If you or someone living with you depends on your mains power to run critical medical support equipment, then you may qualify as a MDC.
According to the Electricity Authority a medically dependent customer is: 'a domestic consumer who is dependent on mains electricity for critical medial support, such that loss of electricity may result in loss of life or serious harm. For the avoidance of doubt, medical dependence on electricity could be for the use of medical or other electrical equipment needed to support the treatment regime (e.g. a microwave to heat fluids for renal dialysis)
View the Electricity Authority's fact sheet for medically dependent consumers (MDC) here.