Consumer Unit Replacements East renfrewshire

Changing a consumer unit

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This article discusses the reasons why you may need to change or upgrade a Consumer Unit (CU) aka "Fuse Box", and covers the procedures to follow. 

Contact WES ELECTRICAL 0141 840 5236

Hyndland electricians

General Guidance

Note that this represent major electrical work, and should not be attempted unless you are confident that you understand the technicalities involved, and can produce an adequate standard of workmanship. 

You will also need access to specialist test equipment such as an earth loop impedance tester, and insulation resistance tester, a low ohms meter, and a RCD tester (or equivalent multifunction tester). 

You should have access to a copy of the IEE on-site guide and a copy of the IEE Wiring regulations.

Note that most of the work described here would be classed as a "notifiable work" under Part P of the building regulations.

Additional Safety Advice

When carrying out earth fault loop tests, and insulation resistance tests on virgin installations, one should take great care to ensure that no other occupants of the house are put at risk of exposure to high touch voltages should it turn out there is a failure in some part of the protective infrastructure, and that adequate warnings are given before testing.

Reasons for a change

There is often an implicit assumption that a modern CU with resettable Miniature CIrcuit Breakers (MCBs) will be "better" than an existing one that has cartridge or re-wireable fuses. It is important to understand that both types of fused circuit protection are still permissible in the current wiring regulations, and can offer the required levels of protection. There are also disadvantages to changing from fuses to MCBs in some cases. 

Reasons to change

1. You need provision for more circuits
2. The existing CU is damaged in some way
3. You need to better integrate (or provide for the first time) RCD protection for circuits.
4. You have a rewireable fuse CU and there is a risk that uninformed people may attempt to re-wire a fuse with the incorrect rating wire.
5. You have older PVC T&E power cabling with undersized earth wires and re-wireable fuses. 
6. You need to separate out circuits to allow independent control - say for time switched electric heating, or for a power feed to an outbuilding.
7. To rationalize or simplify an existing system which is complex (either just to reclaim space, or to make use of the system less prone to errors).

Potential pitfalls

In many cases a new CU fitted with MCBs will be upgrading an older CU fitted with fuses (either cartridge or re-wireable). There are a number of problems that may manifest as a result:

1. Nuisance trips. Compared to fuses, modern MCBs react more quickly to very short term overloads, and may result in loss of power to a whole lighting circuit when a bulb blows. 
2. Discrimination: it can be harder to ensure that the circuit protective device nearest to a fault will be the only one to open when you have cascaded MCBs - sometimes upstream fuses interoperate better with downstream MCBs
3. Expense: Changing a CU can be expensive, and may not bring significant benefits in overall safety. There may be other more serious problems with an electrical installation that are better addressed first.
4. Extra work: Fitting a CU with RCD can often result in the installation not working initially due to hitherto unnoticed faults in circuits such as a borrowed neutral or higher than expected earth leakage. While discovering these faults is not a bad thing, it can force the investigation and repair of a number of other issues not directly related to the original task planned, causing unexpected cost and delay. 

Note that steps can be taken to minimise these potential problems, such as using HRC fuses where more appropriate (e.g. feeding submains to outbuilding CUs), or using type C MCBs on lighting circuits etc.

Planning

Location

Consumer units typically need to be within 2m of the electricity meter unless an additional switch fuse is fitted to protect the tails. They should not be mounted on the electricity suppliers meter board (although this is quite often seen). An ideal location should also make access to the CU easy without need to resort to ladders or climbing past obstructions - since you may be doing it in the dark. 

Ways

The spaces into which circuit breakers and other devices may be fitted are called "ways". Generally each device (and hence often each circuit) will take at least one way. When selecting a new CU, it is wise to choose one with enough ways to accommodate all of the proposed circuits, and to leave a few spare ones for future applications. Note also that some devices that can be mounted in a CU such as contactors, time clocks, bell transformers etc, may be wider than a standard single module and hence take more than one "way", and some of these more exotic devices may also require a space to be left beside them to facilitate cooling.

RCDs

Any modern CU will typically feature at least one RCD, and quite probably more in new designs. 

Split Load Vs Multiple

When selecting a CU, one option that is often overlooked is to use more than one CU rather than one big split load one. For example, it may be simpler to position a pair of smaller CUs in a confined space giving adequate free ways. 

In the case of houses with TT Earthing, the normal 16th edition style single CU solution involves a 100mA time delayed RCD in the position of the main switch, with the 30mA RCD in the split load position (the time delay resolving the problem of discrimination between the RCDs under fault conditions). Using two CUs will allow a normal 100mA RCD to be used on one CU dedicated to circuits that do not require direct contact protection, and the other for socket circuits etc. This will save the cost of a time delayed RCD since there is no need to cascade RCDs in this case.

Service Connector Block / Henley block

Multiple CUs can each be fed from their own set of tails. A Service Connector Block (aka "Henley Block") is a large junction box that can be used to split the tails from the meter or main switch enclosure, to allow the feeding of multiple CUs. Note these are available in single pole and double pole. The double pole devices will accommodate splits of both the Line and Neutral tails of a typical domestic supply in a single unit.

External main switch

When more that one CU is fitted, it is often worthwhile fitting an additional single "main switch" so that the capability to kill all power to all circuits with one action is retained.

Selecting Equipment

The immediate choice you will be presented with is the choice of metal clad or "insulated" (i.e. plastic) CUs. On TN [1] systems either can be used. The metal clad ones are better if you need to terminate cables like SWA with glands. The plastic ones are better for smaller installs where the ability to easily cut out only small sections for cable entry is handy. 

With a TT install you will need to use a plastic CU since this minimises the possibility of a phase to earth fault occurring inside the CU before the RCD (and hence never being cleared due to the high earth fault loop impedance of the local earth spike). 

One should also check that the breaking capacity of the selected protective devices is adequate. Typically modern MCBs can break fault currents up to 6kA. This is usually more than adequate. However if you live in a large densely populated city, or very close to a substation then you should use the appropriate test equipment (most earth fault loop testers will have a capability to measure the prospective short circuit current) to measure the maximum prospective short circuit current to ensure it is below the maximum limit that can be safely broken by the selected MCBs. In situations where 6kA is inadequate, the use of HRC cartridge fuses may be more appropriate, or using some of the ranges of consumer unit and circuit breakers with higher breaking capacity designed for industrial or commercial use.

Finally, many CUs will have their main isolator switch on the right hand side, however this is not universal and different brands of CU may favour placing the main switch on the left. Some can be reconfigured to your preference. The position of your electricity meter and the length of the tails may dictate that tails entry on a particular side is required.

Other work

One job that frequently needs doing with a CU replacement is installation or upgrading of the main equipotential bonds between the main earthing point and the metallic services entering the building. 

Starting work

Plan your work schedule carefully. Make sure you have enough time allotted to complete (or at least advance it to a appropriate intermediate stage) in the time / light available. Make sure any cordless tools you need are charged, and that batteries in test equipment are ok. You will also need to ensure you have enough natural light or suitable additional lighting to carry out the work safely. Head mounted LED torches are ideal for this sort of work. Again make sure you have spare batteries. Ensure you have adequate spare cable / wire to hand plus crimps and junctions boxes etc should you need to extend circuit wires. 

Disconnecting the power

Prior to replacement of the CU it is necessary to isolate the power feed to it. Some installations have an isolation switch for this purpose, however many don't and the other most readily available method is to remove the main service fuse. The official way to do this is to seek a temporary disconnection of the supply. More details on the procedure can be found here.

Removal of the electricity distributor's main fuse yourself is not legal, however it is common practice. Unofficially it is reported that many of the supply companies would prefer electricians do this, rather than take the risk of working live. 

Great care must be taken when removing the fuse. It must only ever be pulled when there is no load on any of the circuits (i.e. all existing CU(s) turned off). These fuseholders may be of historic design (possibly dating from the 1940's or earlier), and may lack even fairly basic safety guarding. Touchable metalwork inside the fuse enclosure can be assumed to be live. Please see the additional notes in this article.

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Working Live

It is possible to remove the tails and tape the ends over, but this is not recommended, as it does constitute a risk of injury, loss of sight and to life. Live working should not be attempted unless one has the correct equipment and knowledge to allow this to be done safely. 

Labelling

Start by identifying and labelling all the existing cables that enter the current CU before disconnecting the wires. One mistake here can cause a fair bit of trouble later!

Removing the Old CU

Depending on the design of the old CU it may be necessary to remove the fuses or circuit breakers first to be able to disconnect the circuit wires. You will probably need to straighten the wires to allow them to be pulled through the cable entry holes in the old CU. 

Take care if there is any old rubber cable present, since these will have fragile insulation easily damaged. As a general rule rubber wired circuits are not fit for re-use typically due to insulation breakdown, and undersized protective conductors. In some limited cases it may be possible to re-connect a rubber insulated cable, in which case great care will need to be taken to not damage the insulation while disconnecting and removing the wires.

Intermediate tests

Once the old CU is out of the way, this is an ideal time to make checks on the existing circuit wiring. Round trip low ohms tests on ring circuits can now be carried out easily since both ends of the ring are readily available. Insulation resistance tests on individual circuits are also easy to carry out. If you find faults at this stage (like a ring circuit that has a broken loop) you may need to mark this for later attention rather than divert activity away from the main task now. You can always leave one circuit disconnected when reconnecting at the CU later. Some simple tests at this stage can also help identify likely causes of nuisance RCD trip later (like borrowed neutrals or earth / neutral shorts). 

(recording the test results as you go can save some work later)

Installing new CU

Prepare the new CU

First check and setup the CU as you require it. This may mean you need to choose where splits will occur on split load units. Often this will require the cutting of the live busbar to the required number of ways for each section. Even if the CU is apparently already setup correctly you need to make sure that all connections are tightly made and in the right place. 

The New CU does not have to be in the same location as the previous one. Obviously if it is some distance away then the existing circuit wires will need to be extended. Even with a CU in the same location as before it is not uncommon for wire extensions to be required inside the box simply due to different layouts. Inside the CU individual wire extensions may be crimped on. Outside the CU then either junction boxes will be required, or fully insulated cable crimped joints be made.

Fix the Equipment

You may find it easier to fit any service connector blocks and smaller switch enclosures before the main CU is in place. 

Fix the CU in place - if this is going to require masonry fixings take care that you are not going to drill into any buried wires!

Connect the supply

Next the main earth connection plus the supply tails from the meter / switch / service block can be installed. These will need to be done using suitable size tails (typically 16mm² for supplies up to 80A, and 25mm² for 100A supplies). Once the main supply connections are in place you can carry out a visual inspection and a a couple of quick sanity checks with a multimeter to ensure you have got the polarity correct and there are no shorts on the supply.

Install protective devices

Depending on the design of the CU it may be easier to install all the protective devices at the start, or it may be easier to do them one at a time as you reconnect each circuit. The latter approach is least open to error. 

Re-connect circuit wires

Connect each circuit in turn following your labelling. If you have new circuits to introduce that were not connected to the old CU it can be worth leaving those until you have restored the original functionality and tested it. 

Labelling

The MCBs or fuses should be labelled to show what circuits they supply. Installations using both wiring colour codes are required to have a notice fixed by the CU stating that both colour codes are in use. It is a good idea to label as you go to save confusion later. 

Testing CU main wiring

Once all the circuits are connected, another visual inspection can be done, and you can go over all the screw connections again to ensure they are tight. Check busbar connections to the main switch / RCD as well. A final sanity check with a multimeter will also catch any silly mistakes. 

You can carry out a full installation insulation resistance check at this point also (taking care to protect any sensitive electronic equipment wired to the circuits first!)

Reconnecting power

With all the CUs turned off the power to the CU can now be restored (fuse replaced etc). All the individual ways should be turned off on the CU before turning on its main switch. 

At this stage you can carry out full RCD tests using an appropriate tester. 

Each of the individual circuits can then be turned back on one at a time, and functional checks be carried out.

Resolving Problems

If all goes well you should now have a working electrical system again. However in a minority of cases you could meet problems. These may be ones that you have introduced during the CU change, or often, they are ones that were always there but did not make their presence felt until now. 

Nuisance RCD trips

It is not uncommon for a new CU to trip the RCD as soon as power is turned on. There are a number of common causes of this, which are addressed in the RCD article.

MCB trips

MCBs trip when too much current flows in the circuit they supply. Since the odds of an appliance fault developing while you replace a CU are small, the likely causes of MCB tripping when a CU is replaced are:

• a circuit miswired during the works (eg when fixing another fault)
• wrong rating of MCB fitted

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Main Consumer Units

Fired-up over consumer units

A number of fire investigators throughout the UK have noticed a recent trend with an increasing number of fires involving plastic consumer units.

In the last five years, the Glasgow Fire Brigade has investigated 107 fires (October 2006 to October 2011), and in the last 12 months it has identified a 100% increase in these incidents, with 45 investigations concluding that the fire originated within a plastic consumer unit. 

There are several types of fault that lead to the ignition of the plastic enclosure/casing. The most common is localised resistance heating at the connection of the neutral link (solid or flexible) terminal connection bar. These conductors are used to connect the main isolation switch and the neutral connection/terminal bar. Other areas where a neutral connection fault can occur are additional neutral conductor links to connect other components (such as the conductor linking the main neutral connection terminal bar to the Residual Current Device (RCD[s]).

In general, electrical installation contractors may perceive neutral connections as less hazardous than the live connections. However, in a single-phase consumer unit the total current for the final circuits is flowing through the main neutral connections, which are just as susceptible to poor connections as the live connections. Other locations of defective connections that have resulted in the ignition of a plastic consumer unit are the connections at the input or output of a main isolator switch or the connections of an RCD.

What are the problems that lead to these defective connections? 

Poor workmanship by the installer is a one factor. The use of inappropriate tools, distraction when making final connections, not re-checking connections (particularly on larger conductors) or not checking the tightness of factory made connections can all lead to localised resistance heating. 

The actual construction of the connections by the manufacturer is another potential issue. Indeed, Nick Carey has noticed a significant change in the construction of connections/terminations within consumer units over the last 10 to 15 years. 

The use of one fixing screw per connection instead of two screws, the use of plated steel fixing screws instead of brass screws, quality issues with threads and quality issues with burrs of metal at the end of screws that limit the conductor/screw contact area. There has also been a change from rigid plastics to more aesthetically pleasing moulded plastic enclosures. 

The change with enclosure construction has also coincided with a product that electricians find easier and quicker to install, with soft plastic openings that are simple to remove and adapt for cable entry points.

Another more recent problem affecting several brands of consumer unit is a manufacturing defect within Miniature Circuit Breakers (MCBs) leading to resistance heating at the switching contacts area.

What are effects of these fires? 

The changes to the type of plastics used to construct consumer unit enclosures in the last 10-15 years and pressures on manufacturers to be environmentally friendly has led to a reduction or even an omission of fire retardants in the plastic used to construct the enclosures.

The results of fire investigations where physical evidence has identified the fire originating within a plastic consumer unit is that defective connections have led to the ignition and destruction of the plastic enclosures. The fire often develops to involve the entire plastic enclosure with burning droplets of plastic falling to the floor that on occasions can start secondary fires below. Other items stored or installed adjacent to the consumer units determine how the fire develops from this point. Some of the fires have also involved gas pipes, which has significantly increased the fire development. 

The fires have also injured a number of occupiers. Typically the injuries are smoke inhalation but there have been some burn injuries. Fortunately, to date, there have not been any recorded fatalities. However, there have been a number of near misses with the fire service rescuing occupiers trapped by the fire within their properties.

In one recent case, the consumer unit was located under the stairs in a terraced three-storey house (as shown in figure 1). The quantity of storage within the cupboard and the involvement of the timber staircase ensured the fire spread to the top floor. The fire was discovered by one of the occupiers at 1am and the other nine occupants were quickly alerted to the fire and they all successfully evacuated. The damage to the consumer unit was so extensive that it was not possible to identify the product brand.

Fires involving plastic consumer units often only leave the remains of the main switch, RCDs and MCBs with the remains suspended by the final circuit conductors. The plastics used in the casings of the main switch, RCDs and MCBs contain flame-retardants and are designed to withstand significantly higher temperatures than the plastics used in the enclosures. 

Figure 2 details the typical fire damage to the enclosure of a plastic consumer unit in a fire confined to the under stairs cupboard of a two storey house.

Ignition tests

A recent series of ignition tests was undertaken on five brands of plastic consumer units. The tests were initiated by the Glasgow Fire Brigade and undertaken with the collaboration of Bureau Veritas Solutions and the Electrical Safety Council. Initial tests identified that three of the five plastic enclosures did not use a flame retardant in the plastic. The other two brands used enclosures with a flame retardant incorporated in the plastic.

The first series of tests were confined to replicating the hot wire material test as specified in BS/EN 60947-1: 2007 + A1:2011. Criticism could be raised by the manufactures of consumer units as BS/EN 60947 is not a ‘product test’. However, the test successfully identified the ease in which the plastics used in the construction of the enclosures were ignited. A pre-conditioned hot wire is wrapped around a plastic sample and the wire is then energised with prescriptive electrical limits for up to 30 seconds. In these tests a maximum wire temperature of 550°C was measured.

The results of the hot wire tests were that with the exception of one sample of plastic that had a flame retardant, all of the plastic samples ignited irrespective of whether they did or did not have a flame retardant incorporated in the plastic. The shortest time to flaming ignition was 11 seconds for a plastic sample without a flame retardant and 16 seconds for a plastic sample with a flame retardant. 

All five plastic consumer unit enclosures were subjected to a needle flame test in accordance with the EN 60695-11-5:2005 standard. The needle flame was introduced into the consumer unit via a small opening to enable access to the main neutral connection at the neutral connection bar.

One of the consumer units with a flame retardant did not ignite and the flame was applied at four additional areas, again without ignition. The second consumer unit with a flame retardant ignited and once the needle flame was removed, the flame self-extinguished within eight seconds. 

The remaining three consumer unit ignition tests resulted in fires that spread from the initial needle flame to involve the entire plastic enclosure. The shortest time from needle flame application to the ignition of the plastic was eight seconds. Two of the ignition tests had to be halted after four minutes as the smoke being produced by the fire began to overwhelm the dedicated extraction system of the test facility (figure 3). 

Plastic Consumer Units in the UK have to be constructed in accordance with BS EN 60439 (replaced in 2011 by BS EN 61438). The plastic enclosures have to withstand 660°C glow wire product tests. The opinion of the author is that this test is not sufficient to ensure the safety of the occupiers in properties where plastic consumer units are installed. 

The data previously detailing fires that have originated within consumer units in the Glasgow area, resulting from various types of defective electrical connections, shows an increase in these life-threatening fires. 

The plastics used in the construction of consumer unit enclosures should therefore be more resistant to ignition from an internal defective electrical connection. In addition, the product should be constructed to ensure that any localised heating within the consumer unit should be contained within the product.

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Christmas 2014 has fast approached many of us this year and there is no better time to up grade an old tv set to a new energy efficient led number. with so many fantastic offers out the at the moment and possibly even better in the january sales you could pick yourself up a bargain and get it fitted on the wall for optimal visual experience, space saving and it just looks cooler on the wall than sitting on the stand.

we are an electrical installation company who over the years pioneered wall mounted tv installation from back in the day when sonos systems where wired and i had to deal with a mass amount of cables to supply and stream video and audio to individual rooms, now of course sonos systems are wireless and use wifi the connect to other devices.

As far as wall mounted tv installations go there are multiple options for what you can do with your installation as i tell all my customers you can get whatever you want done, the only issues are cost and how much disruption you are willing to take in you house until completion, apart from that the sky or the wall in the limit. (i have mounted on a ceiling but thats another matter) when we take on an installation for our customers, we mainly cover the west of scotland - (Glasgow renfrewshire ayrshire,) we do a site survey on what is possible, what you would like, and how much you are looking to spend on the installation products i.e hdmi quality / quantity, bracket type and finish.
once we have all the fundamentals arranges we pencil you in for a time and date and do the installation for you, it can usually take 2-3 hours to complete depending on what is getting installed.

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TIPS FOR CCTV INSTALLATION

Tips on installing CCTV to your home. 

WES ELECTRICAL WESTEND GLASGOW

The prospect of drilling a hole through the outside wall of your house to run the power and video cable for a camera may seem a big job. With a little forethought it can be quite simple. 

Positioning of cameras
Most people want to hide the camera as much as possible. The modern cctv camera can easily be located under or on the fascia/soffit boards where the roof meets the wall. When located here it is sheltered from wind and rain and can be shaded from most sunlight. The height of the camera gives a good area of view and minimizes the risk of vandalism. 

Another advantage of this location is cabling. It is pretty easy to run the cables into the loft from this position. Many houses have a small ventilation gap between the roof tiles and the external wall, or a small hole may be drilled in the fascia board to gain access to the loft. 

Cabling
It is usually quite easy to pick up mains power in the loft or, if additional cabling is required it is now internal. Wireless transmission can be used for the video signal with the receiver being placed next to the monitor or recorder (TV, VCR, PC etc.). That's it, job done. 

A 'hard-wired' system is almost as easy to install. Locate the TV aerial down-lead that may be in the loft or run down the outside of the house, then run the CCTV camera video cable alongside the aerial cable, which will lead directly to the TV. 

A good method of connection is an RF modulator. This changes the camera's video output to an RF output. You can pipe the CCTV images down the existing TV aerial down-lead and view on the TV/VCR as if it were another channel. If your house is fitted with a TV distribution system, this method will allow the pictures to be seen on all the TV sets. 

Addition of Switchers etc.
Consider placing switchers, multiplexers or DVRs in the loft. This keeps all the cabling in the loft with just one output cable to your monitor. It also hides your recording device. 

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ELECTRICAL TESTING IN GLASGOW

WES ELECTRICAL WESTEND GLASGOW 01418405236

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Safe method of isolation.



The recommended procedure for proving dead and safe isolation should be by use of a test lamp or two pole voltage detector as recommended in HSE Guidance Note GS38 regulations.
Non-contact voltage indicators and multi-meters should not be used. The test instrument should be proved to be working on a known live source or proprietary proving unit before and after use. All phases of the supply and the neutral should be tested and proved dead before any work is commenced by a qualified electrician.




Test sequence and descriptions of test procedures.



The following tests are carried out with the main board / Consumers main switch isolated



1. Extenal earth fault loop impedance (ohms)


Reason: To establish that a good earth exists at the electrical installation in order for the remaining tests to go ahead.


Method: Disconnect the main earthing conductor from the main earthing terminal at the main distribution board. An earth fault loop impedance tester is connected at line and earth (main earthing conductor) at the supply side of the electrical installation and a test performed. Reconnect the main earthing conductor. The result is Ze and recorded on the test sheet. The prospective fault current is measured at the same time after the reconnection of the main earthing conductor at the main board.


2. Continuity of protective and equipotental bonding conductors


Reason: To check that all circuit protective conductors are continuous and are present at every electrical outlet / accessory on the circuit. Also to check that the main earthing conductor and main bonding conductors are continuous and correctly connected at the terminals.


Method 1: The line conductor is connected to the circuit protective conductor of the same circuit at the consumer unit and a measurement taken at ALL accesories on that circuit between line and c.p.c. The highest measurement obtained is recorded on the test report. 
Test result is R1 + R2. The line conductor and neutral conductor are then connected and the above repeated to obtain R1 + Rn


Method 2 (used for main earth and main bonding conductors): A wandering lead is connected to one end of the conductor to be tested and a measurement taken between the other end of this lead and the other end of the conductor. 
Test result is R2.
During this test polarity can be checked as well. The continuity of the neutral conductor can also be checked to determine R2.


3. Continuity of ring final circuit conductors


Reason: This test ensures that all ring final circuits are indeed a continuous ring with no interconnects or breaks within it.

Method: The line, neutral and earth conductors of the circuit are identified and a measurement from one end to the other end of each is taken. These results are r1, r2 and rn. 
The incoming line conductor is then connected to the outgoing earth conductor and the outgoing line conductor is connected to the incoming earth conductor. A measurement is then taken at ALL socket outlets on the ring. The highest of which is recorded on the report. 
This result is R1+R2 for that circuit. The above is then repeated using the neutral conductor instead of the earth conductor. This test provides R1+Rn which does not need to be recorded on the report but is essential to check the circuit correctly.


4. Insulation Resisitance testing


Reason: This test checks whether the insulation around a cable is still intact and has not broken down over time or has been separated from the rest of the ring. It is a good indicator of the age of an installation.

Method: An insulation resistance tester is connected across line and neutral tails at the origin of the supply. 500V are then pumped down the conductors to see if any voltage leaks across from one conductor to the other. The same is then done for the line and earth and the earth and neutral conductors.


5. Polarity checks


Reason: To check that all accesories are correctly connected to line, neutral and earth and that all switches and circuit breakers are connected in the line conductor only.

Method: The method for this is the same as for continuity and is usually done at the same time by operating switches etc whilst conducting the test.


6. Earth electrode resistance


Reason: To make sure that any earth electrode used is of a sufficiently low impedance to allow the timely operation of the RCD protecting the installation.

Method: An earth fault loop impedance tester is connected between line and earth at the origin of the supply and a test performed. The result of which is considered the resistance of the electrode (Ra).



The following tests are carried out with the Consumers main switch switch in the on position




7. Live polarity testing


Reason: To verify polarity of supply authorities system.


Method: An approved voltage indicator shall be used or test lamp to GS38. Using the approved voltage indicator, one probe shall be placed on the incoming neutral, and the other on the incoming line conductor, on the main breaker. The indicator should show it is live. One probe shall now be placed on the CPC and the other on the incoming line conductor. The indicator should show it is live. A test shall be preformed between CPC & incoming neutral. The indicator should show that it is not live.


8. Earth fault loop impedance


Reason: This test is done at the furthest point on a circuit in order to make sure the impedance of the earth path is not too high even at the furthest point so that sufficient current will flow under fault conditions to take out the circuit breaker protecting the circuit.

Method: An earth fault loop impedance tester is connected to line and earth at the furthest point on the circuit and the test performed.


9. RCD testing


Reason: To make sure RCD's trip within the correct time

Method: An RCD tester is connected and a test at 1/2 times, 1 times and 5 times the trip current is performed on each side of the cycle and a time of trip obtained. Usually milli-seconds with the highest being recorded. The manual test button is then pressed.


10. Functional testing

Reason: To make sure all switches, isolators, MCB's etc. work as they should.

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