High limit controls are usually what type of switch?

High limit controls are typically designed to prevent equipment from exceeding a set temperature or pressure threshold. When the temperature or pressure rises to the designated limit, the high limit control is triggered to interrupt power to the system, ensuring safety and preventing damage.

When using normally open switches for high limit controls, the circuit is completed only when the temperature or pressure is below the limit. This means that the control is inactive under safe conditions, allowing power to flow. However, if the high limit is reached, the switch opens, cutting off power and protecting the system.

In contrast, normally closed switches would allow power to flow until the limit is reached, at which point the circuit would open. This setup can be less intuitive and may not provide immediate shutdown under high limit conditions. Bi-stable switches and single-pole configurations primarily describe the operational function rather than directly addressing the normal state of the switch in relation to high limit safety operations.

Thus, the use of normally open switches aligns best with the purpose and function of high limit controls in maintaining system safety and ensuring proper operational responses to potential overheating or overpressurization situations.