MIL-HDBK-1004/2A
3.4.3.1 Advantages. Both XLP and EPR are thermosetting, solid dielectric
compounds with excellent electrical insulation properties, good chemical
resistance and physical strength charateristics, and both remain flexible at
low temperatures.
3.4.3.2 Disadvantages. Although EPR is more expensive than XLP and both
have excellent moisture resistance, the degradation phenomenon called treeing
appears to occur more frequently in XLP and is aggravated by the presence of
water. EPR also is less susceptible to corona discharge activity than XLP,
but in a properly designed and manufactured cable, damaging corona is not
expected to be present at the usual operating voltages.
3.4.4
Other Insulations. Use other insulations only where special
circumstances warrant their lower-rated conductor temperatures or their lower
rated maximum voltage class. Use of such cables, especially those with
metallic sheaths, must be functionally or economically justified.
3.4.4.1 Polyvinyl-Chloride. Select polyvinyl-chloride (PVC) mainly for
power and control wiring for ratings of 2 kV or less. This thermoplastic is
highly resistant to moisture, oils, chemicals, and abrasion, but has high
dielectric losses.
3.4.4.2 Polyethylene. Select polyethylene mainly for roadway lighting,
control, and communication cables. This thermoplastic has good moisture
resistance and stable physical and electric characteristics under temperature
variations. Polyethylene exhibits the same susceptibility to treeing and
corona discharge as XLP.
3.4.4.3 Butyl-Rubber. This thermosetting insulation has high dielectric
strength and is highly resistant to moisture, heat, and ozone. It can be used
up to 35 kV, but has lower rated conductor temperatures than either XLP or
EPR.
3.4.4.4 Silicone-Rubber. This thermosetting insulation is highly resistant
to heat, ozone, and corona. It can be used in wet or dry locations, exposed,
or in conduit. It has the highest rated conductor temperatures but can only
be used for applications up to 5 kV.
3.4.4.5 Mineral-Insulated Cable. Mineral-insulated cable is completely
sealed against the entrance of liquids and vapors along the cable run. It is
rated at 600 maximum.
3.4.4.6 Rubber. Use rubber insulated conductors for ease of splicing, good
moisture resistance, and low dielectric losses.
3.4.4.7 Varnished-Cambric. Use varnished cambric insulation for resistance
to ozone and oil and for ease of splicing. Use varnished-cambric principally
in conjunction with paper insulation where oil migration is a problem. Where
installed in wet or highly humid locations or underground, provide varnished-
cambric with a suitable sheath.
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