Rank: New forum user 
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Hi All
I am working with a school that has water ingress issues in their building and as a result there are electrical safety concerns. The organisation who look after the infrastructure of the school are giving assurance that they are doing everything possible to ensure safety of the mains installation - including protection by RCDs. My question is: assuming that they have been tested to be working correctly can RCDs be relied upon 100% to protect from electrocution, fire etc? How often should they be checked under these conditions?
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Rank: Super forum user
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Without knowing the details and the extent of the water ingress it is difficult to comment. I am not an electrical engineer and just speaking from experience. RCD only protects against electrocution from the distribution boards. If the distribution board is wet it is a different matter. RCD are reliable and their tripping is normally the first indication something is wrong. Corrosion of electrical equipment in wet/damp conditions over the medium/long term can be an issue. This is a particular important if this affects the earthing of metal work (heating) or equipment. I have also had 240V socket that are badly corroded. However nothing is 100% reliable and RCDs are a secondary protection. They should try and eliminate the risk first, but in the short term a full electrical inspection may do. As there is clearly a hazard their employer needs to risk assess it. This may focus minds and help to resolve matters. This may also help http://www.electricalsafetyfirst.org.uk
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Rank: Super forum user
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Again without knowing the details but looking at a sports center recently where the walls were soaking wet yet the electrical circuits embedded in those wet walls passed the electrical tests
All present realised that even where the circuits appeared to be OK if walls are soaking wet the possibility of real harm is there irrespective of the results of the tests so rely on noting in particular except to say get the primary problem solves asap and press the duty holder to very regularly test and check the electrical systems ---- to do that the school needs to come down as hard [really hard] as they can on their LA, suppliers of contracted services, church etc. and contact the LA's internal H&S department [if they have one as many have been removed recently] and even try the local EHO's or possibly Ofsted for their support but I feel that they may play politics
U will really need to press the duty holders even where the school has 'bought back' and record everything as councils are very very strapped for cash and are willing to spend as little as possible and church schools appear to be in the same boat noting that all but the newest schools were poorly built especially those built just after the war and until ~ the 90's and little control over maintence and building works has taken place in most situations so we may not know what we are dealing with so we are stuck with what we have
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Rank: Super forum user 
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RCD's are THE most unreliable method of protection used.
You should never rely on an RCD as the primary means of protection.
They should be tested every 3 months maximum under normal circumstances.
You really should get more information, and I would suggest an independent opinion, IMHO especially if it is a failure on the part of the FM contractor that has caused the leak.
The most common insulation on cables is PVC, which is fundamentally "water proof" however, it is the terminations that are the issue.
IF water tracks up the terminations it can travel a LONG way by capillary action.
If this is into an SWA cable, between the sheath and bedding, this will eventually affect the armour and can cause a safety issue with earthing.
In general SWA cables if correctly installed are fine, but, if they are compromised by contaminated water this can have a serious affect on the steel galvanised armouring.
Where is this water coming from?
What is the "water"?
Another thing that I have noticed when working on schools is that they are short of money, so they want the job done for nothing, which often means that the people who do the job are incompetent, and leave the circuit in a dangerous state.
I worked at one school where they had been paying £25 per socket in materials for RCD protection, because the DB's were obsolete.
I did a whole classroom design for £50 in materials to protect all sockets with a 30mA RCD and it complied with BS7671!
£50 vs £250
Hmm...
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