Sometimes with electricity we get inducted heat (induction).

Induction can take place on metalwork exposed to changing magnetic fields, for example generators or cable entry plates. It is a result of the location of the metal and its proximity to electricity.

It is not unusual to find unwanted inducted heat on metalwork located near electricity or electrical components, particularly on cable entry plates in panels where the individual conductors are brought through single entry holes.

For the purposes of this article, we wish to discuss induction in cable entry plates.

The phenomenon only occurs on ferrous (ferromagnetic) metals such as mild steel. As wire passes through a magnetic field a current is produced. If the cycle is reversed and we leave the wire stationary, but move the magnetic field the same thing will happen. In the case of AC electricity the magnetic field expands and collapses at a rate of 50/60Hz, so there is potential for induction to take place.

FLIR3319

 

Where heat caused by conduction is detected it is important to asses if it needs to be repaired or not.

  • Does it present a burn risk or act as an ignition source, it may not be dangerous.
  • Is the temperature sufficient to damage the metallurgical properties. Often the temperatures can be low enough not to cause damage to the metal.
  • Is there potential for secondary damage to other materials such as electrical cables.

Once the above is considered, a decision must then be made whether to monitor the problem, or attempt to eliminate it.

If attempting to eliminate, a couple of things to consider:

Firstly (and often not so practical) is to break the flow path, if possible. Good practice on cable entry panels is to bring all associated conductors through the same hole. The magnetic fields will then cancel each other out.

Secondly, the most common method for eliminating induction is to replace the affected metalwork with a non ferrous material. For example plastics, aluminium or stainless steel. The equipment manufacturer should be consulted to ensure material compatibility and to confirm material certification is not affected.

In electricity, the phenomenon of induction is exploited, particularly with transformers. We use mutual induction to transform electricity from one voltage to another. It is not uncommon to find unwanted heat on metalwork exposed to changing magnetic fields. It is important to identify these areas, highlight and assess them correctly considering all of the above.

Thanks for reading. 

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