Quantcast Solid dielectric cable repairs

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TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
are not in potheads, the terminal ends should be
tial tests should be made to determine that the
checked periodically for leakage of compound and
cable, including the new repair, is suitable for use.
breaks in insulation where moisture can enter and
Refer to section VII.
cause deterioration. Where the cable is not termi-
5-23. Solid dielectric cable repairs.
nated with potheads, leakage of compound may oc-
cur. In such instances, an electrical adhesive tape,
The vast majority of cable used in most installations
designed for medium-voltage splices, should be ap-
will be solid dielectric cable. Solid insulation for
plied over the varnished cambric and should be
power cables is divided into two main cate-
painted with a sealer paint to stop the flow of com-
gories-thermosetting and thermoplastic. A thermo-
pound. If it is suspected that the varnished-cambric
setting material is one that requires heat to vulca-
insulation has absorbed moisture, a moisture test
nize or crosslink it. This process causes a chemical
(as described in section VII) should be made. Should
reaction and the insulation will have little tendency
the insulation become damaged, it may be replaced
to soften if reheated. Thermoplastic insulation will
with varnished-cambric and covered with friction or
soften repeatedly when heated. Ethylene-propylene
adhesive tape, or the ends of varnished-cambric
rubber and cross-linked polyethylene solid dielectric
tape can be secured with cotton tape and painted
cable, which are both thermosetting, should be con-
sidered when replacing any old medium-voltage
with an insulating paint.
cable.
b. Paper-insulated lead-covered cable. A paper-
a. Use. Most facility cable will be single-
insulated lead-covered (PILC) cable always has a
conductor type installed in duct. Direct-burial
lead sheath and therefore requires little mainte-
concentric-neutral cable, usually installed in hous-
nance. Testing at regular intervals will indicate the
ing areas, may be single-phase or three-phase.
condition of the insulation. A break in the lead
Direct-burial or submarine cable, armored or gas
sheath will expose the paper to moisture and a
pressurized, is usually three-conductor cable.
moisture test should be made. If several layers of
paper have been removed, they should be replaced
b. Repair. The repair of solid dielectric medium-
with varnished-cambric tape. In order to do this, it
voltage cable may be accomplished by the use of
may be necessary to remove a longer section of lead
preassembled splice kits, which are available for the
sheath. The section of lead sheath removed should
various types of cables and their protective cover-
be replaced with a new lead sheath and wiped in
ings, if any. Particular attention should be given to
place in the same manner as a splice. The repairs
ensure that the material used for the repair is com-
described above can only be made in a structure. If
patible with the cable insulation. Low-voltage
it appears there has been a break in the lead sheath
cables which do not have cable shields and are not
within a duct, it will be necessary to replace a
provided with armors or metallic sheaths can be
length of cable between structures or between ter-
repaired with jacket repair sleeve kits which seal
minals.
and repair insulation damage. These sleeves may be
appropriate on medium-voltage cables when only
(1) Should a PILC cable fail again shortly after
the jacket is damaged.
a repair or lengthy de-energization, the cable may
be completely unusable. However, prior to replac-
5-24. Other cable insulation and covering re-
ing, make an attempt to "dry out" the cable by
pairs.
forcing a low-voltage, high current through the
cable (via an arc welder) for not less than 12 hours.
Cable insulations other than solid dielectric compo-
Current should be as high as possible but must not
sitions are now being installed only where special
exceed 80 percent of rated cable ampacity.
circumstances justify their use. Varnished cambric
and paper insulated cables, however, may still be in
(2) Do not support PILC cables by using metal
service at this time. Gas-pressurized cable with
straps or supports or by laying them on metal trays
solid dielectric insulation is used for underwater
because of the deteriorating galvanic action.
installations to provide mechanical protection, pre-
c. Lead-sheathed cable. Lead sheaths may crack
vent the entrance of water, and minimize electrical
or suffer other damage as a result of fatigue due to
losses which can arise from armor protection. Pro-
cable movement or bending. If a section of lead
tective cable coverings require appropriate repair.
sheath is seriously damaged or badly cracked, the
a. Varnished-cambric insulated cable. Varnished-
section of sheath should be removed and the area
cambric insulation requires little or no maintenance
covered with a lead sleeve. The sleeve should be
w h e r e cables terminate in potheads. Some
wiped in place in the same manner as a splicing
varnished-cambric insulated cables are provided
sleeve. Where the damage is not too serious, repairs
with lead sheaths. However, where terminations
may be made as follows:
5-12





 


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