APPROVAL No. S/1207/23/F/500315 was S/2349/23/F/500315

The GEC 28 (also known as the Interline 8) is an analogue Micro-PBX with a maximum capacity of 2 exchange lines and 8 extensions. It was made by GEC and introduced late 1985.

It consists of a compact wall mounted central unit which contains all the electronic circuitry to operate the system. There are two major circuit boards contained within the central unit, as well as the power supply for the system.

The main circuit board contains all the circuitry for 4 extensions, 2 exchange lines and 1 intercom circuit. The plug-on expansion board increases this capacity to 8 extensions, 2 exchange lines and 2 intercom circuits.

Any loop-disconnect, earth loop recall telephone approved to BS 6317 can be used as a terminating station. All telephones are connected to the central unit by 3 wires, 2 for speech and 1 for recall, apart from the mains fail extensions (extensions 1 and 2) which require an extra wire as a bell wire under mains fail conditions.

The system takes its power from a mains supply. It will operate from a mains voltage of 220, 230, 240 or 250 volts a.c. at a frequency of 50 Hz. It has a power consumption of less than 20 watts.

The terminating stations draw feed current from the PSTN during external calls, all other power being provided by the power supply module.

The feed circuitry allows a maximum loop resistance from the GEC 28 central unit to a terminating station of 30 ohms.

In the event of a failure in the mains supply, extension 1 will be switched through to exchange line 1 and extension 2 connected to exchange line 2. No intercom facilities will be available.

The GEC 28 consists of a CCU incorporating case and base, 1 main PCB and 1 expansion board.
Item                            Description
D 142846E (or DPA 1409/A)	28 main PCB, version
D 142846G			28 main PCB, version
D 142847A (or DPA 1410/A)	28 expansion PCB
D 142402			Base assembly
D 141409			Transformer

D 143371 A or B	Alerting device

Software generic on main PCB.

	version		Identification
	Version  A	D142717/A
	Version  B	D143177/B
	Version  C	D143313/A
	Version  C	D143313/B
	Version  D	D143516/A


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Last revised: November 05, 2021