CQR Surface Door Contact, Selectable End of Line Resistor, Grade 3, Brown SC570/BR/MD/MULTI/G3

Overview

This is a large contact for fixing on the surface of a door or frame on a higher-grade alarm system. It adds a selectable resistor and magnetic detection, in matching brown housings.

It is a Surface Multi Contact Grade 3 Brown.

How it works

A magnet on the moving part keeps a switch in the contact in its normal state. When the magnet moves away, the switch changes state and the alarm panel sees it.

Magnetic detection usually means noticing a magnet held near the contact, a known way of trying to defeat this type of device.

Where to use it

Use it on doors and frames where a surface fitting is acceptable and the system is rated for grade 3. Environmental class II is an indoor class, so keep it out of the weather.

What the figures mean in practice

• Pull-in gap: this is the distance at which the magnet makes the contact operate. Measure the real gap and allow for doors dropping over time, as a widening magnet gap is a common cause of false alarms.
• Switching current: 500mA @ 12Vdc is the switch's rated load.
• Rhodium contact: rhodium is a hard metal plating used on switch contacts.

Installing it

• Fixing: the contact measures 85 x 25 x 21mm and the magnet 85 x 18 x 21mm, so check there is flat room for both.
• Resistors: end of line resistors let a panel tell a healthy circuit from a cut or shorted cable. Check the choices on the unit against the panel's wiring guide.

Planning your system

The job also needs an alarm panel with a matching zone input, plus cable to the contact. Compare other door contact styles if the gap is wider than this one allows.

Standards and ratings explained

• EN50131-2-6: this is the part of the European intruder alarm standard that covers opening contacts. Read more in the guide to the intruder alarm standard and its grades.
• Grade 3: grades run from 1 to 4, and grade 3 is generally for medium to high risk.