Selecting the Best Cable for your Hazardous Area Work Task - Michael Morley
Michael Morley is Wolf Safety’s Technical Director and has been designing lighting products for Hazardous Areas for over 20 years.
Selecting the best cable for your Hazardous Area lighting application can be as important for safety as choosing the correct ATEX lighting equipment. Having selected the most appropriate lighting for your environment and task, you should then consider the most suitable cabling and the best way to manage it within the Hazardous Area.
For this, six key issues need to be taken into consideration:
- The ambient temperature of the work area
- The risk of mechanical damage to the cable in the work area
- Cable resistance to chemicals or solvents (usage dependent)
- Offshore specification: low smoke, zero halogen
- Cable protection system 110/230V
- Length of cable run, particularly on 24 volt systems
Following the users’ assessment of these six points, the most appropriate cable can be chosen from the wide selection available, each of which has their own advantages.
The most widely used cable type in the on-shore energy and industrial sector is SY Cable, which has a PVC outer sheath and braided armour for protection against mechanical damage. The braided armour, also sometimes known as steel braid or mechanical protection, is particularly important when used in temporary applications where it has a greater risk of becoming trapped, walked on or driven over. With a maximum high ambient temperature of +70oC this cable is ideal for hotter environments.
Ship’s Braided Cable is often chosen for offshore installations and marine applications where a heat, oil and flame retardant cable is required. Like SY Cable, Ships Braided Cable contains steel braid, but it is stronger and more robust, but is less flexible. This cable is compliant with BS6883, using low smoke, halogen free materials.
A further cable option that can be specified is H07RN-F Cable, more commonly used on temporary lighting equipment on sites in continental Europe. This cable is highly flexible and withstands oils, greases and mechanical and thermal stresses, but it has no protective metal braid.
It is the user’s decision which cable best suits their needs and how to manage that cable in the work area. Care should be taken with cable positioning with the aim of minimising risk of cutting, abrading and damage from vehicles . Wolf has a range of accessories available to help with this. ͥ
To increase safety further when using mains power in the Hazardous Area, users often use MCBs (Miniature Circuit Breakers – i.e. electronic fuses) or RCDs (Residual Current Devices). These reduce the risk of the cables overheating (if specified correctly) under fault current conditions, but it should be noted that these will not prevent the risk of a potentially explosive spark.
Low voltage (24 volt) applications present a number of additional issues to be taken into consideration. These include:
- The number of lights (which is determined by the VA you can take from the transformer)
- The length of cable to be used (due to voltage drop over the cable length)
- The fuse value associated with the cable length
When using a 230/110V Input - 24V Output 400VA Transformer, the effectiveness of the fusing within the transformer is dependent upon cable resistance: cable resistance limits how much current can flow, so the longer the cable, the greater the resistance, which is especially relevant in Low Voltage applications where you only have 24V supply.
Users looking to purchase an ATEX Transformer should ensure that information detailing the correct fuse value relative to the size and length of cable used is available to support safe and trouble-free usage in a Hazardous Area application. All Wolf transformers are supplied with supporting documentation detailing this data. Typically, the maximum cable length for 2.5mm2 core cable is 20m and for 4mm2 core cable it is 35m. This is because the 24V power supply cannot physically push enough current down the cable to blow the fuse in the event of a short circuit. The cable will remain live and potentially sparking until something else stops it or it is switched off.
If you need any help or advice regarding cable selection for Hazardous Area lighting products, please contact Wolf at firstname.lastname@example.org
ͥ Wolf has a range of accessories that can help manage cables in Hazardous Areas, see them at https://bit.ly/2qmQfQF