Copyright Goodheart-Willcox Co., Inc. Chapter 10 How Electric Meters Work 187 Voltmeters are rated by category and voltage for safety. The category rat- ing system was developed to protect the meter and user from destructive spikes (transients in the power system). Most HVACR meters are rated for category 3 and 600 V. The Cat (category) ratings are 1 through 4. Cat 4 has the greatest transient protection and voltage ratings above 600 V. Some Cat 3 have a 1000 V rating, but the transient protection is limited to Cat 3. Cat 2 is limited to single-phase power distance from circuit breaker panels where large transients are less likely. Cat 1 is for electronics work where transients are not likely to happen. Cat type, volt- age rating, and certifying testing laboratory information are found on the meter body, Figure 10-25. Manufacturer Error Rate Contact the manufacturer for error rate when using meter outside the specified operating temperature and humidity. Pro Tip Check for Safety Labels Look for nationally recognized testing laboratory labels on the meter for safety, such as Underwriters Laboratory in the US. Refer to OSHA for a full listing. Do not use a meter without the correct ratings or without an approved test laboratory certification. Safety Note Category and voltage ratings Approved test lab symbol Goodheart-Willcox Publisher Figure 10-25. Category rating and certifying laboratories.