Standard motors vs. stainless steel motors


Motors used in food production areas – especially ‘wet’ areas that are hosed down regularly – poses a problem. Typically, at the end of the shift, the machine is turned off and then cleaned with a high pressure cleaner using a caustic solution. This is great for cleaning machinery, but poses a constant potential problem with electric motors. Water entering a motor will inevitably lead to failure and downtime. The majority of standard motors are rated IP55, that is, weatherproof and unsuitable if it is the target of a high pressure jet of water.

Traditionally, standard motors – either of aluminum or cast iron construction – have been used in the food industry and covered with a stainless steel shroud. The shroud offers protection from the direct effect of the water blast and gives the appearance of a ‘clean’ machine. Up until recently, there has been no real alternative. But for some years now stainless steel motors have been available off the shelf and have been designed specifically for the food industry.

There are several issues to consider.


When a shroud is used, the motor is completely hidden from view. This can be dangerous. I am aware of at least one case where a shroud was removed only to find that the caustic cleaning solution had, over time, eaten completely through the aluminum housing of the electric motor. A large opening had completely exposed the windings of the motor, which was situated on a damp floor area. An OHS inspection did not identify the serious safety risk because it could not be seen.

With stainless steel motors, the motors are out in the open, and easy to inspect. Stainless Steel is also much more resistant to caustic solutions.


The importance of hygiene is becoming more critical every day. The worst event a food company can have is a recall of product due to a foreign object being found in packaged food. The damage and loss involved is enormous. There is a loss of respect in the market place, a potential loss of sales, a loss of revenue from recalled items, a large cost in the actual recall and disposal of suspect product. With health inspections, it is vital a machine is perfectly clean.

When shrouds are used over standard motors, the motors are hidden from view. Also, standard motors have cast cooling fins all over the body. With the effect of jets of cleaning solution being directed around the motor, food particles, dirt and grime is often deflected off the floor and onto the motor as it collects between the fins. From there it is difficult to dislodge. If the shroud is not removed periodically and the motor cleaned directly, a potential build-up of grime can occur. Even worse, when this does happen, sometimes vermin are attracted to this area. There is an enclosed space, food particles, and even heat from the motor.

With stainless steel motors, a shroud is unnecessary. The motor is mounted in the open and cleaners can direct a jet from the cleaning machine all over the motor as they are IP66 hoseproof. The stainless motors are smooth all over with no fins and have a highly polished stainless steel finish, making them easy to clean. Further, the Scorpion Stainless Steel motor has full HACCP approval, something standard motors with cooling fins have never achieved.


It can be argued there would be little difference in reliability between a standard motor under a shroud and a stainless steel motor due to the similar internal design. However, over the long term, the improved protection of the stainless steel motor is bound to give greater longevity and therefore more efficient production costs.


With inspections, stainless steel motors out in the open are visually clean. It can be argued that a stainless steel shroud protecting a motor also appears clean. However, current feedback from maintenance staff is that many inspectors feel more confident with ‘open’ motors compared to ‘covered’ motors.

Other factors

There are some areas where a stainless steel motor is preferred because of the environment. For example, in sections of a food factory where salt is prevalent or seriously corrosive vapours such as chlorine vapour is present. The alternative is to have a standard motor coated with a ‘high tech’ paint finish, which can be expensive and even then not as durable.

Cost comparison

The cost of a standard motor fitted with a stainless steel shroud, compared to the cost of a stainless steel motor is an often asked question. The actual cost depends on the quantity required, the brand of the standard motor, the brand of the stainless steel motor and the size of the motor in kW. Another point to consider is if the motor is mounted on the floor, or suspended off a machine. Shrouds for motors suspended off a machine are more expensive, as they are of a circular, ‘hinged’ design, and far more expensive than a simple half-circle shroud.

However, a simple cost analysis is possible to give an indication.

This analysis is based on a standard aluminium motor manufactured in Europe and fitted with a locally made stainless steel shroud versus the Scorpion Stainless Steel motor.

For purposes of transparency, actual costs obtained are shown, as follows:

Cost in Australian dollars

Size Aluminium motor + Shroud = Total Stainless Steel Motor

0.18kW $151 $280 $431 $398

0.37kW $230 $301 $531 $489

0.75kW $272 $326 $598 $684

3.0kW $487 $347 $834 $1092


1) Cost of the shroud is based on a standard semi-circular design, with a 50 mm wide flange for mounting onto a bedplate.

2) Cost of the shroud would increase by approximately 50 per cent minimum for a full circular “wrap-around” or hinged design, for motors suspended off machinery.

3) Shroud quotation based on 1.2 mm thick grade 304 stainless steel sheet.

4) Price of the stainless steel motor is based on a ‘quantity’ enquiry, of more than 5 motors.

It can be seen that for ratings less than 0.75 kW there is a saving in initial cost by specifying a stainless steel motor, compared to a standard aluminum motor with a shroud. Above 0.75 kW, there is a marginal difference in initial cost

Disadvantages of using stainless steel motors

From a logic perspective, there is a disadvantage of using stainless steel motors. In a very few limited applications, the extra weight of a stainless steel motor needs to be considered, especially if it is used as a counterweight.


There is an increasing trend to install stainless steel motors and ‘dump’ the shrouds in many factories. Some factories have a “replace with stainless motor” as existing motors fail.

In some critical areas, for example, where exposed food product is situated directly underneath a motor, there is in some factories a trend to “replace with stainless” when that motor becomes due for cleaning and repainting.

The extra advantages of the stainless steel motor over ‘covered’ motors in hygiene, safety, and reliability speak for themselves. As one maintenance supervisor said, “With stainless motors, it is out in the open; I don’t have to worry about what is hiding in there.”


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