MIL-HDBK-1164
(2)
Required Time. The time required for electrical thawing
varies from 5 minutes to over 2 hours, depending on the pipe size and length, the
intensity of freezing, and several other factors. The best practice is to supply current
until the water flows freely.
(3)
Precautions to Take
a.
In general, do not use a current higher than the one
listed in Table 24 for a particular pipe size. When in doubt, use a lower current for a
longer period.
Table 24
Current and Voltage Required to Thaw Wrought-Iron
and Cast-Iron Pipe
Pipe Size
Pipe Length
Approx.
Approx.
inches
(mm)
feet
(m)
Volts
Amps
Wrought Iron
3/4
(20)
600
(180)
60
250
1
(25)
600
(180)
60
300
1-1/2
(40)
600
(180)
60
350
2
(50)
500
(150)
55
400
3
(75)
400
(120)
50
450
Cast Iron
4
(100)
400
(120)
50
500
6
(150)
400
(120)
50
600
8
(200)
300
(90)
40
600
b.
Select contact points on the pipe as close as possible
to the frozen section.
c.
Make sure contact points are free of rust, grease, or
scale.
d.
Remove meters, electrical ground connections, and
couplings to building plumbing from the line to be thawed.
e.
If pipe joints have gaskets or other insulation, thaw
the pipe in sections between the joints or use copper jumpers to pass the current
around the insulated joints.
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