The short answer
Panel Surge Protection
A controller panel at a lift station or a well is at the end of long conductors that act as antennas for lightning, and its protection is a design rather than a part: every conductor that enters the panel does so at one place, through a protector that lands on a ground bar bonded to the panel ground and the site electrode by a short conductor; the power is protected in stages from the entrance to the supplies; every 4 to 20 milliamp loop, every discrete circuit, and every copper data line that leaves the building has a protector at the entrance; the antenna feed has a coaxial arrestor bonded to the same bar; and the wiring inside the panel keeps the protected side away from the unprotected side so that the surge does not couple around the protector. A panel built that way survives most strikes with a few sacrificed protectors; a panel with one power protector in the middle and nothing on the level transmitter loses its controller on the first storm.
Key points
- One entrance: every conductor enters the panel at one place and its protector lands on one ground bar.
- The ground bar is bonded to the panel ground and the site electrode system by a short, straight conductor.
- Stage the power protection; protect every loop, discrete circuit, and copper data line that leaves the building; protect the antenna feed.
- Keep protected and unprotected wiring apart inside the panel; a surge couples across a wireway.
- Monitor the protectors, inspect after every storm, and keep spares.
The system
| Path into the panel | Protector | Where it lands |
|---|---|---|
| Power supply conductors | Type 2 device after the disconnect; a second stage at the 24 volt supplies where the exposure is severe | Entrance ground bar |
| Level transmitter and other loops from the field | Two-stage loop protector per pair, rated above the loop supply voltage | Entrance ground bar, with the shield |
| Floats and discrete field circuits | Discrete circuit protector per conductor pair or group | Entrance ground bar |
| Drive and starter signals from other enclosures | Protector where the enclosure is on another ground or fed by a separate run | Entrance ground bar |
| Serial or Ethernet copper leaving the building | Data line protector rated for the signal; or fiber | Entrance ground bar |
| Antenna coax | Coaxial lightning arrestor | Entrance ground bar, with the mast grounded to the same electrode system |
| Telephone or cellular antenna | The appropriate line or coaxial protector | Entrance ground bar |
The entrance and the bar
The protectors are mounted where the conduits enter, on a rail or a plate with a ground bar behind it, and the field conductors go from the conduit to the protector before anything else. The bar is bonded to the panel ground bar and to the site grounding electrode system by a conductor as short and straight as the layout allows, in the size the protector manufacturer specifies or larger. The mast ground, the panel ground, and the service ground are bonded together at the site, because a surge that finds two grounds at different potentials goes through the equipment between them. At a remote site, a ground ring or multiple rods bonded together, tested to a documented resistance, is the foundation of the whole scheme.
Layout
- Unprotected conductors run from the conduit to the protector by the shortest path and nowhere else.
- Protected conductors leave the protector on the other side and enter the panel wireway; they do not run parallel to the unprotected side.
- The protector ground lead goes straight to the bar; no loops, no sharing with signal conductors.
- Shields are bonded at the entrance bar, on the unprotected side, and continue on the protected side only if the design requires it.
- The antenna coax enters at the same place as everything else, through its arrestor on the same bar.
Staging the power
The service entrance device takes the bulk of the energy; the panel entrance device clamps what reaches the panel; a third stage at the 24 volt supplies or at the controller catches the remainder where the exposure is severe, such as a hilltop tank site. Each stage has a lower let-through than the one before, and the conductor length between stages gives the upstream device time to conduct first. The controller supply, the switch, and the radio behind a UPS with its own protection have four stages between them and the sky.
After a strike
- 1
Look at the indicators
Every protector with a window or a light; the ones that have sacrificed themselves are replaced.
- 2
Test the loops
Each loop for continuity and the protector for a short; a protector that failed short reads as a grounded loop.
- 3
Check the radio path
The arrestor, the coax, and the received signal against the record.
- 4
Check the grounds
The bonds at the bar and the electrode resistance; a strike can loosen a clamp or burn a conductor.
- 5
Look for the way in
A damaged device tells you which path the surge took, and that path gets a better protector or a better ground.
- 6
Record
The date, the damage, and the replacements, so that the site history shows which paths are weak.
Specification checklist
- A single entrance with a protector rail and a ground bar shown on the panel layout.
- The bonding conductor from the bar to the electrode system sized and routed on the drawing.
- A protector for every conductor that leaves the building, listed on the I/O list beside the point.
- Power protection staged, with the ratings on the one-line.
- Monitoring contacts wired and alarmed where the protector provides them.
- Spares of each type in the panel pocket and on the shelf.
- The site electrode system tested at commissioning and on a schedule.
Frequently asked questions
- The panel has a power surge protector already. Is the loop protection really needed?
- The level transmitter cable in the wet well and the float cables are the antennas at a lift station, and the surge on them arrives at the input modules, not at the power supply. Loop and discrete protection at the entrance is what saves the controller.
- Can I mount the protectors in the field junction box instead?
- A protector in the field box protects the field device, and a second set at the panel protects the panel. Both are used on exposed sites; the panel entrance set is the one that is never omitted.
- How good does the site ground need to be?
- As low as the site allows and, more importantly, bonded: every ground at the site tied together. A single rod at high resistance with everything bonded to it is better than three excellent rods that are not bonded to each other.
- Why does the radio keep dying while the controller survives?
- The antenna feed is a direct path to the radio, and its arrestor or the mast ground is inadequate or not bonded to the panel ground. Bond the mast to the site electrode system, put the arrestor at the entrance on the bar, and check the coax for water.
Related topics
- Surge DevicesSurge protective devices in a control panel: the types and where each belongs, the ratings that matter, supply protection, signal and network protection on conductors that leave the building, stage coordination, grounding, indication, and replacement.
- Surge Protection for Signal CircuitsProtecting 4-20 mA loops, discrete inputs, network cables, and radio feeds from lightning and switching surges: where surges enter, the device types and how they clamp, the grounding that makes them work, the resistance and capacitance they add, and where to put them at a remote site.
- How to Select Surge ProtectionSelect the surge protective devices for a control panel and its field circuits: list every conductor that enters, classify its exposure, choose the device type and ratings for the power, the loops, and write it into the drawings and the I/O list.
- Remote Site Stops CommunicatingOne radio site silent while its neighbors answer: site power, the radio, antenna and coax after a storm, a reset configuration, the controller behind it, or a changed path. What the master diagnostics say before anyone drives, and the order of checks on site.
- Missing Equipment GroundAn enclosure, motor, or device with no effective equipment ground: how it shows up as a tingle, a fault that does not trip, surge protection that does nothing, or instrument noise; how to test the path safely; and why a ground rod is no substitute.
- Ground Loop SymptomsHow a ground loop shows itself: hum on analog signals, offsets that change when large loads switch, serial links that error, and readings that differ by location. The mechanism, the measurements that prove it, and fixes that never lift a safety ground.
Direct contact
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