mentality and a reversal of precedent.
Mike
Is there a BSEN or a letter of conformity or product standard for the Pen fault detector?
Also is there a defined way to test it?
Not yet.
The technology is best described as in development, and in general product standards can only follow after something is pretty much fully developed. Of course all equipment still has to meet all the usual LVD and EMC type safety stuff, but there is no standard for proof of PEN fault detection function.
To truly test it requires one to be able to fake a floating PEN, which one can do by interrupting the supply with a suitable transformer. As far as I know, apart from factory testing, no-one does this, it would not be an easy thing to do in the field.
Mike.
I wonder if the EVSE Code of Practice out in 2 weeks will still recommend the use of a Pen fault detector? I do think the concept is good but
without BSEN or a letter of conformity or product standard and without a defined way to test it seems rather counter intuitive. It seems that a BS EN for Pen fault detectors needs to be expedited as in effect it is a dependancy of the PEN fault detector.
Once this is in place (BS EN) the PEN fault detector can be
Designed, Selected and Errected
Installed
Comissioned
Tested
Signed off
and without a defined way to test it
The only protective device we do test with an independent instrument is an RCD.
Even RDC-DDs are not mandated to be tested by BS 7671.
Is there a BSEN or a letter of conformity or product standard
No product standard as yet, but the IET is working on one.
In terms of legislation, the manufacturer would have a DofC (Declaration of Conformity) regardless of whether the 'standards route' was used.
So why can't we use the same logic in other locations.
Which ones in particular?
There are some problems with PME in some special locations, that differ from the general "electric vehicle" approach.
Caravan sites - Section 708 - and Marinas and shore connections for inland navigation vessels - sections 709 and 730 - issue here is ESQCR prohibits distributor's PME earthing terminal being used (legal issue).
Caravans and Mobile & Transportable Units ... EV (usually on tarmac) different to caravans and mobile & transportable units on muddy fields.
Diverted neutral currents in water can be problematic at lower levels than those which would lead to touch voltages at 50 V AC or more on PEN conductors (as sometimes noted in swimming pools) being another reason why open-PEN (as set up for EV) may not be suitable there even if legislation permitted.
I'm just opening a debate and getting my head around the subject of automatic PEN disconnections.
Most of these the potential difference measured from an artificial/ calculated base voltage.why can't we make them measure the difference between the actual supply earth potential and the true earth potential. Once there is a harmful difference the supply could be disconnected including separating the different earth's. If there no supply or PME there's no path for the high true earth voltage to leak back In to the installation.
All I'm thinking is that we rely on a TT earning arrangement and hope the RCD protect us. Whilst still there could still be a high true voltage present. Which isn't been addressed. If there wasn't any power it would be looked into.
Sorry If I used the wrong terms. I'm just trying to get my head around it and looking for the future. Except places where supply is always needed.ie. Hospital's. Surely identifying the problem and solving it is better than copping with it.
Hope I'm making some sense in my maddness.looking forward to more educated thoughts.
Healthy engineering debate is always good. It is how we make things better
To truly test it requires one to be able to fake a floating PEN, which one can do by interrupting the supply with a suitable transformer.
It seems to me that the O-PEN relay is in essence some form of over/undervoltage protection relay. Could one therefore not use voltage sources akin to test devices used to test G59/99 relays? Not that they're cheap, but in principle the kit and procedures to do it in the field exist already.
I suppose one challenge in cases where it's integrated into a charge point might be encouraging the box to do the PEN test without a load (car) attached, but if the principle were sound and demand were there I'm sure someone would invent a box emulating a vehicle only requesting a trickle charge that a portable voltage source could meet.
why can't we make them measure the difference between the actual supply earth potential and the true earth potential
If you are going to put in a good enough rod (or mat, etc.) to act as a reference earth, you may as well make it TT in the first place.
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