Installing a new IT suite this summer? Make sure you’re not a victim of nuisance trips!
We’ve seen a couple of instances of “nuisance trips” on projects recently. It can be a real pain for staff that need to be educated to switch an IT suite on one PC at a time and to do it slowly enough so as not to trip the circuit. Workstations also generally don’t like being switched on and off by just cutting and reactivating their mains supply.
In most computer rooms it is strongly advised that the rooms are wired with a ‘high integrity’ earth circuit; and that circuits are designed in accordance with BS7671 taking into account voltage drop, design current and other external influences.
Now the science bit. Show this to your electricians or ask us about it…
If it’s an RCD (Residual-Current Device) that trips:
Under the current 17th edition wiring regulations (BS7671:2008) the majority of power circuits installed within most buildings will require an RCD. This normally because electrical sockets are installed for general use by ordinary people. There are cases where cabling is concealed within a wall an RCD may also be required.
The 17th Edition stipulates that the RCD used in these cases to provide ‘additional protection against electric shock’ should have a residual operating current of no more than 30mA. This can present a problem in certain areas where high earth leakage currents are expected; specifically in IT suites where the entire room is protected by a single RCD.
When designing the electrical system for an IT suite the expected earth leakage should be calculated and used as part of the design process to determine the number of circuits supplying the room and also the number of residual protective devices. A safe value to take when calculating such currents is 2mA (milliamps) per workstation. This would mean that in theory any more than 15 computers attached to a single 30mA RCD would cause it to trip.
Unfortunately it’s not permitted to simply ‘up the RCD rating’ on any existing circuits. Instead, the room has to be broken up into several circuits and each one connected to either an individual RCD and MCB (Miniature Circuit Breaker), or an RCBO (Residual Current Breaker with Overload). In some cases these changes can be made by simply rearranging connections within the distribution board, however in most cases additional wiring will be required.
In the event that it’s an MCB (Miniature Circuit Breaker) that trips:
If the device that is tripping is an MCB rather than an RCD, the MCB type may be upgraded to a more suitable one; if ‘B Type’ domestic grade breakers have been installed for use with devices known to have high start up currents, they can regularly ‘nuisance trip’. In most cases the recommended solution is to replace these breakers with a more tolerant ‘C Type’ or ‘D Type’ MCB.
RTS goes beyond the standard implementation of ICT systems. We look for what really matters to each and every user of our technology and ensure that we deliver remarkable results that are still apparent long after each project is commissioned. RTS combines two traditionally separate technology disciplines and creates dynamic solutions that resolve underlying problems and deliver visionary opportunities. You can follow us on Twitter @RTStweets or contact us directly on 0121 285 7222 for further information.
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