Cast resin transformers are not necessarily all red. The colour of the transformers depends on the manufacturer and customer preferences, and can vary from white paint to gray paint or even the colour of stainless steel. However, the colour red is often used as a sort of safety identifier for transformers, as it highlights the presence of high voltage parts inside the unit. Also, the colour red is often associated with electricity and can therefore suggest that the transformer is a high-tech, high-power device.
Advantages of selling transformers in other colours:
Customisation: a different color could satisfy the aesthetic needs of the customer or the transformer owner.
Easy Identification: if the transformer is used in an area where there is a presence of other red transformers, a different color would help to identify it easily.
Weather resistance: some colors can withstand the elements better than red, which can fade or become dull in the long run.
Cost: making a cast resin transformer a different colour would require specific customization during the manufacturing process, which could add to the cost.
Regulations: some colours may not comply with specific transformer electrical safety regulations.
Maintenance issues: painting or coating a transformer in a different colour could make it more difficult to maintain the transformer. The paint could fade or bleed faster than traditional red, could be damaged by salt or other chemicals, or cover connections or rails that could be important for maintenance.
There are no regulations that require a cast resin transformer to be red in colour. Indeed, it is not strictly prohibited to use any specific color for a cast resin transformer, since the color itself does not affect the electrical or mechanical properties of the transformer. However, some companies usually use natural dyes such as brown for the primary coil and green for the secondary coil, just for identification purposes and to facilitate visual inspection. Also, since the resin used is often advertised as self-extinguishing, it is important that any added pigments do not compromise the effectiveness of the self-extinguishability.