Float Switches in Hazardous Environments

Mushroom cloud explosionNothing in our industry seems to cause more stress and headaches than complying with regulation. So it is with hazardous areas. Ensuring the safety of employees and protecting assets is extremely important. Still, navigating these waters can be challenging and, at times, confusing.

In our experience, most control engineers require that any device going into a hazardous location be certified with hazardous approval. This may surprise some of you, but in some circumstances, a device with no certification CAN be installed in a hazardous location! While there are a few scenarios where this is ok, we will focus on the main one that concerns a popular device in our industry; the mighty float switch.

Intrinsic Safety with Float Switches

The key is to use Intrinsically Safe wiring methods to limit available energy.

The intrinsic safety technique allows for the installation of a “simple apparatus.” A simple apparatus is defined as a device that does not generate or store more than:

If it meets these requirements, it will have little effect on the intrinsic safety of a system. Some examples include resistors, junction boxes, semiconductor devices, and switches. This is what makes it possible to install them in an intrinsically safe system without requiring third-party certification.

The reason for this has to do with the Intrinsic Safety technique. As a review, intrinsically safe systems never allow the ignition to happen in the first place. This is accomplished by using devices that require very low power voltage and currents. These devices are wired to barriers and isolators that sit between the power source and the hazardous area, limiting the power that flows through the hazardous area.

While many instruments have circuit boards and other components that condition electrical outputs, a simple apparatus does not. For example, our mechanically activated float switches simply open and close. All that is required is to supply the float switch with current and, depending on the position of the switch, the current is either allowed or not allowed to pass through. The output on the unit is directly correlated with the supply power input. Therefore, if the supply power is intrinsically safe, the float switch is intrinsically safe.

Read More: Is Intrinsic Safety Or Explosion Proof Better For Hazardous Areas?

A Warning About Float Switches in Hazardous Areas

A float switch represents little to no risk to a hazardous area. That said, adding anything to a hazardous area must be a calculated move. Make sure you are familiar with the instrumentation and wiring in your hazardous area and consult with an electrical engineer who can safely assess the risk of modifying your installation.

Always use an appropriate barrier or isolator to control the power coming into your hazardous area and device. Failure to do so will compromise your safety and that of everyone around you.

How Do I Wire Float Switches For A Hazardous Location?

Below are two typical intrinsically safe installation configurations for Dual Level and Single Level installations.

diagram for float switches in hazardous environments

The drawing shows an intrinsically safe relay with multiple inputs. If you don’t have one of these, you can use a safety barrier. You will need one input per switch point – which can mean multiple safety barrier modules.

This can get very expensive if you have multiple switch points. It will likely be worth looking at another measurement solution at this point – such as the PT-500 submersible pressure transducer, or the LPU-2428 ultrasonic sensor.

Float Switches are a Great Choice for Hazardous Areas

A float switch is a handy instrument that has yet to live out its usefulness – even in hazardous areas. So stop wondering if you can do it and get it done! But you must do your homework while you’re at it. If you have questions about instrumentation in hazardous areas, we’re happy to help.

Please contact us with any questions or for technical help concerning the hazardous location installation of any float switch, or any hazardous measurement instruments.

Explore APG Float Switches

top photo credit: r0ckchuck via photopin cc

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