The ultimate goal of a code or standard is to provide a clear set of instructions for the construction, installation, and use of an electrical or alarm product. These instructions come in two different forms; prescriptive rules and performance rules. The results of these rules ensure a safe installation free of any hazards to a person or property from the use of electricity.
Prescriptive rules are more prevalent in the installation standards such as the National Electrical Code or the National Fire Alarm and Signaling Code. Prescriptive requirements provide the what, where, when and how rules for the installation of electrical and alarm products. These rules can be both permissive and prohibitive as discussed in Part 1 of this series. While compliance with the prescriptive rules will result in expected performance outcomes, it may not always be intuitive for the user of the code. In other words, the user of the code doesn’t necessarily need to know why the rule exists in order to comply with the rule.
Performance rules are typically used in the development of a product standard. Performance rules identify the permitted and prohibitive limits on the construction and operation of an electrical or alarm product. The result of product’s performance is typically achieved by testing and is fully measurable. In other words, the rules identify why the criteria is being required in lieu of a certain list of actions or behaviors. As long as the electrical or alarm product meets the performance based criteria outlined in the code or standard, a prescriptive rule of the product is not needed. The product manufacturer or design professional has the responsibility to determine what, where, when, and how the product is constructed and operates in order to meet the performance criteria.
In some cases, a code or standard allows the user to select the method used to achieve compliance. An example of this would be the International Energy Conservation Code. Users can meet all of the mandatory compliance methods which are prescribed throughout the code or they can choose to meet the total building performance method which allows the user to fully design the building’s energy consumption that is equal to or less than a standard reference design.
In other cases, a code or standard may identify a performance goal that is ultimately achieved by a list of prescriptive requirements. An example of this would be the National Electrical Code. For instance, section 680.26(A) states; "The equipment bonding required by this section shall be installed to reduce voltage gradients in the pool area". This is clearly a performance goal. 680.26(B) and (C) go on to provide the prescriptive requirements for equipotential bonding that should result in compliance with 680.26(A). Similar performance and prescriptive criteria can be found throughout the NEC.
There should be no doubt that both prescriptive rules and performance rules provide the necessary instructions to ensure every electrical and alarm product is adequately constructed and will operate in a safe and effective manner when installed and used in accordance with the applicable code or standard. When dealing with codes and standards, make sure you have the correct perspective.