The right cables are essential for making trouble free installations.
A ship is a complex system, where many types of electrical equipment shall work in the same space. In order to maximize the imunity of our systems to external noise sources, the choice of cables is essential. Proper operation of our equipment cannot be expected unless the guidelines in this the manual, and in this FAQ, are followed
Twisted pair common shield
Always use twisted pairs with telephone systems. Telephone lines are best taken from the exchanger to the telephones in twisted pairs. And always use shielded cables. If more than one twisted pair is taken in the same cable, common shield will do, but of course individually shielded pairs is the best choice, but not neccessary for proper operation.
The dimmension of the cables (mm2) depends on the length and on the type of equipment to connect. The simple 2 wire telephones require very little, whereas the stations, using an external 10W speaker, requires the voltage drop over the cable to be at a maximum of 6V at nominal supply voltage of 24V DC.
We advise to follow the below rules:
TX325, SC325 and SC220
Minimum 0.25mm2 length of cable. max. 1800m
SC411 and SC421 with internal speaker only
1 mm2 per 600m lentgth of cable. max. 1800m
SC211, SC411 and SC421 with external 10W speaker in use
1 mm2 per 200m length of cable. max. 1800m
The SC211, SC411 and SC421 requre 24V DC power. Always bring the power to the station in the same cable as the telephone line. This means that these stations require 2x2 twisted pair common shield cable.
Connecting the shield
The shield of the cables must always be terminated inside the SeaCom exchanger, and for the SC211, SC411, SC421 and SC220, the shield shall be terminated inside the station connecting to the internal ground terminal. The figure below shows how shields must be connected:
For the TX325 and SC325, the shield should be left open at the telephone end.
Isolating stations from ships hull
The shield is connected to the body of the stations SC211, SC220, SC421 and SC411. To allow this, the body of these telephones must be isolated from the ships hull. This is easy for the boxed stations SC211, SC220 and SC421, as the brackets for hanging the station provides this isolation. But for the SC411 the isolation from the console, into whitc they are build, requires a little care while cutting and mounting. Refer to the mechanical drawing of the SC411.