Backup Protection Devices Must Be Reliably Safe: Manually Resettable vs. Replaceable Pursuant to the current version of UL 1995, electric heater backup protective devices must be either manually resettable or replaceable. Accordingly, first it is important that the current standard recognizes that an automatically resetting temperature-­‐limiting control (ARTLC) is not reliable or appropriate as a safety device. Automatically Resetting Devices: The adequacy of the automatically resetting device to maintain safe operating temperatures during abnormal, but expected, conditions is and must be completely distinguished from any considerations of the adequacy of an automatically resetting device as a safety backup device. The ARTLC is used in electric heaters as a temperature-­‐limiting control device and cannot be considered a safety device because of its patent unreliability. The mechanical “unreliability” of the ARTLC as a primary control of heater operation has been discussed in detail in the Attachments, Tabs 1, 3, 4 and 6 – 9, in support of the necessity of reliable safety backup protection when the ARTLCs, used as primary controls, fail to open the circuit in heaters capable of producing dangerous temperatures during abnormal conditions. The one characteristic of the automatically resetting device that renders it particularly unsuitable for safety backup protection is the simple fact that it is “Automatically Resetting”. In abnormal conditions the automatically resetting device cycles to maintain safe temperatures automatically and, therefore without providing any warning of the underlying problem. The abnormal conditions and high temperatures triggering the automatically resetting device to cycle can continue or worsen until the automatically resetting device fails. As discussed extensively in the “Tabs” referenced above, when the automatic switch fails it is imperative that there be reliable backup anytime dangerous risks might otherwise result. Manually Resettable Devices: The manually resettable device is certainly more reliable and appropriate than the automatically resetting device, foremost because it is does not automatically reset. When temperatures trigger the manually resettable device, electric input is cut off and it does not reset. Service interruption effectively notifies the user that something is wrong with the system. A service call would reveal the open circuit and service provider would know that high temperatures existed to trigger the device, and be on notice that the temperatures in the unit were excessively high. Before restoring service, it is imperative that the system be inspected to determine the cause of the excessive temperatures, check airflow and check for internal damage from the high temperatures. Only after the heater is determined to be safe to return to service should the device be manually reset (typically a simple push button). If the backup protection device has been triggered to cut off the heater, then it is critical that the ARTLC must be replaced before manually resetting the device. Hence the advantage of the manually resettable device is that it “notifies” the users of a problem before the danger is realized. One of the concerns of the manually resettable device is that the user finds or learns though unwitting or lazy service providers the location of the manually resettable device, and simply “pushes the button”. Restoring service without correcting the conditions creating the high temperatures or replacing the ARTLC is, quite literally, like playing with fire. The only “advantage” of the manually resettable device over the replaceable devices is that one only needs to “push a button”, rather than replace the device when the heater is ready to be returned to service. The ease and cost of replacing the replaceable devices effectively eliminates any “advantage”, and the real risks of someone ignorantly “pushing the button” one time too many. Although fairly reliable, manually resettable devices depend on mechanically activated electrical contacts and therefore are not fail-­‐safe. Replaceable Devices: Like the manually resettable device, the replaceable devices do not cycle without warning. When there is a problem that triggers them to function, they cut off the electricity to the heater until the system and the heater is inspected and deliberately returned to service. The patent advantage of the replaceable device is it removes the option or possibility of simply “pushing the button”. There are two different replaceable devices currently available: A. A device with mechanically spring-­‐loaded electrical contacts that are activated by melt-­‐able thermal material to cut off the electricity to the heating element(s). Dependent upon mechanically operated contacts, this device cannot be considered fail-­‐safe. Like the manually resettable device, this replaceable mechanical device is certainly more reliable and appropriate than the automatically resetting, and substantially safer than no backup protection at all. However, due to its limitations and known failures, the manufacturer specifically warns that this device should not be relied upon to protect persons or property. B. A very simple device consisting of melt-­‐able thermal material only, which disconnects electricity to the heating element(s) directly. Because there are no mechanically operated contacts in this device, it is considered fail-­‐safe, and can be used to achieve the safest reasonable design currently available for electric heaters. Level of Reliability Needed to Make the Product Reasonably Safe: It is vitally important to consider the severity of the danger when evaluating the reliability of the backup protection to be implemented. The current version of UL 1995 requires “one or more” backup protection devices, clearly acknowledging that a high level of reliability should be required to safeguard against such severe anticipated risks. The difference in reliability between potential backup devices or designs is absolutely critical when the consequence is exposing people to fires in their homes – one is too many if it can reasonably be avoided.