Wiring Regs scope, inside 19" rack cabinets?

Question

Hi everyone, 
 The US-based company I work for needs to send a 19" rack cabinet of computers, PLCs and network equipment to the UK for temporary installation in a research facility. We've been advised (quite rightly) that we need to ensure compliance with UKCA marking requirements and be able to provide a technical file for this. It's been a while since I was involved in compliance things, but my understanding is that the technical file is normally just about demonstrating compliance with the harmonised norms, e.g the low voltage directive. However as this will be a cabinet "installed", i.e. fixed, in position, with power distributed within it, I wondered if it is also in scope of the BS 7671? 
 Advice much appreciated on this, especially from anyone with practical experience of a similar situation. 
 Thanks, 
 Will

mapj1 · Accepted Answer

Where I work,we would not normally test a rack to BS7671 unless it contained something that was essentially fixed wiring. We would however treat it like an appliance,or an extension lead and many appliances depending on the internal configuration. 
 Mike

mapj1 · Answer

Is the rack expecting single or 3 phase supply? 
 Easiest is to have a bs4343/en60309 incomer if you can, and then define the supply requirements - eg 32A single phase or 16A 3 phase or whatever and the overload and cable protection becomes the responsibility of the customer, 
 In simple situations it is often easier to buy in ready made block and bolt it in if you are not tooled up for making it. LVD will set requirements on IP rating, creepage and clearances.( Companies like this make a living selling ready wired cables and making unusual distribution blocks to order if a normal extension will not do.) 
 Single phase UK colours for wiring are Brown (live 230V to ground) Blue (neutral - almost 0V to ground) and Green/yellow (earth - what we call what you call ground ...) 
 Wiring should survive a 500V DC test between L+N to earth and manage and have an impedance of many megohms, probably hundreds of megs when new. 
 
 Reduced test voltages if surge arresting components are fitted and cannot be isolated during testing. 
 It would be easiest to use UK mains lead to make up internal wiring. At the least the devices with their leads attached, should then be tested to a level equivalent to a PAT (earth continuity, insulation of supply conductors from earth when dead, and leakage current and total power consumption when switched on). 
 If the components in the rack are already CE marked then there is a large part of the work done. 
 If you are adding earth studs to the rack, then I suggest to go for M6 threads- it meets everyone's requirements I caution that the American use of something in a UNC that we cannot get a replacement nut for that is under 4mm diameter does not impress UK eyes ! 
 Mike.

gkenyon · Answer

Will D said: The US-based company I work for needs to send a 19" rack cabinet of computers, PLCs and network equipment to the UK for temporary installation in a research facility. We've been advised (quite rightly) that we need to ensure compliance with UKCA marking requirements and be able to provide a technical file for this. 
 Is that true for all temporarily installed equipment - I'[m sure there are 'opt-outs' for temporary test, R&D, etc equipment? I guess it depends on the actual purpose, and of course checking to see if the essential requirements are met is always recommended at least for H&S reasons ... certainly, on the safety side, if the normal UK safety standards are not met, other measures would need to be put in place to mitigate any hazards. 
 Will D said: However as this will be a cabinet "installed", i.e. fixed, in position, with power distributed within it, I wondered if it is also in scope of the BS 7671 
 Possibly, at least in part. Certainly the earthing should be checked for compliance with Section 543.7 of BS 7671 (although note this changed in 2022, for example 'dual earth terminal' is not longer a requirement, but of course can still be selected by a designer), and also earthing checked to BS EN 50310 at installation (ultra-low resistance ohm-meter or micro-ohm-meter test).

AJJewsbury · Answer

I've installed a fair bit of US originated kit in the UK over the years (IT kit in racks normally), all according to the supplier's instructions. The black/white/green core colours in the flex can be dealt with by over-sleeving at the terminations on the "UK" end. Voltages are usually OK but worth checking - we typically won't have 115V available, and 230V will have a earthed N - whereas US 230V is typically from a 115-0-115 system - so PDUs come with DP MCBS - which is fine if overkill for the UK. Just check that there aren't any 115V items lurking in there anywhere (small things cooling fans for the top of the rack come to mind). 
 - Andy.

mapj1 · Answer

Single phase makes it very easy. Your easiest choice now reduces to 32A blue plug, or 16A blue plug . 
 Watch total capacitance to earth if you have lots of kit with built in mains filters - it is likely that the users will want to supply it via a 30mA RCD (== GFI) and the out of balance current that flows with 230V between L and E will be proportionally larger than 110V designers are used to. 
 Don't go above 10mA of total earth leakage or the wheels can start to come off in terms of false alarm tripping - as well as making a lost earth first fault to an immediate danger condition. 
 Mike 
 (In general we like metric nuts - spares are available in every hardware shop. Things that use funny threads that have to be ordered off the internet and flown in and arrive a week late are a pain in the bottom .. The other happy alternative is to find a few spare screws and nuts in a bag in the back of the box).

mapj1 · Answer

You do not have to connect via plug and socket, but racks that may need to be isolated to be worked on or pulled out to be got behind very commonly are. Data centres seem to be full of connectors like that. It also makes it easy for the local sparks to decide where his work stops - make socket on wall live, run usual BS7671 polarity and earth impedance checks and then pack tools away and go for an early lunch - that way the power is ready in advance when the rack arrives. 
 It also avoids having to wait and then argue the toss about who is terminating the interlinking cable and if the rack needs testing as part of the fixed wiring - which of course is where we came in. 
 At least over here those connectors are cheap as chips compared to labour, and do make testing and isolation to prove dead particularly easy. 
 But do check with your customer - their local chaps will have their local preferred method. 
 Mike.

AJJewsbury · Answer

Ah well, if the PDU has a C20/C19 inlet - then the simplest thing might be just to plug a UK lead into that - e.g. https://uk.rs-online.com/web/p/power-cords/3119315 (or more likely with a blue 16A BS EN 60309 plug). 
 - Andy.

mapj1 · Answer

When you do the confirming in your shoes I'd be forcing it a bit. Along the lines of (but delete what you do not want) 
 " 
 The rack will consume up to Xxx watts at 230VAC single phase. 
 So we can provide a suitable lead, can you confirm that the supply will be one of the following, and which is your preferred. 
 13A socket to BS1363 
 (do not offer this if there is any doubt it may not be enough, say more than 2000 watts or if you do not want it to share a breaker and RCD (GFI) with everything else of no great importance in the building) 
 16A blue single phase socket to BS EN 60309 
 32A single phase socket BS EN 60309 
 Flex to bare ends for your non standard termination (not preferred) 
 Unless otherwise requested the supplied lead will be nominally ~1.8m (6 feet) long from the bottom left rear of the rack. 
 Or where ever it exits from the rack, so they know where to put the socket. 
 " 
 Avoids doubt, and allows them to get power to the right place at their end in advance. Anything more than the 13A socket will probably have them running in a new line, in 2,5mm cable or larger for the 16A or 4mm cable or larger for the 32A, and that is likely to be more reliable, as no-one will then unplug it to use the vacuum cleaner.... 
 Mike

Wiring Regs scope, inside 19" rack cabinets?

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