Written by Steve Hudgik
The updated 2011 NEC Article 110 includes new labeling requirements. The new labels are for equipment rating purposes. These are not arc flash labels. There are three parts to the new "available fault current" labels:
Field Marking. Service equipment in other than dwelling units shall be legibly marked in the field with the maximum available fault current. The field marking(s) shall include the date the fault current calculation was performed and be of sufficient durability to withstand the environment involved.
This requires that service entrance equipment be labeled with the available short-circuit current available when the equipment is installed. Although the equipment may have been marked by the manufacturer, that is not the label that is needed. A fault study must be done to identify the maximum amount of fault current available. In many cases this information comes from the utility. That information, and the date it was determined, must be put on a label that is field applied to the equipment.
The purpose of this label is to allow the Short Circuit Current Rating (SCCR) of the equipment to be easily compared with the maximum available fault current. A SCCR laberl is usually placed on the equipment by the manufacturer. NEC's definition of SCCR is, "The prospective symmetrical fault current at a nominal voltage to which an apparatus or system is able to be connected without sustaining damage exceeding defined acceptance criteria."
Modifications. When modifications to the electrical installation occur that affect the maximum available fault current at the service, the maximum available fault current shall be verified or recalculated as necessary to ensure the service equipment ratings are sufficient for the maximum available fault current at the line terminals of the equipment. The required field marking(s) in 110.24(A) shall be adjusted to reflect the new level of maximum available fault current.
This states that the maximum available fault current must be verified or recalculated any time there is a possibility it has changed. This can be difficult because, in addition to changes you make within your facility, changes made by the utility can change the maximum available fault current. Fault current varies based on impedance, so any change in impedance will change the available fault current.
Another factor that makes this confusing is that the NEC code is not universally applied. It must be adopted by the governing authority within each state. As of the end of 2011 fifteen states are using the 2012 version, twenty-five states are using the 2008 version and two states use the 2005 version. This means that the Authority Having Jurisdiction (AHJ) determines what labeling must be done to meet code.
Exception: The field marking requirements of 110.24(A) and 110.24 (B) shall not be required in industrial installations where conditions of maintenance and supervision ensure only qualified persons service this equipment.
This exception is included because qualified persons know that the maximum available fault current must never exceed the SCCR of the equipment. As a part of their normal work practices they have the necessary test equipment, will check this when changes are made, and will keep labeling up-to-date.
In addition to having the maximum available fault current and the date this was determined, the NEC code requires that the labels be able to withstand the environment where they are located. This is a good reason to always use labels made with a DuraLabel printer. DuraLabel is the only brand that dares to give a warranty on vinyl labels made with their printers and supplies. That's because DuraLabel labels are extra durable. Plus DuraLabel is the only brand that has over 50 types of supplies available. This means you can always get the right supply for the job.
NEC is also concerned that the electrical system components are suitable for the environment in which they are used. This includes equipment such as cabinets, boxes, cable trays, raceways, conduit, elbows, fittings, couplings, supports, and support hardware. Designers and installers must select the right components based on temperature, the presence of moisture, corrosive gases, liquids, dust, sunlight or other environmental conditions that could deteriorate the equipment. Deteriorating agents include cleaning fluids, lubrication, and other workplace chemicals and substances that might come in contact with the equipment. Labeling that can survive these deteriorating agents should be used to warn about workplace substances that should not come in contact with electrical equipment.
Call 1-888-326-9244 and ask about DuraLabel kits for making electrical labels. You can even get a kit customized to your labeling requirements.