Questions and Answers

Q: Why is there a need for conductors to be tinned?

A: The basics reasons for having tinned conductors are:

1. Protects the core wire from oxidation
2. Gives excellent conductivity in high frequency circuits
3. Improves solderability
4. Provides the barrier between core and wire insulation during high temperature insulating process

Q: Why is there a need for individually screen as well as overall screen for pairs/triples data cables?

A: The overall screen will protect the interior of the cable from external interference, however individual pairs or triples may create interference between themselves, which has the potential to distort signals in adjacent pairs. The use of individually screened pairs reduces this distortion.

Q: Can a fire resistant cable be used and installed in very  hot environments, for example, very close to a furnace?

A: No, a fire resistant cable with a fire rating does not necessarily mean that it is suitable for use in a hot environment. For cables used in hot environments, a heat resistant cable is recommended. These cables are with special insulation and sheath materials such as silicone. teflon or glass fibre to withstand relatively high temperatures (in excess of 110°C) on a continuous basis.

Q: How do we calculate the minimum installation length of the cable when it is installed vertically?

A: The formulae for the calculation of the maximum vertical installation length is defined by VDE 0293-Part 300: for static tensile load harmonised Low Voltage Power Cables which indicates maximum of 15 N/mm².

                    total cross-section (cores x cross-section) x 15 N

Equation:  --------------------------------------------------------------------

                                                        9.81

Q: Why do we have 2 rated voltages -- Uo/U?

A:

• The rated voltage of a cable is the reference voltage for which the cable is designed and which serves to define the electrical tests
• The rated voltage is expressed by the combination of two values Uo/U, in volts
• Uo being the r.m.s. value between any insulated conductor and ground (line voltage)
• U being the r.m.s. value between any two phase conductors of a multi-core cable of a system of single core cables (phase voltage)
• In an alternating current system, the rated voltage of a cable should be at least equal to the values Uo and U
• In a direct current system, the nominal voltage of the system should be not higher than 1.5 times the rated voltage of the cable
• Note: The operating voltage of a system may permanently exceed the nominal voltage of such a system by 10%

A: The term "ATEX" comes from the France word "atmosphère explosive". If you supply or use equipment that may be used in potentially explosive atmospheres, then ATEX applies to you.

There are two ATEX directives, one that applies to equipment manufacturers, and another for its end users. ATEX 100a (also known as Directive 94/9/EC, or the Manufacturers' Directive) is intented to facilitate the free movement of goods throughout the EU by harmonising he technical and legal standards to which equipment for use in potentially explosive atmoshperes is manufactured. The application of such equipment in the workplace - particularly its effect on safety - is one of the subjects of ATEX 137 (Directive 99/92/EC,or the worker Protection Directive). Both directives come into effect on 1 July 2003.

Q: What are intrinsically safe circuits?

A: Intrinsically safe circuits are wiring systems, where no spark or thermal effect is allowed, which can ignite a explosive area. The operating voltage and the energy of working current have to be limited that no explosive can occur.

Q: In explosive environments, I've heard about different zones,in which some equipment cannot be used. How are these specifically defined?

A: Designation of a workplace into zones is part of the risk assessment procedure that is required by the already established Framework Directive (89/391EEC), of which ATEX 100a and 137 are parts. It is, therefore, a procedure familiar to many companies' health and safety officers, site managers, or electrical engineers. However, ATEX 137 stipulates that only suitable equipment may operate in those zones, which is an advance on the current practice of voluntary adherence.

ATEX 100a categorises equipment into three groups, according to the level of production employed:

1. Category 1 - Very high level of protection
2. Category 2 - High level of protection
3. Category 3 - Normal level of protection

These groups correspond to the three zones into which ATEX 137 divides areas in which an explosive atmosphere may occur. The zones are classified as follows:

1. Zone 0 - A place where an explosive atmosphere is present continuously, pr for long periods, or frequently
2. Zone 1 - A place where an explosive atmosphere is likely to occur in normal operation occasionally
3. Zone 2 - A place where an explosive atmosphere is not likely to occur in normal operation but, if it does occur, will persist for a short period only

These zones apply to areas at risk from explosions due to gases, Areas susceptible to explosions caused by dust particles are categorised as Zone 20, 21 and 22, by similar definitions.

ATEX 137 stipulates that only Category 1 equipment can be used in Zones 0 and 20; only Category 1 and 2 equipment can be used in Zones 1 and 21; and only Category 1, 2 and 3 equipment (i.e. only sufficiently protected equipment) can be used in Zones 2 and 22.

Q: What are the 4 main criterias to be taken for consideration in the selection of the right cables for the right application?

A: The 4 main areas in which define the limits of a cable application are:

(1) Physical Environment

Both cable installation and actual operation must be evaluated. Generally, stationary tpe cables are explosed to demage during installation and portable cables during actual service. Factors that contributes to mechanical damage that will reduces the cable reliability includes severe bending, compression, cutting, abrasion, and excessive tension can all contribute to a mechanical type of damage, which reduces the reliability of a cable installation.

(2) Chemical Environment

Cable components are made up of materials and chemical compounds or a mixtures of compounds. Different materials reactes differently to different chemicals. Thus chemical environments, such as halogen free, oil,ozone, etc., can influence the choice of materials for insulations and sheaths.

(3) Thermal Environments

The speed of a chemical reaction increases with a corresponding rise in temperature and will play a vital part in cable application. Elevated conductor temperature or high ambients will accelerate the degradation of insulations and jackets.

(4) Electrical Environment

Magnetic and static electrical fields can influence the desired stability of a cable - for example, causing interference of signals transmissions in control circuits. Thus requiring adjustments in cable design to include screens to filter off this noise.

Q: What is the difinition of Characteristics Impedance as described in Coaxial cables?

A: It is an expression of the ratio of Voltage to Current in a cable of infinite length. For coaxial cables, it is generally fall into 50 ohms, 75 ohms or 95 ohms.

Q: Can 50 ohms coax cable be replaced with a 75 ohms coax cable?

A: NOT recommended, as it is critical that the matching impedance must be match to avoid high signal reflection resulting in high attenuation loss. (i.e. Equipment system with 50 ohms impedance should match 50 ohms cabling!)

Q: What are the general differences between Cat. 5e and Cat. 6 structure cables?

A: Differences are:

1. Cat. 6 has wider frequency bandwidth up to 250MHz (Cat. 5e, BW=100MHz)
2. Cat. 6 has better insertion loss and Near End Crosstalk (NEXT)
3. Cat. 6 is less prone to data error due to wider frequency bandwidth

Q: What are the suitable grades of coax cables used in HD-SDI (High Definition - Serial Digital Interface) for operating frequency of 1.458GHz

A: There are basically 5 primany grades in terms of the thickness of the center conductor and the overall thickness and structure of the cables as shown here:

A: The difinition of the IP protection category is in accordance to EN 60529 (DIN 0470)

The protection category is mentioned as a short mark consists of two unvarying letters

IP and ratios for the protection level, for example IP 65.

(6) The First figure: Protection against contact penetration of foreign bodies.

(5) The Second figure: Protection against liquids.

Protection Classes for protection against contact and foreign bodies

Protection Classes for water protection