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

AncientMariner
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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    It's definitely not TN-S as the protective and neutral functions are combined in the supply cable, especially if the customer has no control over the supply of other customers from that same transformer (and in this case single earth electrode).



    Maybe I'm picturing this wrongly, but with a simple PNB arrangement (with both the only electrode and N-PE link at the single consumer's cut-out) how is the supply cable providing a protective earth function? The means of earthing is connected at the cut-out and the path from consumer's exposed-conductive-parts to that means of earthing doesn't pass along the supply cable. For sure earth fault current will flow back to the source along the supply cable's N - as it would flow back along the N conductor to the star point from the N-PE link on a pure TN-S system - apart from (possibly) larger lengths of conductors I'm not seeing a difference. For me a system is TN-C-S where the N-PE link is downstream of the (first) electrode connection (as then you have a combined conductor between the N-PE link and the electrode).


    I take the point that the DNO might change the arrangement at a later date - and add more electrodes to the N, but that's the case with most TN-S DNO supplies, but we don't say we shouldn't call them TN-S in the meantime. I'm not sure that adding more consumers without adding more electrodes would necessarily be a problem - indeed isn't there a problem with the ESQCR demand for two or more electrodes on a PME system if we start calling a single-electrode (PNB) system PME?


       - Andy.

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  • 0

    It's definitely not TN-S as the protective and neutral functions are combined in the supply cable, especially if the customer has no control over the supply of other customers from that same transformer (and in this case single earth electrode).



    Maybe I'm picturing this wrongly, but with a simple PNB arrangement (with both the only electrode and N-PE link at the single consumer's cut-out) how is the supply cable providing a protective earth function? The means of earthing is connected at the cut-out and the path from consumer's exposed-conductive-parts to that means of earthing doesn't pass along the supply cable. For sure earth fault current will flow back to the source along the supply cable's N - as it would flow back along the N conductor to the star point from the N-PE link on a pure TN-S system - apart from (possibly) larger lengths of conductors I'm not seeing a difference. For me a system is TN-C-S where the N-PE link is downstream of the (first) electrode connection (as then you have a combined conductor between the N-PE link and the electrode).


    I take the point that the DNO might change the arrangement at a later date - and add more electrodes to the N, but that's the case with most TN-S DNO supplies, but we don't say we shouldn't call them TN-S in the meantime. I'm not sure that adding more consumers without adding more electrodes would necessarily be a problem - indeed isn't there a problem with the ESQCR demand for two or more electrodes on a PME system if we start calling a single-electrode (PNB) system PME?


       - Andy.

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