Here's the insides of one I did some work on recently. This is on an electrically heated 3 barrel HERMS system. 300 amp three phase service feeding the panel.
On the DIN rails are the 24 VDC power supplies, relays, fusing, etc. To the right is a breaker box providing ground fault and over current protection for all the individual AC loads. Top center of the DIN rails is a three phase Variable Frequency Drive (VFD) for the mash rake. Bottom of the enclosure has a variety of twistlock connectors for all the loads and sensors.
On the door you see the back side of a Unitronics V1210 PLC. Also the alarm buzzer, main power switch and interlock latch so the door can't be opened with the power on.
Note the long U shaped loop in the wires that cross the hinge to the door. That's the correct way to run wire to a door. When opening and closing there is a small twisting in the length of the wires rather than a bending stress right at the hinge point. Repeated bending can lead to broken wire.
One thing I might have done differently had I built this would be to locate the breaker box outside adjacent to this enclosure. That way an operator could reset a tripped breaker without having to power down the entire system first to open the interlocked enclosure.