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Any similarity between an EVC point and a socket for a refrigerated cargo container?

Unless things have changed since I retired in 2002, I am curious regarding the similarity between an EVC point and a socket for a refrigerated cargo container.


On board ship, refrigerated cargo containers were simply plugged in to the ships electrical system. 3-phase, 3-wire plus earth, so a 4-pole plug and socket. The acceptable voltage being 380 to 460v 60 or 50 Hz. Most ships being 60 Hz, but some I sailed on had been designed for possible MOD charter and were 50 Hz. (there were some dual voltage containers, ie for 3-phase 230 volt supplies which some ships had.)


The lowest power consumption was for frozen cargo, whereas cargo which was carried chilled or even warm, due to fresh air requirements rather than recirculation, resulted in higher power consumption.


Considering that the container was connected via 10 metre or so cable, this looks similar to an EVC connection?  In rough weather, I have experienced heavy seas over the deck causing cables to be ripped out at the container end and when the weather subsided, I found that the doors of a container full of French Fries were having some cooked on deck by a fizzing broken cable.


Circuit protection either three cartridge fuses or a MCB, never came across any RCDs. Some ships fed the sockets directly off the main 440v bus, so an earth fault on a container, usually the defrost heater, would show as an earth on the ship's main 440v bus, other ships had the luxury of a number of isolating transformers. A quick Google tells me that some ships can carry 500 refrigerated containers, some more. This explains why my last ship generated at 6.6 kV.


Containers held on the quay side were plugged into pillars and I guess the same for when containers were at their destination, or awaiting stuffing. I never saw one of these in those days https://catalog.eslpwr.com/wp-content/pdfs/s_3500-02.pdf but certainly looks serious.


Yet the requirements suggested in  http://digitalfizz.com/cargostore/wp-content/uploads/Reefer_Power.pdf of RCD protection and under volt release, seems less stringent to that for a EVC point?


Clive

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  • AncientMariner:


    Actually what I was trying to get discussion on was when the container is off the ship and sitting on the quayside. Many container yards where they would be plugged in are surfaced with brick paviors, just like my driveway! OK the container is metal to brick rather than rubber tyre to brick, so if we have two containers not touching but close enough for a person to place a hand on each, should due to rough handling the earth core have pulled out of one of the plug terminals and there is also an earth fault we would seem to be relying 100% on an RCD somewhere?  




    Agreed - it's like that with mobile/transportable units.






    So going back to an EVC, if the supply to the house where the EVC point is mounted, is TN-S is anything more than an RCD required for shock protection? 

    Clive

     




    The simple answer is, no, nothing more than an RCD would be required, but for a house it's not that simple. If you're sure the supply is definitely TN-S, and is guaranteed to remain so, protection by RCD is definitely be OK, and none of the messing around with the requirements for PME supplies in 722.411.4.1 applies.


    However, is the supply really TN-S? determining whether the supply is really TN-S (and will remain so) is difficult these days. The problem is that DNOs carry out repairs on TN-S networks with CNE (combined neutral and earth) cable, or occasionally make a CNE joint with earth electrodes. This is explained in Sections 4.5 and 5.1 (12 and 18) of ENA Engineering Recommendation G12/4.


    Therefore, the published guidance from the IET recommends Regulation 722.411.4.1 for PME conditions is applied to TN-S from a public supply, and this would be the costs for most houses, unless the DNO confirms it's really TN-S and won't change (typically, therefore, only TN-S from a privately operated dedicated transformer is considered TN-S).

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  • AncientMariner:


    Actually what I was trying to get discussion on was when the container is off the ship and sitting on the quayside. Many container yards where they would be plugged in are surfaced with brick paviors, just like my driveway! OK the container is metal to brick rather than rubber tyre to brick, so if we have two containers not touching but close enough for a person to place a hand on each, should due to rough handling the earth core have pulled out of one of the plug terminals and there is also an earth fault we would seem to be relying 100% on an RCD somewhere?  




    Agreed - it's like that with mobile/transportable units.






    So going back to an EVC, if the supply to the house where the EVC point is mounted, is TN-S is anything more than an RCD required for shock protection? 

    Clive

     




    The simple answer is, no, nothing more than an RCD would be required, but for a house it's not that simple. If you're sure the supply is definitely TN-S, and is guaranteed to remain so, protection by RCD is definitely be OK, and none of the messing around with the requirements for PME supplies in 722.411.4.1 applies.


    However, is the supply really TN-S? determining whether the supply is really TN-S (and will remain so) is difficult these days. The problem is that DNOs carry out repairs on TN-S networks with CNE (combined neutral and earth) cable, or occasionally make a CNE joint with earth electrodes. This is explained in Sections 4.5 and 5.1 (12 and 18) of ENA Engineering Recommendation G12/4.


    Therefore, the published guidance from the IET recommends Regulation 722.411.4.1 for PME conditions is applied to TN-S from a public supply, and this would be the costs for most houses, unless the DNO confirms it's really TN-S and won't change (typically, therefore, only TN-S from a privately operated dedicated transformer is considered TN-S).

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