C-TEC 24V Relay, 5A Isolatable with Keyswitch, on a Plate BF366

Overview

A relay lets one circuit switch another without connecting them together. On a fire alarm, that means a signal from the panel can operate separate equipment through a set of contacts.

This C-TEC part adds a way to take that link out of action for a short time. That is useful when a weekly test would otherwise start an autodialler or close a rollershutter.

How it works

• Polarised relay: polarised means that the input must be connected the correct way round, so follow the marked terminals.
• Change-over contacts: NC is normally closed, NO is normally open and C is common. Choose NC or NO depending on whether the equipment should switch off or on in a fire.
• Open collector output: this is a panel output that switches to negative when active rather than supplying a voltage of its own.

Where to use it

The operating temperature runs from -10ºC to +60ºC, and the rating is IP40.

That rating gives no protection against water, so keep it away from wet areas.

A key belongs with the person who runs the fire alarm tests, so an isolated output is a deliberate step.

What the figures mean in practice

• Resistive and inductive: the contact rating drops from 5A to 2A with an inductive load, such as a motor or solenoid. Use the lower figure for those.
• Coil range: the 17-30V DC range covers a nominal 24V panel supply as its voltage changes between mains and battery.
• Activation current: typically 30mA @ 24VDC, which counts towards the load on the panel output or sounder circuit.

Installing it

The 85 W x 85 H plate fits a standard UK 25mm single gang back box, flush or surface. The total depth of D 50mm is worth checking against the space behind and in front of the wall.

Mains-rated contacts mean the job may carry 240VAC into this box, so isolate first and follow the wiring regulations.

Planning your system

A relay fed from a sounder circuit returns to normal when the fire condition is cleared or silenced. If the linked equipment must stay in its fire state after silencing, that wiring may not be suitable, so check with the approving authority first.

The guide to commercial fire alarm systems covers how a design begins, and other control relays suit jobs that do not need a keyswitch. The range of fire alarm accessories holds further interface parts.