Electric motors for dry and wet areas

Motors used in food production areas are primarily selected for either ‘dry’ areas or ‘wet’ areas. These are entirely different situations with very different demands. We assume we are looking at safe areas, where there is no hazard from combustible gas or liquids.

When selecting motors, the ‘IP’ rating is an important consideration. There are other factors, of course, but the ‘IP’ rating is very important.

Dry areas - IP55 and IP65

Typical ‘dry’ areas are found in industries such as bakeries, dry pet food processing and cereal processing. Standard industrial motors having a rating of IP55, normally considered ‘weatherproof’, are suitable for dry areas.

The term ‘IP55’ is worth explaining. In simplified terms, the first number ‘5’ means ‘protection against dust’, and the second number ‘5’ means ‘protection against water’. This is commonly understood as water from steady rain or water from a low pressure spray. So, for a ‘dry’ area, IP55 is commonly used. In fact, a clean, dry area indoors is one of the most ideal places to install an electric motor.

In ‘dry’ areas, most industrial electric motors have been found to be very reliable. The main consideration is dust and powder. There is the possibility that, over time, an accumulation of dust may restrict air flow around the fan and the motor cooling fins. A regular cleaning program using compressed air is commonly used to keep the motors clean and guarantee plant reliability.

In some applications where dust is extreme a motor with a rating of IP65 might be nominated. In this case, the first number ‘6’ means ‘dust tight, no ingress of dust’ and is a stronger barrier against dust. Again, the second number ‘5’ is protection from rain or low pressure water spray. So ‘IP65’ is a dust tight motor protected from water.

Wet areas - IP56 and IP66

‘Wet’ areas, meaning areas of a factory that are hosed down regularly, pose a special problem. The most serious threat to an electric motor is water. Typical ‘wet’ areas are obviously the chicken, turkey, meat and fish processing industries, but also others such as salad, milk and cheese processing.

Considerations

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. These motors are totally unsuitable if they are the target of a high-pressure jet of water. If used in wet areas, industrial motors should have an IP56 or IP66 classification. To explain ‘IP56’, the first number ‘5’ means protection against dust, and the second number ‘6’ means protection against high-pressure water jets, commonly termed as ‘hose-proof’.

Most standard motors can be modified to a rating of IP56 with simple modifications.

Generally, stainless steel motors for the food industry have an IP rating of IP66 as standard. For ‘IP66’, the first ‘6’ means dust tight (as before) and the second ‘6’ means high-pressure hose-proof. So, IP66 is dust tight and high-pressure hose-proof.

For many years there has been a tendency in the food industry to make one of two choices for wet areas:

1. Modify standard motors to IP56 to withstand wet area conditions.
2. Cover standard motors with stainless steel shrouds or covers, to protect them from the harmful effects of high-pressure cleaning jets.

There has not been any other option, until the turn of this century, when purpose-designed stainless steel motors started to enter the market from several suppliers. These are especially designed with wet areas of the food industry in mind. Apart from far better sealing, they are smooth all over, with no fins, making cleaning easier, and some are ‘tropic proofed’ internally.

When a stainless shroud is used, the motor is completely hidden from view. An OHS inspection may not identify any safety risk - simply because it cannot be seen. If a shroud system is used, it is essential the shrouds are routinely removed so the motor can be inspected.

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

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.

There are many variables. The actual cost depends on the actual 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 a common stainless steel motor on the market.

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

* All prices in Australian dollars

Notes

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% minimum for a full circular ‘wraparound’ 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 five motors.

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

Motor longevity

With wet areas, there is convincing evidence that, no matter how good a motor is sealed, if there is an air pocket inside there will inevitably be condensation. This is because the motor is heating and cooling constantly.

From speaking to many maintenance staff and production managers over many years, there is compelling evidence that, if there is a drain or weep location on the motor, motor life is extended. This can be anything from as simple as an open drain hole to a porous plug. Some staff insist on having a drain point on every electrical device, to ensure maximum life. Merely as an observation, this appears to be the case, providing water is not allowed to enter the motor during cleaning periods.

Conclusion

Dry areas

Standard industrial electric motors of proven quality with an IP55 rating have proven to be very reliable, provided excess dust is not allowed to collect on the motor.

Wet areas

For wet areas, there are now several choices:

• Modify standard industrial motors to a minimum IP56 rating.
• Fit stainless steel shrouds over standard motors.
• Use stainless steel motors with a standard IP rating of IP56 or IP66.