Skip to
11th Certified Predictive Maintenance Ultrasound Training Course in Greece →

← All tools

Delta T Criteria for Electrical Systems

The infrared thermographer may use the following Delta T (temperature difference) criteria to evaluate the temperature severity of an exception. These Delta T criteria are reported as the temperature rise of the exception above the temperature of a defined reference, which is typically the ambient air temperature, a similar component under the same conditions or the maximum allowable temperature of the component:

NETA Maintenance Testing Specifications, for electrical equipment

Priority Delta T between similar components under similar load Delta T over ambient air temperature Recommended Action
4 1 to 3C° 1C° to 10C° Possible deficiency; warrants investigation
3 4 to 15C° 11C° to 20C° Indicates probable deficiency; repair as time permits
2 - 21C° to 40C° Monitor until corrective measures can be accomplished
1 >15C° >40C° Major discrepancy; repair immediately

Military Standard, for electrical equipment

Priority Delta T Recommended Action
4 10 to 25C° Component failure unlikely but corrective measure required at next scheduled routine maintenance period or as scheduling permits
3 25 to 40C° Component failure probable unless corrected
2 40 to 70C° Component failure almost certain unless corrected
1 70C° and above Component failure imminent. Stop survey. Inform cognizant officers

Experience-Based, for electrical and/or mechanical equipment. Any Delta T classification system based on experience, such as the following

Priority Delta T Recommended Action
4 1 to 10C° Corrective measures should be taken at the next maintenance period
3 >10 to 20C° Corrective measures required as scheduling permits
2 >20 to 40C° Corrective measures required ASAP
1 >40C° Corrective measures required immediately

Motor Cores, (on test bench, not in service)

Priority Delta T Recommended Action
3 1 to 10C° No exception likely
2 >10 to 20C° Possible exception, consult motor core test data
1 >20C° Exception likely