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Frequently Asked Questions
Electrical Contractors
Q: Where can I get a reliable Electrical Contractor?
A: There are two Registers of Approved Electrical Contractors in Ireland whose members claim that their work complies with the National Rules for Electrical Installations - "The Wiring Rules". These are:
- Electrical Contractors Safety & Standards Association (ECSSA). (Tel: 064-37266)
- Register of Electrical Contractors of Ireland (RECI) (Tel: 01-4929966)
Routine Safety Checks
Q: Are there any simple checks which a non-technical person can make to monitor an electrical installation?
A: Yes, any change in the behaviour of an electrical installation should be checked e.g. fuses blowing more than once, lights flickering. Installations should be tested by a competent electrician about every 5 years.
On a regular routine, sockets, switches and appliances should be inspected by the householder or equivalent for signs of overheating, wear on flexes, plugtops are properly connected - the colour of the wires in a flex entering a plug-top should not be visible from outside the plugtop. A cord grip should hold the outer sheath of the flex, not the coloured cores. Other faults include:
- Damage to plug tops such as cracking, heat discoloration, missing screws etc.
- Damage to flexible cables
- Unearthed equipment. If the flex has 3 cores it normally requires earthing.
- Dangerous joints in flexible cables including taped joints. Proper extension units should be used.
- Appliances should not be used in unsuitable locations, or if damaged.
- In replacing fuses the correct fuse should be used.
Since 1980 socket circuits should be protected by a trip-switch (RCD) to prevent electric shock. There should be tested every 3/6 months by pressing the test button.
Airing Cupboards
Q: Are there special requirements relating to electrical equipment in airing cupboards?
A: Yes, because of the temperatures and low humidity in an airing cupboard timbers tend to dry out and become more flammable. The electrics in an airing cupboard should be limited to those items mentioned in the Wiring Rules such as the wiring to the immersion group. Preferably, switches should be mounted outside the airing cupboard but where this is not possible or desirable they can be installed within the cupboard provided certain precautions are taken as outlined in the Wiring Rules. Because of the daily use and frequent and rough usage in an airing cupboard the electrical installation tends to deteriorate quickly and it should be examined regularly to ensure that there is no damage to the cabling and switches etc. which might cause a fire.
Attics
Q: Is there some change in requirements for wiring in attics?
A: Not really, wiring anywhere requires the use of common sense and the protection of cables and equipment. However, in recent years the conversion of attics into habitable rooms by laying floors, etc by unqualified and incompetent people has introduced a new hazard. In the past contactors frequently just laid cables over joists in attics without the expectation that these rooms might be floored. Laying flooring panels over joists and sandwiching or trapping cables between the panels and the joints can cause damage to the cables resulting in a breakdown in insulation and possible fires etc. This danger in now being highlighted.
Bathrooms
Q: Why are Wiring Rules so strict for bathrooms?
A: Because in the normal house the bathroom is the most dangerous room in the house. An electric shock in a bathroom is often fatal. Nearly every year someone is electrocuted in a bathroom because of breaches in the wiring. Remember with electricity, because it works does not mean that it is safe.
Q: Is it safe to install an instant shower in an existing installation?
A: Showers nowadays are amongst the most demanding of all domestic appliances. It is not unusual to find showers of 9 or 10 kW and obviously their installation could impose unacceptable demands on the system, particularly if it is an old installation.
Any installation to which it is proposed to add an instant shower should always be checked by a competent person to see that the supply and existing installation is capable of handling the additional load without reinforcement.
Where two showers are proposed to run concurrently, reinforcement or controls will almost certainly be necessary and two separate circuits should be used. Where the two showers do not have to be on simultaneously this can be arranged by electrical interlocking.
Cables
Q: Why was it necessary to change the colour cores of fixed cables after so many years?
A: With the establishment of the EU, or as it was known in earlier days the EEC, it was decided to rationalise the electrical installations rules for member countries so that the same Rules applied throughout Europe.
It was accepted that this would be a slow process as the Rules in each country had been set up many years before. Hence negotiating changes would be an extremely difficult process. This would be particularly difficult in what might be called the non-technical areas such as the colours of various cable cores and other traditional practices.
Of immediate concern was adopting a common colour code for flexible cables on appliances and this was driven hard by appliance manufacturers so that they could export their appliances throughout Europe and world-wide. This was achieved in the early 1970s and was indeed a major achievement when one remembers that while we regarded red as a phase colour, in Germany red was the earthing conductor. Similarly various conductor colours were used by different countries.
Agreement was not as quickly reached with regard to fixed or permanent wiring, although Europe did agree to a common colour for the neutral during the 1970s.
It was only recently that agreement was reached on phase colours and henceforth these will be:
Neutral - Blue
Phases - Brown, Black, Grey.
We can expect to see cables manufactured to these colours in the near future.
Distribution Boards
Q: Why do the Wiring Rules place so much importance on the location of the Distribution Board?
A: The Distribution Board is an extremely important part of an electrical installation. It is the safety control of the electrical installation. It provides two essential functions:
(1) - The overload, short circuit and earth fault protection.
(2) - the isolating function of the installation.
Obviously to provide these functions it must be protected against abuse either mechanical or environmental. It must be readily accessible at all times and it must properly ventilated. Distribution Boards, dissipate heat and have been known to overheat and this must be considered in their installation and location.
Q: We have heard of holiday cottages that do not appear to have an adequate supply for the installed load. The problem seems to occur particularly at night when new tenants arrive after the cottage has been unoccupied for a while.
A: Problems such as this probably occur where people switch on an abnormal load in the cottage perhaps to heat up the rooms. No domestic installation is designed to have every appliance switched on at the same time.
The designer normally assumes that only a certain percentage of the total load will be on at any one time and designs accordingly. If he were to assume that every electrical appliance and light in a domestic house was switched on at the same time the electricity supply from the Supply Authority would seldom be used to its capacity and would be much more expensive to provide than the normal supply which is based on an average maximum usage.
Users should remember this and, particularly in cold weather, when arriving at a holiday home they should not switch on everything together. This of course applies to any normal installation but holiday homes seem to suffer more.
Sockets, Light Switches, Lights
Q: Do brass wall light switches and metal luminaires (light fittings) have to be earthed?
A: Yes, since January 1998 all wall light switches and lighting points must be earthed.
Q: Must sockets be mounted away from sinks?
A: There is no specified distance given in the Wiring Rules. Common sense would require that they are not mounted where sockets or where connected appliances can be splashed from the sink or taps.
Q: Why do the Wiring Rules not specify the numbers of socket outlets that should be provided in the kitchen?
A: The National Wiring Rules do recommend a minimum of 10 socket outlets in a kitchen. This however is not a question of electrical installation practice but rather a matter of house design for the Department of Environment or the Building Regulations. The fact that the recommendation of 10 socket outlets is made in the Rules could be regarded as a considered view, not alone of the ETCI. The installation of less of 10 socket outlets in the kitchen might be regarded as inadequate for a normal kitchen in this day and age.
Q: How many points should a final circuit in a domestic premises supply?
A: This depends whether the circuits are radial or ring final circuits.
For a radial circuit the maximum number of points recommended is 10 per circuit. This applies to either lighting circuits or socket outlets etc. In the case of socket outlets a twin socket outlet would count as one point. For final socket circuits it is recommended that a radial circuit should not serve more than two rooms. For ring final circuits the number of points is unlimited within a floor area of 100 sq. meters.
Q: Why are the heights of wall switches for lights, lower than
before. Is this not more dangerous as children can now operate them?
A: The Department of Environment has directed that lighting wall switches should not be higher than 1200mm or lower than 900mm. This is to allow easier access for handicapped people.
It will of course be easier for children to operate them but if properly installed
there should be no great danger. After all sockets and table lamps are
frequently below this height.
Q: Some lampholders seems to become brittle after a relatively short time in use. Why is this?
A: This is usually due to overheating either because of inadequate ventilation of the bulb or lampholder or by installing a bulb rated above the thermal capability of the lampholder.
Lampholders marked T1 for example are not designed for incandescent lamps rated above 60W.
Q: Are there special plugs and sockets for outdoor installations and if so why?
A: Yes. We like most mainland Europe countries do not consider indoor plugs to be suitable for outdoor installations subject to weather and rough handling and so ordinary 13A sockets to I.S. 401 are not suitable for outdoor use. Like all socket outlets up to 32A, they should be protected by an RCD. The Rules require that outdoor sockets and industrial sockets comply with IS/EN60309 standard. In this system both the plug and socket are hard wearing and are deemed to be suitable for outdoor use. The single phase plug is coloured blue and the socket is inclined towards the ground to prevent the ingress of moisture. They may be more cumbersome than the flat pin plug system but they are safer.
Industrial and Commercial Installations
Q: When working on 20kv switchgear e.g.. resetting tripped breakers etc., should there be a second electrician present who is trained in high tension practices?
A: This query is not covered by anything in ETCI's Wiring Rules as these rules relate to LV only. However this question does have an answer when considered under statutory requirements (refer to the Safety, Health and Welfare at Work (General Application Regulations) 1993 (S.I. 44, 1993, Part VIII - Electricity)) under two headings as follows: Is the work classified as 'live work' or 'work on or near any exposed live parts'? (see regulations 46 and 48 of S.I. 44 of 1993 and see also ETCI's publication 'The Management of Electrical Safety at Work ET206:2000'). The HSA guide to the regulations recommends that:
- 'where high voltage live working is being carried out another person should be present at all times' and
- where work on or near a live part is unavoidable, the system of work used should:
- allow only a person who is competent (see regulation 48) to work on or near exposed, live conductors. Such a person should be accompanied by a second person who is trained and able to act in an emergency, e.g. switch off power and give first aid treatment for electric shock'
- 'indicate the extent of the live work'
- 'indicate what levels of competence apply to each category of work' and
- 'incorporate procedures under which the person carrying out the work will report back if the limits specified in the system are likely to be exceeded. This usually requires detailed planning before the work is started'
- Where the work is not 'live work' or 'work on or near any exposed live parts', then it's your 'risk assessment' that should guide you towards having the necessary controls in place to ensure that the work can be carried out safely.
In general:
- 'With properly installed and maintained equipment that is rated for the intended operating conditions (i.e. is suitably covered/insulated/screened, is rated to make or break fault currents and has properly designed control and protection systems), there is minimum risk to the person operating this equipment and therefore such an person could safely undertake this work while alone.
- If your risk assessment showed that it was unsafe for a person to work alone, would two or more persons not also be in danger in such circumstances.
- Whenever and wherever possible it is best to operate switchgear remotely. Local operation should only be a last resort. That said, quite an amount of switchgear is manually operated and is so designed to be safely operated in this way.
Note: All references to regulations in the above question are to the Safety, Health and Welfare at Work (General Application Regulations) 1993 (S.I. 44, 1993, Part VIII - Electricity).
Effects of Electricity on the Human Body
Q: Why is Electricity Dangerous?
A: Electricity can and does KILL people.
Electricity for domestic use is normally supplied at 230V. For industrial use it can be supplied at 230V or 400V. On building sites it is common practice to find isolation transformers with a secondary voltage of 110V which has the centre point connected to earth. This ensures that if the user touches a live wire the maximum voltage on the body will be 55V, which is considered to be safe. IEC (the International Electrotechnical Commission) actually specifies 50V as the maximum safe touch voltage. However, most people have to use electricity at 230V and this is clearly well above the recognised safe levels.
Q: What are the Effects of Current Flow Through the Human Body?
A: The following information is based on studies carried out by Professor Biegelmeier, Dr. Osypka, and the IEC.
The behaviour of the human body when exposed to an AC voltage is interesting in that the resistance of the body falls as the voltage increases. According to IEC data, 95% of people could be considered to have a body resistance of less than 4,375 ohms at 50V, but at 220V the body resistance falls to about 2,125 ohms for the same grouping. The reason for the fall in body resistance is mainly due to breakdown of skin resistance with rising voltage, the internal body resistance remaining relatively constant for voltages up to about 500V. It is also important to note that the value of 2,125 ohms is an average for the 5% group and that lower body resistances may apply depending on age, gender, climatic conditions, etc. For guidance we can assume that the body resistance will rarely exceed 2000 ohms at 230V. This would result in a current of at least 115mA flowing through the body at that voltage.
When a person touches a live part the current flow through the body will usually be through hand and feet, or hand and feet and other hand if the other hand is touching an earthed part. The body resistance falls as the touch voltage increases, and in the case of touch voltages >1000V the body resistance can fall to such an extent that currents of ampere levels can flow through the body. However, for RCD protection we are generally dealing with touch voltages of around 230V, although touch voltages of up to 400V can apply in industrial situations. The current that will flow through the body from hand to feet will depend on the body resistance. However, this current will also depend on the resistance at the contact point, e.g. touching or holding a live wire, and the resistance at the earthing point, e.g. rubber or leather shoes, etc. Due to this combination of resistances, the actual current flow through the body at 230V can vary from virtually zero upwards.
The usual reaction to an electric shock is to instinctively pull away from the live part. However, a person holding rather than touching a live wire may not have the ability to let go because when the AC current through the body exceeds a certain level (the release level) the muscles can freeze and prevent normal muscular action.
According to IEC60479, two key levels of electric current need to be considered with regard to shock protection.
The first is the "let-go" level, which is generally accepted to be around 7mA. At or above this level, muscles may seize, and a person touching or holding a live part may not be able to let go of the live part. RCDs rated up to 10mA are intended for protection against "let-go" currents, and are recommended for use in hospitals and old people's homes or similar locations.
The second is the "fibrillation" level, which is generally accepted to be around 50mA. At or above this level, heart fibrillation is likely to occur. RCDs rated up to 30mA are the upper limit for RCDs intended to provide shock protection.
The following provides an indication as to likely effects on the body for currents at different levels.
- For currents up to about 1mA, there will be little or no sensation of a shock.
- For currents of 1 - 10mA there may be a moderate to strong sense of pain in the joints and muscles of hands, arms and feet. Let go may be difficult.
- For currents of 10 - 200mA, muscular freezing is likely to prevent let-go. There may be severe pain in muscles and joints, increased blood pressure and difficulty in breathing. There is a risk of heart fibrillation.
- For currents >200mA there will be an increasing risk of heart fibrillation and irreversible heart damage.
Q: How is the use of electricity made safe?
A: There are three basic measures used to provide protection against electric shock. These are;
- Isolation of live parts: Consider the basic socket outlet where live parts are concealed within the socket. Modern socket outlets are fitted with shutters to further improve isolation.
- Insulation of live parts: Electric wires and cables are usually covered with plastic insulation to prevent people touching live wires.
- Earthing: Metalwork such as cooker bodies, etc. are connected to earth to prevent them from becoming live and dangerous to touch.
Residual Current Devices (RCDs)
Q: What are RCDs?
A: RCDs are devices that provide protection against electrical currents flowing to earth. Such current could flow to earth through a person's body and present a shock risk, or flow through wiring or electrical appliances and present a fire risk
Q: Why use RCDs?
A: The three basic measures do provide a very high degree of protection against
electric shock. Just imagine how dangerous your home or workplace would be if
any one of the above protective measures was not provided. However,
circumstances do arise where one or more of the three basic protective measures fails, for example a breakdown in insulation between a live part and metalwork, exposure to live parts when changing fairy lights in a Christmas tree, cutting of a cable with an electric lawn mower, etc. Under such conditions, an RCD can provide an additional level of protection against electric shock.
Q: How do RCDs work?
A: Under normal conditions the current flowing in the live conductor (I L) will be the same magnitude as the current flowing in the neutral conductor (I N). The two conductors are passed through a current transformer (CT) in the RCD, and the CT will produce an output when it sees a difference in these two current magnitudes. Under a fault condition, for example a person touching a live part, an additional current (I F) will flow to earth back to the supply. Current I L will now be greater than current I N and the CT will produce an output in proportion to this differential current. If the differential current is above the predetermined trip level of the RCD, the contacts will automatically be opened thereby providing protection against electric shock.
The term "Residual" in Residual Current Device implies that there is a residual current flowing in the circuit over and above that required to provide power to a load.
Q: At What Current Level Do RCDs Operate?
A: The operating current level of RCDs depends on the application of the RCD. If the RCD is intended primarily for electric shock protection, the operating level will typically be 10mA or 30mA. RCDs can also provide some protection against electric fires caused by larger current flows to earth. These RCDs typically have an operating current of 100mA or 300mA. It is important to note that 100mA and 300mA RCDs are not suitable for personal protection against electric shock because the operating current would exceed the let-go and heart fibrillation current levels.
Q: How Fast do RCDs Operate?
A: In general, RCDs respond faster to higher fault currents and slower to lower fault currents. There are two reasons for this.
- The studies into the effect of current flow through the human body indicate that the body can withstand relatively low current levels for longer periods than higher currents. If this characteristic was plotted on a graph it would reveal a body withstand duration which was roughly inversely proportional to the current levels. The RCD can be designed to mimic this characteristic by making it respond faster to higher fault currents and slower for lower fault current levels.
- If RCDs were made to respond equally fast for high and low fault current levels, there would be a high risk of nuisance tripping of the RCD in response to momentary earth currents, such as those arising from voltage spikes, surges, starter motor inrush currents, etc. Bear in mind that the RCD is intended to provide additional protection only in the event of failure of one of the three basic forms of protection, and as long as these are intact the RCD does not need to operate.
Q: In What Form Are RCDs Available?
A:The term RCD is a generic term which is applied to the whole family of RCD products. RCDs are generally available in four forms as follows:
- RCCB, which is a Residual Current Circuit Breaker.
This is basically a mechanical switch which can be manually opened and closed, and which is fitted with an RCD function to enable it to automatically disconnect power in the event of an earth fault. These are available with trip current ratings of 10 - 500mA.
- RCBO, which is a Residual Current Breaker with Overcurrent protection.
This is basically a circuit breaker which can be manually opened and closed, which can automatically open in the event of an overload current condition, and which is fitted with an RCD function to enable it to automatically disconnect power in the event of an earth fault. These are available with trip current ratings of 10 - 500mA.
- SRCD, which is a Socket outlet which is fitted with an RCD function to enable it to automatically disconnect power in the event of an earth fault. These are available with trip current ratings of 10 or 30mA.
- PRCD, which is a Portable plug or adaptor which is fitted with an RCD function to enable it to automatically disconnect power in the event of an earth fault. These are available with trip current ratings of 10 or 30mA.
Q: What Standards Cover RCDs?
A: RCDs are generally covered by international or national standards. IEC, which is the world body responsible for standardisation in the electrical industry, publishes product standards for countries world-wide. These standards usually have the prefix IEC, e.g. IEC61008. Adoption of these standards is not mandatory but many countries adopt IEC standards as national standards, sometimes with modifications.
CENELEC is the European body responsible for standardisation in the electrical industry and seeks to maximise standards harmonisation within Europe. International standards published by IEC are usually adopted by CENELEC (possibly with modifications). CENELEC usually replaces the IEC prefix with one of two prefixes as follows:
- EN, a European Norm, e.g. EN61008. When an EN is published, CENELEC member countries must replace any conflicting national or IEC standard with the EN version.
- HD, Harmonisation Document, e.g. HD60384. When an HD is published, member countries are required to adopt the HD but may modify it to suit national conditions or practice.
- When a CENELEC member country adopts a CENELEC standard, it usually adds a prefix to indicate that country's identity. In Ireland's case the identity is IS, e.g. ISEN61008.
RCDs are covered by the following standards. In some cases the IEC standard is still under review in IEC or CENELEC and awaiting formal adoption by member countries.
RCCBs IEC61008, EN61008, ISEN61008
RCBOs IEC61009, EN61009, ISEN61009
SRCDs IEC61541 (presently being prepared)
PRCDs IEC61540 HD61540
IEC, CENELEC and National Standards can also have subsections to cover different types of RCDs within the main standard, as follows.
RCCBs ISEN61008-1 = Main body
ISEN61008-2-1 = Section applicable to voltage independent RCCBs
ISIEC61008-2-1 = Section applicable to voltage dependent RCCBs
RCBOs ISEN61009-1 = Main body
ISEN61009-2-1 = Section applicable to voltage independent RCBOs
ISIEC61009-2-1 = Section applicable to voltage dependent RCBOs
Q: Where Should RCDs be Fitted?
A: The Irish Wiring Rules, (the Rules), more correctly known as the National Rules for Electrical Installations, Third Edition, ET 101, current edition, as published by the Electro-Technical Council of Ireland sets out the requirements with regard to the use of RCDs in Ireland.
Q: Where can I get more information about the use of RCDs?
A: ETCI has published a Guide to the Use of Residual Current Deices, ET214, which is available from ETCI offices.
Q: I have a 30mA RCD fitted in my house and it keeps tripping for no apparent reason. What can I do?
A: A Get an electrician to check the installation. The RCD tripping could be an indication of a deterioration in the electrical insulation of wiring or appliances.
Q: I have a 30mA RCD which occasionally trips for no apparent reason. Can I simply change it for a 100mA unit?
A: No. The 30mA RCD was installed to provide shock protection. This cannot be assured by a 100mA RCD because it may prevent let-go and heart fibrillation. The RCD may be of an older design which is prone to nuisance tripping. Try having it changed for a new one.
Q: How often should I test the RCD?
A: Manufacturers tend to advise users to "test often" or "test frequently", but these terms are not defined. Testing every 3 - 6 months would be considered acceptable where the RCD is fitted in a consumer unit and may be slightly inaccessible. However, SRCDs and PRCDs could certainly be tested more frequently because of their ready accessibility.
Use the changeover from Winter Time to Summer Time or vice versa as an opportunity to test the RCD. You have to reset clocks anyway, so why not test the RCD also.
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