Electrical Systems

Manufacturer Requirements

This section applies only to wiring in circuits of 50 volts or more. However, conductors meeting any one of these alternate requirements will also qualify for circuits of less than 50 volts. The alternating current (AC) systems of 120 and 240 volts are the systems normally in use on boats to which these requirements apply.

Paragraphs (a)(1), (a)(3) and (a)(4) apply to conductors in general, while (a)(2) applies specifically to various types of flexible cords.

Types

Conductors for circuits of 50 volts or more may be used if they:

(a) are classified as “moisture resistant” and “flame retardant” in Article 310 of the National Electrical Code, such as those designated:

THW, TW, THWN, XHHW, MTW or;

(b) are flexible cords type SO, STO ST, SJO, SJT, or SJTO, listed in Article 400 of the National Electrical Code, (see Table 6);

(c) are conductors that meet the IEEE Standard 45, such as those
designated:

R, B, T, V, AV, TA, M, S; or

(d) are conductors that meet the requirements of UL Standard 1426.

There may be other cords or wires on the market, such as S, SE, SEO, SJE, SJEO, SJOO, SJTOO, and SOO, which have been accepted by the U.S. Coast Guard. If you are considering a cord or wire other than one listed above, check with the supplier for a copy of the Coast Guard’s letter of acceptance.

Conductors, as purchased, often do not indicate whether or not they conform with the above requirements and standards. If the conductors or their packaging are not so marked, then an alternative means of assurance of compliance should be obtained. Certification of compliance by the cable vendor is one acceptable means.

Sizing

Table 5 is used to select the size of conductors. Correction factors are provided for conductors used in engine spaces (Note 1) and also for bundling of conductors used in circuits of 50 volts or more (Note 2).

Tables 5A through 5E have been developed for this guideline, and include corrected values, so it is not necessary to perform the calculations required if using Table 5. Select the proper table according to the number of 50 volts or more current carrying conductors in a bundle and then read the wire gauge needed according to the temperature rating, location of the conductor and the circuit lead. Refer to “How to Select a Conductor” which follows, for further information.

Conductors, as purchased, often do not display the temperature ratings of conductor insulation. If the conductors or their packaging are not so marked, then an alternate means of assurance of compliance should be obtained. Certification of compliance by a vendor is one acceptable means.

How to Select a Conductor

FACTORS

To select a conductor in accordance with the regulation, there are a number of factors to consider:

1. Temperature rating of conductor insulation.
2. Current rating required for the circuit.
3. Is the conductor in an engine space?
4. Is the system voltage less than 50 volts, or is it 50 volts or more?
5. How many conductors will run in a bundle?
6. What type of conductor is permitted; i.e. SAE, NEC, IEEE, UL or other?

PROCEDURE

1. Determine the circuit load - add up the rated loads of the electrical devices in the circuit.

The boat manufacturer will have to determine the circuit loads in the boat in order to properly size conductors and the related overcurrent protection. If a conductor is supplying a single load, sizing the conductor and its overcurrent protection is simple. If, however, a single conductor is supplying multiple or cumulative loads, such as a distribution panel, the boat manufacturer does not have to size the conductor to carry the summation of all the loads connected to the panel, but only a percentage of these loads, due to loading factors. The regulation does not require that a conductor be sized to carry the full load of a distribution panel, but does require that proper overcurrent protection be provided for the size of the conductor chosen.

The boat manufacturer has a choice between the extremes of providing a conductor that can carry the full load, and using a smaller conductor that is adequate because of load factors, but still large enough to avoid nuisance tripping of its overcurrent protection.

Of course, whichever size conductor is used, it must be protected with the proper size overcurrent protection. It must also be noted that 183.425(b) restricts the maximum load a conductor may carry to that specified in Table 5, except for intermittent higher currents. (See 183.455 and 183.460 for Overcurrent Protection Requirements).

2. Decide what temperature rating of conductor will be used.

3. If in an engine space, apply the correction factor to the amperage values in Table 5 for the temperature rating selected. Tables 5A through 5E provide a column of corrected amperages for use in engine spaces.

4. If the electrical system is 50 volts or more, determine the number of current carrying conductors (grounding conductors are not normally current carrying) that will be bundled together. If more than two, select the appropriate correction factor and apply it to the amperage values in Table 5 or as corrected for use in engine spaces. Tables 5B through 5E provide corrected amperages for various numbers of conductors in bundles and also provide a column for conductors used in engine spaces.

5. In Table 5 or Tables 5A through 5E under the column for the selected temperature rating of the conductor, find the amperage that, when the necessary correction factors are applied (not needed when using Tables 5A through 5E) equals or exceeds the circuit load.

6. Read the gauge of the conductor to be used.

7. Select a conductor of STRANDED COPPER construction with insulation properties permitted in accordance with the system voltage, as follows:

a) less than 50 volts - SAE conductors are permitted in addition to those for 50 volts and over. (See 183.430).

b) 50 volts or more - NEC, IEEE and UL conductors are permitted. (See 183.435).

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