Plug/socket earth pin length

Question

Hello, 
 The earth pin on UK plugs and industrial IEC EN 60309 connectors are longer to make the earth connection first and break last. This seems sensible but i have a question 
 I have several 19" rack enclosures that require interconnecting with power and control circuits. I cannot fit a typical power connector (eg 60309) but instead have found many other circular power connectors (eg Mil-spec) that are adequately rated and with designated earth pins, however, the earth pin is invariably the same length as the live pins i.e. the earth will not make first break last. This equipment is for use indoors, sockets less than 32A and with added protection with an 30mA RCD. 
 My understanding is that a longer earth pin is required under BS7671 but I can't actually find it stated explicitly any where in the regs. I'm probably not looking hard enough or is this a myth?? 
 Can anyone point me to the regulation in BS7671 or other guidance notes where it states the earth pin must be longer than the live pins of a power connector? or is this implied where BS7671 states the use of IEC 60309 connectors - and it is in that standard where it states the earth pin must be longer? And just to be sure, would you agree that the use of 60309 connectors is not a requirement for indoor installations, but is for outdoor installations? 
 
 Thanks

gkenyon · Accepted Answer

Without knowing the type of equipment, ir's difficult to properly advise, because other standards may well apply. For example, if the equipment is part of Machinery as defined in the Supply of Machinery (Safety) Regulations then BS 7671 does not apply at all to these interconnections, but BS EN IEC 60204-1 does. 
 If it is within the scope of BS 7671, then BS 7671 requires electrical equipment to comply with the latest British or Harmonized standard ... or the installer has to ensure "at least as safe" as, at a minimum, relevant provisions in BS 7671 (See Section 511) ... in the case of plugs, socket-outlets, and couplers (e.g. to BS EN IEC 60320), that are referenced in the general requirements (Parts 1 to 6) of BS 7671, most , if not all, have a longer protective conductor pin, and therefore it could be argued that you'd have a bit of a job covering 'at least as safe' without looking at the complete risk assessment of withdrawing or uncoupling the particular connectors you are looking at. However, if you have to operate an isolator before you have access to remove the plug, for example, that might be considered equivalent safety.

mapj1 · Answer

If you are using say 38999 series III for mains (or higher ;-) ), as is actually quite common on NATO military kit, please realise that these connectors are not designed to be used for making and breaking on load ( - actually a similar caveat applies to IEC 'kettle leads' but the earth pin is early make..) for equipment solidly connected because it is part of an mechanical assembly like a vehicle fitment, you are not relying on the cable for the sole earth connection anyway. The connector keying is normally chosen so that the use of a particular connector is unique, as there is no generic agreement about pin out. What standard are you building to ? If commercial you may be better with something like the Binders that are aimed at mains. 
 
 Mke.

AJJewsbury · Answer

Yes, a common c.p.c. is permitted by BS 7671 in general (if that is the applicable standard) - it just needs to be sized to suit the most onerous fault condition - see reg 543.1.2. Keep in mind earth leakage currents (sorry, protective conductor currents) though - as if they might get above 10mA then duplicating c.p.c.s might be back on the agenda (and some kinds of heating elements - esp mineral insulated ones - are well known to be leaky, let alone IT equipment). 
 - Andy.

gkenyon · Answer

Udtwmc said: there are some control valves and pumps on this rig but I wouldn’t class it as machinery. 
 Interestingly, commercial laundry and dishwashing equipment is classed as Machinery, and so is HVAC. A dishwasher really mainly only contains heaters and pumps (the moving spray arms are driven by water pressure and can be stopped by hand without injury usually. However, if this is a test rig for engine emissions, perhaps BS EN 61010-1 is the most appropriate standard to use (although it wouldn't preclude the use of that with BS EN 60204-1? It doesn't matter how big the 'machinery' or 'test equipment' is, provided you've adopted the standard). 
 IN any case, I don't think you'd find much different to BS 7671 in terms of plugs and socket-outlets, or connectors/couplers, except that there are not the provisions of Regulation 511 in those other standards (hence no messing around with extra paperwork statements if you want to use SY, CY and YY cables, for example), only the requirements of the relevant legislation to consider (i.e. keep on file manufacturer's specifications and DofCs as appropriate).

Plug/socket earth pin length

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