Quick answer
Specify an RMU fault passage indicator (FPI) as a complete detection and signal package, not just a small front-panel device. The purchase scope should state the fault types to detect, the sensing method, local indication, reset method, auxiliary power, remote contacts or communications, signal ownership, and the tests required at the factory and site. Whether an FPI is included, loose supplied, optional or excluded must be written into the ring main unit quotation.
Why the FPI needs its own RFQ line
An RMU can switch a ring network while a fault indicator helps the operator locate the affected section. These are different functions. A switch position tells the operator what was commanded; an FPI indicates that a detected fault passed a sensing point. A remote indication may then carry that event to a local panel, RTU or SCADA system. Do not treat “RMU with protection” as proof that the required indication and communications are included.
FPI terminology varies by supplier and project. Treat it as a defined project option whose fault types, sensing, local or remote indication, reset, power and interfaces must be written into the quote. Do not infer availability, compatibility or a default accessory list from a generic RMU catalogue; confirm each item against the offered Jinxing configuration.
Separate the indication layers
Use one schedule to show what a person sees at the RMU, what a technician can reset, and what another system receives.
| Layer | Buyer decision | Evidence to request |
|---|---|---|
| Sensing | Which phase or earth-fault conditions are detected, and at which functional unit? | Sensor arrangement, detection principle and applicable fault threshold information |
| Local display | Is the status visible on the RMU front, through a window, or on a separate indicator? | Front-panel drawing, indicator legend and visibility statement |
| Reset | Is reset manual, magnetic, push-button, timed or remote? Does the status remain latched after the circuit is restored? | Reset procedure, wiring diagram and functional test method |
| Auxiliary supply | Is the indicator self-powered, battery powered or connected to an external DC/AC source? | Power budget, battery details if applicable and terminal schedule |
| Remote signal | Which dry contacts, digital inputs or communication points are delivered? | Point list, contact ratings, terminal numbers and cable responsibility |
| SCADA integration | Who supplies the RTU, modem, protocol mapping, configuration and network test? | Interface matrix, protocol list and FAT/SAT acceptance records |
Keep “fault detected,” “switch open,” “earth switch closed,” “low gas or pressure,” and “communication healthy” as separate status points. Combining them into one alarm makes later diagnosis and acceptance difficult.
Confirm the sensing and operating context
Ask the project engineer to define the network earthing method, feeder arrangement, expected fault types, cable screen or sheath arrangement, and the utility’s indication convention. The FPI selection can depend on the RMU functional unit, sensor placement, directional requirements, and whether the network is operated locally or from a control centre. A device that indicates a phase fault may not meet an earth-fault or directional indication requirement.
For an RMU used in a compact substation, also define whether the transformer feeder, ring ways and low-voltage package are supplied under one contract. The indicator may sit on the RMU, but its remote contacts may terminate in a low-voltage control compartment or a separate RTU. Link the decision back to the RMU panel configuration guide and the RMU remote-control scope guide before issuing a combined quotation.
Decide what is tested and handed over
Write acceptance evidence into the enquiry. At minimum, ask how the supplier will simulate the specified fault indications, verify the local display, prove each remote contact, check reset behavior, and record the final terminal numbers. If the system uses a protocol, agree which party tests the point mapping and time stamps. A generic product reference is not a completed FAT record.
| Procurement question | Why it changes the order |
|---|---|
| Is the FPI factory-installed or supplied loose? | A loose device can change mounting, wiring, commissioning and warranty responsibility. |
| Are sensors and terminals part of the RMU price? | The indicator may be unusable if the sensing or terminal hardware is excluded. |
| Is remote indication required now or only future-ready? | A spare contact or communication port is different from a complete RTU and tested point list. |
| What is the reset and alarm philosophy? | Local operators, protection engineers and SCADA teams need the same event meaning. |
| Which documents are required? | Drawings, manuals, point lists and test records must match the delivered serial number. |
RFQ checklist
Send the following with the RMU enquiry:
- Single-line diagram showing ring ways, transformer feeder, normally open point and protection philosophy.
- Voltage class, continuous current, fault level, frequency, installation environment and earthing method.
- Required indication: short circuit, earth fault, direction, phase identification, voltage presence or other project function.
- Local display position, reset method, auxiliary supply and battery expectations.
- Remote contacts, RTU or gateway scope, communication protocol, cable lengths and termination point.
- Required FAT, SAT, point-to-point, wiring, alarm and communication test records.
- Utility or owner signal naming, language, drawing format, document register and handover deadline.
- Quantity, destination, trade terms and any compact-substation or room-interface constraints.
Use the Ring Main Units page for product-family alignment and the Request a Quote page for the project documents. Final FPI availability, sensing range, protocol, certification and delivery scope must be confirmed in the project quotation.
FAQ
Is an FPI the same as an RMU protection relay?
No. An FPI is normally used to indicate that a fault has passed a sensing point and to support fault location. A protection relay may measure, make decisions and trip a circuit breaker. The required functions depend on the RMU arrangement and project protection philosophy.
Can an RMU fault indicator be added later?
Sometimes, but do not assume it. Retrofitting can require compatible sensors, mounting space, wiring, auxiliary power, communication interfaces and a safe installation procedure. Ask the supplier to state whether the offered RMU is factory-ready, field-retrofittable or fixed in scope.
Does remote indication mean the RMU is SCADA-ready?
No. Remote contacts, an RTU, a protocol gateway and a tested SCADA point map are separate deliverables. List each one and assign the supplier, integrator or owner responsibility before comparing bids.