Acrel Meter Selection Guide for Generator and Mains Monitoring
A meter that looks right on a panel drawing can still be wrong for the job. Generator and mains monitoring need clear choices on voltage, current, supply, communications, and energy direction. If those details are vague, the result can be missing data, incorrect readings, or a meter that cannot connect to the wider system.
This guide helps buyers prepare a clear specification for ProSense Instruments when selecting an Acrel meter for generator and mains monitoring. The focus is monitoring, not generator control. The meter measures and reports electrical values. It does not start the generator, synchronise sets, open breakers, or replace a generator controller.
Monitoring and control are not the same task
Generator systems often combine several devices. A generator controller handles engine start, shutdown, alarms, breaker logic, and sometimes synchronising. A protection relay may trip a breaker during a fault. A power meter records values such as voltage, current, power, power factor, frequency, and energy.
An Acrel meter fits into the measurement and reporting part of that system. It can support operators, energy managers, BMS platforms, SCADA systems, and maintenance teams by showing what is happening electrically.
A monitoring meter can usually help answer questions such as:
What voltage is present on the generator or mains incomer?
How much current is flowing on each phase?
What is the real power demand?
Is power factor leading or lagging?
How much energy has been imported or exported?
Is frequency within the expected range?
Can the data be sent to another system by Modbus, Ethernet, or another supported method?
It should not be specified as if it were a generator control unit. If the requirement includes automatic start, load transfer, breaker closing, synchronising, load sharing, or engine protection, state that separately. Those functions need the correct control and protection equipment.
For a meter specification, keep the wording direct:
Supply and configure an Acrel meter for electrical monitoring of the generator incomer and mains incomer. Generator control, breaker control, and synchronising functions are excluded unless specified under separate equipment.
That single sentence can prevent a lot of confusion during pricing, design, and commissioning.
Start with the electrical system being monitored
The first part of an Acrel Meter Selection Guide for Generator and Mains Monitoring is the supply arrangement. A meter can only be selected correctly when the electrical system is clear.
Confirm the phase and wiring arrangement
Most generator and mains monitoring projects involve one of these arrangements:
Supply arrangement | What to specify | Why it matters |
Single phase two wire | Line and neutral voltage | The meter must suit single phase measurement |
Three phase three wire | Phase to phase voltage, no neutral reference | The meter must support 3P3W connection |
Three phase four wire | Phase to neutral and phase to phase voltage | The meter must support 3P4W connection |
Split supply or multiple incomers | Each supply point and connection type | One meter may not be enough |
Generator and mains side by side | Which meter measures which source | Prevents mixed readings and unclear data labels |
Do not just write “three phase meter”. State whether the system is three phase three wire or three phase four wire. If the neutral is present, say so. If the meter is measuring a generator output before an ATS, note that. If it is measuring the load side of an ATS, the meter may see either generator or mains depending on switch position.
State the nominal voltage
Voltage affects meter input selection and wiring. A useful specification gives the nominal voltage and the measurement points.
Examples include:
230 V single phase
400 V three phase four wire
415 V three phase four wire
480 V three phase three wire
Medium voltage system measured through voltage transformers
For low voltage systems, many panel meters can measure directly within their rated input range. Check the selected Acrel model data sheet before assuming direct connection is suitable.
For medium voltage or higher low voltage applications outside the meter’s direct input range, specify the voltage transformer ratio. For example, a system may use VTs to step voltage down to a safe metering input. The ratio must be entered into the meter so the displayed values match the real system.
Specify current measurement before choosing the meter
Current measurement is just as important as voltage. In many generator and mains installations, the meter reads current through external current transformers rather than by direct connection.
Choose the CT ratio carefully
The CT ratio should suit the maximum expected current, the generator rating, and the load profile. If the CT rating is far too high, low-load readings may lack useful resolution. If it is too low, the system may exceed the CT range.
A good specification names the CT ratio and secondary output.
Common examples include:
100/5 A
250/5 A
400/5 A
800/5 A
1600/5 A
250/1 A
800/1 A
The meter must match the CT secondary, such as 1 A or 5 A. Do not leave this open. A meter ordered for 5 A CT inputs is not automatically correct for 1 A CTs.
Decide whether CTs are existing or new
This detail matters for supply and commissioning. Existing CTs may already feed another device. New CTs must suit the busbar or cable size and the installation space.
Include the following where possible:
CT ratio
CT secondary current
CT accuracy class if needed
CT type such as solid core, split core, or busbar mounted
Number of CTs
Whether CT shorting terminals are required
Whether CTs are dedicated to the new meter
If CTs are shared, take care. CT circuits should never be opened while energised. Any work on CT wiring should follow site safety rules and be done by competent personnel.
Match CT placement to the data required
The CT location decides what the meter actually measures. For generator and mains monitoring, placement can change the meaning of the readings.
CT position | What the meter sees | Common use |
Generator output before breaker | Generator production only | Generator performance monitoring |
Mains incomer | Utility import and export at the incomer | Grid supply monitoring |
Load side of ATS | Load supplied from either source | Site load monitoring |
Generator parallel bus | Combined generator contribution | Multi-set generator monitoring |
Solar or battery connection point | Local generation or storage flow | Bidirectional energy tracking |
A meter cannot infer where current is flowing if the CTs are installed in the wrong place. State the physical measuring point in the specification.
Decide what values need to be displayed and logged
Acrel meters are often selected to show live electrical values at the panel and send readings to a higher-level system. The right model depends on the required measurements.
Typical monitoring values include:
Voltage per phase
Current per phase
Frequency
Real power in kW
Apparent power in kVA
Reactive power in kVAr
Power factor
Imported energy in kWh
Exported energy in kWh where supported
Demand values where required
Total harmonic distortion if power quality information is needed
Not every project needs every value. A simple generator status panel may only need voltage, current, frequency, kW, and kWh. A site energy monitoring system may need import and export energy, demand, power factor, and communications.
Include bidirectional measurement when power can flow both ways
Bidirectional measurement is needed when energy can flow in both directions through the metering point. This is common on sites with embedded generation, battery storage, solar PV, grid export, or generator paralleling arrangements.
For a mains incomer, bidirectional measurement may be needed to separate:
Imported energy from the grid
Exported energy to the grid
Positive and negative power flow
Net energy where required by the monitoring platform
For a generator, bidirectional measurement may be relevant if there is a risk of reverse power or if the generator operates in parallel with another source. The meter can report the direction and size of power flow if the model and configuration support it. Protection against reverse power is a separate function and should not be assumed unless a suitable relay or controller is specified.
Use clear wording such as:
Meter shall support bidirectional active power and separate imported and exported energy registers for the selected metering point.
That is much clearer than saying “smart meter required”.
Confirm the auxiliary supply for the meter
The meter needs a power source for its electronics. This is separate from the measurement inputs, even where the same system voltage may be used.
Specify the auxiliary supply clearly. Common options may include AC or DC control supplies, depending on the chosen model. Do not assume the meter can be powered by any available voltage in the panel.
Useful details include:
Auxiliary supply voltage
AC or DC supply
Whether the supply is from mains, generator, UPS, battery, or control transformer
Whether the meter must remain powered when the generator is off
Whether monitoring is required during mains failure
This is especially important for generator monitoring. If the meter is powered only from the generator output, it may turn off when the generator stops. That may be acceptable for some panels, but not for sites that require communications or event visibility during standby periods.
For mains incomer monitoring, a meter powered from the same mains supply will usually turn off during a supply failure unless backed by UPS or another control supply. If the monitoring system must know that the mains has failed, the design may need a powered communications path and a suitable status input or relay elsewhere.
Choose communications early
Communications should be specified before the meter is ordered. The physical port, protocol, addressing, and data mapping all affect model selection and commissioning time.
Common requirements may include:
RS-485 communications
Modbus RTU
Ethernet communications
Modbus TCP where supported
Pulse output for energy counting
Digital input or output options where supported
Integration with BMS, SCADA, PLC, or an energy platform
The most common problem is incomplete wording. “Meter with comms” is not enough. State the protocol and connection type.
Better wording would be:
Meter shall provide RS-485 Modbus RTU communications for integration with the site BMS. Contractor shall provide network address, baud rate, parity, and register requirements before commissioning.
Or:
Meter shall provide Ethernet communications using a supported protocol suitable for connection to the site monitoring platform.
If the receiving system already exists, ask for its requirements. Some platforms expect specific registers, scaling, byte order, or data intervals. Acrel meters can often provide standard electrical data, but the integration team still needs the correct map for the selected model.
Plan the labels and data names
Generator and mains values must be easy to identify once they reach the monitoring system. Avoid vague device names such as `Meter 1` and `Meter 2`.
Use names that match the electrical drawing:
`Generator_Incomer_Meter`
`Mains_Incomer_Meter`
`ATS_Load_Side_Meter`
`Generator_1_Output`
`Utility_Import_Export`
Good naming reduces confusion during alarms, reporting, and maintenance.
Decide whether one meter or several meters are needed
Some projects try to use one meter for both generator and mains information. That is only suitable if the meter is installed at a point where it genuinely measures the required source or load.
Use separate meters when separate measurement points are required. For example, a generator incomer and a mains incomer are normally different physical points, so each may need its own meter and CT set.
Requirement | Likely metering approach |
Monitor only total site load after ATS | One meter on the ATS load side |
Monitor generator output and mains import separately | Two meters, one per source |
Monitor several generator sets | One meter per set, or a defined metering point per generator |
Monitor grid import and export | One bidirectional meter at the mains incomer |
Monitor generator plus solar plus site load | Multiple meters at defined points |
If cost is a concern, reduce the number of monitored points only after deciding which data can be lost. Do not assume one meter can report values from two different incomers unless the electrical arrangement makes that possible.
Prepare a clear specification for ProSense Instruments
A good enquiry gives ProSense Instruments enough information to select the right Acrel meter and accessories without repeated back-and-forth questions. It does not need to be long, but it should be specific.
Use this checklist when preparing the request.
Project and application details
Include:
Generator monitoring, mains monitoring, or both
Number of metering points
Whether the meter is for panel display, remote monitoring, or both
Whether the installation is new or a retrofit
Any space limits in the panel
Indoor or outdoor panel environment if relevant
Electrical supply details
Include:
Single phase or three phase
Three wire or four wire arrangement
Nominal voltage
System frequency
Direct voltage measurement or VT ratio
Fault level or protection requirements if the panel builder needs them
Current measurement details
Include:
Maximum expected current
Generator or incomer rating
CT ratio
CT secondary output, usually 1 A or 5 A
CT type if required
Existing or new CTs
Metering point location
Measurement requirements
Include:
Voltage, current, frequency, kW, kVA, kVAr, power factor
kWh energy
Import and export energy if needed
Demand readings if needed
Harmonics or power quality values if needed
Any required alarm outputs or status signals, if supported by the selected meter
Communications requirements
Include:
No communications, local display only
RS-485 Modbus RTU
Ethernet or Modbus TCP where required and supported
Pulse output
BMS, SCADA, PLC, or energy platform connection
Baud rate, parity, address range, IP requirements, or site standards where known
Power supply and installation details
Include:
Auxiliary supply voltage
AC or DC auxiliary supply
Whether supply remains live during generator standby
DIN rail or panel mount preference
Required approvals or documentation
Any matching CTs, fuses, terminals, or accessories
Avoid the common selection mistakes
Most metering issues come from incomplete specifications rather than poor equipment. These are the problems to catch early.
Wrong wiring assumption
A three phase four wire meter configuration used on a three phase three wire system can give incorrect voltage and power readings. State the wiring arrangement.
Incorrect CT secondary
A 1 A CT and a 5 A meter input are not interchangeable. Match the meter to the CT secondary.
Unclear CT location
If the CTs are on the load side of an ATS, the meter measures the load, not the generator or mains source separately.
No bidirectional requirement stated
If import and export must be separated, specify bidirectional measurement and separate energy registers.
Communications added too late
A meter ordered without the right port or protocol may not connect to the site system. State communications at the buying stage.
Monitoring treated as control
A meter can support visibility, reporting, and analysis. It should not be expected to manage engine starting, breaker operation, synchronising, or protection unless those functions are provided by other specified devices.
A clear meter request saves time later
The best Acrel meter choice comes from a clear description of the electrical system and the data required. Before asking for a quotation, define the monitored point, voltage arrangement, CT details, auxiliary supply, communications method, and whether power flow is one-way or bidirectional.
For generator and mains monitoring, clarity matters more than a long specification. State what the meter must measure, where it will be installed, how it will be powered, and where the data must go. Keep generator control and protection as separate requirements. That gives ProSense Instruments the information needed to recommend a suitable Acrel metering solution and helps the finished system deliver readings that people can trust.
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