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From: Dan Hall (no email)
Date: Mon Aug 01 2005 - 01:29:37 EDT
This is an interesting table Tom. The cable may well be rated at 105* C.
Unfortunately no other part of the system will be rated at that temperature.
So if you terminate this 105* cable in a breaker rated at 75* you will only be
allowed to use the 75* rating of the wire. If you were to load a #18 wire with
20 amps I would not be at all surprised if the temperature of the wire would
soar above 75*C. Such temperatures would quickly break down the internal
workings of a breaker or fixture.
This does not mean that the 105* rating is wasted. What it means is that if
the temperature of the wire is raised to 105* at some spot locally in it's
routing, perhaps where in close proximity to a heat source, the insulation
will not break down and cause a short circuit.
We run into this derating situation in the field all the time. The higher
temperature wires are of course better for many installations but may not be
ideal where flexibility or resistance to other stressors may be required.
For all around use I prefer XHHW-2. This may not be ideal on a boat because it
gives off some pretty nasty chemicals when burned. There are Teflon
insulations (spendy) that are required for aircraft use. I dunno if they are
used on boats.
Dan
----- Original Message -----
From: Tom Manning
To: ;
Sent: Sunday, July 31, 2005 2:13 PM
Subject: T&T: wire size
Are you guys saying the Ancor Table below is incorrect? Or, am I assuming
something different from you guys? 120 volt, 54.167 amp generator are my
assumptions. Along the same line, what would you recommend for a 120 volt
only, 42 amp generator? Assuming the generator is 120 volts, it can produce up
to 55 amps. According to a table I have, you should use #6 wire from the
generator to the distribution panel. > If the generator is 120/240 Volt, then
you'll have up to 27 amps in each > leg, so #10 wire is adequate.< WARNING:
Incorrect and dangerous thinking. This statement would only be true in a
perfectly balanced system. Never the less, the National Electrical Code and
good practice would call for #6 in most wire types. TECHNICAL INFORMATION
Table F: Allowable Amperage of Conductors of 50 Volts or More
The current values shown in Table F and also on Table D do not
consider voltage drop for conductors under 50 volts. The values shown on the
ampacity table are the maximum safe amperages which the conductor can carry on
a continuous basis. They do not apply to intermittent starting loads such as
motor start currents. Since all ANCOR Boat Cable is 1050 C insulated, only
that temperature rating is shown.
Due to the higher ambient temperatures in engine spaces and the heat
retention of large wire bundles, a "correction factor" must be used to derate
the wire by increasing conductor size. Table F takes into consideration these
factors and should be used to select conductor sizes for circuits over 50
volts. Note that for electrical systems under 50 volts, voltage drop is the
controlling factor and the tables on pages 14 and 15 should be used.
2 Conductors 1050 C (2210 F)
3 Conductors 1050 C (2210 F)
4 to 6 Conductors 1050 C (2210 F)
7 to 24 Conductors 1050 C (2210 F)
Conductor
Outside
Inside
Outside
Inside
Outside
Inside
Outside
Inside
Size
Engine
Engine
Engine
Engine
(AWG)
Space
Space
Space
Space
18
20
17.0
14.0
11.9
12.0
10.2
10.0
8.5
16
25
21.3
17.5
14.9
15.0
12.8
12.5
10.6
14
35
29.8
24.5
20.8
21.0
17.9
17.5
14.9
12
45
38/3
31/5
26.8
27.0
23.0
22.5
19.1
10
60
51.0
42.0
35.7
36.0
30.6
30.0
25.5
8
80
68.0
56.0
47.6
48.0
40.8
40.0
34.0
6
120
102.0
84.0
71.4
72
61.2
60.0
51.0
4
160
136.0
112.0
95.2
96.0
81.6
80.0
68.0
3
180
153.0
126.0
107.1
108.0
91.8
90.0
76.5
2
210
178.5
147.0
125.0
126.0
107.1
105.0
89.3
1
245
208.3
171.5
145.8
147.0
125.0
122.5
104.1
1/0
285
242.3
199.5
169.6
171.0
145.4
142.5
121.1
2/0
330
280.5
231.0
196.4
198.0
168.3
165.0
140.3
3/0
385
327.3
269.5
229.1
231.0
196.4
192.5
163.6
4/0
445
378.3
311.5
264.8
267.0
227.0
222.5
189.1
Table F is supplied to eliminate the need for calculating the
corrections for multi-conductor cable bundles to Table E. The values are
already corrected.
Number of current
Correction
carrying conductors:
Factor
3
0.70
4 to 6
0.60
7 to 24
0.50
25 and above
0.40
a.. Note: These tables only apply for 1050 C (2210 F) wire and other
premium wire and should not be used for lesser grades of wire and cable.
b.. Reprinted at the courtesy of the United States Coast Guard
Electrical System Compliance Guideline.
*There is NO LIMIT on conductors in a bundle under 50 Volts.
ANCOR Marine GradeT Products . (800) 424-WIRE . www.ancorproducts.com
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