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6. Direct Current Service Systems for Ships other than Tankers
6.1 The following distribution systems are considered standard for dc generation on ships other than tankers:
- 2-wire insulated; and
- 3-wire with neutral wire grounded, but without hull return.
6.2 The voltage of supply shall not normally exceed the maximum values given in Table 6-1.
TABLE 6-1
DC Supply Voltages
| Application |
Maximum Voltage |
| Power |
1000 |
| Cooking and Heating |
250 |
| Lighting and Receptacle Outlets |
250 |
| Internal Communications |
250 |
7. Alternating Current Service Systems ^
7.1 The following distribution systems are considered standard for ac generation on ships:( for tankers Refer to Section 26 .4 and 26.17 )
- 3-phase, 3-wire insulated;
- 3-phase, 4-wire with neutral grounded solidly at one point at the main switchboard but without hull-return;
- single-phase, 2-wire insulated or one side grounded without hull-return; and
- single-phase, 3-wire without hull-return and neutral grounded solidly at the main switchboard.
7.2 The following frequencies are recognized as standard:
- 60 hertz; and
- 50 hertz.
7.3 The voltage of supply shall normally not exceed the maximum values given in Table 7-1.
TABLE 7-1
AC Supply Voltages
| Application |
Maximum Voltage |
| Power, heating and cooking equipment securely fixed and permanently connected |
600 |
| Fixed lighting, heaters and controls which are bulkhead mounted in cabins and public rooms, and other applications not mentioned above * |
250 |
| Internal communications |
250 |
* This does not preclude the use of electric-discharge lighting systems operating at voltages in excess of 250 volts.
7.4 Generation and distribution at voltages in excess of 600 volts may be utilized when necessary for systems having large generating capacity and high fault power.
7.5 The vital services on all vessels which have a grounded neutral distribution system shall be supplied from an insulated distribution system.
7.6 The grounded neutral conductor of a distribution system in accordance with 7.1 (b) , (c) or (d) shall be independent of those conductors employed for the grounding of the non-current carrying parts of electrical equipment noted in Section 4; the size of the grounding conductor shall be based on the size of the current carrying supply conductor of the electrical equipment as follows:
If A is the size of the supply cable then:
A <= 3mm A=A
A 3mm <= 120mm A/2 the minimum is 3mm
>120mm A/2
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