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Stamping Guidelines for Electrical Test Equipment

Electrical test equipment falling into Category III (1000V) and Category IV (600V) must be stamped to indicate the appropriate category. Please check your electrical test equipment to verify that components within these categories are stamped appropriately. If your equipment is not stamped as Category III or IV, it should only be used for Category I and II work.

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Additional Common Questions and Answers on Category III and IV Equipment Supplied by Joe Curtiss, BNL Electrical Safety Officer

Q. Are the voltage ranges associated with Category III and Category IV backwards?

A. A transient in the utility power system can deliver a great deal of energy into a meter, so the use of meters in Cat IV applications is limited to 600V. The service entrance equipment and wiring adds impedance, which limits the effect of a transient, so that Cat III measurements at major switchgear and motor control centers are permitted up to 1000V. These ratings are stamped on electrical measuring instruments, even though the next higher nominal system voltage in the U.S. above the 600V class is 2400V.

Q. Do I have to use a Cat III & Cat IV instrument, or can I just use a Cat III?

A. If your work involves only Cat III situations, then a meter marked for Cat III is just fine. Do not lend your meter, since it might mistakenly be used for a Cat IV measurement.

Q. Where can I use older meters that are perfectly good, except they don’t have stamps indicating the category?

A. General industry use of the category stamp system is relatively recent. Meters obtained before the Cat stamp system may be assumed to qualify as Cat II meters. Cat III circuits include feeders, branch circuits, and permanently-installed loads, and you should not be using a Cat II meter to check, for example, a 460V 20 HP compressor fed from a motor control center. A transient could damage the meter (and the person holding it) when used in this low-source-impedance application. You can use Cat II meters on circuits having plug-in loads, which are, of course, supplied through conventional building power distribution panels. Many devices at BNL are hard-wired to such panels for convenience, although they could just as well be supplied through a receptacle. A Cat II meter may be used in these applications in the same way it would be if it had been wired to a receptacle.

Q. I like using a Wiggins solenoid tester when checking for the presence of voltage, because I can feel it vibrate and don’t have to look at the meter. It also loads the circuit so I don’t get the false voltage readings common with high-impedance meters. Why can’t I use a Wiggins?

A. I like the Wiggy too, for just those reasons, but the old-fashioned Wiggy does not have a category rating. While Ideal offers a Cat III meter, it is not stamped for Cat IV and there has already been one recall because, as the company stated, “These testers can short out at high voltages.” Furthermore, solenoid-type meters are not fused and rely on their impedance for to protect the user. For these reasons, the DOE Electrical Safety Manual states that, “…solenoid-type devices should not be used to test for the absence of AC voltage.” Since such testing would be the chief use of solenoid meters, and any such meters left around for other purposes could mistakenly be put to this use, the simplest solution is to declare them not acceptable at BNL.

Q. Does BNL have a list of acceptable meters that can be purchased for the Cat III and IV usage?

A. Meters to be used for "zero energy" checks must be stamped for the Category in which they will be used. The most versatile meter would be a CAT III & CAT IV, since they can be used almost everywhere and they provide the most protection against injury.

An additional requirement is that equipment bearing the UL, CSA, FM, or another Nationally-Recognized Testing Laboratory (NRTL) must be acquired whenever labeled equipment is available, even if similar unlabeled equipment is available. Based on OSHA rulings, only such equipment can be accepted by the Authority Having Jurisdiction (the Laboratory Electrical Safety Committee) and used at BNL. After-the-fact review of similar unlabeled equipment acquired, perhaps due to low price or other expediency, is not an option. Please note that the CE label, a self-certification by the manufacturer, is not acceptable as a notice of approval by an NRTL.

While any appropriate meter can be purchased subject to the above criteria, the Allied catalog shows the Fluke 170- and 180-series meters to be CSA listed, and CAT III & CAT IV.

If you have any additional questions, please contact John Aloi at extension 7018 or Al Boerner at extension 5990.