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Why do industrial panels for oil and natural gas compressors or other industrial equipment use terminal blocks for wire management? I have been doing some repairs for companies and was wondering why they chose that layout. I was thinking instead of all these wires going to different terminal blocks why not make a industrial PCB? Is this possible? Is it considered bad practice?

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A picture of the inside of your panel, which is wired with screw terminal blocks, would make this question a lot better. – Nick Alexeev Apr 13 '12 at 4:26

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Why of course, making industrial PCB is possible.

But also, there are good practical reasons for using wires and terminal blocks.

Control panels can be large

A typical limit on PCB size is about 0.5x0.5m. The limit is set by the size of a PCB laminating press. Control panels can be much larger than that.

High currents

Dealing with high currents (above 10A) on the PCB is possible, but it requires wide traces. A medium sized 18AWG wire is rated for 15A. High currents encourage to use wires.

Relatively low quantities

Makers of industrial control panels like to use ready-made blocks (thermostats, displays, alarms). They come in standard sizes: 1/8, 1/16, 1/32, DIN rail. They have screw terminals as a way of interfacing to the rest of the system, so you have to have wires to interface to them.

Maintenance

Long service life requires maintenance in place. Ideally, maintenance should be possible without specialized tools. Screw terminals need only a screwdriver.

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Vibration is killer on connectors. Screw terminal blocks are more resistant to it than pin connectors or card edge connectors. Connectors are one of the most common causes of failure in electrical systems - reduce the risk of their failure with more secure connectors like screw terminal blocks or mil-spec connectors and you stop seeing as many failures.

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