1. Metallic resistance has a positive temperature co-efficient, normally 12% per 100⁰C. Therefore during starting at 300⁰C, the initial resistance R will increase to 1.36R. This can be detrimental to starting performance. High current peaks will be generated when shorting unless adequate number of steps, requiring more switchgear components, are provided.

1.AOYP electrolyte has a negative temperature co-efficient, normally 1% per 1⁰C. If 50⁰C thermal chamber temperature rise is allowed, the initial resistance R decreases to 0.5R, which is complimentary to the starting performance. Lesser switchgear components are required.

2.Metallic resistance has a very low thermal capacity, hence it is susceptible to thermal shocks and burn-outs.

2.Rotastat has high thermal capacity. Hence can be better withstand current peaks, overloads and shorting contactor failures.

3.Since metallic resistance operates at high temperatures, they require safety enclosures or have to be kept away from the motor, needing costly cabling.

3.Rotastat on the other hand, operating at low temperatures, is safe to human touch and can be safely kept near the motor, saving on cabling.

4.The joints of  metallic grids or coils have to be frequently checked, so also the quality and leakage of cooling oil, if used.

4.Rotastat is practically maintenance - free except occasional topping up of electrolyte with distilled or soft drinking water.

5.It is cumbersome to replace a metallic resistance element on site, hence down time may be long.

5.Increasing or decreasing electrolyte concentration is simple with a Rotastat, done at site without dismantling of any mechanical components and with minimum down time.

6.Metallic resistance cannot be adjusted on site to suit changes in machine torque or change of motor.

6.Rotastat can be easily adjusted on site to meet changes in operating conditions by alerting the strength of the electrolyte.

7.In case of metallic resistance, operator's skill is required to prevent burn out because of too quick shorting of drum/face contacts.

7.Rotastat is always designed for automatic operation, free of any operator skill or judgement.