18 guage stranded wire max amperage

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  #1  
Old 09-30-01, 03:45 PM
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I recently purchased some 18 guage stranded wire and am trying to figure out the maximum amount of amps which can pass thru the wire safely.

Is there a standard calculation which relates wire guage with max allowable amps?

Note: I plan on using this wire as part of a circuit which provides power to a number of NEON lights...each of which has a draw of approximately 1 amp. Although the amp draw for these bulbs is low, I do plan to have more than one light on each circuit..therefore I'm trying to determine just how many I can safely connect to this 18guage wire being used for power supply.

TIA
Kevin
 
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  #2  
Old 09-30-01, 04:07 PM
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The NEC does not allow any permanent installation of wire smaller than 14 gauge, except for low voltage wiring.

If this wire is like a lamp cord, and is not permanently installed, I wouldn't run more than 3 to 5 amps through it. I must confess, however, that I just made this number up.

Why not spend a few bucks and buy some 14-gauge wire.

I'm interested to hear what others think too. Is there a defined amp limit for 18-gauge wire, perhaps by the UL rather than the NEC?
 
  #3  
Old 09-30-01, 11:00 PM
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If your lamps are really NEON, the typical current draw for a neon lamp is on the order of thousandths or millionths of an amp, not one amp.
 
  #4  
Old 10-01-01, 02:28 AM
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The lamps I am using are listed at being just under 1 amp.

As far as running larger wiring...well....I have already run all the wires necessary. Now i am just trying to determine exactly what i can run off of the existing wires.

I have heard the 3-5amp guess before. When I had asked the individual to specify why...frankly he had the same response...it was merely a guess with no specific data or calculations to back it up.

I really didn't think this would be a complicated question :-)...I thought for sure that wire had a 'rating' based on size. I basically don't want to smell burning insulation someday :-)...or worse.

Kevin
 
  #5  
Old 10-01-01, 02:36 AM
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Kevin,

You're asking for specifications on an illegal setup. I don't know of any organizations that write such specifications. If such specifications were written, they would say the maximum is zero amps.
 
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Old 10-01-01, 03:07 AM
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...I'm not asking for the legality of the setup or about the setup itself for that matter. I simply want to know the rating of the wire..that's all.

If there are recommendations for a particular wire size (ie 14 guage) then there must be limits to how much a particular size can draw? I would expect this to be standard information which is available somewhere?...I had thought this forum would be a good place to start :-(
 
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Old 10-01-01, 04:05 AM
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Fortunately after scouring the net for information I came across two references relating wire guage to max amps. Here is the info I have found:

18guage - 7amps
16guage - 10amps
14guage - 15amps
12guage - 20amps
10guage - 30amps
8guage - 40amps
6guage - 55amps


THIS is the kind of info I have been searching for. Although I would like to know HOW these numbers were calculated..the fact that I have seen this info at a couple of locations (in table format)suggests they have been calculated in the same manner.


 
  #8  
Old 10-01-01, 04:52 AM
Guy
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I think part of the problem is that the amperage capacity of wire as specified in electrical codes are not absolute values for the wire itself, you could make a device that carries 25 amps through 14 guage wire that will work, BUT that wire will get fairly warm if not just plain hot, and you will see a significant voltage drop due to the wire too. The electrical codes take into account the risk of heat buildup around a wire due to its sheathing, being enclosed in a wall, etc. Since no wire smaller than 14 guage can be used inside walls, etc., you will have a hard time finding similar "heat constrained" amperage ratings for wire smaller than 14 guage, although the table you did find appears to have plausible values for situations with similar heat rise constraints.
 
  #9  
Old 10-01-01, 07:38 AM
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Kevin,

I am glad you were able to answer your own question. Could you please cite the references you quoted?

In answer to your follow-up question, the current-carrying capacity of a wire is primarily computed based on its diameter. The smaller the diameter, the smaller the capacity. The calculation is more complicated, however, since it also depends on exactly what type of material the insulation is made out of. We often deal with NM cable, which today all has the same kind of insulation. I have no idea what kind of insulation might be on your 18-gauge wire.

The calculation also depends on the raceway (i.e., where the wire is running) and what else shares that raceway.

As Guy said, this is all based on the desire to limit the heat produced, increase the heat dissipation, keep the insulation from melting, and control the voltage drop to reasonable values.

The table you found is quite useful, but I hope it also came with a lot of footnotes, exceptions, modifications, ...
 
  #10  
Old 10-01-01, 01:02 PM
Wgoodrich
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Boy have you guys picked a deep subject now !

John the following chart is used for fixture wires 18 awg or larger.

Now as for below be very careful that you meet the requirements of use for fixture wires. Liability and life safety is involved in this situation. Most commonly these fixture wires are installed by manufacturers protected by testing lab reports of tested applications of a product.


402-10. Uses Permitted
Fixture wires shall be permitted (1) for installation in lighting fixtures and in similar equipment where enclosed or protected and not subject to bending or twisting in use, or (2) for connecting lighting fixtures to the branch-circuit conductors supplying the fixtures.
402-11. Uses Not Permitted
Fixture wires shall not be used as branch-circuit conductors.



Table 402-5. Allowable Ampacity for Fixture Wires

Size (AWG) Allowable Ampacity
18 6
16 8
14 17
12 23
10 28


240-3. Protection of Conductors

240-4. Protection of Flexible Cords and Fixture Wires
Flexible cord, including tinsel cord and extension cords, and fixture wires shall be protected against overcurrent by either (a) or (b).
(a) Ampacities. Flexible cord shall be protected by an overcurrent device in accordance with its ampacity as specified in Tables 400-5(A) and (B). Fixture wire shall be protected against overcurrent in accordance with its ampacity as specified in Table 402-5. Supplementary overcurrent protection, as in Section 240-10, shall be permitted to be an acceptable means for providing this protection.
(b) Branch Circuit Overcurrent Device. Flexible cord shall be protected where supplied by a branch circuit in accordance with one of the methods described below.
(1) Supply Cord of Listed Appliance or Portable Lamps. Where flexible cord or tinsel cord is approved for and used with a specific listed appliance or portable lamp, it shall be permitted to be supplied by a branch circuit of Article 210 in accordance with the following:
20-ampere circuits — tinsel cord or No. 18 cord and larger
30-ampere circuits — No. 16 cord and larger
40-ampere circuits — cord of 20-ampere capacity and over
50-ampere circuits — cord of 20-ampere capacity and over
(2) Fixture Wire. Fixture wire shall be permitted to be tapped to the branch circuit conductor of a branch circuit of Article 210 in accordance with the following:
20-ampere circuits — No. 18, up to 50 ft (15.2 m) of run length
20-ampere circuits — No. 16, up to 100 ft (30.5 m) of run length
20-ampere circuits — No. 14 and larger
30-ampere circuits — No. 14 and larger
40-ampere circuits — No. 12 and larger
50-ampere circuits — No. 12 and larger
(3) Extension Cord Sets. Flexible cord used in listed extension cord sets, or in extension cords made with separately listed and installed components, shall be permitted to be supplied by a branch circuit of Article 210 in accordance with the following:
20-ampere circuits — No. 16 and larger


The following is part of the requirments involved concerning neon design;

600-31. Neon Secondary-Circuit Conductors, 1000 Volts or Less, Nominal
(a) Wiring Method. Conductors shall be installed using any wiring method included in Chapter 3 suitable for the conditions.
(b) Insulation and Size. Conductors shall be insulated, listed for the purpose, and not smaller than No. 18.
(c) Number of Conductors in Raceway. The number of conductors in a raceway shall be in accordance with Table 1 of Chapter 9.
(d) Installation. Conductors shall be installed so they are not subject to physical damage.
(e) Protection of Leads. Bushings shall be used to protect wires passing through an opening in metal.
600-32. Neon Secondary Circuit Conductors, Over 1000 Volts, Nominal
(a) Wiring Method. Conductors shall be installed on insulators, in rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, liquidtight flexible nonmetallic conduit, flexible metal conduit, liquidtight flexible metal conduit, electrical metallic tubing, metal enclosures, or other equipment listed for the purpose. Wiring methods shall be installed in accordance with the requirements of Chapter 3. Only one conductor shall be installed per length of conduit or tubing. Nonmetallic conduit or flexible nonmetallic conduit, when operated at 100 Hz or less, shall be spaced at least 1Ŋ in. (38 mm) from grounded or bonded parts; and, when operated at over 100 Hz, shall be spaced at least 1ž in. (44.45 mm) from grounded or bonded parts. Metal parts of a building shall not be used as a grounded or equipment grounding conductor.
(b) Insulation and Size. Conductors shall be insulated, listed for the purpose, rated for the voltage, not smaller than No. 18, and have a minimum temperature rating of 105ēC (221ēF).
(c) Installation. Conductors shall be installed so they are not subject to physical damage.
(d) Bends in Conductors. Sharp bends in insulated conductors shall be avoided.
(e) Spacing. Conductors shall be separated from each other and from all objects other than insulators or neon tubing by a spacing of not less than 1Ŋ in. (38 mm). GTO cable installed in metal conduit or tubing requires no spacing between the cable insulation and the conduit or tubing.
(f) Insulators and Bushings. Insulators and bushings for conductors shall be listed for the purpose.
(g) Conductors in Raceways.
(1) Damp or Wet Locations. In damp or wet locations, the insulation on all conductors shall extend not less than 4 in. (102 mm) beyond the metal conduit or tubing.
(2) Dry Locations. In dry locations, the insulation on all conductors shall extend not less than 2Ŋ in. (64 mm) beyond the metal conduit or tubing.
(h) Between Neon Tubing and Grounded Midpoint. Conductors shall be permitted to run from the ends of neon tubing to the grounded midpoint of transformers or electronic power supplies listed for the purpose and provided with terminals at the midpoint. Where such connections are made to the grounded midpoint, the connections between the high-voltage terminals and the line ends of the neon tubing shall be as short as possible.
(i) Dwelling Occupancies. Equipment having an open circuit voltage exceeding 1000 volts shall not be installed in or on dwelling occupancies.
(j) Length of High-Voltage Cable. Not more than 20 ft (7 m) of high-voltage cable shall be permitted in metal conduit or tubing from a high-voltage terminal of a transformer/power supply to the first neon tube. Not more than 50 ft (15.2 m) of high-voltage cable shall be permitted in nonmetallic conduit from a high-voltage terminal of a transformer/power supply to the first neon tube.
600-41. Neon Tubing
(a) Design. The length and design of the tubing shall not cause a continuous overcurrent beyond the design loading of the transformer or electronic power supply.
(b) Support. Tubing shall be supported by listed tube supports.
(c) Spacing. A spacing of not less than ŧ in. (6.5 mm) shall be maintained between the tubing and the nearest surface, other than its support.
600-42. Electrode Connections
(a) Accessibility. Terminals of the electrode shall not be accessible to unqualified persons.
(b) Electrode Connections. Connections shall be made by use of a connection device, twisting the wires together, or use of an electrode receptacle. Connections shall be electrically and mechanically secure and shall be in an enclosure listed for the purpose.
(c) Support. The neon tubing and conductor shall be supported not more than 6 in. (152 mm) from the electrode connection.
(d) Receptacles. Electrode receptacles shall be listed for the purpose.
(e) Bushings. Where electrodes penetrate an enclosure, bushings listed for the purpose shall be used, unless receptacles are provided.
(f) Wet Locations. A listed cap shall be used to close the opening between neon tubing and a receptacle where the receptacle penetrates a building. Where a bushing or neon tubing penetrates a building, the opening between neon tubing and the bushing shall be sealed.
(g) Electrode Enclosures. Electrode enclosures shall be listed for the purpose.


18 awg wire is allowed by the NEC on the secondary side of neon lighting. Use the above charts setting overcurrent device and load calculations allowed per conductor.

Also be aware that many more rules exist concerning this use of 18 awg. Just know what you are doing before you do it, and HAVE THIS INSTALLATION INSPECTED BY YOUR AHJ!

Hope this helps

Wg
 
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