Heating cables
Heating cable is manufactured to meet the demands of the industry and have been tested by CSA through a battery of tests to confirm compliance and use for purpose. Commonly used products can be manufactured along with custom designs required for your project. From cold lead copper conductor cable up to 11 ohm/ft heating cable. Various conductor materials are available to properly focus in on the resistance requirements of each cable.
Both heating cable and cold lead cables using an Incoloy 825 sheath are certified to CSA Std. C22.2 No. 130-16 certificate #70119587 Class 2872 01 and 2878 01 heaters.
Note: that heating cables and cold leads are also available using 321 sheath upon request.
MAGNESIUM OXIDE INSULATION SPECIFICATIONS
MICT uses only high quality MgO complying to ASTM standard EI652
Mgo theoretical max density 3598 kg / cu meter
Minimum compaction density in the cable must be > 70% of theoretical maximum, an ASTM not CSA or FM requirement. MICT measures 72%, a high value for a drawn Ml cable.
Why comply to ASTM Standard EI652
1. Easier assembly of the finished heater set if the powder does not fall away upon stripping the sheath. Poor compaction has the powder fall away when the sheath is stripped. You can control your hot cold splice with less backfill of the joint good for voltage withstand testing.
2. The Dielectric withstand voltage is higher. Voids may lead to a crack and reduced dielectric strength. This can be especially evident upon bending should the MgO develop a fracture along which a fault current can track and trip off the circuit on a ground fault. Powder properties matter a great deal in order for MgO particles to interlock properly.
3. Heat transfer from conductor to sheath to minimize temperature differential between heater element and sheath. This leads to longer element life as oxidation of element is reduced as is the operating temperature of the conductor.
Insulation Characteristics
MOISTURE PENETRATION
The magnesium oxide insulation is hygroscopic and the presence of free moisture will quickly reduce its insulation resistance, if the cable end is left unsealed, moisture will penetrate for several inches reducing the insulation resistance of this section of cable. The moisture does not continue to penetrate for any distance and may be easily removed by applying heat to the cable in such a manner as to force the moisture back out the open end.
If this moisture is allowed to remain in contact with the insulation, for a prolonged period of time (approximately 1 year at 25 degrees Celcius), it will combine with it to form magnesium hydroxide. Since magnesium hydroxide occupies a considerably greater volume than the oxide, it can result in swelling of the cable sheath. Magnesium hydroxide can quickly be changed to magnesium oxide by the application of heat.
DIELECTRIC STRENGTH
DIELECTRIC CONSTANT
The dielectric strength of the insulation also decreases with temperature. However, this decrease is relatively unimportant for temperatures at which the cable normally operates.
The dielectric strength of the insulation also decreases with temperature. However, this decrease is relatively unimportant for temperatures at which the cable normally operates.
THERMAL CONDUCTIVITY
INSULATION RESISTANCE
Unlike most electrical insulations, well compacted magnesium oxide has a high thermal conductivity. This enables the heat to be quickly conducted from the conductor to the outside sheath and dissipated to the surrounding air. This conductivity increases with the density to which the magnesium oxide is compacted.
The manufacturing process produces a specific gravity of approximately 2.2 and a thermal conductivity of 16.4 BTU/°F/ sq.ft./in./hr.
POWER FACTOR
The power factor of magnesium oxide is very low compared to that of most electrical cable insulation. When measured at room temperature, 60 cycles per second and 40 volts per mil, it is approximately 0.1%. This value increases with temperature to approximately 1.0% at 250°C.
The insulation resistance decreases rapidly with increases in temperature as shown. It may be noted that this decrease in insulation resistance is relatively insignificant at temperatures below 250°C.
825 SHEATH MATERIAL
ALLOY 825 - Proven to be the best sheath for electric heat tracing cable and cold leads
MICT has a controlled manufacturing environment, bulk heating cable, and cold lead are seamless and valve filled.
METALLURGICAL CHARACTERISTICS
Incoloy 825 is a nickel base alloy with an austenitic structure. It is a homogeneous solid solution which has been annealed at high temperatures followed by rapid cooling to make it superior in corrosion resistance.
APPEARANCE
Metallic, 32 micro inch rms finish or smoother with a polished "silver" finish
CHEMICAL COMPOSITION
EQUIVALENT ANALYSIS
Material No. 2.4858
DIN/SEW 17744
ASTM/ASME B423-425
UNS No. N 08825
BS 3072-3076
BS No. NA 16
LIMITING CHEMICAL COMPOSITION, % BY WEIGHT
Nickel...............................................38.0 - 46.0
Carbon............................................. 0.05 max.
Manganese........................................1.0 max.
Iron................................................... Balance
Sulfur................................................. 0.03 max.
Silicon................................................0.5 max.
Copper...............................................1.5 - 3.0
Chromium...........................................19.5 - 23.5
Aluminum............................................0.2 max.
Titanium..............................................0.6 - 1.2
Molybdenum........................................2.5 - 3.5
Corrosion Behaviour
CORROSION BEHAVIOR
Its homogeneous blend of metals makes 825 highly resistant to stress corrosion cracking in chloride or alkaline environments. The relatively high nickel content of alloy 825, plus molybdenum and copper, makes it more resistant to reducing environments (such as sulfuric or phosphoric acid).
The chromium in combination with the nickel makes the alloy resistant to a variety of oxidizing environments (such as nitric acid solutions, nitrates, and oxidizing salts).
825 unlike most austenitic stainless such as 304 and Inconel 600 is relatively resistant to intergranular attack due to the presence of titanium.
Our alloy 825 sheath was developed to meet the demands of corrosive environments that are severe and/or unusual. Independent reports have shown alloy 825 to be superior to most other alloys including Inconel 600.
MICT MI Bulk Cables consist of one or two conductors surrounded by magnesium oxide (MgO) encased in a metal Alloy 825 sheath. For heating cable, the heat output of the cable is mainly determined by the type of conductor material used (which determines the conductor resistance) and the total length of the circuit. Refer to Technical Bulletin S0705 Series for a list of the 600V and 300V Heating Cables that are available.
MICT MI Bulk Cold Lead Cables consist of one or two conductors surrounded by magnesium oxide (MgO) encased in a metal sheath Alloy 825. The conductor is copper and drawn to American Wire Gauge (AWG) Standards to determine the required ampacity. Refer to Technical Bulletin S0705 Series for a list of the 600V and 300V Cold Lead Cables that are available.
