The short answer
UL 698A
UL 698A is the listing standard for industrial control panels that relate to hazardous locations, in two ways: a panel that is itself installed in a classified area, which must be built in an enclosure and with components suitable for that classification, and a panel in an unclassified area that contains intrinsically safe barriers or isolators for circuits that go into a classified area, which is by far the more common case in water and wastewater. The second kind is built to UL 508A for its ordinary parts, with the intrinsically safe apparatus, its separation from other circuits, its wiring, and its control drawing meeting the additional requirements. Wet wells, headworks, digesters, and chemical rooms are the classified locations of the industry, and the level transmitters, floats, and gas detectors in them are the circuits that pass through the barriers.
Key points
- Two cases: a panel in a classified area, or a panel in a safe area with intrinsically safe circuits entering a classified area.
- Intrinsically safe barriers or isolators, their separation and wiring, and the control drawing are the additional requirements.
- Wet wells, headworks, digesters, and some chemical rooms are the classified areas of a water utility.
- Field wiring methods and seals at the boundary are installation requirements alongside the panel listing.
- The control drawing ties the barrier, the field device, and the cable parameters together and must be kept with the panel.
Two kinds of panel
| Panel | Where | What the listing covers |
|---|---|---|
| Panel in a classified location | Inside the Division 1 or 2 area | Enclosure and components suitable for the class, division, and group; purged, explosion-proof, or nonincendive as applicable |
| Panel with intrinsically safe circuits | In an unclassified area, circuits into the classified area | The barriers or isolators, their mounting and separation, wiring identification, and the control drawing |
Almost every water and wastewater application is the second kind: the panel is in the electrical room or on the lift station pad, and the wet well is the classified area. The float switches, the level transmitter, and sometimes a gas detector are in the wet well, and their circuits pass through intrinsically safe barriers in the panel. The panel is a UL 508A panel with a UL 698A element.
Intrinsic safety in the panel
- Barrier or isolator
- A listed device that limits the energy delivered to the field circuit; Zener barriers need a high-integrity ground, galvanic isolators do not. The device is listed for the class, division, and group of the field area and has entity parameters.
- Entity parameters
- The maximum voltage, current, and power the barrier can deliver, and the capacitance and inductance it can tolerate, matched against the field device parameters and the cable. The match is the control drawing.
- Separation
- Intrinsically safe wiring is separated from non-intrinsically safe wiring by distance or a partition, kept in its own wireway, and identified, usually with light blue.
- Grounding
- Zener barriers require a dedicated ground path of low resistance to the system ground; the control drawing states it.
- Control drawing
- The document that lists the barrier, the field device, the cable limits, and the installation conditions; it is part of the panel and of the installation.
Where the classified areas are
| Location | Typical classification | Note |
|---|---|---|
| Wet well | Class I, Division 1 within the well; Division 2 around the hatch | NFPA 820 is the reference for wastewater facilities |
| Headworks and screening rooms | Division 1 or 2 depending on ventilation | Ventilation rate changes the classification |
| Digesters and gas handling | Division 1 near gas equipment | Methane |
| Chemical rooms | Depends on the chemical | Corrosion is often the larger issue |
| Water plant | Usually unclassified | Except for fuel, chlorine gas rooms have their own rules |
Installation side
- Conduit seals at the boundary of the classified area for the wiring methods that require them.
- Cable and conduit types suitable for the location.
- The field device listed or approved for the location and matched to the barrier on the control drawing.
- The cable capacitance and inductance within the control drawing limits, which for long runs means checking.
- A purge system, where a panel in a classified area uses one, with its alarms and interlocks.
Habits
- Keep the control drawing in the panel pocket and in the engineering library.
- Replace a barrier only with the same model or one whose parameters are verified against the drawing.
- Do not add a non-intrinsically safe circuit to the intrinsically safe wireway, ever.
- Test the barrier ground periodically where Zener barriers are used.
- Treat a float switch replacement as an intrinsic safety change: same rating, same drawing.
Frequently asked questions
- Can I use a relay instead of a barrier for the floats?
- Not for a circuit into a Division 1 wet well. The float circuit must be intrinsically safe, which means a listed barrier or isolator with a control drawing, or the float and its wiring must be otherwise suitable for the location. Intrinsically safe float relays exist and are listed as barriers.
- Do I need UL 698A if the panel is outside the wet well?
- If circuits from the panel enter the classified area through intrinsically safe barriers, the panel falls under UL 698A for that element. The panel shop that builds hazardous location panels carries that listing scope.
- What about the level transmitter in the wet well?
- A submersible or radar transmitter in a Division 1 wet well is either intrinsically safe through a barrier, or explosion-proof with the appropriate seals. Most designs use an intrinsically safe loop through a barrier or isolator with a control drawing.
- Who classifies the area?
- The engineer of record on the area classification drawing, using NFPA 820 and the code. The panel designer works from that drawing and does not classify areas.
Related topics
- UL 508A Industrial Control PanelsWhat the listing actually covers, what has to appear on the label, and the requirements that most often cause a panel to fail inspection.
- NFPA 70 and the Control PanelThe National Electrical Code inside an industrial control panel: Article 409 and the listing it points to, the short-circuit current rating, overcurrent protection for control circuits, grounding and bonding, working space, and what an inspector asks.
- Float SwitchesThe oldest level instrument and still the one that saves a station: how tilt and stem floats work, the wiring conventions, mounting and spacing in a wet well, classified-area ratings, and how to use them alongside a continuous instrument.
- Wet Well Level MeasurementHow lift station wet well level is measured, which technology suits which well, the failure modes that flood a station, and why the high level float must stay hardwired.
- UL Standards for ControlsThe UL listings behind the components and the panels: UL 508A for industrial control panels and its SCCR supplement, UL 508 and UL 60947 for the components in them, UL 489 and UL 1077 for breakers and supplementary protectors, UL 248 fuse classes, UL 50 and 50E for enclosures, UL 698A for hazardous-location panels, and what a listing, a recognition, and a mark actually mean.
- NFPA Standards for ControlsThe National Fire Protection Association documents that reach into a control system: NFPA 70, the National Electrical Code, and the articles that govern panels, motors, and instrumentation; NFPA 70E for electrical safety at work; NFPA 79 for industrial machinery; NFPA 820 for wastewater plant hazardous area classification; and NFPA 110 where standby power meets the controls.
Direct contact
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