Barrier strip for power distribution

TLDR: better design is not affordable.

Technical root cause is the limited speed of light. Natural root cause is the conflict of economy of scale vs redundancy requirement.

Every energy supplying element in system is protecting itself by disconnecting, stopping the supply. Disapperance of supplier, causes increase of individual load on other suppliers. Which in their turn disconnect themself. The blackout escalation behaves very much like an avalanche.

The proper design must have granularity of demand control (consumer's pool) be finer than smallest individual supplier, and total supply capacity must be greater than total demand by at least one unit of supplier's granularity. In theory the redundance of suppliers must protect from blackouts. But in reality the granularity on both sides is too coarse, and is impossible to be made finer. Because downsizing is in conflict with economy of scale. Every power plant, distribution line and other elements are built to be as large as possible and point of connection to consumer always exceeds the optimal size granularity wise. Just because of market competition it is not possible to limit the size of lines, power plants and other elements.

The solution can be found only in regulatory space. Say: add the smart load control capability to all household Energy-Star rated equipment and introduce concept of "quality of service", complex system of tariffs, uplinks, protocols, etc.

First, here are a few questions for more information. Do you have a general idea on what's the max current in the power line? Is it 50/60Hz frequency? If you know the model of the sensor, could you post it too?

Capacitively coupled interference is effectively blocked by a Faraday cage, which is a grounded metal box or cage.

Magnetically coupled interference is blocked by ferrous alloys with high permeability. Steel might work for this purpose. There is also an alloy especially useful for shielding called Mu-metal. Magnetically coupled interference disappears more quickly with distance than capacitively coupled.

On sensor's susceptibility to interference. Well-designed industrial sensors reject 60Hz (at least to some extent). Make sure that it's connected by a good shielded cable, and the shield is grounded properly.

You could make an experiment to check the susceptibility of your sensor. Put your sensor (or a sensor of the same model) in a sealed container, so that it always sees the same humidity. Bring it closer or further from the source of interference. Observe the signal.