Shut off valves with a wheel or other multi-turn valves operate by spinning the handle. Think of this like the difference between a shut off valve for your toilet that is normally open and your outside hose bib that is normally closed. As a result, a shut off valve can isolate a plumbing fixture from the rest of the plumbing in your home or hold water back until you need it. Water shut off valves are designed to stop the flow of water. Going into details like what valves are used for, what they are made of, and where you find them inside and outside your home. Our guide will walk you through the main water shut off valve through to fixture valves and everything in between. And it can be confusing to tell what each valve controls and how it operates. You will have several different types of water shut off valves that regulate the flow of water in your home. Many of these are offered by Alarm Grid.By Trevor Woods | Last Updated: August 1, 2020 There are hundreds of different contacts to choose from in various sizes and configurations, from surface mount, to recessed mount. Form A, SPST (Single Pole, Single Throw) contacts are always normally closed. Honeywell contacts usually indicate Form C with a -2 after the part number. When buying contacts, look for Form C, SPDT (Single Pole, Double Throw) contacts if you require a normally open device. It is difficult, and in some cases impossible, to mix Normally Open and Closed contacts on a single zone. When replacing an existing contact, you also need to know if the contact being replaced was normally open or closed, especially if more than one contact is wired into a zone. If we program for Normally Closed, but wire Normally Open, the system will tell us the door is faulted when it's closed, and that it's in the normal condition when it's open. For example, if we tell the panel to treat a zone as Normally Closed, we're telling the panel that when it sees a short on the zone, it is in the normal, non-faulted condition, and when it sees an open on the zone, it should show that zone faulted. In order to properly program and wire each zone, we must know what the normal state of each contact is. There may also be other options, but we won't discuss those here. Newer panels offer the option of using End of Line Resistors, or specifying Normally Open, or Normally Closed. So, in order to wire the zone correctly, you had to know the contact(s) normal state. The resistor orientation (series or parallel) depended on whether the contact(s) on the circuit were Normally Open, or Normally Closed. Older panels usually required an End of Line Resistor be installed on each wired zone. Why do we care? The alarm panel does what we tell it to do, and different panels have different capabilities when it comes to wired zones. Put another way, if you have a meter capable of displaying when it sees a closed circuit (short), or an open circuit, and you attach the meter to the wires or screw terminals for the contact, with the magnet next to the contact (the "normal" position) if you read an open, then the device is normally open, and if you read a short, then the device is normally closed. If for no other reason, because it's much less confusing! What this means is, if you have a magnetic contact, usually consisting of a reed switch inside a plastic housing, and a separate magnet in a matching plastic housing, connected to a door, when the door is closed, the reed switch within the contact is closed, and when the door is opened, or the magnet and the contact are separated, the reed switch within the contact is also open. Fire devices are normally open.įor the most part, normally closed contacts are used on normally closed protection points.
For doors and windows, this is usually closed. When talking about circuits or zones on an alarm panel, "normal" indicates the normal state of the opening being protected. Normally opened or closed refers to the state of a contact attached to an opening.
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