Archive for Training

Alarm Circuit Supervision – Why You Should Care

EOL resistors installed at panel instead of terminating device.

The wrong place for EOL resistors.

Nearly every project we work on, we recommend that alarm initiating devices, especially door contacts, are to be configured using end of line (EOL) resistors for 4-state supervisory circuits.  The actual resistance value and configuration can vary by system manufacturer, but typically it involves wiring a 1K Ohm resistor in series and another in parallel with the switch, at the terminating device itself (not in the panel or junction box above the door).   This ensures that we have circuit supervision from the alarm panel (or card reader panel) all the way down to the device termination, so we know if the device is in a normal state (1), an alarm state (2), shorted state (3), or cut state (4).   This is known as 4-state supervision, because it distinguishes between 4 possible scenarios for the supervised device.

This simple addition offers greater security to the system, yet often gets omitted by vendors in the installation because it requires extra time and expense, and even causes confusion with some installers (really).  Worse, we sometimes end up with installations like the picture above that adds the EOL resistors to the panel with Dolphin connectors.  This type of installation does not offer any real security, and potentially introduces the opportunity for spurious connections inside the panel.  Thankfully, vendors like GRI manufacture magnetic contacts that come pre-assembled with the resistor array included.  They include 1K, 2K, 3.3K, 5.6K, 10K, and 33K resistors in a variety of contact packages, and also sell resistor packs for retrofit installations.

Years ago, one of the best explanations I ever read about alarm circuit supervision was from an Andover Controls card access panel installation guide.  I had learned already about 4-state supervision and why you should do it, but the following illustration shows it more clearly than anywhere else I ever saw it.  I ran across it again the other day and decided I would put it in an article here on the site.  The illustration below shows how the first two iterations of EOL resistors do not offer any significant line supervision, and could easily be defeated.  The third configuration offers 4 unique resistance values that correspond with the 4 possible state conditions.

Credit to Schneider Electric / Andover Controls for the illustration.

 

Posted in: Security Technology, Training

Leave a Comment (0) →

Training Class – Preparing for the North Carolina SP-FA/LV Electrical Examination

Protective Resources is the premier provider of training for individuals who are planning to take the North Carolina Board of Examiners of Electrical Contractor SP-FA/LV examination. Our one-day class, “Preparing for the North Carolina SP-FA/LV Electrical Examination,” is a proven method for applicants to learn about the exam and to review the major topics it covers. We have classroom exercises that emphasize using the exam references, including many charts and tables, to derive the correct exam answers.

We are currently scheduled to present this class on the following schedule:

  • January 28, 2015                  ADI, Greensboro, NC
  • March 25, 2015                     ADI, Raleigh, NC
  • May 27, 2015                         ADI, Raleigh, NC
  • July 29, 2015                         ADI, Greensboro, NC

We are also happy to provide a quotation on presenting private class sessions for two or more students. If you are planning on sending two or more students to our regular class, it may be more economical to have us bring the class to you.  We are also able to offer coaching sessions, if you think you need more personalized help to ensure being successful.

Contact us at training@protectiveresources.com for more information.

Posted in: Training

Leave a Comment (0) →