Every IT manager or Engineer in the field has their story.


One of my best ones is a "business critical" IT rack, which had been located in a rarely-visited "repurposed" room in an airport. Someone noticed AirCon was required for the hottest days, so one was installed ...over the top of the Rack, which had the top and side panels removed because of the overheating issue.


And then the aircon unit went south on a hot day and started dripping ... all over the rack and the kit inside, so the "business critical" kit of course stopped working ?

Ah, yes, I can vouch for air con dripping problems - everything from freezing up and melting, to condenate pumps failing to being installed with the wrong condensate tubing so it suffered from an air lock and soaked the machine room less than 12 hours after being installed.


Best one for me was after a load of "production" systems were moved from our small office machine room (where we'd kept them running without any unplanned downtime for several years) to a big professionally run data centre - complete with redundant 1+1 UPS protected generator backed power supplies to everything - which failed completely after a few weeks. Apparently no-one at the data centre had noticed the gradual load creep to the point that both feeders were somewhat over 50% utilisation - when one failed and all the affected loads automatically transferred onto the other, it was then overloaded and tripped out an hour or two later leaving the entire data centre blacked out.


  - Andy.

Thanks one and all for your comments and tips.


I think the applications I have in mind (Clean rooms in an electronics assembly plant) to power IT equipment, Microscopes, pick and place equipment etc. RCDs should be used because there is a slight risk of additional unsanctioned equipment being plugged in although this is strictly monitored due to the introduction of noise on the line. Cleaners and general sockets are supplied but! 


To reduce down time for testing or spurious faults multiple circuits could be installed so production could be split or at least not be halted completely.


Thanks again


Andy

Interestingly the National Rules for Electrical Installations in Ireland (ET 101:2008) permit omission of RCD protection for socket outlets for IT equipment and socket outlets used for isolation of fixed equipment. Caveats apply. Not sure if this will alter in the new edition scheduled for publication in January 2020.

I had to look into providing a test bench function for testing electrical equipment. Issue was that the equipment ocassionaly had an issue that would trip an RCD and this RCD fed a wider area. I looked at a way to resolve this in a way that was both safe and ensured that any issues with the equipment being tested were identified. Using an isolating transformer only served to stop the RCD function form working when testing the item of equipment, However by making a TN-S by earthing the neutral of the isolating transformer and putting in a local RCD and an MCB to provide a test point that would trip on an earth fault without tripping the source RCD. 


Again creating zones provides a way to sectionalise the distribution while maintaining some safety overall.

Hi Andy H.


I see your post related to more IT systems but still, I have, after much head bashing and trying desperately to find ways not to fit RCDs when adding to existing commercial systems - come to the conclusion that there is no way to avoid fitting RCDs other than with the use of a Risk Assessment to say that it is not required to be fitted. Which no one is willing or able to take responsibility for and do. So as shown below I - too- dance around the issue on occasion. 


Even in a server room when we build one - usually these days smaller than they used to be in offices - a risk assessment is the only way around not fitting an RCD I think. I commonly fit RCBOs that supply a commando socket - that supplies the UPS. This is probably impractical in bigger situations such as yours I'd guess............If there are UPS involved in your situation then that could be taken into account too. (How well would an RCD work down stream of a UPS?)

In your situation I'd get the M&E Consultant to draw up a risk assessment to avoid fitting RCDs - every one knows its sensible, but someone needs to take personal responsibility for this decision, Consultants are usually happy to charge  to take on this sort responsibility..... usually with so many caveats that it means its not their responsibility at all if something goes wrong - the client has not followed the caveats, hence its the clients' responsibility. (You may be, said consultant - in which case this is all a lot of waffle.............)


Small example of my issues: commercial offices and underfloor bus bars supplying electrac floor boxes - Its common practice to RCD protect the underfloor bus bars especially in a CAT A fit out, and I come in on the CAT B fitout stage - so arrive to find the underfloor bus bar 30mA Protected and every floor box with just double sockets.........but I hate this practice as a single small fault will knock out multiple desks and - over time - with more staff being crammed onto a floor space,  I have seen 30 desks on a single RCD protected underfloor bus bar...........common practice for me  - a single bus bar will supply 10 desks at the most if on a single RCD protected Bus bar (So I recommend we fit more bus bars - which is good for me, but often the client is less willing and wants to find another way to utilise the bus bars he/she has now in this beautiful CAT A space......... Either I fit RCD sockets in the floor box or what I do is I get the client to assure me that each desk will be fitted with its own RCD in line to the desk sockets. I don't then need to fit RCD protection to the underfloor bar. BUT......Each floor box has 2 x DSSOs in it that are not RCD protected. This then becomes a problem for now as it does not forfil the letter of the regs with regards to floor box sockets. If I fit RCD sockets it becomes a problem for the future - maintenance and inspections. Often I need to do additions or shuffling around of the desks to accommodate desk moves/staff..... 

These floor boxes are - when I do them - always located centrally under the desk and not really easily accessible for general use by other than the desk user. Essentially this IS a risk assessment done by me but I have no control over future use of this installation so I'm not about to formalise this statement in a risk assessment that I'm going to sign...........(This is a good design, I Believe, and the one that I recommend if we cant fit tap off leads such as the electrac IAB Intersock range or Rotasoc for example as long as lots of RCD protected "cleaners sockets" are also scattered around, but someone has to Risk assess this and put it into some kind of formal document, which never ever happens.) I have now resorted to adding this caveat to the EIC Comments section when applicable. 


The above scenario is quite common because the client often takes on a floor space populated with existing floor boxes


Something along the lines of: The Client has stated they will ensure that RCD protection is afforded to each desk with the use of an in line RCD between floor box and under desk sockets for example and these floor box desk supply sockets are not for general purpose use. Cleaners sockets that are RCD protected and readily accessible, shall only be used for general purpose use. 


I'm not sure how legally exposed this leaves me or the legal implications of this sort advice so Id treat it with caution. 

Hi tattyinengland 


good way of doing it but we still have to make sure that the RCD need is not bypassed, one way round this is to ensure that all non RCD protected outlets are through a non standard plug socket - thus your average joe can not plug into a non rcd protected supply.


all 13A sockets being supplied through an RCD and you have 16A commandos or the like for the unprotected supplies.

(How well would an RCD work down stream of a UPS?)

Humm, depends on how the load side of the UPS is configured - if as a TN system then the RCD operates the same as anywhere else, if an IT system then it doesn't matter since it's safe under single fault conditions anyway.


Maybe a better question is how would an RCD upstream of a UPS work to protect from electric shock - yes the RCD might trip but if the UPS then immediately reconnects the victim to 230V it's probably not having the intended effect...


   - Andy.

surely any protection such as an RCD should be between the user and the supply source, and of course the UPS would have to be considered as a source. brilliant bits of kit UPS units but do they ever complicate matters somewhat ! 

I understand exactly where you are coming from Andy.  I used to look after maintenance in a large factory and know what disruption can be caused.  However, we mustn't forget how amazing these things are and how many lives they must have saved so far.


How about an RCD assembly incorporating a switchable parallel feed (by a special key?) which could be put in circuit whilst the RCD is tested?  Straight away I can see that for the duration of the test the circuit may not conform to regs, but maybe with a Risk Assessment and suitable control measures in place this could be overcome.    Just an idea.....