Sim's Electrical Companion
Insulation - Thermosetting, Thermoplastic & MICC
Thermoplastic is the most common type of cable insulation. It is cheap, easily manufactured but has a low melting point. Thermoplastic insulation is only for use where the cables will operate up to a temperature of 70°. Most thermoplastics will melt when their operating temperature is exceeded. This means they are not really suitable for common ways of public buildings unless adequately protected.
Common thermoplastic compounds include:
Polypropylene, Vinyl, Poly Vinyl Chloride (PVC), Polystyrene, Polycarbonate, Polyethylenetheraphthalate & Polyethylene.
Thermosetting cables can operate up to 90° and are employed for use in high ambient temperatures. Their other main purpose is for fire, safety and security applications. When subject to a direct flame thermosetting cables will set hard maintaining some mechanical integrity and potentially working for a longer period of time in a fire. This type of cable is specified for most fire safety services and heating applications.
Common thermosetting rubber compounds include: Butyl Rubber, Natural Rubber, Nitrile, SBR, Silicone, EPDM, Neoprene, Hypalon & Synthetic polyisoprene
Mineral Insulated Copper Cable (MICC) is insulated with magnesium oxide and affords a high level of mechanical and fire protection with a high operating temperature of 105°. Used in heritage or listed buildings & in buildings with an increased risk of fire eg thatched or timber framed. Termination is a skilled job and requires specialist tools. See further on for details on how to make off a mineral gland.
Conductor Materials
Three main metals are used for cable construction though some others are used more rarely:
Steel - used for its low cost and its high tensile strength. It is a poor conductor but can provide mechanical protection and is employed in overhead power line cores to add strength. Steel is also used in Steel Wire armour for mechanical protection and often as the earthing conductor. Steel has iron in it and is affected by magnetic fields.
Copper - The most common material used for low voltage and extra low voltage installations. It is a reasonable, malleable and is the best non precious metal for conductivity. It is non magnetic which can be an advantage.
Aluminium - Cheaper than copper but less effective as a conductor it is used for its extra light weight. Most overhead pylons use Aluminium with a steel centre to add the required tensile strength. If steel or copper were used the span distance would be drastically reduced between pylons. Aluminium is also used for screening or shielding some cables.
Solid, Stranded and Multi Fine Wire
Solid conductors are used in PVC/PVC Multi-core cables, PVC singles or panel wiring and other areas where a rigid cable has benefits. Solid core cables are prone to repeated stress so they are not suitable for environments where vibration is likely e.g. in mobile or transportable units & motor connections.
Stranded cables have more flexibility than solid core conductors. Often 7 cores are packed into a circular insulator. Stranded cables are best used over short distances if attenuation (signal loss) could be problematic. They are suitable for fixed wiring in conduits, ducts and trunking. For single conductor applications this is the most common choice.
Multi-fine wire cables are the most effective where large amounts of vibration is expected. It is especially used where a high level of flexibility is advantageous. Production costs are greater than the other two types. Worthy of note is that in fixed electrical installations ferrules must be used for terminations and the use of soldered multi-fine wire is not allowed by BS 7671. Applications include automotive, robotics, avionics, shipping and connection to machinery or motors.
Common Installation cables
Singles
As the name suggest singles are individually packaged conductors. They come in solid, stranded and multi-fine wire forms. Used for fixed wiring in conduits, trunking and ducts. Solid conductors are generally used with small cross sectional areas as they become harder to dress and terminate the larger they get. Solid core cables are used in panel building and applications where rigidity is an advantage. Stranded are easier to pull through conduit systems. Multi fine wire are the most flexible but also most expensive.
BS6231 Tri-Rated cables are single installation cables that have passed stringent tests in America, Canada and the UK. They are multi-fine wire and are highly flexible. They are favoured by control panel builders and in robotics. They are insulated with a specialised heat resistant PVC insulator.
Available in sizes 0.5 - 16mm². Tri-rated cables are used for panel building and in scenarios where resistance to vibration is beneficial. Example applications include vehicles, mobile electrical installations, marinas, circuses, pumps, motors and fayres etc.
Multi fine wire cables should be terminated in a crimp to prevent whiskers becoming disconnected. Soldering the terminations is not accepted by BS7671 Requirements for electrical installations.
BS 6004 BS6242Y PVC/PVC Multicore
Often referred to a twin and earth or three core and earth this is the most common installation cable for domestic and light commercial applications. It is cheap and packaged with colour coded conductors which makes termination easier. Smaller cross sectional areas have solid cores and larger ones have stranded.
They have PVC insulated live conductors and the circuit protective conductor (cpc) is uninsulated. The intention is that if the cable is damaged it will have a higher chance of completing an earth fault loop path increasing the chance of automatic disconnection if damaged. The illustrations shows that where the cable is terminated the earth is sleeved manually to prevent danger of short circuits.
The cpc is usually smaller than the current carrying conductor to save on weight and cost. As sheathed cables it is very easy to dress the cables and they are less prone to mechanical stresses and electromagnetic effects. Most common methods of application are clipped direct or buried in the building fabric.
The earth is a smaller cross sectional area to the live conductors. The reason is the cpc only needs to carry a fault current for a very short time. Available in Thermoplastic or thermosetting (white sheath) or thermoplastic (grey sheath).
Aluminium Wire Armour
This cable is used where magnetic effects need to be avoided where current is induced into the wire. If the armour was magnetic this effect would be greatly increased producing more losses and heat. With multi-core cables this is counteracted by opposing magnetic fields in the other live cable/s.
AWA has another advantage of being more ductile and lighter than steel or copper equivalents. Mostly applicable to Medium or higher voltage applications. Can be used outdoors or buried.
Flex & Communications Cables
Flexible multi-core cable
Used essentially to power movable or portable appliances. Not to be used for fixed installation wiring. Standard flex has a round PVC thermoplastic sheath and multi fine wire conductors individually insulated and either colour coded, numbered or lettered.
Butyl Rubber Flex
This is commonly used to connect to heat producing devices like immersion heaters or electric underfloor heating. Oddly this use of the cable is called for that purpose is called a cold tail! It is a 900 thermosetting plastic.
Arctic Flex
As the name suggests this is designed for use in colder environments. It maintains is pliability and effectiveness down to -40⁰C. It comes in two common colours Blue to signify single phase 230V and Yellow to signify 110V single phase. Common uses include festivals, outdoor events, caravan sites, boat yards and construction sites.
Braided 3 Core Iron Flex
Heat and scorch resistant this is primarily used on electric irons where the chance of the cable coming into contact with the heating element is quite high.
Armoured Communications Cable
Multiple PVC insulated copper conductors - designed to protect telephony or computer communication systems. Can be buried or submersed. As well as armouring the cables a screened to reduce or eliminate magnetic effects which could cause failures in data transfer or crosstalk.
Data Cable - Ethernet
This is commonly used for data transfer and is available in a wide variety of options. The main differences being the maximum length of run and data transfer speeds. Categories are commonly Cat 5, Cat 5e, Cat6, Cat 6a, Cat 7 & Cat 8. The differences are in whether the cables have solid core conductors or stranded and the method of shielding if any is applied. Solid core cables are usually only used for the fixed installation where durability is more desirable than flexibility.
The cables have 8 core pairs which are twisted to prevent cross talk where a magnetic field could induce a current in another core. The accuracy and amount of twists and method of shielding greatly affects how effective a cable is at resisting magnetic effects and therefore its data transfer rate. Shielding is in the form of a metallic foil or foil faced plastic. U/UTP is unshielded, F/UTP is as pictured above with a foil shield under the outer insulation. U/FTP is unshielded outer but the twisted pairs are foil shielded. F/FTP has both types of shielding offering the highest amount of protection but at a higher manufacturing cost. Cat 8 can support PoE Power over Ethernet and communications over a single cable.
Installation Cables
Steel Wire Armour
Steel wire armour has at least 2 conductors and the steel can be used as the circuit protective conductor. Commonly used for distribution circuits and where there is increased risk of mechanical damage. SWA can be buried and used in wet conditions providing the connections to accessories also meet the required rating for ingress and impact.
SWA commonly utilises the armour as a parallel path to earth or it can be the sole circuit protective conductor. This is often the case with DNO / supplier cables to TN-S earthed properties. Termination requires the application of brass glands internal or external types. With this in mind termination is slower than some other methods but is mechanically strong.
NYJJ-3
This is a double insulated cable that can be used outside or for increased mechanical protection. It does not need the complex glands that SWA requires so it is far quicker and easier to install. The NY stands for Nylon J stand for PVC so the outer insulation is nylon then PVC and finally each conductor has its own PVC insulation. The number afterward states how many conductors it has. Also known as Hi Tuff but this is a trade name.
SY Control Flex
A specialist cable designed for circumstances where there is a requirement for increased mechanical strength and resistance to vibration. It requires proprietary glands as shown in the illustration. The steel braiding is designed to reduce interference as the main purpose of the cable is for control as opposed to power purposes.
LSZH Cables
PVC cables have the undesirable property of producing noxious smoke if they are subject to fire. In may locations this can increase the liklihood of death by asphyxiation in a fire. Black smoke can also disorientate and may obscure exits. Many locations require that low smoke Zero Halogen cables are selected to increase the chance of survival in a fire. Examples include underground railways, tunnels, mines, railways, ships, motor vehicles and in public buildings. Part B of the building regulations - Fire safety in Buildings recommends that the propogation of smoke in fire exits and public ways be minimised to aid successful egress. On method is to specify LSZH cables.
LSF Cables
Low Smoke / Fume not to be cofused with LSZH cables. These cable produce less smoke and fumes but are not tested to the same degree as LSZH cables so should be treated with caution if specified. They do produce harmfull gases but less so than standard PVC cables.
Coaxial Cable - COAX
Commonly used for connections to TV aerials and satelite boxes coaxial is a communications cable that is designed for transmission of Radio Frequency signals. The centre solid copper conductor carries the RF signals and the sbraid is to block electromagnetic interference which can affect the RF signal. Coaxial cables can have much longer runs than twisted pair and can support speeds of arounf 10 Mb/s.
Shotgun Cable
This cable is often used to connect CCTV, cameras and monitors and recording equipment it saves on installation time by proving both signal and power cables in one package. The two are easily separated for end point connections. The two cables are allowed to be run together as they are both insulated for the highest voltage present.
Common Cable Connectors
USB Type A - The most commonly used connector for Universal Serial Bus applications. Ethernet aka RJ45 (Registered Jack - number 45 in the standard) This has an added feature of a locking mechanism to prevent accidental disconnection. This type of connector can be used for most types of Ethernet category cable.
USB Type C introduced in 2016 has the benefit of being inserted both ways around. This standard has been adopted by many electrical companies like Samsung, Nokia, Ipod Pro© etc. This connector supports 10 Gb/s. More costly to produce than the other micro/mini varieties so they are mostly reserved for devices that are high end or need higher power or data transfer speeds.
Display Port adaptor similar to HDMI can carry audio and visual data in fact you can get adaptors to convert to HDMI. Mostly found on modern PC's, laptops. Supports high bandwidth 8k plus applications.
HDMI High Definition Multimedia Interface. The most commonly used standard for home entertainment systems, games machines televisions, projectors etc. Supports High definition graphics and sound up to 4k HD.
Thunderbolt connections are mostly adopted by Apple MAC© applications. Adaptors are available for PC and other devices but are uncommon. The thunderbolt connection is being superseded by USB-C.
USB micro B - used for 5 pin connections most commonly for smart phones to communicate with other devices. Employed by several mobile phone manufacturers including Samsung, Nokia, Motorola & Oppo. Superseded the previous mini B usb standard. Used in applications where the power and speed of type C is not required.
Lightning connectors developed by Apple© and used for many of their mobile devices like phones and tablets.
USB mini A/B - The earliest small form factor usb. Ubiquitous until very recently they are still used for some devices like cameras and MP3 players. Many cheap electronic device manufacturers are still producing them. Now superseded by USB micro B.
Jack plugs - Used for several applications the amount of connections they have can be determined by the insulating rings. The ones shown have between two and five connections. Commonly used in small form factor for audio applications like light headphones short distance patches, and small microphones. If there are only two separate conductors it is for mono applications three can support stereo with a shared common. 4 and 5 can be used to combine mic and phones in one, like gaming or operator headsets.
As well as 3.5mm there are 2.5mm and 6.5mm (1/4 in). The 6.5mm is used heavily in the music industry for amps, keyboards, guitars and microphones etc. The 3.5mm connectors have barely changed since their introduction over 70 years ago. The larger variant is robust, reliable and has its historical uses in phone exchanges since the 1870's.
Micro B super-speed
Used for high speed/bandwidth devices like external hard drives and some mobile devices. This is designed for USB 3 standard and is likely to be rapidly superseded by the type C standard. Expected transfer rates of about 10Gb/s.
Phone connectors
RJ 11 (Registered Jack type 11) This has been used in telephony for decades since its introduction by Bell laboratories in the early seventies. Pictured right with a standard 4 pin BT phone connector above it.
RCA plug and Jack (Phono)
(Pictured left) Theses have been ubiquitous in all audio and some video applications since their introduction by Radio Corporation of America in the 1930's. Robust and reliable they are easy for a user to terminate effectively with basic soldering skills. They are usually colour coded for audio left (white) audio right (red) video (Yellow).
SATA Vs IDE
Serial Advanced Technology Attachment. This standard was introduced to improve data transfer speeds in information technology devices like hard disk drives, Blu-ray drives & solid state drives. Its predecessor the IDE cable used a ribbon cable up to 18inches long that had the negative aspect of affecting cooling efficiency in PC and server cases. IDE had transfer rates of 133 Mb/s compared with SATA 6 Gb/s. Its only likely you will find IDE in old PC towers. SATA also support hot plugging, like usb devices, meaning they can be added or removed when the computer is running.
DSUB
Ubiquitous in computing connections for hardware accessories invented by James Cannon in the late 1950's. The connector is shaped like a D to prevent incorrect connection. They come in a variety of pin outs, the ones shown are 9 and 15 pin but many others are available all the way up to 104 connections!
Molex
Dating back to around the 1940's Molex are commonly used for connecting DC power in PC's radio controlled devices and many other DC items. The are wide ranging in their application and have a great variety of pin commonly 4 way ones are used to power PC peripherals internal to the tower case. Many Molex connectors also have a safety lock to prevent unintended disconnection.
Socket Outlets
