Surge protectors - Metasys - LIT-12011034 - General System Information - Metasys System - Release 11.0

MS/TP Communications Bus Technical Bulletin

Product name
Metasys System
Document type
Technical Bulletin
Document number
Release 11.0
Revision date

Surge protection is strongly recommended if the MS/TP bus is wired between buildings. The protection is provided by a voltage surge suppressor, which is installed on the MS/TP bus near the MS/TP device. Example applications are shown in Figure 1.

Figure 1. Surge protector installation on MS/TP Bus

Note: Fiber-optic bus connections between buildings are immune to transient voltage and other problems associated with hard-wire bus connections. Fiber-optic bus connections do not require surge protection and may be less costly to install. See Fiber-optic modems for information.

The surge protector protects the MS/TP bus from indirect lightning, and shunts both common and normal mode voltage surges to ground repeatedly without damage to MS/TP bus components.

Important: The surge protector is capable of protecting the MS/TP bus from indirect lightning strikes, not direct lightning strikes. A direct strike may cause actual damage to the bus cable or surrounding property. An indirect lightning strike may cause induced voltage transients that could cause electronic malfunction without visible damage to equipment if the equipment were not protected.

Use the surge protector with the standard MS/TP bus wiring. Do not use it with any other type wiring such as leased line. If you need surge protection for other wire types, contact a transient noise protection company.

Table 1 lists the specifications of the surge protector.

Table 1. Surge Protector Specifications




Three stage solid-state design using both metal oxide varistors and silicon avalanche diodes for suppression

Response time

Less than 1 nanosecond

Maximum impulse current (8/20 ms current impulse)

10 kA per conductor

Maximum energy dissipation

80 Joules per conductor (10/1000 us)

Maximum operating voltage

12 VDC


Common and normal modes

Suppression voltage levels (common mode)

100 kHz ringwave at 200 A: 15.8 volts 100 kHz ringwave at 500 A: 16.8 volts 3 kA combination wave: 20.8 volts

Maximum number of protectors allowed on MS/TP Bus

One pair per bus segment

Maximum length of MS/TP Bus between two buildings using protector

1,524 m (5,000 ft) (standard MS/TP bus specification)

One pair of surge protectors is required whenever the MS/TP bus wire is routed outside between two buildings. Install the protector close to the MS/TP device that first receives the bus wires from the outside. Figure 2 shows an FC bus surge protector wiring example.

The protector does not require that you use any special type of wire for the MS/TP bus, such as double-shielded twisted cable. Use the standard recommended twisted cable types.

Figure 2. FC Bus surge protector wiring example

The surge protector consists of two sections: the terminal block and the main assembly. These sections separate to make the unit easier to install and replace (Figure 3).

Figure 3. Sections of surge protector

The surge protector is wired depending on which device requires protection. Follow these general steps:

  1. Mount the surge protector device in accordance with local codes. Install in an enclosure, if required, as close as possible to the first MS/TP device connecting the trunk segment entering the building. Any electrical box with a cover is acceptable. Bond the surge protector enclosure to the MS/TP device enclosure by connecting the two with the conduit that carries the MS/TP cable.
  2. Connect the MS/TP segment from the outside to the unprotected side of the device. If possible, run the segment inside metallic conduit because the conduit acts like a shield for lightning.
  3. Connect the MS/TP segment that goes to the MS/TP device to the protected side of the device. Keep this segment away from the unprotected segment.
  4. Connect the protector to earth ground with 12 AWG stranded green wire (Figure 2). The total length of ground wire cannot exceed 4.57 m (15 ft), which means an earth ground must be available within 4.57 m (15 ft) of the MS/TP device. Your installation design must accommodate this requirement.
  5. For hard ground installation, connect the shield to Pin 9. For soft ground installation, connect the shield to Pin 7.

For more details on installation, refer to the specific manufacturer’s literature.