Q: What is the difference between the grading of contacts?
A: Since the adoption of the new EN standards in April 2007, there’s been a lot of discussion and opinions expressed on the subject of the new graded magnetic contacts, most of which were based on the first generation of products available in early 2007.
This new standard recognises the importance of magnetic contacts as an essential part of an alarm system, and the critical importance of specifying and installing the correct product to ensure the integrity of the entire system.
To be consistent with the standard, magnetic contacts must be individually identified to meet each of the relevant four security grades:
- Grade 1 – Suitable for use in ungraded and grade 1 systems.
Tamper protection to connection is not required. Allows use of the traditional five terminals ‘open backed’ flush contact and surface contacts without a tampered lid. Used in Double Pole systems (and therefore do not incorporate resistors).
- Grade 2 – Suitable for use in upgraded grade 1 and 2 systems (however, connections cannot be exposed as in grade 1).
Includes mechanical tamper protection which protects access to terminals, or alternatively are sealed which requires them to be pre wired. Detection of removal from mounting is an additional requirement for wire free detectors (this is not required for hard-wired detectors). Used in FSL (Fully Supervised Loop) systems incorporating resistors (but may also be used in Double Pole systems without resistors).
- Grade 3 – Suitable for use in all systems up to and including grade 3 and must be either immune to magnetic attack or can detect the introduction of a rogue magnetic field and generate a tamper signal to alert the system.
This requirement was previously achieved by some manufacturers utilising biased contacts. Manufacturers, such as CQR and Elmdene, now produce non-biased grade 3 contacts which can be fitted in any orientation and are classed as universal. All monitored systems need to be grade 3. Used mainly in FSL systems incorporating resistors.
- Grade 4 – Tighter tolerance on the detection of magnetic interference compared to other grades.
A remotely powered contact should generate an alarm signal in the event of power loss and generate a fault signal when low voltage is detected. The need for grade 4 contacts is rare and should be the subject of special enquiry.
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