Load Cell Wiring Colour Code: How to Identify the Wires

Wiring a load cell sounds simple until you open the cable and find four, five or six wires in colours that do not match the diagram you were expecting. The important thing to know first: there is no single universal load cell colour code. Different manufacturers use different schemes, and some change them between product lines. The datasheet for your exact model is always the final authority. This guide explains the common conventions, what each wire does and how to identify an unknown cable safely.

The four basic connections

Every strain gauge load cell contains a Wheatstone bridge, which needs four main connections:

• Excitation positive (EXC+ or E+): the positive supply to the bridge.
• Excitation negative (EXC− or E−): the negative supply, or 0 V.
• Signal positive (SIG+ or S+): the positive output from the bridge.
• Signal negative (SIG− or S−): the negative output.

The indicator supplies a stable excitation voltage, commonly 5 V to 10 V, and measures the small voltage difference between the signal wires. At full load, that difference is typically only a few millivolts, which is why clean wiring matters so much.

A common colour scheme

Many cells use a pattern like this one. Treat it as a starting point, not a guarantee.

Function	Frequently used colour
Excitation +	Red
Excitation −	Black
Signal +	Green
Signal −	White
Shield	Bare wire or yellow

Variations are common. Some manufacturers use blue and yellow for the sense wires, others swap the signal colours or use a different colour for shield. If a supplier’s cable is not documented, do not assume.

4-wire vs 6-wire load cells

A basic cell uses four wires. A six-wire cell adds two sense wires, SEN+ and SEN−, connected to the excitation points at the bridge. They carry almost no current, so they report the true voltage at the cell. The indicator uses that to correct for voltage drop and temperature-related changes in cable resistance.

When should you use 6-wire connection?

• When the cable run is long, usually beyond a few metres.
• When the cable passes through changing temperatures.
• When the highest accuracy is needed, as in legal-for-trade scales.

If your indicator has only four terminals, link each sense terminal to its excitation terminal. If the cell has sense wires but the indicator does not, join the sense wires to the matching excitation wires at the end of the cable.

What about the shield?

The shield is a bare or foil-wrapped conductor that surrounds the signal wires and reduces electrical interference. In general:

• Connect the shield to ground at the indicator end only. Grounding at both ends can create ground loops.
• In a junction box with several cells, join the shields together and take one connection back to the indicator.
• Keep the shield intact all the way through glands and connectors.

Identifying unknown wires with a multimeter

If you have a cell with an unlabelled or damaged cable, you can find the function of each wire with a meter. Disconnect the cell from the indicator and switch off all power first.

1. Measure resistance between each pair of wires. A typical bridge shows two pairs with similar values. The input (excitation) pair often reads a slightly different resistance from the output (signal) pair. Common bridge resistances are 350 Ω and 1000 Ω, so expect values near those, adjusted by temperature compensation resistors.
2. Group the wires. You should end up with an excitation pair and a signal pair. Wires with very high or very low readings may be the shield or a damaged conductor.
3. Apply a safe excitation voltage. Use the voltage in the cell’s datasheet, for example 5 V DC from a stable supply, to the suspected excitation pair.
4. Measure the millivolt output between the suspected signal pair while loading and unloading the cell. The output should change smoothly with load.
5. Check the polarity. If the output becomes more negative when you apply compression, swap the signal wires.

If the output does not move or the readings are erratic, the pair may be wrong, the cable may be damaged or the cell may have failed. Re-check each step before assuming the cell is faulty.

Wiring multiple load cells

Platform and tank systems wire several cells in parallel through a junction box. To keep the system accurate:

• Use cells of the same type, capacity and sensitivity.
• Keep the cable lengths equal. Do not cut one shorter unless the manufacturer allows it, and never coil excess cable tightly.
• Use a sealed junction box with trim adjustments for corner balancing.
• Keep the box dry, and use proper cable glands.

Best practice for reliable signals

• Run load cell cable away from motor cables, variable-speed drives and contactors. Cross them at right angles if you cannot avoid them.
• Do not splice with twisted connections. Use soldered joints with heat shrink or a proper junction box.
• Use ferrules on stranded wires in screw terminals.
• Label wires clearly at both ends.
• Protect the cable from sharp edges, hot surfaces and moving parts.

Troubleshooting wiring problems

Symptom	Possible wiring cause
No output or no change with load	Excitation missing, broken signal wire or reversed excitation
Reading goes down when load goes on	Signal wires reversed
Reading drifts or jumps	Moisture in cable or junction box, poor terminal contact
Noisy readings	Shield not grounded, cable near drive cables
Different readings across cells	Unmatched cells, unequal cable lengths, poor trim

Safety and handling reminders

Load cells are delicate instruments. Treat them carefully during wiring and installation.

• Never carry or hang a cell by its cable. The cable gland and internal connections can be damaged.
• Do not apply excitation voltage above the rated maximum. Over-voltage can overheat the bridge and cause permanent drift.
• Do not weld near an installed cell without a bypass. Welding currents passing through a cell can destroy it, so connect a heavy cable around the cell to carry the current.
• Keep the cable end sealed if you cut it. Water can wick up the cable and into the cell.
• Protect the cell from lightning and power surges with suitable surge protection in exposed installations.

Frequently asked questions

Which wire is positive on a load cell?

That depends on the manufacturer. Red is often excitation positive, but always check the datasheet. If the signal polarity is wrong the display moves the wrong way, and you can correct it by swapping the signal pair.

Can I extend a load cell cable?

Yes, with a proper junction box or shielded cable of the same type. Extending a four-wire cell adds resistance and error, so six-wire connection is preferable for long runs.

What happens if I swap excitation and signal wires?

The cell will not work correctly and may be damaged by the voltage applied to the wrong terminals. Confirm the pairs before applying power.

Once the wiring is correct, the next step is to calibrate the load cell. For background reading see how a load cell works and the complete Load Cells Australia guide.

Talk to Sands Industries

Not sure which load cell, capacity or accessory fits your application? Contact Sands Industries with your capacity range, accuracy needs and operating environment, and we will help you shortlist the right option.

Keep reading

• Load Cells Australia – Accurate Measurement Solutions by Sands Industries
• How Does a Load Cell Work – The Science Behind Accurate Industrial Measurement
• Load Cell Types – Choosing the Right Sensor for Accurate Industrial Measurement