Protection Location

The Location Chart below shows the various protector locations as defined by the National Electric Code and the appropriate protector specifications issued by Underwriter’s Laboratory. It is very important to understand that each of these locations represented by letters “A” through “F” are distinctively different from one another.


The picture directly below shows the various locations of protectors relative to a workstation environment.


The last chart at the bottom of this page shows the various UL requirements for primary, secondary, and isolated loop protectors. It is very important in each of the locations shown on these two charts that grounding of the protector and the system is done properly. UL has three classes of specifications for voice and data line protection:

UL 497 Primary Protectors –
  • Defined as the first protection product that an outside communications cable is terminated with once the cable enters the building from an exposed outdoor environment.
UL 497A Secondary Protectors –
  • Defined as the protection product position after or between the primary protector and the protected equipment for the purpose of providing supplemental protection.
UL 497B Isolated Loop Protectors –
  • Defined as the protection product used on cabling that is electrically or optically isolated from the outside world. This network is contained within a building and is not connected to the public network outside the building.

The chart below serves as quick reference to highlight the main test conducted for primary and secondary protectors. Please note that the tests for primary protectors are different from secondary protectors, with only two exceptions. These differences reflect the electrical requirements and test goals for each protection location.

Not all UL Listed Protectors are the same; so choose the appropriate UL Listed Protector for your applications. Linx has a full line of protectors that are listed for both primary and secondary locations.


Limited Current:
600V; 30V – with fuse link wire I, III
Limited Short Circuit Current:
60A; 600V I
120A; 600V I
350A; 600V I
Impulse Voltage:
Vbrk < 1500V I, II I, II
Vbrk = Vbrk(nom) +/25%
dv/dt < 100V/usec.
Overvoltage Tests:
40A, 600V, 1.5 sec I, II, III
7A, 600V, 5 sec. I, II, III
2.2A, 600V, 30 min I, II, III
1.0A, 600V, 30 min I, II, III
0.5A, 600V, 30 min I, II, III
0.25A, 600V, 30 min I, II, III
25A, 120V, 30 min I, II, III
Endurance Conditioning:
> 10 x 1000, 10A I, II I, II
10 x 1000, 14A (See Note A) I, II
10 x 1000, 100A I, II
8 x 20, 5000A I, II

Note A: Protector must function normally after completion of this test.