Triton’s Relays: Normally Open vs. Normally Closed - What does that mean, and how are they used?
The eight electro-mechanical relays in the Triton controller each have two parts, which stated simply are the
“circuit” part, where the incoming AC voltage from the power cord can be allowed to flow out or not, and the part
we are referring to when we say a relay is “activated” or “deactivated” (the coil). Associated with the relays are the
Wet / Dry switches, but for now, this discussion assumes those switches are in the Wet (powered) position.
Normally Closed vs. Normally Open
The circuit part of the relay has two ways to which the wires leaving the relay
can be connected, as either “Normally Closed” or as “Normally Open”. On the
connector these two options are indicated as “NC” and “NO” as seen in Figure 1.
The black wire of the “pigtail” plugs is connected to one of these two terminals,
depending on what is being controlled by relay and how that device operates.
An electric circuit can be a “closed” circuit, where the power flows, or an “open”
circuit where the power is interrupted. In the Normally Closed circuit, power
flows out until the relay is activated, which interrupts the power, and when the
relay deactivates, the power is on again. Normally Open is the opposite, the
power is off until the relay activates, which allows the power to flow through,
and when the relay deactivates, power is again interrupted.
Relay Deactivated
Figure 1
NC and NO Terminals
Relay Activated
Normally Open (NO)
Normally Closed (NC)
When Would I Use Normally Closed?
Most circuits encountered are Normally Open, like a light switch on the wall. But some devices are made to be
connected to a Normally Closed circuit. Some Bleed Valves for example, are made so they close when power is
applied to them, and open when the power is interrupted. (This design is so if there is a power failure, the valve
opens. Some water treaters prefer to bleed if the controller power fails, rather than chance that scaling will occur.)
Another way to think about this is that if a valve is supposed to open when the relay activates, then the valve’s
unpowered state is the opposite of the circuit it should be wired to. So, if the valve is open when it comes out of the
box, it would be wired it to the relay’s Normally Closed circuit, and if the valve is closed when it comes out of the
box it would be wired it to the relay’s Normally Open circuit.
“Wet” vs “Dry”
Associated with each relay is a Wet/Dry switch that controls whether the incoming AC voltage is sent through the
relay circuit or not. The upper “Wet” position sends that power through the relay circuit, while the lower “Dry”
position makes the relay circuit unpowered. In the Dry mode the relay now acts like a switch for a device that has its
own source of power, where the switch can be “open” or “closed”.
And again, most switches are expected to be used with the Normally Open circuit, like a typical On/Off switch, but
there are some switches that are expected to be used with a Normally Closed circuit, like many alarm switches that
will cause an alarm if the circuit opens.
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