- October 9, 2026
- Posted by: Aceget
- Category: RECD & Emission Control Devices
Electrical questions arrive late on many RECD projects. The device is chosen, the frame is designed and the exhaust route is drawn. Then, a week before installation, someone asks where the controller plugs in. The electrician runs a spare circuit from the nearest board, and everybody moves on.
Sometimes that works. Often it leaves a monitoring system that switches off whenever the grid fails, which is exactly when the generator runs; a heater circuit that trips the moment it is energised; or a controller that resets every time the DG starts because the battery voltage dips. None of these are faults in the device. They are consequences of skipping a short piece of planning.
This guide sets out that planning in four parts: what on an RECD actually uses electricity, how much and at what voltage, when it needs power, and how the supply should be protected, isolated and documented.
Part 1: Build the Load List
The first step is to write down every electrical consumer associated with the device. RECDs vary widely in technology. Some are largely passive filters with monitoring. Others have active regeneration heaters, blowers, dosing systems or electrostatic stages. The vendor’s data sheet is the authority, but the categories below cover most designs.
Typical consumers
| Consumer | Present on | Typical supply type | Relative power | When it runs |
|---|---|---|---|---|
| Backpressure and temperature sensors | Almost all designs | Low-voltage DC from the controller | Very small | Whenever monitoring is on |
| Controller or display unit | Most designs | 230 V AC single phase, or 12 V or 24 V DC | Small | Continuously, or whenever the DG runs |
| Data logger, IoT gateway or modem | Many designs | 230 V AC or low-voltage DC | Small | Continuously, to send data |
| Alarm beacon or hooter | Some designs | Low-voltage DC or 230 V AC | Small | On alarm |
| Electric regeneration heater | Designs with active electric regeneration | Often 230 V single phase or 415 V three phase, depending on size | Large, often several kW | During regeneration cycles |
| Blower or fan for regeneration air | Some active designs | Single or three phase | Moderate | During regeneration |
| Dosing pump or valve | Designs with fuel or reagent dosing | Low-voltage DC or 230 V AC | Small | During dosing |
| Electrostatic power unit | Electrostatic precipitator type devices | 230 V AC input to an internal high-voltage supply | Moderate | Whenever the device is treating exhaust |
| Trace heating on sensor lines | Cold climates or special cases | 230 V AC | Small to moderate | In cold conditions |
The “relative power” column is deliberately vague, because real numbers depend on the design and the engine size. Ask the vendor for a load schedule with voltage, phases, rated power, starting current and duty cycle for each item.
Why the heater changes everything
Without a heater, an RECD’s electrical load is usually tiny: a controller, a few sensors and a modem, often well under a few hundred watts. A heater can multiply that by tens. A circuit that is perfect for a controller is completely wrong for a heater, and a heater that runs from the DG’s own output takes real capacity from the loads the generator is meant to serve. Our article on whether an RECD changes a generator’s usable power output covers the wider question of what the device costs the set.
Our explainer on what an RECD is and how it works describes the main device types. If you are unsure which type yours is, the RECD test certificate guide explains where to find the technology description.
Part 2: Answer the Three Supply Questions
For each consumer on the list, answer three questions.
Question A: What voltage and phase?
Controllers and loggers are commonly supplied for 230 V single-phase AC or for low-voltage DC, usually 12 V or 24 V. Heaters and blowers may be single phase or three phase. Mixed requirements are common: a 230 V controller with a 24 V DC sensor circuit inside, plus a 415 V heater.
Question B: How much?
Record the steady running power and any inrush or starting current. Heaters draw high current as soon as they are switched on. Blowers have motor starting current. Modems and power supplies have small inrush currents that can still trip sensitive protection if several start together.
Question C: When?
This is the question that most often goes wrong, and it gets its own section.
Part 3: The “When” Problem
An RECD sits on a generator, and a generator runs mainly when the normal supply has failed. Any RECD electrical load fed only from the grid will lose power precisely when it is needed.
Map the operating states
| State | Grid | DG | What the RECD’s electrics need to do |
|---|---|---|---|
| Normal, DG off | Available | Stopped | Logger may need to send data; offline regeneration may run in some designs |
| Outage, DG starting | Failed | Cranking | Controller should ride through the start without resetting |
| Outage, DG running | Failed | Running | Sensors, controller and logger must work; electrostatic stages must be powered; heater may run |
| Test run, grid present | Available | Running on test | Same as above, with the grid available as a source |
| Shutdown, DG cooling | Either | Stopped | Logger should record the end of the run; some designs run post-shutdown functions |
Source options
Grid-only supply. Simple, but fails the main operating state. Only acceptable for loads that are needed solely when the DG is off, such as an offline regeneration heater designed to run on grid power.
DG output supply. Taking power from the generator’s own output, usually from an auxiliary or essential board downstream of the changeover, means the supply is present whenever the DG runs and also when the grid feeds the same board. This suits controllers, loggers and electrostatic stages. It does not cover the start-up moment before the generator builds voltage.
DG battery supply. The engine’s starting battery, usually 12 V or 24 V DC, is present at all times. A DC controller can use it, with protection and a suitable converter. The catch is that battery voltage dips sharply during cranking. A controller fed directly may reset every time the engine starts. Check the controller’s rated input range against the dip, or use a DC to DC converter designed to ride through it. Our article on why a generator battery is not charging explains why battery health also matters if you add load to it.
UPS-backed supply. A small uninterruptible power supply on the controller and logger circuit bridges the gap between grid failure and DG voltage, and keeps the logger alive long enough to record a shutdown. This is often the neatest answer for the small loads.
Combined approach. Many good installations combine sources: controller and logger on a UPS fed from the essential board, sensors powered by the controller, heater on a separate dedicated circuit with its source chosen to suit the regeneration strategy.
Heater source: the strategy question
Where a design uses an electric heater, ask the vendor:
- Does regeneration happen while the DG runs, while it is stopped, or either?
- If while running, is the heater fed from the DG output? How many kW does that take from the set, and for how long?
- If while stopped, does it need the grid? What happens on a site with no grid, or long grid failures?
- Can regeneration be scheduled, inhibited or deferred?
- What happens if power is lost part-way through a regeneration cycle?
A remote telecom site with no grid connection, for example, cannot rely on grid-powered offline regeneration. Our guide on RECDs for telecom sites discusses unattended sites. A standby set that runs rarely and lightly, on the other hand, may depend on active regeneration more than a busy prime-power set. See whether an RECD suits a DG set that runs only occasionally and prime power vs standby DG sets and RECD specification.
Part 4: Protection, Isolation and Earthing
Once source and size are settled, the circuit itself needs proper design. India’s wiring practice is set out in the relevant Indian Standards and the National Building Code; your licensed electrical contractor applies them. The points below are what a review should look for.
Dedicated circuits
- A dedicated, labelled circuit for the RECD controls
- A separate dedicated circuit for any heater or blower
- No sharing with lighting, sockets or other plant, so a fault elsewhere does not switch off monitoring
Overcurrent protection
Each circuit needs a breaker sized for the load and the cable. Heaters need protection that tolerates their inrush without nuisance tripping. Motor loads such as blowers may need motor protection.
Earth leakage protection
Residual current devices protect people from electric shock. They are particularly relevant where equipment is outdoors, near water or touched during maintenance. Heater elements can develop small leakage currents when damp, which can trip sensitive devices; the vendor should state what leakage to expect so the right protection is chosen.
Local isolation
A lockable isolator close to the device lets a technician switch off and lock the supply before opening the controller, removing a heater or working on the filter. The isolator should be within sight of the device, clearly labelled and able to be padlocked off. Electrical isolation is a core part of any lock-out procedure on the device.
Earthing and bonding
- The device housing, frame and controller enclosure should be bonded to the site earthing system
- Electrostatic devices have specific earthing requirements for safety and performance; follow the vendor’s instructions exactly
- Sensor cable screens should be earthed at the point the vendor specifies, usually one end only, to avoid earth loops
The general principles of protective earthing are covered in the ground (electricity) article.
Surge protection
Rooftop devices and long cable runs pick up surges from lightning and switching. A surge protection device on the controller supply, and on communication lines where they leave the building, protects electronics. Our guide on rooftop RECD installation discusses exposed roof locations.
Part 5: Cable, Enclosure and Environment
Cable sizing and voltage drop
Long runs from the electrical room to a rooftop device cause voltage drop, especially on heater circuits. Size cables for the full run length and check the drop at the device end. Low-voltage DC circuits are particularly sensitive: a few volts lost on a 24 V circuit is a large fraction.
Routing near heat
Cables to the device inevitably approach hot surfaces. Insulation types, clearances and support methods matter. Our companion guide on RECD cable routing near hot exhaust lines covers this in detail.
Enclosures and ingress protection
The controller enclosure must suit its location. Outdoors or in wash-down areas, it needs a suitable IP rating against dust and water, and protection from direct sun. Indoors near the engine, it needs protection from heat and oil mist. Ask the vendor for the enclosure rating and maximum ambient temperature.
Placement of the controller
- Close enough to the device for sensor cable lengths the vendor allows
- Far enough from hot surfaces to stay within its temperature rating
- Readable and reachable, so operators can see alarms without climbing
- Above any flood level in low-lying plant rooms
Our guide on assessing an RECD for very hot ambient conditions explains why electronics near a DG struggle in summer.
Part 6: Supply Quality From the Generator
When the RECD’s controls run from the DG, they run on generator power, which behaves differently from the grid.
- Start-up transients. Voltage and frequency settle over the first seconds after the set takes load.
- Load steps. Large motor starts cause voltage dips. Our article on RECDs for generators with rapidly changing loads discusses load steps.
- Frequency variation. Some electronics are sensitive. See generator frequency problems.
- Voltage fluctuation. Older sets or sets with tired regulators may vary more than the grid. Our guide on diagnosing voltage fluctuations helps.
A small UPS or a power supply with a wide input range insulates the controller and logger from all of these.
Part 7: Communication and Data
Many RECDs now report backpressure, temperature and alarms remotely. The communication link has its own power and connection needs.
- Cellular modem. Needs power and signal. Check signal strength at the controller location, which may be in a basement or behind concrete.
- Wired network. Needs a data cable from the building network, with surge protection if it runs outdoors.
- Power during outages. If the modem loses power when the grid fails, the remote system sees nothing during the very runs it is meant to monitor. Put it on the UPS-backed circuit.
The Electrical Information Pack
Before installation, the vendor and electrical contractor should agree a short pack. It prevents most site arguments.
| Document | Contents |
|---|---|
| Load schedule | Every consumer, with voltage, phase, power, inrush and duty |
| Single-line diagram | Source board, breakers, RCDs, UPS, isolator, controller, heater circuit |
| Cable schedule | Each cable’s type, size, length, route and termination points |
| Control wiring diagram | Sensors, alarms, interlocks with the DG controller |
| Earthing details | Bonding points and screen earthing |
| Enclosure data | IP rating, ambient temperature range, mounting position |
| Interlocks | What the RECD controller signals to the DG, and vice versa |
The single-line diagram and cable schedule should be referenced on the general arrangement drawing. Our companion guide on what an RECD general arrangement drawing should include explains how electrical interfaces appear there.
Interlocks with the DG controller
Some installations link the RECD controller to the generator’s own controller: a high backpressure alarm that shows on the DG panel, or a signal that inhibits regeneration while the set is starting. These links should be agreed with the generator’s service provider. Our article on whether installing an RECD affects the OEM warranty explains why changes to engine controls need care. Electronically governed and mechanically governed engines offer different integration options; see RECD on mechanically governed vs electronic DG engines.
Commissioning Checks for the Electrical Side
- Confirm supply voltage at the controller terminals with the grid on, and again with the DG running
- Start the DG with the grid off and check the controller does not reset during cranking
- Simulate a grid failure and confirm the UPS carries the controller and modem until the DG takes over
- If a heater is fitted, energise it and check current, breaker behaviour and voltage drop
- Test the RCD and check earth continuity to the housing and frame
- Check that alarms appear locally and remotely
- Lock off the isolator and confirm everything downstream is dead
- Record all readings in the commissioning file
A Walkthrough: Diagnostic Laboratory in Nagpur
This is an illustrative case.
The site
- A 125 kVA set beside a diagnostic laboratory, used as standby during frequent short outages
- RECD fitted outdoors on a frame next to the canopy, with remote backpressure monitoring
- Controller supplied for 230 V AC, with an internal 24 V DC sensor circuit
- The installer had fed the controller from a socket circuit in the laboratory’s grid-only lighting board
The symptoms
The remote dashboard showed perfect records for days at a time, then blank periods. The vendor initially suspected the modem. A facility engineer noticed that the blank periods matched power cuts exactly, which were the only times the generator ran.
The review
| Item | Finding |
|---|---|
| Source | Grid-only lighting board; dead during outages |
| Ride-through | None; controller lost power at grid failure and stayed off while the DG ran |
| Circuit | Shared with corridor sockets; occasionally tripped by a kettle |
| Isolation | No local isolator at the device |
| Enclosure | Controller in direct afternoon sun; internal temperature high in May |
| Earthing | Frame not bonded to site earth |
The correction
- A new dedicated circuit was run from the essential services board, which is fed by the grid normally and by the DG during outages
- A small online UPS was fitted for the controller and modem, sized to bridge the start and changeover
- A lockable isolator was mounted beside the controller
- The controller was moved to the shaded side of the canopy, with a sun hood
- The frame and housing were bonded to the site earth
- A surge protection device was added on the controller feed
After the change, the dashboard recorded every outage run from start to finish, and the laboratory could show complete records to its auditors. Healthcare and diagnostic facilities often have similar critical-load arrangements; see RECDs for hospitals. The 125 kVA DG set RECD page covers this rating.
Common Power Supply Mistakes
| Mistake | Result |
|---|---|
| Controller fed from a grid-only circuit | No monitoring during outages |
| Controller fed directly from the starting battery without ride-through | Resets every crank |
| Heater on a circuit sized for the controller | Breaker trips on regeneration |
| No local isolator | Unsafe maintenance |
| Controller in direct sun or beside the engine | Overheating and faults |
| No earth bonding on the frame | Shock risk; interference on sensors |
| Modem not on backup power | Data gaps during the runs that matter |
| Heater load not counted on the DG | Capacity shortfall during regeneration under load |
Several of these overlap with our list of common RECD installation mistakes.
Compliance Note
Device approval is set by CPCB’s System and Procedure for Emission Compliance Testing of RECDs. The electrical supply is a site installation matter, but a monitoring system that is off during generator runs leaves gaps in the record you may be asked to produce. Keep the load schedule, single-line diagram and commissioning readings with your installation documents, and see our guide on verifying a CPCB tested RECD on a DG set for related paperwork.
Frequently Asked Questions
What voltage does an RECD controller use?
Commonly 230 V single-phase AC or 12 V or 24 V DC, depending on the design. Check the vendor’s data sheet.
Can the RECD controller run from the generator battery?
Often, if the controller accepts the battery voltage and can ride through the dip during cranking. A suitable DC to DC converter may be needed.
Does every RECD need a heater?
No. Many designs rely on exhaust heat and a catalyst for regeneration. Some use electric heaters for active regeneration. Ask the vendor which applies.
Should the heater run from the DG output?
It depends on the design and site. Running from the DG means the heater uses some of the set’s capacity. Running from the grid fails on sites without grid power. The regeneration strategy decides.
Why does my RECD monitoring go blank during power cuts?
The controller or modem is probably fed from a grid-only circuit. Feed it from a supply that is live when the DG runs, preferably with a small UPS.
Is a local isolator necessary?
Yes. It allows the supply to be switched off and locked before maintenance on the device or controller.
Power the Device for the Moments That Count
An RECD’s electrics are small compared with the generator, but they decide whether the device can be monitored, regenerated and maintained safely. Write the load list, answer the voltage, size and timing questions for each item, pick sources that are live when the generator is, protect and isolate every circuit, and document it in a short electrical pack. The result is a controller that never misses a run and a heater that never trips a breaker at the wrong moment.
Aceget supplies a load schedule and electrical interface details with every RECD and works with site electricians on supply, protection and monitoring. To plan the electrical side of your installation, get in touch with Aceget, or see the full retrofit emission control device range.