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Topic Title: Number of IT Components on RCD
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Created On: 01 October 2013 02:31 PM
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 01 October 2013 02:31 PM
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I need some advise, I am involved in the redesign of our head office, one of the options we are considering is an electrack under a raised floor. My concern is there would be circa 13 stations including computers and monitors on one track (protected by BS61009 RCBO).

I have heard there is a maximum amount of IT equipment per circuit. Any one know what is the regulation/best practise?
 01 October 2013 02:43 PM
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Regulations just say that the expected protective conductor current (i.e. earth leakage) should be unlikely to cause unnecessary tripping of the RCD (531.2.4). There are no hard and fast number-of-items as it depends on the type of equipment as well as the sensitivity of the RCD.

A correctly functioning RCD may trip anywhere between 50% and 100% of its rating - so for a 30mA device you'd be looking at keeping leakage current well below 15mA. The leakage from each item of equipment is variable - often new equipment is less of a problem than older kit. Some seem to leak more during switch-on surges too, which is worth considering. For myself, if I had no other data, I might start off thinking along the lines of 0.5mA to 1mA per item of (class 1) equipment.

Do you really need whole-circuit RCD protection? Might individual RCD-protected sockets be a better solution (especially from a discrimination point of view), or indeed if the circuits can be dedicated to specified equipment, can additional protection by RCDs be omitted altogether?

- Andy.
 01 October 2013 05:36 PM
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1 - Do you need RCD protection at all

2 - If the risk asssessment suggests that it is required, consider RCD units in the floor boxes or on the sockets (as an example, if you look at MITA from Schneider, you should find thier floor boxes can accomodate RCBO's or RCD's within the compartment to protect local sockets

3 - High protective conductor currents should form part of your design thinking so consider dual earth bar busbar and more importantly dual earth tap off leads if you suspect you are approaching a total of 10mA on the circuit/busbar

4 - You need to seriously consider inrush currents onto each busbar as you'll be forever unplugging computers to get the power back on after any significant failure of supply. A lot of PC's still exhibit inrush surge even if the appear to be turned off - be warned. If seen a floor of PC's take down 160A MCCB tap offs with no problems at all - some very p****d off users

Taking all that into account, and assuming you want a simple 3 pole busbar system, I would limit the number of tap off boxes to say 12 and further limit the specific number of PC's to about 8.

If you want more per bar, then all of the above need thinking about.



Let the wind blow you, across a big floor.

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