In response to many customer's questions regarding the safety of electrical installations in their homes, this page is designed to give you some guidance as to the main things to look for regarding electrical safety. If after reading the following information you feel that you may have a safety issue in your home, then I would be pleased to advise and quote on any action required.
Earthing Provided by Water Pipes
If your property has a metal water service pipe which is used for earthing, this is no longer thought to be safe and has not been allowed since 1966, many buildings built before this date are still earthed in this way. In most cases the metal pipe in your home is now connected to plastic water pipes in the street, this reduces the effectiveness of the pipe as your main earth. In this case should an electrical fault occur in your house you are in real danger of getting a potentially fatal shock from your taps, radiator, bath etc.
The problem can be rectified reasonably simply by upgrading the earth wiring within in your property to comply with BS7671 and requesting an earth be supplied with your electrical supply. Responsibility for safe earthing of appliances in your house is your responsibility.
Earth Provided by Your Electricity Supplier
This type of earth connection is the most common and will almost always be the case in modern houses built within the last 15 years. A typical earth connection seen somewhere near your electric meter is shown below (the green/yellow wire).
Where an earth is supplied as part of your electricity supply, the actual earth connection to your home may still not meet current regulations. In many cases the cabling to the earth connection is not thick enough, this increases the earth resistance such that it may not be sufficient to protect you in the case of an electrical fault. For a domestic dwelling, the yellow/green earth cable should have a cross sectional area of at least 16mm2 (approximately the size of as thin pencil)
Earthing Provided by an Earth Rod
In some properties (more common in rural areas) the main earth is provided by a metal rod sunk into the ground outside. A typical installation is shown below:
In these cases the quality of the earth is vary variable. If the rod is in good condition and located deep enough into moist ground then the earth connection is good, however if the rod is badly corroded, is loose in the ground or not connected soundly then it may not be sufficient to protect you in the case of an electrical fault. The quality of the earth can be easily tested, in addition the cabling should be sufficiently thick enough to carry any fault current safely. For a domestic dwelling, the yellow/green earth cable should have a cross sectional area of at least 16mm2 (approximately the size of as thin pencil)
Earthing of your gas and water pipe work
In addition to your main earth connection, your main incoming water and gas pipes should also be earthed. This is done using a metal clamp on the pipe work with an earth wire being run back to your main earthing connection or consumer unit. Typical connections are shown below:
In addition to the above, it is now also recommended that "cross bonding" be applied to all the pipe work into a boiler. This involves earth cabling being attached between all the pipe work coming out of your boiler, a typical installation is shown below:
2. Old wiring
Another major cause of house fires in Britain is where household cabling has deteriorated and the insulation has subsequently failed. This is more common where the cable has been in place for a very long time. Modern cable is made from plastic and takes a very long time to degrade, however older properties may still be wired with rubber cables which over time become brittle and disintegrate into a powder, this leaves the exposed bare copper which can then arc and cause fire. Exposed cables can also touch pipe work, which in turn could generate an electric shock hazard.
If you are worried as to the age of your cable then there is a very quick way of identifying the type you have in your house. If any cables you can see in your loft, fuse cupboard etc are light grey or white in colour then they are likely to be the newer plastic coated cables. If they are black there is a good chance they are the older rubberised cables.
3. Fuse boxes and Consumer units
Older properties will be equipped with a fuse box, this typically looks like the picture below and consists of a box with a series of re-wirable fuses for the different circuits in the house. these fuses have different current ratings depending on the circuit type, however they will only blow when their rating is exceeded.
Houses built more recently will be equipped with a consumer unit, this does exactly the same job as a fuse box but consists of resettable fuses called MCBs. MCBs will trip much faster than an equivalent fuse will blow but will still only trip at their rated current. A typical more modern consumer unit is shown below:
Finally, very modern properties or those that have been re-wired in the last few years will have an up to date consumer unit consisting of MCBs and one or more Residual Current Devices (RCDs). An RCD monitors the balance of the live and neutral electric current flow. An imbalance occurs if electrical current leaks from a circuit because of faulty insulation or because someone has touched a live part and received an electric shock. If the RCD detects an imbalance, it switches off the supply immediately - fast enough to prevent the shock from becoming fatal. The latest version of the British Standard (BS7671) recommends that all circuits are now protected by RCDs. A typical modern consumer unit with RCDs is shown below:
4. Electrical Connections and Water
Water and electricity clearly do not mix and when they do the consequences can be fatal. With this in mind electrical sockets and appliances are not generally permitted in bathrooms unless they are specifically designed to be used in a wet environment. Where electricity is present in the bathroom it is recommended that the supply is protected by an RCD as discussed above.
5. Safety in the garden
The risk of electrical appliances coming into contact with water or being severed is in much higher outside the home, with this in mind it is recommended that all electrical appliances used outside are protected by a Residual Current Device. If your home is not equipped with RCDs in the consumer unit then the simplest way of achieving this is by using a plug in RCD as shown below:
Even better is to upgrade the relevant socket to one that has an RCD built into it. These can be supplied and fitted both for inside and outside weatherproof situations.
6. Rodent Damage
I was recently called to a house whose lighting circuit kept tripping at the Consumer unit, further investigation revealed that the people had recently had mice in their loft and the mice had chewed through several of the cables! All that was left in places was the bare copper cables, quite clearly a fire risk. In this case 4 lengths of cable had to be replaced. If you have had a mouse problem in your loft, I recommend that you check the cables (or call me in for an inspection). The pictures below speak for themselves.
Copyright © 2011 Richard Coombs. All rights reserved.