Knowledge

This section will serve as THE beginners guide to conduit systems, providing you with everything you need to know.

Chapters in this section will cover topics such as the various types of conduits, connectors, standards & approvals, IP ratings as well as ducting. So whether you use conduit regularly or are new to our product ranges, there is sure to be something for you.

The Guide to Conduit System
Chapter 2 - Connectors

Connectors
Connectors or fittings are used to join conduit to switch boxes, isolator boxes, electric motors and so on. This is usually done by pushing the connector thread through a pre-punched hole in the box called a knock-out and tightening with a locknut.

On some installations such as hazardous areas, the equipment is more robust and the hole for the cables already has a thread i.e. threaded entry. This allows the connector to be screwed straight in, without the need for a locknut.

Occasionally connectors join two ends of conduit (usually for long runs or when the customer under-orders on conduit length). This is bad practice but can be done by screwing two connectors into a threaded coupler, not forgetting to seal the threads.

Compression connectors or fittings
Compression fittings squeeze or hang-on to the outside of its conduit like "C" types. These versions can be used for insulated systems. Insulated systems make sure that when conduit and cables become damaged, the equipment and you do not become "live".

The opposite of an insulated system is an earthing system. This has metal contact from the core through the connector and down to "earth". When a fault occurs, stray electricity is directed away for safety. In pliable systems the metal core is exposed to make the necessary contact inside the connector body. This is the principle used for screening where a combination of connector and fitting will protect sensitive computer cables from foreign signals and interference by conducting them down to Earth.

Screw-In connectors or fittings
Connectors for steel flexible conduits generally screw directly into the metal core which provides the earth path as well as giving a high pull-off load. Conduits must not be used for Earthing and a separate earth wire must be run inside or outside the conduits.

Connector materials
Connector materials vary, partly because of where they are used, but largely depending on how they are made. Most are machined from steel bars which are strong but have to be plated in zinc, nickel etc. to stop corrosion.
Angled connectors, because of their awkward shape, have to be cast in malleable iron. Like steel these are usually protected by coating in zinc.
All plastic parts, sleeves, claws seals and throat insulators, etc, are moulded. This permits smooth intricate shapes to be produced.

Chapter 3 - Threads

What is a Thread?
A thread is a "bump" wrapped around a connector body, or inside a locknut like a spiral. When the lump is big and the coils spaced apart, it forms a coarse thread like NPT or BSP, or if it is small and neat then it can be made into a UNEF or metric thread. Different thread types mean a different pattern of "bumps" or "spiral" has been used on that connector or locknut.

The Pitch of a thread is the distance from "bump" to "bump".

As threads on connector bodies can vary, it is important to specify the correct size of thread, particularly with threaded entries. This will ensure that connectors are suitable for either the threaded entries or locknuts they are used with, and vice versa!

Adaptors and Reducers
There are two types of threads which can be used for connectors. These are female types on the inside, like a nut, and male types around the outside like a screw.

If the female is larger than the male one, then the resulting component is called an adaptor. This allows a large connector to be fitted into a small hole. Alternatively if the female thread is small and can be made inside the male, then the component is known as a reducer so it can make a big hole smaller.

Adaptors and reducers can be made from metal or plastic, depending on where they are used. They are usually steel or aluminium to go with pliable / steel flexible connectors and plastic such as nylon to match Plastic conduits and connectors.

Flameproof Adaptors are generally made from brass so they will not produce a spark when hit accidentally. To specify either an adaptor or reducer the size and thread type of both holes, as well as whether male or female, needs to be known.

Chapter 4 - Materials

Material resistances
The plastic coatings on conduits are fairly soft and yielding but they are still able to resist attack from many substances in solid, liquid or gaseous forms. The resistance charts in the Kopex Technical Data Sheets (TDS) will give a "guide" to the conduits performance when in contact with these substances.? These are compiled from Laboratory tests and sometimes could be different from the actual conditions on site.? Before referencing the Technical Datasheets it is important to have the details of the chemical, etc. which may cause a problem, for example oil is not just oil, there are mineral, vegetable, hydraulic, lubricating, etc. etc, etc. so it is important to know exactly which one is being used.

Smoke
When things go wrong, the plastics in a conduit system can start to burn. The smoke produced can vary from a slight wisp to billowing black clouds.

Standard PVC is messy when it burns and more users are turning to alternative Low acid PVC materials, which provide lower or no smoke and reduced or no dangerous gases. These include special material mixes, treated nylons and materials like PEEK all of which can provide varying improvements over and above normal PVC. These can be particularly important when used in confined spaces or public places where safety is highly important.

Radiation
A few materials found in nature are radioactive and send out radiation signals like a miniature radio transmitter. In addition man made radioactive isotopes exist varying between "pace-maker" batteries and nuclear power stations.

Radiation such as X-rays and gamma rays, flow through the air passing through most materials including bodies and conduits. Depending on the dosage, human tissue could die and conduit materials, particularly the plastic coverings will be degraded giving only a fraction of their original performance.? The amount or dose of radiation absorbed is measured in Rads., the Kopex Technical Data Sheets details conduits with resistance to radiation.

Hazardous areas

A Zone 1 area is a place where the working conditions could easily result in an explosion such as an explosives factory, gas/chemical plants, dust filled flour mill. Because of the obvious dangers in a Zone 1 area, minimum standards of work have been set to keep the number of accidents as low as possible.? Electrical systems are notorious for sparking off an explosion and so any conduit systems must be able to resist explosions or prevent the spread of flame outside the area.

All Zone 1 equipment must be tested and approved by a recognised testing authority (BASEEFA, SIRA etc.). The Flameproof Gland (HAM's and HAA's) has approval against the ATEX directive (for use in Europe) but it must be used with one of the conduits from the Kopex Liquid Tight Conduit range or Kopex Stainless Steel equivalent. The epoxy putty inside the gland stops the spread of flame through the conduit system during an explosion and so prevents further fires.

Below Zone 1 and with safer working conditions are Zone 2 areas. These are places where explosions are unlikely to occur but equipment must still be certified accordingly for use in such areas. In these cases, flexible conduits with KF-F connectors may be used.

Chapter 5 - Approvals

Approvals
Many products have been approved by someone for something. A number of countries have their own ideas on how good a product should be, how it should perform etc. They write their own rules e.g. British Standards, IEC, Canadian Standard Association, and Underwriters Laboratories.

Products are tested against these rules and provided they reach the minimum requirements they can be approved.

Approvals are very specific. Only the products included on the "Approval Certificate" are approved and no more.

Usually proof of approval is shown on the product, either printed on conduits or stamped on connectors, as well as being marked on the pack labels and sometimes on an extra label.

Chapter 6 - Technical

Cable capacity
Cables are electrical conductors; they have a metal core covered in PVC insulation. The core is generally made up of a single thin solid length of copper wire or even thinner strands of fine copper twisted together to make them more flexible.

The size of cable used depends on the amount of electricity it has to carry. Small currents (measured in AMPS) mean small cables. Lots of current will require lots of copper area to prevent overheating. Just as cables are sized by the customer to suit his currents, so conduits can be sized for the cables they carry and protect.

Cables are usually pulled through a conduit in a bunch. The main concern is that there is plenty of spare "hole" to get all the cables through without jamming up. To make this possible a space factor of only 40% is generally used, or in layman's terms 40%, just under ?, of the conduit is filled with cables. The spare space (i.e. 60% minimum) will help ventilation to keep cables cool, and allow cables to be changed or added later.

Crush strength
The crush resistance of a conduit is the measurement of how well the conduit resists being squashed under foot. In depends on such things as strip materials and thickness, depth of conduit wall, shape of corrugations, etc.

Crush is usually graded by pushing a 50mm wide steel block into the conduit. There are various degrees of "push" or load between "very light" to "extra heavy" as detailed in BS EN 50086 part 2.

The conduit will be graded depending on what weight it will hold, without collapsing more than a quarter of its own diameter. It must also return to within 10% of its original shape. This might seem a small amount but by not allowing too much crushing, the cables inside the conduit will not be damaged.

Halogens
Halogens is the name given to a group of elements occurring in nature (they are astatine, bromine, chlorine, fluorine and iodine). The important note is that some of these halogens are contained in certain plastics such as PVC's. When there is a fire the burning plastic will release its halogen in the fumes.? These are poisonous as well as being corrosive. This is why many more customers are requiring halogen-free materials like nylon or type "T", particularly in confined spaces or where there is delicate computer equipment.

IP Rating (Leakability)
If a conduit or connector has a hole in the side, it will not protect the cables or equipment on the inside.? Obviously the larger the hole the bigger the object which could get in and damage the electrics.

A series of tests have been drawn up to show the amount of protection a system will provide.

Commonly known as IP Rating (Ingress Protection) it is a simple measure of how much dust and water the conduit and connectors will keep out.

The IP Rating is specified in BS EN 60529 by two individual numbers, each referring to a scale given in the standard. The first is the size of the solid object the conduit system will keep out varying between a golf ball and talcum power. The second figure shows how waterproof it is, from a drip to complete submersion. Generally the higher these numbers, the greater the protection, although the IP Rating should always be checked against the application for suitability.

Often an IP68 is required, and this should always state pressure and time, in order for the customer to determine suitability.

Minimum bend radius
If a conduit is bent back on itself as tightly as possible without crunching up the metal core or distorting the plastic form, then it is at its minimum bend radius. At this point the conduit can be reversed and bent back again without permanent damage.

Although conduits are happy to sit at their minimum bend radii, it is not good practice to continuously work in this position. Particularly on flexible applications it means that the whole construction is being pushed to the limit and could affect the life expectancy of the tube.

Pull off load
Even when assembled correctly, the weakest link in a conduit system is the joint between the conduit and connector. In some applications this joint can be under tension, for example when equipment is moved dragging conduit and cables along the floor. Connector pull-off loads are quoted in technical literature to advise customers on the strength of this joint.

Temperature rating
The temperature range of a conduit system depends on the materials used to make the connector or conduit. The temperature range quoted in literature is the lowest and highest temperatures where the conduit will still function and protect the cables inside.

Pliable conduits tend to have a wider temperature range because they only have to "sit" at the extreme temperature.

Parts containing soft materials such as PVC tend to have a smaller temperature range than all metal versions.

Flexible conduits working below freezing grow stiff, if they can move about without damage they are said to cold flex. As temperatures drop and they could continue to be bent, termed cold bend.? Eventually the PVC cover will become brittle and crack open.

High temperatures have an opposite effect on conduit behaviours. Most of our plastics (with the exception of PEEK) will begin to soften above 100°, and extruded coverings will wrinkle and begin to sag.

Long periods of high temperature can "age" plastics turning them hard, brittle and eventually cracking them. Alternatively, uncovered pliables will "stew" happily up to 150° c. Above this temperature any paper lining begins to smoulder and smell.

Lead coatings on steel begin to melt at 200°c and when cool the core becomes soldered together and is not longer pliable.

UV Resistance
Ultra violet rays occur in natural sunlight somewhere between visible light (the blue end of the rainbow) and x-rays. UV can make whites seem whiter as well as damaging living tissue.

Strong sunlight particularly in overseas applications will cause a breakdown of plastic materials over a long period of sunbathing. Plastics can be given additives to increase their UV resistance, black being better than coloured materials. It is not easy to give definite advise, but generally black conduits will survive a minimum of ten years without deterioration.

Chapter 7 - Ducting

Ducting
In addition to Conduit systems Kopex also supplies Ducting products designed for the transport of hot or cold air, fumes, dust and powders in any direction.

Pliable ducting is made on the same machines as pliable conduits. Strips of paper or metal foils are wrapped in layers to make a tube and then corrugated to give it some strength. It is not as strong as a conduit so it generally needs more support when installed. Often it is fitted for air conditioning into suspended ceilings or flooring which provides adequate support and protection.