Glossary – Descriptions of Heating Elements

Here, we will attempt to give you an explanation, in plain terms – we hope, of any technical, or commonly used description (to us) of the specification or component parts used in the manufacturing and supply of Metal Sheathed Rod Heating Elements.

Because we work with these products every day, we sometimes forget that some of the words we use may make no sense to our customers.

If there is anything we have missed from other pages, or in the list below; please contact us to ask for an explanation, we will be pleased to assist and clarify.

Term

Definition (According to TPFay Ltd)

4BA British Association or BA screw threads are a set of small screw threads. 4BA is approximately 3.6mm O/D
19/16” THREAD / HEAD / NUT Thread size used on small water boiler and vending machine elements, size was used for Old Style Kettle Elements
Amp (Ampere) Unit of current (flow) (l)=E/R
AC Alternating current.
Ampacity The current-carrying capacity of the conductor under stated thermal conditions.
Annealing To facilitate complex bend geometry Metal Sheathed Tubular Heating Elements are heat treated after they have been rolled to the desired diameter.
ATEX ATEX directive consists of two EU directives describing what equipment and work environment is allowed in an environment with an explosive atmosphere
Bain Marie Also known as a water bath or double boiler for cooking or maintaining food at a specified temperature. Often manufactured as Dry used with heat source and no water bath.
Bead Ceramic or Aluminium Oxide Insulator used to maintain centralised position of heating element terminal.
Beaded Tailwire Ceramic, interlocking bead, used to insulate and protect tail wire at high temperature.
BiMet, Bi-Met, Bi-Metalic Cutout, Button Thermostat Small thermostat control or limit device. Oven used in Water Boiler Elements to improve protection against Boil-dry failure.
Boil-dry Failure of a high watt density heating element designed to heat liquid due to lack of adequate control, once exposed to air the element sheath temperature increases beyond recommended limits causing premature failure.
Boil-dry protection A combination of control device and special bending design usually seen in Water Boiler Elements installed in manually filled vessels. One small section of element sheath above the rest of the formed element this is attached mechanically or by welding to a Bi-metalic Cut-out Thermostat. This Thermostat can be manual or auto resettable. It is not designed to prevent failure if the entire element is exposed whilst energised. If possible this should be used with additional devices to ensure the elements are completely immersed.
Bottom Entry Formation of an element usually installed in a vessel or tank where the terminals are formed to protrude through the base. Secured by Bushes, Plates, Flanges or Heads.
BSP The British Standard Pipe (BSP) is a family of standard screw thread types that has been adopted internationally for interconnecting and sealing pipe ends by mating an external (male) with an internal (female) thread and has been adopted as a standard scale used in plumbing fittings, except in the United States where NPT is the standard used.
BS Standard Elements BS7351 1990 Specification for Metal-sheathed heating elements for industrial use
BS Standard Immersion Heaters Industrial British Standard Specification for Industrial Immersion Heaters using Metal-Sheathed Elements BS 7798 1998
BS Standard Immersion Heaters Domestic
Bush Metal threaded sleeve usually brass or stainless steel, with a round or hexagonal flange face. Used to secure or fix heating elements in place. Crimped using special dies for Dry applications. Silver Soldered for Wet applications. Compression Bushes, are secured using spanners to tighten a cap nut compressing a brass olive onto the sheath. this is suitable for wet and dry applications and performs well under pressure and in vacuum.
Bung Heater Heater assembly used in Removable Core Heaters. Single or multiple U bent Heating Elements fixed into a step sided flange. Heater assembly slides into a Stainless Steel or Carbon Steel tube welded or bolted into a vessel with one closed end. The element transfers the heat to the heating tube by conduction and convection. Bung Heaters can be easily removed or replaced without requiring the tank to be drained (Oil Tanks, Bitumen Heaters, Food and Dairy, Pharmaceuticals, Aggressive Chemical Solutions, Liquids containing heavy suspended solids that may clog the space between the legs of a Standard FI Industrial Immersion Heater), The heater tubes are more easily cleaned within the vessel without damage to the heating elements.
But Crimp A hollow terminal connecter, usually made from copper or brass, crimped to the Terminal Pin of a Heating element to allow tail wires to be attached with in the profile of the heating element diameter. Usually for application where the terminal and wire are at lower temperatures. 105°c for PVC 180°c for Silicone tail wire (depending on Amps)
Calcium Carbonate (Calcification) Calcium carbonate is the active ingredient in agricultural lime, and is created when Ca ions in hard water react with carbonate ions creating limescale.
Usually termed as limescale. Minerals, of varying concentrations, usually in suspension in most tap water. Deposit settle easily on metal surfaces such as heating element particularly when at elevated temperatures. Deposits can corrode the surfaces of most stainless steel alloys such as incoloy. Water treatment or regular cleaning and de-scaling of heating elements is highly recommended to prevent premature failure.  Calcium Carbonate is also a very effective thermal insulator, even a small build up around the sheath of a heating element can prevent effective heat transfer and cause premature failure of the element due to localised overheating or “furnacing”.
Cartridge Heater Tubular Heater assembly usually with the terminals at one end. Designed to be inserted into heating Dies, Molds, Platens and various other applications demanding localized heating and are suitable for temperatures up to 800°c .
Cavitation Cavitation is the formation of vapour cavities in a liquid – i.e. small liquid-free zones (“bubbles” or “voids”) – that are the consequence of forces acting upon the liquid. It usually occurs when a liquid is subjected to rapid changes of pressure and or temperature that cause the formation of cavities where the pressure is relatively low. When subjected to higher pressure, the voids implode and can generate an intense shock wave.
CE Mark The CE marking or formerly EC mark, is a mandatory conformity marking for certain products sold within the European Economic Area (EEA) since 1993.
CNAF Gasket Material Compressed Non-Asbestos Fibre
CNC bending Equipment Proprietary equipment used by TPFay to perform repetitive and complex bend formations of metal sheathed tubular heating elements.
CNC Milling Machine Computer Numerically Controlled machinery to perform repetitive, cutting, drilling, threading, surface finishing and profile cutting of components for Heating Element assemblies by TPFay.
Coiled Element Formation of metal sheathed tubular heating elements to helix shape. Ideal for concentrating heat in a small space to increase surface area and reduce watt density.
Coiled Element Flat Formation of metal sheathed tubular heating elements to flat spiral shape, ideal for clamping against flat surfaces or placed in tubular air ducts.
Cold End (Cold Zone), CE, C/E Un-heated zone at each end of a metal sheathed tubular heating element. Designated in inches or mm. The terminal pin at each end of the element is made from various length rods that protrude into the heater tube where it is welded to the resistance wire. The most common cold end length is 50mm (2″). The cold end must be selected carefully when designing elements to pass through insulated voids in oven or furnace walls or air gaps or stand-offs. Care must be taken when designing bends so that the junction of the cold end and resistance wire is not within the bend zone.
Condensate Element A metal sheathed tubular heating element used in Refrigeration or Air Conditioning equipment to ensure any condensate produced can be removed by evaporation.
Compression Bush Metal threaded sleeve usually brass or stainless steel , with a round or hexagonal flange face. Used to secure or fix heating elements in place. Compression Bushes, are secured using spanners to tighten a cap nut compressing a brass olive onto the sheath. this is suitable for wet and dry applications and performs well under pressure and in vacuum.
Conductor A conductor is the current-carrying, non-heat producing component of a heating element.*
Conduction The transfer of energy within or between two bodies in physical contact.
Convection The movement of a mass with its associated energy (liquid or gas) from one location to another.
Cool Zone Similar to or adjacent to cold end, created by elongating the internal resistance coil wire of the heating element prior to assembly to create a lower watt density heating zone.
DC Direct Current.
De-Frost Element A metal sheathed tubular heating element used in Refrigeration or Air Conditioning equipment to ensure ice build-up on coils are removed quickly.
Delta Connection A system energized from three substantially equal voltages that differ in phase by one-third cycle or 120°.
Diameter Generally a measurement of the thickness of a heating element.
In geometry, the diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle
Dielectric Breakdown The ability of the electrical insulation to withstand an applied voltage
Duct Heater An array of Heating Elements inserted into a duct usually with forced air my means of a fan.
Earth A conducting connection between an electrical circuit or equipment and the earth or some conducting body that serves in place of the earth.
Earth Stud Connection Stud usually welded to the metal sheath or other connected metal component in order to facilitate easy connection of the earth connection.
Element An element is a resistor encased in an acceptable insulating material covered with a protective sheath. The finest examples of these are made by TPFay Ltd.
EN 60335-2-73 The European Standard, EN60335-2-73, replaces the old BS3456 Part 2 and introduces new requirements of construction and, for the first time, stipulates a maximum water temperature for installations using a fixed immersion heater
Ex-Rated Definition of a  hazardous location is defined as a place where concentrations of flammable gases, vapors, or dusts occur.
Finned Element Finned tubular air heating elements are constructed like basic tubular elements with the addition of continuous spiral fins. Attached by means of specialist machinery to roll and crimp the spiral fin material to create good contact and thermal heat transfer away from the element by increasing the surface area. The fin is generally crimped or welded at each end.
FI Immersion Heater Fay Industrial Immersion Heater Range. Specially designed to provide robust protection for wiring connection.
Flange Heater Designed for heating liquids and gases in tanks and pressure vessels, metal sheathed tubular rod elements are fixed to a metal flange of standard or special geometry.
Flash Test Also known as High Voltage (HV), Dielectric Strength or HiPot.  Flash testing is designed to detect gaps or clearances between conductive parts and earth, pin holes in insulation and other degrading as a result of production processes and /or wear and tear.
Flat Bar Element Solid Bar Element 38mm wide 8mm thick, supplied in various lengths and wattage outputs. End sections usually flattened with holes punched for ease of fixing against a surface. Not Manufactured by TPFay.
Flat Coil Element As Coiled Element Flat
Furnace Higher temperature oven used for industrial or commercial process.
Furnacing (failure) Failure of a heating element due to overheating because the heating zone is completely surrounded by a material with thermal insulation properties. Heat cannot effectively transfer from the element and continues to increase, control thermostats will be unlikely to sense this temperature rise sufficiently. Premature element failure will be likely to occur or be accelerated.
Also can occur due to limescale deposits. See Calcium Carbonate.
Ground A conducting connection between an electrical circuit or equipment and the earth or some conducting body that serves in place of the earth.*
Gland See Bush
Hazardous Location Locations are classified depending on the properties of the flammable vapors, or gases, or combustible dusts, or fibers which may be present and the likelihood that a flammable or combustible concentration or quantity is present.*
Head Screw-plug, boss used for Immersion Heaters. Usually made from Brass or Stainless Steel, occasionally Mild Steel. Usually with BSP threads. Can also be supplied with Metric or NPT threads. Can be Hexagonal, Octagonal or round profile to aid securing.
Heat Heat is energy in transition, or transfer, from one body to another by virtue of temperature difference existing between the bodies.
Heater A heater is a completed, usable assembly containing one or more elements.
Heat of Fusion Heat necessary to change solid to liquid.
Heat of Vaporization Heat necessary to change solid to gas.
Hertz Unit of frequency of charge reversal for alternating current.
Hi-Pot A high voltage quality assurance test performed on electrical components and systems.
Hygienic Flange Hygienic or Tri-Clover fittings are developed to facilitate safe and easy installation that ensures optimum integrity of the piping installations. A broad selection of dimensions and specification which meet the strict standards of the Food and Dairy, biotech, pharmaceutical and chemical industries.
Immersion Heater Water is most often heated electrically by putting a heating element in direct contact with it. Such an element is therefore called an immersion heater. The water to be heated is usually enclosed inside an insulated cylinder: a hot water tank. Such a heating element consists of a thin metal tube that contains an electrical resistance heater; this, in turn, is encased in an insulating material. To control the temperature of the water, a probe inserted alongside the element triggers a switch according to the temperature of the water, the system as a whole constituting a Thermostat.
Immersed Length Length of heater measured from the flange face of the head to the furthest bend of the element sheath.
Ingress Protection Rating (IP Rating) The IP Code, Ingress Protection Rating, classifies and rates the degree of protection provided against the intrusion of solid objects (including body parts such as hands and fingers), dust, accidental contact, and water in mechanical casings and with electrical enclosures.
Incoloy (I/LOY, ILOY) Sheath Material commonly used for heating elements.
Incoloy refers to a range of superalloys produced by the Special Metals Corporation group of companies. They are mostly nickel-based, and designed for excellent corrosion resistance as well as strength at high temperatures; there are specific alloys for resistance to particular chemical attacks. Heating elements are commonly produces in Incoloy 800, also referred to as Alloy 800, Nicalloy.
Insulation Electrical insulation is the dielectric material surrounding the resistor and/or conductor in order to electrically isolate the current-carrying components from earth or other components. Thermal insulation is any material that retards the transfer of heat to the environment or other components.
Insulation Resistance Insulation resistance is the ability of the insulation to resist a percentage of current.
Insulation Resistance Test Insulation resistance testing provides a quantitative measurement of the high quality of insulation.
IP Rating The IP Code, Ingress Protection Rating, classifies and rates the degree of protection provided against the intrusion of solid objects (including body parts such as hands and fingers), dust, accidental contact, and water in mechanical casings and with electrical enclosures.
KB Ring Element A solid heating element in circular formation, with a hollow centre section often fitted in nested pairs. Fitted clamped against the surface of hotplates or tanks. Originally manufactured by  another manufacturer.
KB Ring Element Replacement As Coiled Element Flat, used as a low cost replacement for KB Ring Elements.
Leakage The undesirable passage of current flow through or over the surface of an Insulator.
Leakage Current The total electrical current flow from the resistor through or around the insulation to a point external to the resistor when the element is energised.*
Limescale See Calcium Carbonate
Limit Thermostat, Hi-Limit Thermostat, Safety Thermostat
Looped, Loop the Loop, Double Looped Triple Looped
M4 Metric Thread Size nominally 4mm 0.8mm thread pitch
M5 Metric Thread Size nominally 5mm 0.8mm thread pitch
M20 Metric Thread Size nominally 20mm 1.5mm thread pitch commonly used for cable glands and conduit connections
M25 Metric Thread Size nominally 25mm 1.5mm thread pitch commonly used for cable glands and conduit connections
Magnesium Oxide MgO Magnesium oxide (MgO) is chosen for application in sheathed heating elements due to its particular combination of physical and chemical properties in that it offers exceptionally good electrical resistance together with high thermal conductivity. By varying the physical and chemical properties of the magnesia, powders can be produced with specific physical and electrical properties appropriate to individual applications, from simple water heating to the most advanced industrial applications.
MegOhm (MΩ) Descriptive term for multiple (1000nds) of Ohm the electrical measure of resistance. Usually used as a measure of insulation resistance.
MilliAmp (mA) Descriptive term for fractional (1000th) of an Amp. Unit of current (flow) (l)=E/R
Nickel Chrome (NiCr) A non-magnetic alloy of nickel, chromium, and often iron, usually used as a resistance wire
Nickel Tail Wire Stranded Mangonic Nickel wire used as a high temperature conductor cable. Supplied bare, insulated with fibreglass sleeve or ceramic beads.
NPT A U.S. standard for tapered threads used on threaded pipes and fittings.  In contrast to straight threads that are found on a bolt, a taper thread will pull tight and therefore make a fluid-tight seal.
OHM The electrical unit of resistance (R or Ω) R=E/I
Olive A brass or sometimes copper ring used in Compression fittings that will compress to form a water or pressure tight seal against the element sheath.
Open Circuit Failure of a circuit within a heating element. Can occur due to wear and tear, oxidation, overheating, stress fracture or other physical damage.
Out of Water Failure Failure of a heating element, sometimes manifested by sheath damage
Oven Dry We use special ovens to remove residual moisture that may be present at the end of unsealed (or sometimes sealed) elements after prolonged storage. When dry the elements are sealed by a method appropriate to the designed use of the element.
Over The Side Heater Special Immersion Heater assembly, that can be placed into an open top tank or container and can be easily removed. Designs can include extended rigid or flexible cold end section to facilitate positioning of heater at the base of a tank through an open top. No requirement to cut holes in the side of the tank, ideal where the tank has a bund or restricted access.
Over temperature cut-out Secondary protection device or thermostat set to a higher temperature than the control thermostat; in case of failure of the control thermostat the secondary device will open the circuit. Helping protect the heating device.
Oxide A coating often found on the surface of tubular metal sheathed heating elements after annealing, heat treatment or prolonged use at elevated temperatures. Inert and generally harmless, though can cause staining to material it comes into contact with. Special annealing processes can prevent the build up of oxide for aesthetic or performance related design.
Parallel Circuit A circuit in which the identical voltage is presented to all components and the  components according to the resistance or the impedance of components.
Plate Metal bracket fixed to a heating element, usually close to the terminals. Used to fix the element in place in the piece of equipment.
Polymer Coating Used on selected element designs to help prevent corrosion and adhesion of limescale / Calcium Carbonate.
Polyolefin A thermoplastic polymer, Polyolefins are used for heatshrink electrical insulation sleeves for crimped wire terminals
PTFE heating Element Used on selected element designs to help prevent corrosion when immersed in highly corrosive liquids.
Radiation The transfer of energy from one body to another through space by electromagnetic wave phenomena.
Rating Rating is the performance characteristic of an element or heater and is normally expressed in power output (watts) for a specific input voltage.
Removable Core Heater Imersion Heater Assembly containing Removable Core Heaters. Single or multiple U bent Heating Elements fixed into a step sided flange. Heater assembly slides into a Stainless Steel or Carbon Steel tube welded or bolted into a vessel with one closed end. The element transfers the heat to the heating tube by conduction and convection. Bung Heaters can be easily removed or replaced without requiring the tank to be drained (Oil Tanks, Bitumen Heaters, Food and Dairy, Pharmaceuticals, Aggressive Chemical Solutions, Liquids containing heavy suspended solids that may clog the space between the legs of a Standard FI Industrial Immersion Heater), The heater tubes are more easily cleaned within the vessel without damage to the heating elements.
Removable Tank Heater Special Immersion Heater assembly, that can be placed into an open top tank or container and can be easily removed. Designs can include extended rigid or flexible cold end section to facilitate positioning of heater at the base of a tank through an open top. No requirement to cust holes in the side of the tank, ideal where the tank has a bund or restricted access.
Resin Seal Special two part epoxy resin seal used to prevent ingress of atmospheric moisture into a heating element. Use is dependent upon the temperature limits of terminal area during service life and storage.
Resistance Wire Resistance wire is a type of high resistance electrical wire. Application for resistance wire includes resistors, heating elements.
The most common type used is Nickel Chrome, NiCr, a non-magnetic alloy of nickel and chromium, is commonly used to make resistance wire because it has a high resistivity and resistance to oxidation at high temperatures. When used as a heating element, resistance wire is usually wound into coils.
Resistor A resistor is the heat-producing component of an element.
Ring Terminal Ring terminals allow for optimum fit and maximum electrical performance when crimping with screws or threaded posts and are widely used in solder-less wiring applications. For High Temperature applications such as Heating Elements TPFay recommend the use of special Nickel Steel Terminals, Available to Purchase in our on-line shop.
Rosamon Trade name of a range of Special Immersion Heaters Produced by TPFay since purchasing Heating Equipment Ltd in 2004. Rosamon Heaters have been produced since 1931.
Run Dry Immersion Heater Specially designed Immersion Heater, utilising complex bending or coiling techniques to using low watt density elements by maximising the surface area of the element surface. Particularly useful where boil-dry or accidental operation of the Immersion heater cannot easily be prevented, Knife sterilisers, utensil washers.
Saddle Terminal A shaped clamp terminal connector in 3 pieces, a flat plate with a threaded hole is spot welded to a heating element terminal pin, a shaped plate with a larger plain hole is screwed down to clamp connecting wires in place.
Screwplug Boss used for Immersion Heaters. Usually made from Brass or Stainless Steel, occaisionally Mild Steel. Usually with BSP threads. Can also be supplied with Metric or NPT threads. Can be Hexagonal, Octagonal or round profile to aid securing. Commonly refered to as a HEAD
SDN TPFay Document type Sales Delivery Note. Your delivery from TPFay will carry a unique 6 digit reference prefixed with SDN.
Sealed Tails Shrink Sleeved cable joint on a heating element when using Tri-Rated PVC or Silicone Fibreglass Tail-wire. Double Polyolefin Shrink Sleeve.
Series Circuit A circuit in which the components are arranged end to end to form a single path for current.
Side Entry Formation of an element usually installed in a vessel or tank where the terminals are formed to protrude through the side(s). Secured by Bushes, Plates, Flanges or Heads.
Silicone Fibreglass Tail-wire High Temperature resistant tail-wire / cable fitted to TPFay Heating Elements. Maximum Temperature 180°c Constant – 250°c Intermittent (Subject to current draw of element)
Silicone Mat Heater Silicone Heater Mats have been deigned for use in areas where standard heating elements are difficult to apply. All mats are self adhesive and have etched foil or wire wound elements embedded into a glass cloth supported silicone rubber compound which provides a highly robust but very flexible heater.
Silicone Seal RTV RTV (Room Temperature Vulcanising) seal used to prevent ingress of atmospheric moisture into a heating element. Use is dependent upon the temperature limits of terminal area during service life and storage.
Silver Solder High Temparature, High Silver content welding alloy used to secure heating elements to heads, bushes, flanges plates etc.
SIN TPFay Document type Sales Invoice. Your invoice from TPFay will carry a unique 6 digit reference prefixed with SIN. If you have a credit account, we would urge you to pay on time, we love customers who do, we will not apologise for our stance with those that don’t without good reason. We aim to pay our suppliers on time or earlier if we can, credit offered to us is a privelage, not a right.
Single Phase A system energized from a single alternating voltage.
Sheath The metal tube used for heating elements. Sheath Material Use of Alloys.
Sheath Diameter The outside dimensions of the element sheath
Sheath Length The length of an element, measured and defined as the length of the sheath (tube) only, terminals are variable, therefore measured and defined separately.
Shrink Sleeve Special polyolefin tubes used to protect heating element – tailwire connections. Shrink to the profile of the components using special equipment providing a water-resistant tamper proof seal
Solid Boiling Plate Usually a cast iron plate with an embedded heating element, round square or oblong, TPFay can usually fabricate a replacement
Solid Ring Element Usually a cast iron plate with an embedded heating element, round.  TPFay can usually fabricate a replacement
Spade End, Spade Terminal Electrical Connector (Male) spot welded to the terminal pin of a heating element, to facilitate quick connection. Used extensively in domestic appliances. For High Temperature applications such as Heating Elements TPFay recommend the use of special Nickel Steel Terminals to make the female connection to the cable, available to Purchase in our on-line shop.
SHEL Post Terminal Post Brass, Nickel Plated, Approximately 8mm diameter female threaded 4BA or M4 hole at the base connect directly to the heating element terminal pin. Connection to the cable is made by inserting the wire through a side hole and compressing the connection using a supplied 2BA grub screw.
SOR TPFay Document type Sales Order. Your order from TPFay will carry a unique 6 digit reference prefixed with SOR, this cab be easily quoted to trace your original order if you wish to purchase more items of the same design.
Specific Heat The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius
SQU TPFay Document type Sales QUotation or Proforma. Your Quotation or Proforma from TPFay will carry a unique 6 digit reference prefixed with SQU. Unfortunately, our system discards this reference if we convert your quote to a Sales ORder (SOR). This new number will however, be retained and can be used as a reference to enable us to make your item again.
SRN TPFay Document type Sales Return Note. In the unlikely event that you have to return an item to TPFay, you should contact our offices to obtain a unique authorised return number  this will carry a unique 6 digit reference prefixed with SRN, use of this number will enable us to effectively track and trace any items to enable any issues to be resolved quickly.
Star Connection A three phase connection allows the use of two different voltages from all three phases, such as a 230/400V or 240/415V system which provides 230V or 240V between the neutral (Star point) and any one of the phases. A neutral connection is optional and is often referred to as a floating neutral.
Stainless Steel A steel alloy with a minimum of 10.5% chromium content by mass. Stainless steel does not readily corrode, rust or stain with water as ordinary steel does, but despite the name it is not fully stain-proof, most notably under low oxygen, high salinity, or poor circulation environments. There are different grades and surface finishes of stainless steel to suit the environment the alloy must endure.
Heating elements are produced in the following alloys AISI304, AISI309, AISI316, AISI321. Please contact us or refer to our guide to select the most suitable grade for your application
Stamp A unique identification mark on a heating element to show the Watts output at the designed Volts. The manufacturer ID or Logo is also required (FAY) and a batch or date reference to enable full traceability of production and component supply.
Stat, Stat Pocket Short name for thermostat or the thermostat pocket it is to be housed in
Thermal Resistance The property that opposes the flow of heat (energy) through the material.
Thermostat Switch operated by a thermal device, a mechanical bi-metalic device, thermal expansion of liquid in a losed vessel or bulb and reservoir, or a digitally controlled switch with thermocouple type sensor.
Thermostat Pocket A steel tube usually closed at one end to house a thermostat rod or bulb when immersed in liuid as part of an immersion heater or for mechanical protection in other heaters.
Terminal Terminal is the device or point at which external power is connected.*
Terminal Pin The point at which the external power is connected to a heating element, commonly made of nickel plated mild steel. Can be threaded as 4BA, 2BA, M4, M5, sometime plain pin. This pin continues into the heating element by a defined distance (referred to as the Cold End) where it is joined to the resistance wire of the element by welding.
Terminal Box, Terminal Cover A cover secured by means of screws or bolts to protect the element terminals and connected wiring, and sometimes controls, from damage, environmental conditions, accidental contact. See IP Rating guide for further guidance required to select the most appropriate type for your application. For example TPFay FI Immersion Heaters have terminal covers rated as IP67, before this rating was externally tested and qualified our design criteria was to have the cover able to withstand complete immersion in 1 metre of water without ingress of water when correctly gasketed. This exceeds the qualified rating.
Terminal Bridge A raised terminal block support used in Immerion Heaters
Thread A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread.
Three Phase A system energized from three substantially equal voltages that differ in phase by one-third cycle or 120°.
TIG Weld Tungsten Inert Gas (TIG) welding, is an arc welding process that uses a non-consumable tungsten electrode to produce the weld. The weld area is protected from atmospheric contamination by an inert shielding gas (argon or helium), and a filler metal is normally used, though some welds, known as autogenous welds, do not require it. A constant-current welding power supply produces energy which is conducted across the arc through a column of highly ionized gas and metal vapours known as a plasma.
Used in Stainless Steel FI immersion Heaters and Flange Heaters.
Titanium Titanium is a chemical element with the symbol Ti and atomic number 22. It is a lustrous transition metal with a silver colour, low density and high strength. It is highly resistant to corrosion in sea water,  chlorine and other chemicals. It is often used for Immersion Heater construction in very hard water areas.
Tolerance Permissible limit(s) of variation in an object
Tolerance Length Permissible limit(s) of variation the straight length of a Heating Element, commonly +/-1% however alternative tolerances can be specified. As heating elements are produced with a length tolerance design of formed elements must take this into account on one or more bend. Please contact us for guidance or assistance in designing your heater.
Tolerance Resistance Permissible limit(s) of variation in the finished (cold) resistance of a heating element, commonly +/-7%, however alternative tolerances can be specified
Tolerance Wattage Permissible limit(s) of variation in the specified watt output of a heating element at the specified applied voltage. This is dependent upon the resistance tolerance specified.
Tolerance Voltage Permissible limit(s) of variation in the applied voltage, dependent upon your electrical supplier.
Top Entry Formation of an element usually installed in a vessel or tank where the terminals are formed to protrude through the top. Secured by Bushes, Plates, Flanges or Heads. Care must be taken when designing top entry heating elements if heating liquids where the level can fluctuate, see Cold End.
Tri-Rated PVC Tail wire Temperature resistant tail-wire / cable fitted to TPFay Heating Elements. Maximum Temperature 105°c Constant, Minimum Temperature -5°c (or -40°c if specified in design)  (Subject to current draw of element)
U Bent – U Shape Simple element formation with one bend of 180°, specify the dimension from centre to centre of element legs required. TPFay elements can be formed and processed to a U shape where there is no space between the legs if required, we do not recommend that this bending is attempted without our special equipment.
Value! Value!

There is scarcely anything in the world that someone cannot make a little worse and then sell a little more cheaply.

The Man who buys on price alone is lawful prey of these people!

Remember, that a thing is worth what it can do for you, not what you choose to pay for it.

John Ruskin (1819-1900) attributed

VAT Heater Special Immersion Heater assembly, commonly used in chemical processing, that can be placed into an open top tank or container and can be easily removed. Designs can include extended rigid or flexible cold end section to facilitate positioning of heater at the base of a tank through an open top. No requirement to cut holes in the side of the tank, ideal where the tank has a bund or restricted access.
Volt Unit of electrical pressure. 1 volt is the amount of pressure that cause one ampere of current under a pressure of one volt. (W) W=EI
W Bent – W Shape Simple element formation with three bends of 180°, specify the height of the outer legs first from the end of the tube (sheath) to the centreline of the bottom bend and then the dimension from centre to centre of element legs required. Contact us for assistance in designing your heating element.
WW Bent – WW Shape TAs above with five bends, ideally spcified with a drawing, to avoid error.
Wall Thickness The specified thickness of the material used to form the tube or sheath of the heating element.
Watt Unit of electrical power. One watt is equivalent to the power represented by one ampere of current under a pressure of one volt.
Watt Density Watt density is the output of the element or the resistor in watts per square inch (or watts per square centimetre) of surface.
 Wattage rating Tolerance  Wattage output tolerance is the acceptable manufacturer’s wattage variation allowed from rated wattage at rated voltage.*
These definitions are for guidance only, and are terms commonly used by TPFay in manufacturing and supplying quality heating elements and associated components.
For the avoidance of doubt definitions should be checked.