Figure 14.2 - Cable Testing
Injecting a heating current from a welding set can dry out cables. The procedure requires ore not to overheat the cables, which could cause further damage. The cable should be disconnected at both ends from the equipment, and connected as shown in Figure 14.2. The injection cables must have good connections at each end. Current flow and cable temperature should be carefully monitored. When satisfactory insulation values have been restored, a final check should be made with the cable at normal ambient temperature.
The injected heating current must never exceed the rated current for the cable - it is advisable to use an ammeter and to start at the lowest setting on the welding set. The voltage should be in the region of 30V to 55V depending upon the current setting. The cable temperature can be measured with a stem thermometer (mercury in glass) secured to the cable and should not exceed a temperature rise of 30°C (86°F). Readings of temperature and insulation resistance should be recorded every hour and a graph plotted.
Practical Tips on Wiring
Wiring is not always difficult, but there are some special considerations afloat. Corrosion is a major problem. That's why only marine-grade tinned wire and cables are used. It lasts longer and provides better service in the process. Use a crimping tool rather than solder for connections. A good crimping kit is inexpensive, convenient, and easily replenished with new connectors. When you 'heat shrink' crimped connections, you've made a permanent fix.
Wire size is important, too. Some power loss occurs in virtually every wire - but like plumbing and water pressure, the bigger the carrier, the less the power loss. For electric motors and critical uses (bilge pumps, electronics, navigation lights, etc.) no more than 3% voltage drop at the appliance is suggested. For cabin lights, etc., 10% is acceptable.
Remember, the longer the cable-run and the smaller the size (conductor cross-sectional area), the greater will be the voltage be drop. Conversely, the shorter the cable-run and the larger the wire size (conductor cross-sectional area), the lower will the voltage drop be experienced. So, use the shortest run and the largest diameter (largest wire gauge size) wire you can to reduce the voltage drop.
Anchor windlasses are a particular challenge. These motors are much like automobile sorters, and use tremendous amounts of current. Follow the manufacturer's recommendations wire sizes completely! Don't use welding cables!
Run your connectors as high as you can and try to keep electrical connectors away from compasses and sensitive electronic components (such as electronic compass sensors). If you can't avoid it, use twisted pair conductors within three feet of these devices. This avoids creating a magnetic field that normally arises from current flow, which reduces electromagnetic interference thereby aiding electromagnetic compatibility. Colour coding of course will enhance the value of your vessel when the time comes to sell land survey) it; it also makes troubleshooting much easier. Some simple daily-use terms sated to conductors are mentioned below:
Cable Tags
Embossed metal tags are used to identify cables throughout the vessel. The tags are heated at the distribution panel and the component. Tags are also attached to the cables where penetration of the bulkhead is necessary.
The first part of tag code indicates the type of circuit. In many cases, the cores are also numbered and they correspond to those given in the manuals.
Cables
These are heavy-duty conductors used to carry current between a source and a load. Alternating current cables should contain all three current-carrying conductors (in a single cable) in order to cancel out heating caused by inductive effects.
Distribution Cables
These cables are used for power distribution up to the rated voltage and current of the cable. Low-voltage (600-volts) cables are generally found on ships for this purpose. They are used for most electrical connections.
Control Cables
These are multiple parallel conductor multi-coloured cables used for:
• Control circuits where an electrical signal energizes a magnetic control device to physically open or close the main contacts of a motor. The control cable does not carry the motor's operating current, but only the current used in energizing the coil of the magnetic control device (found in switchboards too).
• Indicating circuits in meters and other audio and visual indicating apparatus.
• Communication, electronic, and other similar circuits.
Signal Cables
Signal cables of twisted pairs of conductor cables are used for signal transmission. Each twisted pair of conductors will have a shield to prevent interference. They may be single-cored, screened, co-axial cables too.
Portable Cords
Portable cords are used for the temporary connection of portable appliances. They are not to be used for fixed wiring.