Selec MFM383A Wiring and Settings: CT, PT, Password and Modbus
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The Selec MFM383A is a 96 × 96 mm LCD multifunction meter that measures voltage, current, frequency, power factor, kW, kVA, kVAr and energy. You wire three CTs to I1–I3, the phase voltages to V1–V3 and N, and an 85–270V AC auxiliary supply to L and N; then set the network type, CT ratio and PT ratio in the configuration menu. This guide follows Selec's operating instructions (OP354-V03).
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MFM383A or MFM383A-C?
| Model | Pulse output | RS485 Modbus RTU | Price (incl. GST) |
|---|---|---|---|
| Selec MFM383A | Yes | No | ₹3,390 |
| Selec MFM383A-C-CE | Yes | Yes | ₹3,988 |
Choose the -C model only if the readings must go to a PLC, SCADA or energy-monitoring software. Both measure the same parameters.
Key specifications
- Auxiliary supply: 85 to 270V AC, 50/60 Hz, less than 8 VA.
- Measuring voltage: 11–300V AC line to neutral, 19–519V AC line to line.
- Current input: 5A AC nominal (11 mA to 6 A), through CTs with a 1 A or 5 A secondary.
- CT primary: 5 A to 10,000 A (1 A to 10,000 A if the CT secondary is 1 A). PT primary: 100–10,000V; PT secondary: 100–500V (line to line).
- Accuracy: ±0.5% for voltage and current, Class 1 for active energy.
- Panel cutout: 91.5 × 91.5 mm. Operating temperature −10 to 55 °C.
Before you wire
- Switch off and isolate the supply, and prove it dead with a tester.
- The meter has no built-in fuse. Selec recommends a fuse in each voltage line; its wiring diagrams show 0.5 A fast-acting fuses.
- Use copper cable of 0.5 to 2.5 mm² with lugs, and tighten terminals to 0.68–0.79 N·m.
- Never open a CT secondary while current is flowing. Short the CT's S1 and S2 before disconnecting it from the meter.
Terminals
| Terminals | Connect to |
|---|---|
| I1 (S1, S2), I2 (S1, S2), I3 (S1, S2) | Secondary of the CT on L1, L2 and L3 |
| V1, V2, V3, N | Phase voltages L1, L2, L3 and neutral (through fuses, or from PT secondaries) |
| L, N (auxiliary supply) | 85–270V AC supply for the meter itself |
| Pulse output (+, −) | Energy pulse to a PLC input or a counter, 24V DC max, 100 mA max |
| RS485 (+, −) | Modbus RTU network, MFM383A-C only |
Wiring a 3-phase 4-wire system (most common)
- Fit one CT on each phase, with the P1 side facing the supply.
- Wire CT S1 and S2 of L1 to I1, L2 to I2, and L3 to I3. Keep each CT on the same phase as its voltage input.
- Wire L1, L2 and L3 through fuses to V1, V2 and V3, and neutral to N.
- Give the meter its auxiliary supply on L and N (85–270V AC).
- In settings, choose network 3P4W.
3-phase 3-wire (no neutral): use V1, V2, V3 without N, with two or three CTs as in Selec's diagram, and choose network 3P3W. The meter then shows line-to-line voltages.
Single-phase 2-wire: one CT on I1, phase to V1 and neutral to N, and choose network 3P4W. Selec uses 3P4W for 3-phase 4-wire, 2-phase 3-wire and single-phase wiring.
Settings (configuration menu)
Hold the two configuration keys together for 3 seconds to enter or leave the menu (the key symbols are printed in Selec's manual). Inside the menu, two keys increase and decrease the value, one key goes back, and one key saves and moves to the next page. Enter the password first.
| Page | Setting | Range or options | What to set |
|---|---|---|---|
| 1 | Password | 0000–9998 | Factory password is 1000 |
| 1.1 / 2 | Change password / new password | No / Yes; 0000–9998 | Change it if others can reach the panel |
| 2 | Network selection | 3P4W, 3P3W | 3P4W for 3-phase 4-wire, 2-phase and single phase; 3P3W for 3-phase 3-wire |
| 3 | CT secondary | 1 A or 5 A | As printed on the CT, usually 5 A |
| 4 | CT primary | 5 A to 10,000 A (from 1 A with a 1 A secondary) | As printed on the CT, e.g. 100 for a 100/5 A CT |
| 5 | PT secondary | 100–500V | Without a PT: same value as PT primary (e.g. 415) |
| 6 | PT primary | 100–10,000V | Without a PT: same value as PT secondary, so the ratio is 1 |
| 7–10 | Slave ID, baud rate, parity, stop bits | 1–255; 300–19,200 bps; none/odd/even; 1 or 2 | MFM383A-C only. Default 9600 bps, no parity |
| 11 | Backlight | 0–7200 s | 0 keeps the backlight always on |
| 12–13 | Max page, page sequence | 1–20 | Choose which pages scroll, and in what order |
| 14 | Factory default | No / Yes | Restores factory settings |
| 15 | Reset energy | No / Yes | Needs the configuration password + 1 (1001 by default) |
The display scrolls through the pages every 5 seconds in automatic mode. Hold the A/M key for 3 seconds to switch between automatic and manual scrolling. The VI, VAF and P keys jump straight to voltage/current, voltage/current/frequency and power pages.
Common mistakes
- Negative kW or a strange power factor: a CT is reversed, or a CT is on a different phase from its voltage input.
- Readings 5 times too high or too low: the CT secondary (1 A or 5 A) or CT primary is set wrongly.
- Voltage far off: PT primary and secondary differ although no PT is fitted.
- Missing pages on a 3-wire system: normal. With 3P3W, the meter shows only line-to-line and total pages.
Pulse output and RS485
The pulse output gives one pulse per 0.1 kWh or 1 kWh, depending on the CT ratio × PT ratio, with a 100 ms pulse width. It can feed a PLC input or a preset counter that switches a contactor when an energy limit is reached.
On the MFM383A-C, RS485 uses Modbus RTU, addresses 1–255, up to 500 m, with a 120 Ω terminating resistor suggested at the end of the line. Readings are floating-point values, two registers each. Some useful input registers from Selec's list:
| Register | Value |
|---|---|
| 30000 / 30002 / 30004 | Voltage V1N / V2N / V3N |
| 30016 / 30018 / 30020 | Current I1 / I2 / I3 |
| 30042 | Total kW |
| 30054 | Average power factor |
| 30056 | Frequency |
| 30058 | kWh |
Frequently asked questions
What is the default password of the Selec MFM383A?
The factory configuration password is 1000. The password for resetting energy is always the configuration password plus 1, so 1001 by default.
What is the difference between MFM383A and MFM383A-C?
Both measure the same parameters and have a pulse output. Only the MFM383A-C (sold as MFM383A-C-CE) has RS485 Modbus RTU communication for a PLC, SCADA or energy software.
Which network setting should I choose for a single-phase connection?
Select 3P4W. Selec uses the 3P4W setting for 3-phase 4-wire, 2-phase 3-wire and single-phase 2-wire wiring, and 3P3W only for 3-phase 3-wire.
How do I set the PT ratio if I connect the voltage directly without a PT?
Set the PT primary and PT secondary to the same value, for example 415 and 415, so the PT ratio is 1.
Why does the MFM383A show negative power or a wrong power factor?
Usually a CT is reversed (S1 and S2 swapped) or a CT is on a different phase from its voltage input. Check that each CT's current matches the phase wired to V1, V2 and V3, and that S1 and S2 go to the right terminals.
Related products and guides
Selec MFM383A (₹3,390) · Selec MFM383A-C-CE (₹3,988) · all digital panel meters · Selec price list · digital panel meter guide · how to connect a digital ammeter.
Source: Selec operating instructions MFM383A / MFM383A-C (OP354-V03) and the MFM383A datasheet. Always follow the manual supplied with your meter; installation should be done by a qualified electrician.