#Cable #protection, #conduits made of steel

Boxes and #connectors are available with cable protection conduits made of steel.

Devices with reinforced cable

It can be an external braid or a conduit of galvanized steel (stainless steel upon request).
Metallic flexible tube increase stensile strength, mechanical abrasion and impact resistance, temperature and fire resistance.
Steel braid. In the case of metal braid (armoring), a further option is to put a second external sheath in order to protect the metal for outdoor applications, facilitating cable cleaning and preventing corrosion, but the diameter becomes bigger.
Steel flexible tube, compared to armoured cable, offers a better protection against crushing and could be even used just for a partial length (limiting the tube to the length where it is really useful, you get a cheaper cost and more flexibility where the tube is not necessary); on the other hand its external diameter is bigger.
Conduits of polyamide (nylon) are available as well; their dimensions are bigger than conduits of steel, but they have a very good chemical resistance and sometimes they are cheaper.
Halogen free polyester braided sleevings can instead offer flexibility and high temperature resistance, 150°C working temperature, 200°C melting point.
Typical applications are with welding machines, construction equipment, agricultural machinery, food industry machinery, earth moving machines, lifting or air platforms, warehouse and moving goods plants.
Another interesting application is to prevent rodent (rats, mice) and termite attacks. In many areas steel armouring (armoring) is the best way to stop or reduce serious damage.
See more details at http://www.shield.net/?news/index/product .
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#Current-carrying #Capacity. Ambient Air and Cable Temperature

How to choose the #cable #section.
The current flow in a connector and in its cable generates heat, thus a temperature rise. Any connector or cable insulating material has a maximum safety temperature that should never be exceeded to ensure the stability of their mechanical properties.
After verifying the insulating material quality and the working ambient air temperature, the maximum current-carrying capacity permitted in the connector can be calculated in function of the terminals size and the conductors section.
Table 2 on page http://www.shield.net/files/catalogue/support/2.2.pdf shows the maximum current values for a pvc cable (quality 70°C) with 2 or 3 wires without metal sheath, with copper conductors, employed for normal use and inserted into cable tray. For open air applications a current about 10% higher is admitted.
The ambient air temperature is measured around the cable, for example inside the cabinet or close to the machine interspaces. The right ambient air temperature is found after the normal functioning of the machine, under full load for a sufficient period of time, without taking into account the variations of the temperature due to heating of the cable. If the use does not require a higher temperature project, the conventional value of 40°C (IEC 60204-1) must be considered.
The table takes into account that in most of the machines not all cables are used simultaneously for long periods. In special cases (many wires used at the same time or high ambient air temperatures), a reduction factor of between 0,3 and 0,9 must be used to reflect the overheating of cables in the same group, otherwise verify that the temperature remains within the limits allowed. Particular attention must also be paid to vertical and limited ventilation routes.
Values and comments refer to IEC 60204-1 (Machinery Safety, edition October 2005) and IEC 60364-5-52 (Wiring Systems Security).