Iskra MC 7x0A

Compatibility

Compatible with EpiSensor Edge over Modbus RTU or Modbus TCP

The MC 740, MC 750 and MC 770 are compatible with EpiSensor Edge over Modbus RTU on an RS485 port (COM1 ordered as RS232/RS485, or COM2 as I/O module 3/4), read through a ZMB-31 Modbus Interface or a Gateway serial port, and over Modbus TCP on port 502 of the Ethernet and USB option. Iskra publishes the main measurement registers, their types and the decoding of each type in appendix A of the user's manual.

MC 740, MC 750 and MC 770 marked MC 7x0A (hardware version D and above), read with appendix A of user's manual version 1.01. Site check: read frequency at table address 30105 (wire address 0x0069) and compare it with the supply. Read-only monitoring: no writes to settings, resets, tariffs, digital outputs or passwords.

Connect it with

• Modbus Interface ZMB-3X From €399 ex VAT Configure
• Gateway ZGW-20 From €899 ex VAT Configure
• Evaluation Gateway on a Raspberry Pi Edge with one device licensed Free Set up

Models

Specifications

The MC 7x0A family samples 4 voltage and 3 current channels at 32 kHz with automatic range selection up to 12.5 A and 1000 V rms, and measures more than 140 quantities including harmonics to the 63rd, unbalance and, on the MC 770, flicker. Up to three communication ports carry Modbus and DNP3: COM1 as RS232/RS485 or Ethernet and USB, and an optional RS232 or RS485 COM2.^1, 2

Ordering code

MC 740, MC 750 or MC 770 followed by: nominal frequency (S 50/60 Hz, A 400 Hz, B 16 2/3 Hz), auxiliary supply (U universal, D 110 V AC, E 230 V AC, F 400 V AC), COM1 (T RS232/RS485 terminal, R RS232/RS485 DB9, E Ethernet and USB), I/O module 1/2, I/O module 3/4 (including G RS232 COM2 and C RS485 COM2), RTC backup (C supercap, B battery) and current connection (T through-hole, C screw terminal).^2, 3, 4

Accuracy

To IEC 61557-12: active energy class 0.5S on the MC 740 and MC 750 and 0.2S on the MC 770; active power 0.2; rms current 0.2 (MC 770: 0.1); phase voltage 0.2 (MC 770: 0.1, class A); frequency 0.02. Class S to EN 61000-4-30 on the MC 740 and MC 750, class A on the MC 770.¹

Voltage inputs

4 channels, the fourth for earth to neutral; nominal 500 V L-N, 866 V L-L; maximum measured 600 V L-N, 1000 V L-L continuously; 1.2 × UN permanently, 2 × UN for 10 s.¹

Current inputs

3 channels, nominal 1 A or 5 A, maximum measured 12.5 A, 15 A continuous thermal, 300 A for 1 s; VT and CT ratios set in the meter.¹

Communication

RS485 (1000 m) or RS232 on terminals 21 to 25 or a DB9, 2400 to 115200 bit/s, Modbus RTU and DNP3 detected automatically; factory address 33, 115200 bit/s, no parity, 8 data bits, 2 stop bits. Ethernet 10/100 Mb/s with Modbus TCP and DNP3 on port 502, DHCP by default; USB 2.0.¹

Auxiliary supply

Universal 48 to 276 V AC (40 to 65 Hz) or 20 to 300 V DC, or AC 110, 230 or 400 V; under 8 VA with all I/O.^1, 2

Housing

96 × 96 × 96.5 mm (101.5 mm with through-hole CTs), 92 × 92 mm panel cut-out, PC/ABS to UL 94 V-0, 550 g; IP40 front with the memory slot cover, IP20 rear.¹

Environment

Operating -10 to 55 °C (K55 to EN 61557-12), storage -40 to +70 °C, 75% r.h. without condensation.¹

Safety and EMC

Protection class II to EN 61010-1:2010, 600 V rms CAT II or 300 V rms CAT III, pollution degree 2; EN 61326-1:2013 for industrial environments.¹

Interface

Documented measurements and integration boundaries for MC 7x0A.

• Iskra states that the memory reference for input and holding registers is 30000 and 40000, and prints each address as that reference plus the register offset. Subtract 30000 for the zero-based address on the wire: frequency at 30105 is 0x0069. A client that numbers input registers from one takes the table value plus one. Read the measurements with function 04.
• T5 (unsigned) and T6 (signed) take two registers: the top byte is a signed power-of-ten exponent and the remaining 24 bits are the value. Iskra's example stores 123456 × 10⁻³ as FD01 E240. The table has no unit column, so check the first decoded value of each quantity against the display before choosing units in Edge.
• Frequency at 30105 (hex 0069), T5. Phase voltages U1, U2 and U3 at 30107, 30109 and 30111 (hex 006B, 006D, 006F) and their average at 30113 (hex 0071); line voltages U12, U23 and U31 at 30118, 30120 and 30122 (hex 0076, 0078, 007A) and their average at 30124 (hex 007C); all T5.
• Currents I1, I2 and I3 at 30126, 30128 and 30130 (hex 007E, 0080, 0082), calculated neutral current at 30132 (hex 0084), average current at 30136 (hex 0088) and total current at 30138 (hex 008A); all T5.
• Total active power at 30140 (hex 008C) and phase active power at 30142, 30144 and 30146 (hex 008E, 0090, 0092), T6 signed; total reactive power at 30148 (hex 0094), T6; total apparent power at 30156 (hex 009C), T5.
• Total power factor at 30164 (hex 00A4) and phase power factor at 30166, 30168 and 30170 (hex 00A6, 00A8, 00AA), T7: the first byte flags import or export (00 or FF), the second inductive or capacitive (00 or FF), and the second register is the value with four decimal places.
• Voltage THD U1 to U3 at 30182 to 30184 (hex 00B6 to 00B8) and current THD I1 to I3 at 30188 to 30190 (hex 00BC to 00BE), one register each, T16, unsigned with two decimal places. Internal temperature at 30181 (hex 00B5), T2.
• Energy counters E1 to E4 at 30406, 30408, 30410 and 30412 (hex 0196, 0198, 019A, 019C), T3 signed 32-bit, each with its own exponent register, T2, at 30401 to 30404 (hex 0191 to 0194). The counter is the value times ten to the power of its exponent; Iskra's energy settings describe that exponent as a power of ten of Wh, so -3 is mWh and 4 is 10 kWh. Tariff counters follow from 30414 and the active tariff is at 30405.
• Which quantity each energy counter holds (import or export, active, reactive or apparent, total or one phase) is a setting of the meter. Read the counter settings in MiQen or on the display before labelling a counter in Edge, and after any change Iskra says the counters should be reset, so earlier recorded values no longer compare.
• Maximum demand since the last reset: positive real power at 30542 (hex 021E), negative real power at 30548, apparent power at 30536 and phase currents at 30518, 30524 and 30530. Dynamic demand values from 30502 to 30517.
• The appendix lists the main registers only; Iskra says the other registers are subject to change and points to its web site for the complete table. Settings from 40143 (connection mode, CT and VT values in T4) need a level 2 password to change, and digital outputs can be driven by writing Modbus registers. Keep every write out of a monitoring poll.

Setup

1. Identify the hardware and the port

   Check the side label for MC 7x0A, which this register map covers, and read the ordering code: COM1 T or R is RS232/RS485, E is Ethernet and USB, and C in the I/O module 3/4 position is an extra RS485 port.

2. Set a unique address

   Every meter leaves the factory at Modbus address 33. Change it under Settings, Communication before several meters share one RS485 bus, and note the speed, parity and stop bits (115200 bit/s, no parity, 8 data bits, 2 stop bits by default).

3. Wire RS485 or connect Ethernet

   For RS485, wire A to terminal 21 and B to terminal 22 and leave the RS232 terminals unused. For Ethernet, fix or reserve the meter's DHCP address and connect Edge to port 502 with the unit identifier set to the device address.

4. Read frequency first

   Read two input registers with function 04 from wire address 0x0069 (table 30105) and decode them as T5. The result should be close to 50 Hz or 60 Hz; a value that makes no sense usually means the exponent byte was ignored or the address is one register out.

5. Add the measurements

   Add voltages, currents and power in register pairs from the appendix A tables, decoding T5, T6 and T7 values with their own exponent or flag bytes, and compare each new quantity with the display.

6. Map the energy counters

   Check which quantity each counter E1 to E4 is set to measure, read each counter with its exponent register and compare the scaled result with the energy screen. Do not reset counters or change energy settings from Edge.

Common questions

Why send 0x0069 when the MC 750 table says 30105?

Iskra's appendix A states that the memory reference for input registers is 30000, so the printed address is the reference plus the register offset. 30105 is offset 105, or 0x0069, read with function 04. A client that takes one-based 3xxxx numbers subtracts 30001, so it needs 30106 to reach the same register.¹

How is a T5 or T6 value from the MC 7x0A decoded?

Read both registers in one request. The top byte of the first register is a signed 8-bit exponent and the remaining 24 bits are the value, unsigned for T5 and signed for T6. Multiply the value by ten to the power of the exponent. Iskra's examples are FD01 E240 for 123456 × 10⁻³ (T5) and FDFE 1DC0 for -123456 × 10⁻³ (T6).¹

How do I scale the MC 7x0A energy counters?

Each counter E1 to E4 at 30406 to 30413 is a signed 32-bit value with its own exponent register at 30401 to 30404. The reading is the counter times ten to the power of the exponent, in Wh according to Iskra's description of the energy prefix (-3 is mWh, 4 is 10 kWh). The exponent follows the meter's common and individual counter resolution settings, so read it with the counter rather than fixing a scale.¹

What are the MC 750 factory communication settings?

Serial COM1: Modbus address 33, 115200 bit/s, no parity, 8 data bits and 2 stop bits, with Modbus RTU and DNP3 detected automatically. Ethernet: DHCP, Modbus TCP on the fixed port 502, which allows several connections, and a terminal port 10001 that allows only one.¹

Can Edge and MiQen read the MC 7x0A at the same time over Ethernet?

Yes on port 502, which accepts multiple connections. A connection to the user-defined terminal port, used for firmware updates, blocks all other connections including port 502, and a USB cable on COM1 takes priority and ends the Ethernet connection until it is unplugged.¹

Does Edge read the MC 770 power quality reports?

No. Edge reads present values from the input registers, including frequency, voltages, currents, power, THD and the flicker registers. The EN 50160 reports and recorded data are stored in the meter's memory and retrieved with Iskra's MiQen software or the memory card.^1, 4