When noninsulated terminals and splices are used, some form of insulation must be used to cover the bare conductor. The two most common forms of insulator used for noninsulated terminals and splices are transparent tubing (commonly called spaghetti) and heat-shrinkable tubing. If spaghetti is used, it must be tied with lacing twine, as illustrated in the first figure below.
Heat-shrinkable tubing is shrunk to the desirable size by applying dry heat. It is also a good way to insulate terminals and splices, as illustrated in the second figure below.
This tubing shrinks to approximately one-half its original diameter when heated with an electrical hot-air gun (the last figure below). The steps for using a hot air gun are given below.
Spaghetti tied with lacing twine.
Typical hot air gun.
1. Hold the heat source 4 to 5 inches away from the wire. Apply a heat of 275º F to 300º F for about 30 seconds. Rotate the wire while applying the heat so that the heat is evenly distributed.
2. Remove the heat as soon as the tubing conforms to the shape of the wire. Allow the tubing to cool for at least 30 seconds before handling.
CAUTION: Do not apply heat higher than 300º F as
this may damage the wire. Do not continue to apply heat after the
tubing has shrunk onto the wire. Further application of heat will not
cause additional shrinkage of the tubing.
COMPRESSED AIR/NITROGEN HEATING TOOL
The compressed air/nitrogen heating tool (see the figure below) is a new tool in the fleet and was designed as a portable source of heat. This tool is safe for use around fueled aircraft because an open heating element is not required. The compressed air/nitrogen heating tool can be used on heat-shrinkable tubing.
Compressed air nitrogen heating tool.
The compressed air/nitrogen heating tool comes in two styles: ac or dc electrical power supplies. The power requirements are listed below for both styles.
- Electrical Power, HT-900B 115 VAC, 50-400 Hz, single-phase, 7 Amps
- Electrical Power, HT-920B 220 VAC, 50-400 Hz, single-phase, 3.5 Amps
- Heat gun output temperature 550-920°F (290-495°C)
- Compressed air/nitrogen 80-200 psig, 4 SCFM (Dry and oil-free)
Refer to the operator's manual for safe operating procedures for the compressed air/nitrogen heating tool. A brief summary of these procedures follows:
1. Push down and fully turn the air regulator knob counterclockwise. This is to ensure that the air regulator is off.
2. Remove the dust cap from the air inlet nipple. The inlet nipple is what we connect the air or nitrogen source line to.
WARNING: If nitrogen is used, make sure that you are in a well-ventilated area. Using nitrogen is a poorly ventilated area. Using nitrogen is a poorly ventilated area can result in suffocation.
CAUTION: As noted in table 2-1, the compressed air/nitrogen source CANNOT be greater than 200 psig.
3. Attach the air/nitrogen hose to the inlet nipple, making sure there is a firm connection.
4. Once the air/nitrogen source is properly attached, push down and turn the air regulator knob clockwise until the pressure on the air pressure gauge indicates between 5 to 7 psig.
5. Plug in the power cord to an appropriate grounded power supply.
6. Set the power switch to the ON position. The power lamp and heated-air-on lamp will both illuminate. (If the lights do not come on, check the switch on the gun handle. The switch must be positioned toward the front of the handle.)
7. There is a 1-minute warm-up time. During this warm-up period, ensure that the indicated air pressure increases to 10 to 15 psig on the air-pressure gauge.
8. You can now adjust the temperature control knob to the desired temperature setting.
9. You can turn the air/nitrogen pressure off and on to the gun without powering down the module by using the switch mounted on the gun handle.
After you complete your task with the compressed air/nitrogen heating tool, use the following shutdown procedures:
1. Push down and fully turn the air regulator knob counterclockwise. Observe that the air pressure gauge indication drops to 0 psig and the heated air lamp goes out.
2. Position the switch on the heating gun toward the rear of the handle.
3. Place the power switch to the OFF position and observe that the power lamp goes out.
4. Allow the air/nitrogen to flow for a minimum of 1 minute to cool the heating gun. (This procedure is done to extend the life of the heating element.)
5. Disconnect the power connecter from the power source.
6. Turn off air/nitrogen source at place of origin and disconnect.
7. Disconnect the compressed air/nitrogen hose from the air inlet nipple and install the dust cap on the air inlet nipple.