Spur line

Spur line is the oldest form of signal wiring. The 100 Volt output of an amplifier is connected to a signal cable and actually you can still connect a very large number of speakers to this signal cable.

You should ensure that the total power of all speakers together does not exceed the outgoing power of the amplifier, because the amplifier will be switched-off by the security system or will even be irrevocably destroyed.

A resistor is mounted at the end of the wire, so a security check can be made by testing the presence of resistance. This will let you determine whether there is an interruption or short circuit.

‘There is a maximum of 25 speakers to be mounted on a spur line for evacuation purposes’

The mounting of the speaker is really simple. Connect connection 1 of the speaker to wire 1 and connection 2 to wire 2. The speaker is thus always connected in parallel to the cable. Therefore it is called a spur line.

The speaker includes a condenser in order to separate this DC technically from the cable . When you do not do this, it is hard to test the line. Spur line is reliable in everyday use and it is still widely used, however, some caveats are in place and important:

A cable for spur line should always be performed in functional integrity. This is expensive concerning the installation costs and the use of materials. Therefore, a spur line has its limitations. Also, in case of an interruption of the cable, the system will only work partially or not at all. In case of a short circuit in the cable, the system will stop working and may cause problems in the amplifier, with all its consequences. However, this can be solved by using a different technique: loop wiring.

An evacuation central with spur line is interesting in acquisition, but when the costs of the installation are added a system with loop wiring will be cheaper. The big differences with loop wiring are the following:

- By loop wiring the use of a functional integrity cable is not necessary, so the price of the cable is lower:

- When using loop wiring the cable does not have to be braced every 30 cm, so the cost of the installation is lower.

Therefore, it is important to take a critical look at the total investment of the type of cabling and the proceedings.
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