Ml cable

MI cables can maintain temperatures up to 1200°F and withstand exposure to up to 1500°F. The major disadvantage of Ml cable is that it must be factory-fabricated to length. It is very difficiilt to terminate or splice the heater in the field. This means pipe measurements are necessary before the heaters are ordered. Also, any damage to an MI cable generally requires a complete new heater. It s not as easy to splice in a good section as with self-regulating heaters. 

MI Cables (mineral insulated cables. Fig. 10-181) are the electric heat tracers of choice for high-temperature applications. High-temperature applications are generally considered to maintain temperatures above 250°F or exposure temperatures above 420°F where self-regulating heaters cannot be used. Ml cable consists of one or two heating wires, magnesium oxide insulation (from whence it gets its... 

Brass is a non-ferrous alloy of copper and zinc which is easily cast. Because it is harder than copper or aluminium it is easily machined. It Is a good conductor and is highly resistant to corrosion. For these reasons it is often used in the electrical and plumbing trades. Taps, valves, pipes, electrical terminals, plug top pins and terminal glands for steel wire armour (SWA) and Ml cables are some of the many applications. 

Figure 3.40 Ml cable with terminating seal and gland.

A mineral insulated (Ml) cable has a seamless copper sheath which makes it waterproof and fire- and corrosion-resistant. These characteristics often make it the only cable choice for hazardous or high-temperature installations such as oil refineries and chemical works, boiler houses and furnaces, petrol pump and fire alarm installations. 

The copper conductors are embedded in a white powder, magnesium oxide, which is non-ageing and non-combustible, but which is hygroscopic, which means that it readily absorbs moisture from the surrounding air, unless adequately terminated. The termination of an Ml cable is a complicated process requiring the electrician to demonstrate a high level of practical skill and expertise for the termination to be successful. 

FP 200 cable is similar in appearance to an Ml cable in that it is a circular tube, or the shape of a pencil, and is available with a red or white sheath. However, it is much simpler to use and terminate than an Ml cable. 

Connection of Ml cables can be made directly to motors, but to absorb the vibrations a 360° loop should be made in the cable just before the termination. If excessive vibration is expected, the Ml cable should be terminated in a conduit through box and the final connection made by flexible conduit. 

Copper Ml cables may develop a green incrustation or patina on the surface, even when exposed to normal atmospheres. This is not harmful and should not be removed. However, if the cable is exposed to an environment which might encourage corrosion, an Ml cable with an overall PVC sheath should be used. 

Compare PVC/SWA cables with Ml cables and give their advantages, disadvantages and typical applications. 

Where special tools are required, for example, those required to terminate mineral insulated (Ml) cables or the bending and cutting tools for conduit and cable trays, as shown in Fig. 4.7, they will often be provided by an employer, but most hand tools are provided by the electrician. 

Where special tools are required, for example, those required to terminate mineral insulated (Ml) cables or the bending and cutting tools for conduit... 

---