Seller guide · Louisiana
Instrumentation cable versus control cable
They look similar, they are sold in the same stores, and they are not interchangeable. The difference is in the pairs and the shield.
Guide 01
Control cable carries switching and status signals: start, stop, open, closed, alarm. Instrumentation cable carries measurement: a 4–20 mA loop, a thermocouple, an RTD. Both are small-gauge and both are often shielded, which is why they get confused.
The practical differences
| Construction | Control: multi-conductor, often 14–10 AWG. Instrument: pairs and triads, usually 24–16 AWG. |
|---|---|
| Shielding | Control: sometimes overall shielded. Instrument: individually shielded pairs, overall shield, or both. |
| Signal level | Control: switching, tolerant of noise. Instrument: low level, sensitive to noise and grounding. |
| Colour coding | Control: numbered conductors. Instrument: pair numbers with plus and minus legs. |
| Voltage rating | Control: typically 600 V. Instrument: 300 V or 600 V, with thermocouple extension cable rated for its type. |
How to identify each from the print
The print on the jacket will say which it is. Look for pair counts and shield descriptions on instrument cable — '12 PR 18 AWG IND SHLD' — and conductor counts on control cable — '7C 14 AWG'. Thermocouple extension cable will name its type, such as Type J or Type K, because the alloy matters.
Why mixing them costs money
Instrument cable is a more specialised product with a narrower buyer pool but a higher value per foot. Control cable is broader and cheaper. A lot described as 'control cable' that contains instrument cable will be valued as control cable, and the instrument material will be lost in the average.
In a Louisiana plant store, instrument and thermocouple cable are usually the highest-value small cable on the shelf. Count the pairs and read the shield description before describing the lot.
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Questions —
Questions this guide raises
Is thermocouple cable instrumentation cable?
It is a specialised form of it. The alloys match the thermocouple type, so the type letter must be identified and stated separately.
Can instrument cable be used as control cable?
Physically sometimes, but the reverse is often not true, and a buyer will not pay instrument prices for control cable or vice versa.
What is a triad?
Three conductors treated as one signal group, common in instrumentation for a positive, negative and shield connection.
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