I understand that there are common IEC standards for switchgear and controlgear whereas there are different standards in the US for switchgear and MCC/panelboard. The US standards are reflected in IEEE 1584 in that there are different working distances and calculation constants for LV switchgear versus LV MCC & panelboards. I am performing calculations for a LV MCC which is a Form 3b switchboard (i.e. separate cubicle for each supply, separate compartment for the 415V bus and separate compartments for cable connections) built to IEC standards. Should I perform the calculations for this switchboard treating it as LV MCC/panelboard or as LV switchgear?

18 inches / 45.7 cm is the safer option.

The 24 and 36 inch values were assuming there would be a greater distance to the worker due to the racking mechanism. We have been talking about this among ourselves and are considering changing it to 18 inches for LV switchgear in the future with a note about allowing a greater distance i.e. 24 inches if racking in/out the device is being performed. Just an idea for now, nothing definite yet.