Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Suggested Answer
  • Replies 7 replies
  • Helpful Answers 1 Helpful answer
  • Subscribers 38 subscribers
  • Views 1488 views
  • Users 0 members are here
Options
You may also be interested in

How big does a 3 phase in-balance need to be to mask an open pen fault

Alan B

This is looking at the previous project I was  discussing with two EVCP's on two phases of a 3 phase supply.
Just realised that I may have issues relying on single phase voltage based open pen detection when connecting to a 3 phase supply.


AI says Regulation 722.411.4.1(iv) of BS 7671:2018+A1:2020 prohibits the use of a protection device for open-PEN (Protective Earth and Neutral) detection in single-phase EV charging points supplied by a three-phase installation. This is because this specific type of open-PEN protection is designed for single-phase installations only, and a three-phase supply has different electrical characteristics that are not compatible with this protective measure. 

Looking at amendment 2 I can't see this wording, am I just missing it, or has it been removed?


  • 0

    The clue is, "artificial", whose intelligence has got it wrong.

    Aren't all SP circuits (or indeed installations) derived from TP ones?

    My understanding is that TP EVCPs (please forgive the alphabet soup) are inherently safer than SP ones. Thus it is not that open-PEN devices are incompatible with TP installations, but that they are unnecessary.

  • 0

    AI's confused (again).

    There used to be a limitation on using L-N voltage monitoring for open-PEN detection where 3-phase is available, but that's long since gone (and the current version of BS 7671 is 2022, not 2020).

    There was some logic to the limitation - the L-N voltage approach isn't exactly 100% - because of the phase differences you can, in some circumstances, have PEN-true Earth voltages of well over 100V and still not have the open-PEN device notice and open - which is a bit of a flaw.  If 3-phase is available you would, in principle, be better measuring PE against an "artificial N" point derived from the 3 lines instead - so the old limitation tried to encourage better approaches where available. But if we accept the ("flawed") method for single phase installations (derrived from 3-phase LV public distribution), it's hard to then say the same risk is unacceptable just because the installation has a 3-phase supply (which might be a very inconvenient distance from the EV point). Many modern designs incorporate additional methods of protection - e.g. tripping on c.p.c. currents over 10mA to reduce the risk these days too.

       - Andy.

  • 0

    Speak to the Open-PEN protection manufacturers and the EVSE manufacturers, the measurement methods vary between single and three-phase Open-PEN equipment and a reference earth rod may be required to take the measurements in a three-phase installation. 

    You will probably need a three-phase Open-PEN protection upfront of the single phase EVSE, because it is a three-phase installation, allowing the use of single-phase EVSE without built in Open-PEN protection. 

    You need to take guidance from equipment manufacturers, not AI.

  • 0
    Alan B said:
    Looking at amendment 2 I can't see this wording, am I just missing it, or has it been removed?

    It was true for Amendment 1:2020, the wording of 722.411.4.1(iv) changed for Amendment 2:2022.

    Amendment 1 wording:

    (iv) Protection against electric shock in a single-phase installation is provided by a device which electrically disconnects the vehicle from the live conductors of the supply and from protective earth in accordance with Regulation 543.3.3.101(ii) within 5 s in the event of the utilisation voltage at the charging point, between the line and neutral conductors, being greater than 253 V rms or less than 207 V rms. The device shall provide isolation and be selected in accordance with Table 537.4. Equivalent means of functionality could be included within the charging equipment. Closing or resetting of the device shall be possible only if the voltage between line and neutral conductors is in the range 207 to 253 V rms.

    Amendment 2 wording

    (iv) Protection against electric shock is provided by a device which electrically disconnects the vehicle from the live conductors of the supply and from protective earth in accordance with Regulation 543.3.3.101(ii) within 5 s in the event of the utilisation voltage at the charging point, between the line and neutral conductors, being greater than 253 V rms or less than 207 V rms. The device shall provide isolation and be selected in accordance with Table 537.4. Equivalent means of functionality could be included within the charging equipment. Closing or resetting of the device shall be possible only if the voltage between line and neutral conductors is in the range 207 to 253 V rms. See Note 1.

    Alan B said:
    Just realised that I may have issues relying on single phase voltage based open pen detection when connecting to a 3 phase supply.

    Most single-phase installations on PME systems are derived from a three-phase supply.

    In three-phase installations, OPDDs that work along the lines of 722.411.4.1 (iii) ... M2a and M2b in IET 01:2024 ... are much less susceptible to non-detection on phase unbalance, and also unwanted operation due to voltage variation, then 722.411.4.1 (iv) devices ... M1a and M1b in IET 01:2024. Hence, it's better to use the (iii) devices in a three-phase installation if you can, although this may mean protecting a three-phase distribution circuit rather than single-phase final circuits.

    Alan B said:
    How big does a 3 phase in-balance need to be to mask an open pen fault

    In a real open-PEN fault, the phase unbalance changes over time ... every few minutes if not more quickly ... as loading changes. The issue is that we want to avoid, is OPDDs on more than one phase not seeing the fault in certain ratios of unbalance in certain conditions (because if OPDDs on at least one phase operate, phase unbalance will change, and it's highly likely any that didn't detect will operate). Those conditions were carefully explored in between Amendment 1:2020 and Amendment 2:2022, and it was discovered that you would need serious unbalance, plus very unusual conditions of power factor, for two phases at once to fail to see the conditions.

  • 0 in reply to Sparkingchip

    and a reference earth rod may be required to take the measurements in a three-phase installation. 

    The reference electrode approach (iii) can be used with either 3-phase or single phase - and in theory is the ideal approach if the electrode accurately represents the ground surface potential around the vehicle. The trouble is making sure that the electrode isn't unduly influenced by other voltages (e.g. buried PME cables or bonded metallic pipework) and not hitting any services when banging the thing in. If you do go to the effort of installing a good electrode, then in many (although not all) cases you could just TT the EV using it, and not bother with the expensive open-PEN device at all.

    The difference with 3-phase is that it gives the option of inferring a 0V reference by averaging together the three line voltages (like an artificial N point) - it's like having a perfectly balanced star connected load - the star point naturally sits at 0V even without needing a N conductor. As long as the three phases are all present and correct (e.g. all have 400-ish volts between them) the implied N point should be reliable reflection of the substation's electrode, even during open PEN events - so that can make a good reference for the open-PEN device.

    Single phase open-PEN devices without an electrode can only monitor L-N (or L-PE) voltages ... which has its flaws ...  Open PEN detection for 722.411.4.1 (iv) 

       - Andy.

  • 0

    Hi All

    Thanks for the answers, I would never have noticed the two words changed between amendment 1 and amendment 2.
    I know Ai can't be trusted, but it normally gives a good indication on where to look in the big book.

    I will just be using the single phase open pen detection built in to the EVCP, it's more or less standard on the products I trust to be user-friendly, reliable and have reasonable customer service. I may TT the house DB or more likely the individual EVCP if there aren't any extraneous parts around. the incoming supply is 50 or 60 meters away and overhead, so not a concern.

    Looks like you agree with me on having a 3 phase supply to the property not making much difference. 
    I am going to avoid the 3 phase open pen detectors because
       Getting the third phase to the distribution point opens up more challenges
       It would have to be something like a matt e box, personally I don't like the way they just make a hard cut to the supply if there's a problem. Causes spikes, generally electrical stress, doesn't inform an non electrician what's going on. EVCP' software doesn't like going through power cycles.
       Most of the time when these things trigger it's because the DNO are making a poor job of managing the supply voltage, the main benefit of OPEN devices seems to be keeping the DNO honest with managing supply voltage. With luck only one of two phases would be out by enough to cause the EVCP to shut down and the customer will still have one EVCP working while things are sorted out.

    There is only one single phase EVCP that allows open pen voltage measurement relative to real earth that I am aware off. Personally I don't like the user interface on the product and I have had 8 of the 10 units I install fail with burnt out connections. I know they have redesigned things, but still not sure I would want to take the risk again.

  • 0
    Alan B said:
    This is looking at the previous project I was  discussing with two EVCP's on two phases of a 3 phase supply.

    Alan, what conclusion did you reach on the two distribution circuits please?

Community Rules & Guidelines