Multi-stranded PVC covered wire RATED for higher voltage: ‘FVT’ Rated 250v @ 105degC ‘FVK’Rated 600v/1Kv@105degC 


Multi-stranded PVC covered wire suitable ONLY FOR LOW VOLTAGES <32Vdc and Low temperature <75degC (Ratings improve with the use of ‘Heat Shrink’).      


A CLEAR ALKYD LOW VISCOSITY VARNISH (Sterling Brand B8 or equivalent) in which the whole transformer is immersed.   


Means two wires of same size WOUND SIDE-BY-SIDE so that both have exactly the same length (not necessarily connected together). See also Quadfilar &Trifilar.  


A walled former with a central hole sized to fit a specific lamination type and stack. This allows for a JUMBLE type winding that is always contained and insulated from the laminations by the bobbin walls.   


The packing of laminations–‘BUTT’ means NOT INTERLEAVED i.e. A pile of ‘E’s is directly ‘butted” to a pile of ‘I’s. Used for chokes (where a specific gap can be introduced into the magnetic circuit) or other specific applications, such as BUTTED ‘E’s, where the ‘E’ type laminations only are butted together with no ‘I’s.   


A toroidal type core (See TOROIDAL CORE) formed into a rectangular shape and then cut into two ‘C’ shaped halves.  


Means the TOTAL LENGTH ( including any stripping) of wire protruding from the outside edge of a bobbin, OR if covers are fitted, from the exit-hole of the cover.


A container into which a transformer is inserted for sealing and mounting in a resin. (See Encapsulate)


An ISONEL Type 642 coating bath (or equivalent), in which coating the whole transformer is immersed in a bath to coat it to protect it from humidity and/or other corrosives.

DIA. (mm)

Refers to the COPPER diameter (NOT the overall diameter including insulation) when used to describe copper winding wire.

’E’s & ‘I’s

Lamination steel punched into ‘E’s & ‘I’ shapes which allow LAMINATIONS them to fit around a bobbin or former. Other shapes include ‘U’ ‘L’ ‘F’ ‘T’ ‘C’.


To seal a transformer in a coffin using epoxy (or other) resin. This is usually done to provide the transformer with a weather or damp-proof seal or to provide both a form of mounting and security against movement or vibration. There can also be electrical advantages to encapsulating.


Core made up of magnetic materials composed of oxides containing ferric ions as their main constituent. Similar properties to steel laminations but having a magnetic circuit that is more suitable for higher frequencies. Composite moulded construction of compressed ferrite granules.


A box shape manufactured (usually from paxolin) to provide a winding base for LAYER-WOUND transformers.


High voltage test to check insulation after assembly and usually (not always) before varnishing.


Specification for type of electrical steel, most commonly STEEL used is H14 grade which is typically 0.5mm thick 4.5% silicone steel. Or G.O. (Grain Oriented steel) which is typically 0.35mm thick grain oriented material, annealed after punching. Other grades used include H50, etc.


Winding wire having only ONE layer of protective enamel winding coating (lower electrical insulation).


Winding wire having TWO layers of protective enamel coating (higher electrical insulation). Can also get Grade III.


Tubular PVC Sleeving that can be SHRUNK-ONTO the cable (or connection) with the use of a heat-gun, forming a strengthened insulated termination.


COMPOSITE MYLAR/PRESSPAHN consisting of 0.001” mylar + 0.005” presspahn. Used as insulation mostly between windings and as an outer wrap.

Imag Test

Also know as Magnetizing Current Test or “No Load Current” test. Measures the NO LOAD current drawn by a transformer when a specified winding is connected to a specified voltage. This is the current required to energize the magnetic circuit with secondary windings UNLOADED. Most possible faults (but not all) will show up as a higher than expected current.


On a winding sheet, the Type and Thickness of insulation that must be used between each winding layer in “layer wound” or high voltage transformers.


Fibre-washers inserted ON ONE SIDE ONLY under the bolts WASHER (or nuts) of a transformer to reduce core losses due to the bolt’s short-circuiting the magnetic circuit of the lamination stack.

KEY (Bobbin)

An identifiable feature on a bobbin that is used as a DATUM for the orientation of terminations and windings, etc.


Absorbent thin brown paper used normally to stabilise and separate the layers in small high voltage transformers. Normally 0.002” is stocked.

” L “

On a winding sheet, the number of layers (including parts of layers) to complete a winding.


Standard size of a lamination (eg. 120 or 279 or EI57). The addition of an ‘A’ (e.g. 279A) means there are holes in the laminations to allow insertion of bolts for mountings using feet and straps. On winding sheets this will also include core type or any reference to the type of magnetic circuit.


Layer winding (as opposed to jumble winding) is done by using a manufactured former and winding successive layers in such a way that: a) There is a gap of at least 6 mm (depending on voltage) between the ends of each layer and the end of the former (separation from the lamination). b) Each layer is held in place & stabilised with a layer of insulation material and (in the case of larger wires) tapes may be “wound – in” to support the end turns of each layer.


Multi-stranded PVC covered wire RATED “FVT” (250v @ 105 deg C) Cross Section Area 0.5mm2.


A wire conductor made up of a number of strands of wire- a) 10/.010 means 10 strands of wire, each strand being .010” diameter. b) Appliance wire 0.75mm2 means total CROSS SECTIONAL AREA of 0.75mm2


The physical orientation of the transformer mounts. Different Types are:


CLEAR POLYESTER FILM insulation usually used between windings or externally for additional high voltage protection. Usually nominated as a thickness –eg. “Mylar cheeks 0.003” refers to mylar fitted between the outer winding wrap and the core for added insulation. Thicknesses of 0.003”, 0.005”, 0.007” & 0.010” are normally available.


Refers to mylar sheet insulation inserted between the bobbin and laminations,to provide increased insulation, where: a) The wires pass too chose to the lamination steel in the window area b) The bobbin slots are too close to the laminations.


See Imag Test


NOMEX 410 CALENDERED ARAMID PAPER is a composite high temperature paper reinforced with Kapton polyamide film. Used in situations where high temperatures would prevent use of normal insulations. Thicknesses normally available range from 0.05mm to .76mm.


Means “Open Circuit” – usually used during the testing phase when the “Open Circuit Voltages’ are checked without any connected load.


Outer wrapping covering the winding in a transformer, usually at least two layers of Hyply 5+1.


A small piece of insulation material (like 5+1) used under and over Terminations to provide insulation and prevent damage to the windings.


Copper winding wire with POLYESTER-IMIDE COATING.


Copper wire Insulated with polyurethane enamel.


Should be PVF: copper wire Insulated with polyvinyl formal enamel.


Electrical grade Insulating paper. Usually used to cushion larger diameter wires where the pressure from these wires would normally damage and penetrate other types of insulation. The actual insulation properties of this paper are not high. Sizes normally available are 0.002” , 0.003”, 0.005”,0.010”, 0.016”.


On a winding sheet, means the “Primary winding” of a transformer. Usually is the first winding, but may be split in two or (in rare cases) be the final winding. This winding is usually the INPUT winding.


When four wires of the same size are WOUND SIDE-BY-SIDE so that all four have exactly the same length. They are not necessarily connected together.


Means filling the specified bobbin side-slots (usually high SIDE-SLOTS voltage or primary side) with a thickened opaque mixture of epoxy resin after final assembly and varnishing.This strengthens the leadouts and protects against accidental access or damage to the higher voltage windings.


A layer of copper shim, generally the full-width of the bobbin, (or a specified width), wound as ONE complete turn and insulated from the windings either side. It is most important that the OVERLAPPING END be INSULATED FROM THE START to prevent an internal short circuit that would destroy the transformer. The screen has a GREEN or GREEN/YELLOW flexible lead (usually NO SMALLER than the Primary lead) soldered to its surface. To increase insulation between windings and reduce possible damage from screen edges – the edges (which must be ROLLED SMOOTH) are often taped.


On a winding sheet means SECONDARY windings of transformer (usually, but not always, wound after primary). These are usually OUTPUT windings and there may be as many as six or more.


Winding wire run-out from the windings to act as leads for external connection.


Lamination material arranged (with appropriate insulation) to vary and control the magnetic circuit of the transformer. This is often done using ‘I’ lamination pieces.


Refers to the THICKNESS and TYPE of MATERIAL of a spacer in ‘butted’ laminations or ferrite cores that require a spacer. This may be taken as the THICKNESS for EACH LEG (or the TOTAL THICKNESS where only one sheet is used across all three legs). Any variations of this will be specified.


Means tubular PVC or woven fibre placed around the winding wire for additional protection and insulation. (Also known as spaghetti).


Refers to the total THICKNESS of the pile of laminations that go into a transformer.


An intermediate point in a winding brought out for termination.


Polyester Thermosetting Tape which is the standard in the industry for use in transformers. Available widths normally 6mm, 9mm,12mm,15mm & 24mm. Thickness of each is 0.05mm.


Means connecting an internal winding wire, either to a PCB bobbin pin or to another more flexible lead that can safely exit the transformer.


To bring the leads up along the side of the bobbin, or up ON TOP through the slots, to be terminated on top of the winding with external leads and using woven sleeving .


A protective fuse wound-into or placed on top of a winding, usually the primary. The fuse blows when HEATED to a temperature which can vary with type from 100 degC to 130 degC. Once heated to this temperature, the fuse becomes useless and the transformer must be replaced (or rewound). The fuse is usually wound in and wired in series with the “finish” lead (normally the phase or brown lead).


The central limb of a lamination or the section of a lamination PASSING THROUGH THE WINDING. Tongue is one dimension of the interior rectangle, stack (total thickness is the other.


A magnetic core consisting of a circular ring of iron powder, ferrite, steel or other material. Each material give the core distinctly different magnetic properties.


In a winding sheet means “Turns Per Layer”. Usually used to describe layer winding – but can be Useful for bobbin winding to estimate winding progress. TPL is the number of turns of wire (including enamel insulation) calculated to fit into one layer. Or TPL is the number of turns that MUST NOT be EXCEEDED in any one layer, to ensure side tolerances are maintained during layer winding.


Three wires of same size WOUND-SIDE-BY-SIDE so that all three Have exactly the same length and which are not necessarily connected together.


Refers to the TOTAL (cumulative) number of turns commencing from zero to the end of the winding. Any taps are shown at intermediate figures.


Two wires of same size, often wound together, CONNECTED to act as ONE WIRE.


Exiting self-leads for termination are twisted over themselves several times to strengthen wire and prevent breakage. eg. “4-TWISTED” means the wire is twisted over itself four times.


On a winding sheet, abbreviation for “winding” ie. Primary, Secondary, etc.


When spags or multi-strand wire are SECURED WITHIN THE WINDING either by continuation of the winding over it or, if it is on the last turn, by tape and insulation binding it into position.