How NOT to Terminate 3 Core SWA Cable


I had problems with a low resistance fault on a ring final circuit during testing last week. After breaking the ring into sections I identified the defective section. I had to lift the floorboards in a bedroom to check for any cable defects or jointed connections. I was surprised to find the following junction box connection. It was connected to a supply to the detached garage outside.

How NOT to Terminate SWA Cable

The picture above shows SWA cable supplying a detached garage. The cable was connected into domestic Ring Final Circuit [RFC] under upstairs bedroom floor. SWA outer armour was not bonded at either end of cable run. PME/TNCS earthing system, so no adequate means of earthing in the garage. The SWA circuit cable was disconnected for safety reasons.

The picture below shows what should be done. A correct gland coupler has been used to connect outer armour to the accesory. This provides mechanical protection of the inner cores and a means of earthing of the outer SWA strands.

SWA Cable and Gland Coupler

I now use an adjustable pipe cutter to prepare SWA cable for connection to gland couplings.

Adjustable pipe cutter can be used to prepare SWA cable for termination into a gland coupler.

Two turns to cut outer PVC, then five to ten turns to cut individual SWA strands. This process is much quicker and cleaner than using a hacksaw.

The picture below shows the quality of preparation using an adjustable pipe cutter.

 

Hand cut SWA using a hacksaw and/or side cutters can be subject to failure due to uneven SWA strand lengths.

SWA cable cut using a hacksaw. Note uneven strand lengths. This makes connection to gland difficult with possible failure of coupling and bonding of SWA strands.

A little extra care and attention in the preparation can make for a much improved and long lasting installation.

Please let me know if you have any tips to improve the standard of electrical installations.

Fatally Flawed Socket Covers Should NOT be Used


Socket Covers should NOT be inserted into sockets – they are dangerous!

  • British 13 Amp sockets have built in automatic shutters to protect against children poking things in them. First introduced 65 years ago, they are considered the safest in the world and do not require external covers.
  • No responsible national body recommends using socket covers.  That includes the UK Government, RoSPA, Ofsted, Child Accident Prevention Trust and Electrical Safety Council.
  • Sockets are made to accept plugs which meet very exact requirements.  Anything which is not a standard plug MUST be made to the same dimensions as required for plugs. No socket covers which meet those dimensions are available!
  • Socket covers introduce a variety of dangers; they make sockets less safe, not more.

Dangerous socket cover

Please follow the link to the Fatally Flawed website http://www.fatallyflawed.org.uk/ and spread the word. It may just save someones life.

The Problem With Ring Final Circuits


The conventional set up in most UK homes is for socket outlets to be supplied by a ring final circuit [RFC]. This came about after the Second World War due to austerity and a National shortage of copper. It became possible to supply a 32 Amp circuit utilising 2.5mm conductors. The earlier standard was 2.5mm² radial circuit, protected by 15 Amp over-current protection device [fuse].

Ring Final Circuit [RFC] outlet missing line conductor

Socket outlet with line conductor missing from termination point.

The picture above shows the main problem with RFCs. The line conductor [red] is missing from one leg of the ring. However this circuit was protected by a 30 Amp fuse, but 2.5mm cable rated at 20 Amps, when NOT in RFC configuration.

The picture below shows the schematic layout of a ring final circuit.

Circuit diagram for Ring Final Circuit RFC

The diagram below shows the basic terminology for circuit layouts.

The damaged circuit would function without any clear problems. Appliances plugged in would still work and no one would be aware of what is going on behind the scenes. The two main problems are imbalanced loading causing overheating and possible failure of protection devices to operate in the correct time to offer fault and/or shock protection.

I prefer to install radial circuits with 4mm² conductors. The radial circuit is quicker to install as there is no need for a return leg. So the actual copper content [material costs] is broadly similar to a RFC installed with 2.5mm² conductors. The circuit will not function if any line conductors are not connected. The testing of radial circuits is much quicker than RFCs due to no need to undertake the three-step ‘continuity of ring final circuit conductors’ tests. The three steps are:

1. End to end test of each conductor, line [r1], neutral [rn] and [earth] circuit protective conductor [r2]. Using a low-resistance Ohmmeter test results must be within 0.05 Ω for conductors of the same size or 1.67 times for 2.5mm²m line and 1.5mm² CPC conductor combinations.

2. Line conductor [outgoing leg] connected to neutral conductor [return leg]  Line conductor [return leg] connected to neutral conductor [outgoing leg]. Using a low-resistance Ohmmeter test results must be taken at every socket outlet, and point of utilisation if appliances connected by double pole switch or fused connection unit. For points of utilisation connected in the ring, the test results should be broadly the same. The approximate calculated value should be (r1 + r n)/4

3. Line conductor [outgoing leg] connected to circuit protective conductor [return leg]  Line conductor [return leg] connected to circuit  protective conductor [outgoing leg]. Using a low-resistance Ohmmeter test results must be taken at every socket outlet, and point of utilisation if appliances connected by double pole switch or fused connection unit. For points of utilisation connected in the ring, the test results should be broadly the same. The approximate measured equivalent to the calculated value should be (r1 + r2)/4. Substantially different values will indicate a spur connected to the ring. Test results rising or falling from the calculated value will indicate a radial circuit or break in the ring following an interconnection within the ring. This is a dangerous condition as  the possibility of fire, overload or failure of shock and/or fault protection is possible. Care should also be taken as socket outlets may give dissimilar results due to dirt or other obstructions increasing resistance readings. If possible visual inspection must be undertaken by examining the electrical connections within the accessory.

The three step test identifies polarity so the remaining ‘dead tests’ are insulation resistance between all conductors [between live conductors and between live conductors to earth] and functional switching.

The reduced testing requirements for radial circuits are:

1. Continuity of conductors [r1 + r2] at furthest point.

2. Polarity at each point of utilisation

3. Insulation resistance of all conductors [between live conductors and between live conductors to earth].

4. Functional switching

The three-step test is not needed for radial circuits.Therefore the time needed to comply with BS7671 testing requirements is greatly reduced.

What’s Cooking?


Overheated conductor due to loose connection

Wylex 3036 fuseboard

I went to repair a faulty central heating boiler recently. When I opened the meter cupboard I found the cooker supply had got very hot! It is amazing how quick a loose electrical connection can overheat, especially when a high current load is supplied.

I have some other photos on my Pinterest board. http://pinterest.com/greendealeco/   Please have a look and let me know what you think.

Domestic Electrical Photos on Pinterest


I’ve updated the Pinterest page with some more horrors found when inspecting and testing domestic electrical installations.

http://pinterest.com/greendealeco/

There is far too much shoddy work and poorly maintained systems in use. Don’t take chances, get your electrical wiring inspected. It may just save your home, or someones life.

Green Deal Ecologic improving your world without costing the earth

Electrical Testing Saves Lives and Homes


Last week I spent a couple of hours, or so I thought it would be, sorting out a faulty central heating control unit. The old Randal unit was life expired. I replaced it with a modern digital unit. Whilst testing the supply, I found that the cable had been jointed four times in a fifteen feet run. Cable went from 0.75 flex to 1.5 twin & earth to 2.5 twin & earth then finally 1.5 flex. A connector block had burned through under the gas fire due to loose connections. Fire had been recently serviced, I pointed out the gas service only sorted gas issues. Electrical checks are not undertaken by Gas Engineers. I replaced all cables and tested, OK so far.

Once all checks completed I powered up the system for live testing. A spark flashed across the central heating pipes; bang, then the fuse blew in the switch! Turned out the pump had seized and was short circuiting through the pipework.

I checked the consumer unit, old BS3036 Wylex board with 2.5mm main bond, no bonding to gas or water services.

Came back the next day to change central heating pump, install 16mm main bond and 10mm bonds to gas and water services. All done working well, Ze 0.21Ω and Zs 0.08Ω throughout system, including radiators and water cylinder.

Each year an average of 34 people fatally electrocuted, 1100 houses fires and 2,500000 people receive electric shocks.

Electric testing saves lives and homes.