The meter contains four tariff energy records, but its internal-clock schedule does not provide three daily changeovers. It supports a maximum of two tariffs per day. To use three rates every day, select communication-based tariff control and have an external scheduler command T1, T2, or T3 at each rate boundary.
Reject the quick fixes first
Do not spend the shift duplicating weekday and weekend entries. Those entries separate schedules by day type; they do not expand the internal clock beyond two tariff selections per day. A schedule that needs three rates on every weekday and weekend cannot be represented by that mode.
Do not rotate three rates through the four records manually either. That may move the immediate reading into another record, but it does not create automatic daily changeovers. It also makes accumulated energy difficult to reconcile if the operator changes the selection late or chooses the wrong record.
The four records and the number of internal daily schedule periods are separate limits. Think of T1 through T4 as accumulation destinations. The control mode decides which destination is active. Internal-clock control can schedule no more than two of them in a day; communication control can select all four as required.
Read the control mode before changing the schedule
| Reading or observation | What it means | Next check |
|---|---|---|
| Tariff control is set to the internal clock | The meter owns the switching schedule and the two-tariff-per-day limit applies. | Confirm whether the billing plan requires more than two daily rates. |
Tariff control is set to by communication
|
An external Modbus master must select the active tariff. | Check communication protection and then test a commanded change. |
| The displayed or reported tariff never changes | The command may not be reaching the meter, may be blocked, or may use the wrong structure. | Read communication status, protection state, and the active tariff after a test command. |
| The tariff changes but at the wrong time | The meter is accepting commands; the scheduler clock, calendar, or event mapping is wrong. | Compare scheduler time and the configured rate boundaries. |
If the requirement is only one or two rates per day, keep the internal clock and correct its weekday/weekend schedule. If the requirement is three rates every day, stop editing that schedule and move to communication control.
Confirm the external scheduler can own every changeover
Communication control transfers the timing function from the meter to a workstation, PLC, SCADA system, or other Modbus master. The external device must keep the calendar, determine which rate applies, and issue the tariff-selection command at every boundary. The meter then accumulates energy in the selected record.
Before changing modes, confirm that the master runs continuously. A calendar stored only in an operator workstation is a production dependency: if that workstation is shut down, disconnected, or its scheduling service stops, the next tariff change will not occur. The meter does not infer the missing change from the three-rate plan.
Check the master clock and its time zone against the billing schedule. Record the required transitions as explicit mappings, such as first period to T1, second period to T2, and third period to T3. Leave T4 unused unless the billing design assigns it a purpose.
Clear the command path before testing
The meter setting for communication protection must be disabled for the tariff command to operate. Treat this as a direct branch in the diagnosis:
- If communication protection is enabled, disable it in the meter settings and repeat the test.
- If it is already disabled, verify that the Modbus master can communicate with the meter before investigating the schedule.
- If ordinary communication succeeds but tariff selection fails, compare the transmitted request with the meter manual's tariff command definition.
The documented command structure is identified as 2008. Use the exact function, data format, and selection value specified for that structure in the applicable meter manual; the identifier alone does not define the complete Modbus request. Do not guess the write value for T1, T2, T3, or T4.
Capture the request and response during commissioning. A Modbus exception points to addressing, function, access, or data problems. A normal response followed by no active-tariff change calls for a readback check and confirmation that communication protection is actually disabled.
Configure three daily tariffs through Modbus
- Record the current control mode, active tariff, accumulated values in
T1throughT4, meter time, and external scheduler time. This creates a reconciliation point before control changes. - Build the daily calendar in the external controller. Apply the same three rate boundaries to weekdays and weekends because the rate plan does not vary by day type.
- Map each period to its intended record:
T1,T2, orT3. Check the mapping against the billing definition before sending commands. - Configure the meter tariff control mode as
by communication. - Disable communication protection in the meter settings.
- Implement the tariff-selection request using command structure
2008and the manual-defined payload. - Send one supervised test command for each required tariff. After each command, read or observe the active tariff and confirm that it matches the request.
- Enable the calendar only after all three selections work. Monitor the first scheduled boundary rather than waiting for the entire day to discover a bad mapping.
Get production running with the external schedule, then make the control durable. Store the schedule in a device expected to remain powered, document its time source, and restrict unplanned edits to the rate table.
Verify switching and catch recurring failures
| Verification | Pass condition | Failure action |
|---|---|---|
| Manual selection test | Commands for T1, T2, and T3 each produce the matching active tariff. |
Check protection, command 2008, request format, and Modbus response. |
| Scheduled boundary test | The active tariff changes at the intended external-calendar boundary. | Check scheduler time, calendar logic, and event execution. |
| Day-type test | The same three transitions run on both weekday and weekend dates. | Remove unintended day-type exclusions from the external calendar. |
| Accumulation check | Energy advances in the record selected for the current period. | Recheck the tariff-to-rate mapping before billing data is collected. |
| Restart check | The scheduler resumes control without sending an incorrect tariff. | Define startup logic that calculates the tariff from current date and time. |
A one-time startup command is not a complete solution. The controller must issue later changeovers and recover correctly after a restart or communication interruption. Alarm on failed commands or tariff readback mismatch where the controlling platform supports that comparison.
Frequently Asked Questions
Can I configure three iEM3255 tariffs per day with the internal clock?
No. Internal-clock tariff configuration is limited to a maximum of two tariffs per day. Use by communication control for three daily rates.
Can I use all four iEM3255 tariff records in one day?
Yes, communication-based control can select all four records. For a three-rate plan, command only the assigned T1, T2, and T3 records unless T4 has a defined billing purpose.
Does the weekday and weekend setup provide four daily periods?
No. Weekday and weekend entries distinguish day types; they do not raise the maximum of two internal-clock tariffs in a day.
Can I keep testing if Modbus works but the tariff will not change?
Check that tariff control is by communication, communication protection is disabled, and the request follows command structure 2008. Stop if valid commands still produce no tariff change, the active tariff cannot be read back, or accumulated energy moves into the wrong record. Escalate to Schneider Electric official support with the meter configuration and captured Modbus request and response.