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Use of 16 and 32A radial sockets in data centres

Russell Bulley
Radial sockets seem to be detailed in BS7671 appendix 15 as domestic only. Are there any regulations providing guidance for the above?


I was quite surprised to see strings of IEC type sockets CEE arrangement (with earthed pins) linked together with a single radial feed from another socket, of course all unfused. The whole are protected by 20A RCBO’s. Generally the arrangement is as the left hand side of fig.15b, without the junction box. I assume this is standard practice in Europe?


Russ
  • 0
    This is not unusual and is perfectly fine, but it is not BS7671 territory either as this is the consumer (data centre) installation. The reason why there is no problem is simple, the loads are known and each is protected internally against faults causing overload (usually fuses). So 6 servers with a maximum demand of 500W each or less is not overloading anything, and a short circuit fault in the cables or supply cable to the original presumably blue BS4343 one will happily disconnect the supply quite quickly. As the whole place is under the control of supposedly competent people, no one is going to plug a kettle into the sockets and if they did the 20A fuse would probably blow quite quickly but anyway it takes time for any significant damage due to overload to occur.


    A fault in a server would blow its own device fuse (maybe a small circuit breaker) and leave the rest operating normally, at least that is how it is designed.
  • 0
    David's advice is along the right lines.


    IEC 60320 outlets are not classed as "socket-outlets", and certainly not "standard socket-outlets" and therefore the guidance in Appendix 15 is not an appropriate analogy (Appendix 15 is specifically giving guidance on BS 1363-series socket-outlets, connection units and spurs from rings and radials in relation to Regulation Group 433.1). Instead, IEC 60320 products are referred to as:
    • Cable couplers (what is on the end of flexible cable)

    • Appliance outlets (as on the power strip)

    • Appliance inlets (as on the power inlet of a


    Collectively they would be referred to as "cable couplers" in BS 7671, if they were part of a fixed-wiring installation.


    Each "power strip" is an individual piece of electrical equipment, that is connected either via:
    • a 16 A or 32 A plug to a socket-outlet forming part of the fixed wiring installation (in which case a 30 mA RCD is required, unless a risk assessment is provided concluding the RCD is not required)

    • some form of connection unit forming part of the fixed wiring installation (so that in theory 30 mA RCDs are not necessary in accordance with Regulation 411.3.3, although whether this is "in the spirit" of the BS 7671 requirement is open to debate)


    I don't fully agree the data centre installation is outside BS 7671 - whilst I agree functional earthing, and, where required common-bonding and mesh-bonding is in accordance with BS EN 50310, BS 7671 does cover the use of the common bonding or mesh bonding network for additional protective earthing because of high protective conductor currents in the final circuits or items of equipment.
  • 0
    Just to be clear, this particular installation is not using PDU's they are "daisy chaining" sockets together with an in and out flexible cable from socket to socket.


    Russ
  • 0
    To clarify, you are referring to this sort of IEC CEE socket?

    https://www.ceesockets.com/knowledge/what-is-ceeform-cee-form-fully-explained/
  • 0
    Is there a single plug on the end of your chain plugged into the fixed socket? If so this is not BS7671 territory but is perfectly acceptable for loading to 16A long term. The kind of plugs or sockets does not matter.
  • 0
    davezawadi (David Stone):

    Is there a single plug on the end of your chain plugged into the fixed socket? If so this is not BS7671 territory but is perfectly acceptable for loading to 16A long term. The kind of plugs or sockets does not matter.


    High protective conductor currents depending on how the socket-outlet is supplied?


    Can't stop users doing things with pluggable appliances, I agree ... but the electrical duty holder of the premises should perhaps be made aware if this is a potential issue?


  • 0
    Well, typically Graham, all the racks holding everything are Earth via bonding anyway so the protective conductor current is perfectly dealt with. This is largely brought into play due to EMC considerations, but obviously works equally well for the safety too.  You would find it very difficult to find much PD in a typical server environment. We have been told that it is this kind of place in the OP.
  • 0
    As 2400 asks - are we talking CEE 17 (industrial plugs & sockets to BS EN 60309 - BS 4343 of yore) or CEE 22 (BS EN 60320 / "kettle connector")?


    Certainly a 19" horizontal or many U vertical unit of tens of BS EN 60320 outlets mounted in a rack and connected via a flex to a suitable plug & socket is bog standard PDU arrangement in the UK (as elsewhere). Some may have some fuses or circuit breaker built in, but many don't - where they do it's more a matter of providing some discrimination (keeping the other servers running, or at least restarting quickly, when one PSU goes pop) than safety.


      - Andy.
  • 0
    Just want to say thanks for all the replies. 


    Russ.

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