{"id":45,"date":"2020-01-13T13:29:47","date_gmt":"2020-01-13T18:29:47","guid":{"rendered":"https:\/\/opentextbc.ca\/basicmotorcontrol\/chapter\/switches-and-pushbuttons\/"},"modified":"2023-03-02T11:53:02","modified_gmt":"2023-03-02T16:53:02","slug":"switches-and-pushbuttons","status":"publish","type":"chapter","link":"https:\/\/opentextbc.ca\/basicmotorcontrol\/chapter\/switches-and-pushbuttons\/","title":{"raw":"Switches and Pushbuttons","rendered":"Switches and Pushbuttons"},"content":{"raw":"Click play on the following audio player to listen along as you read this section.\r\n\r\nhttps:\/\/media.bccampus.ca\/id\/0_hh6o9v8q?width=608&height=80&playerId=23449753\r\n

Pilot Devices Overview<\/h1>\r\nThese are some of the most basic control devices that we use to start and stop our motors. They can be provided with [pb_glossary id=\"211\"]fuses[\/pb_glossary] for [pb_glossary id=\"209\"]overcurrent[\/pb_glossary] protection, and if a [pb_glossary id=\"236\"]switch[\/pb_glossary] is horsepower rated, it is designed to make and break line current to a motor.\r\n

Pushbuttons<\/h2>\r\n[pb_glossary id=\"235\"]Pushbuttons[\/pb_glossary] are momentary [pb_glossary id=\"237\"]contacts[\/pb_glossary] that come available as either [pb_glossary id=\"229\"]normally open (NO)[\/pb_glossary] or [pb_glossary id=\"230\"]normally closed (NC) contacts[\/pb_glossary], although many pushbuttons come with both NO and NC sets of contacts.\r\n\r\nWhen you depress the button, you change the state of the contacts, and when you release the button, a spring returns the contacts to their original state.\r\n\r\nThese are ideal for use in low-voltage [pb_glossary id=\"242\"]control circuits[\/pb_glossary].\r\n\r\n[caption id=\"attachment_44\" align=\"alignnone\" width=\"1024\"]\"\" Pushbuttons[\/caption]\r\n

Switches<\/h2>\r\nSwitches are identified by the number of conductors (poles) they connect to, and the number of positions (throws) they can switch to. Switches are also rated for [pb_glossary id=\"219\"]voltage[\/pb_glossary] and [pb_glossary id=\"223\"]power[\/pb_glossary] and must be operated within their limits.\r\n

Single-pole, single-throw (SPST)<\/h3>\r\nThis switch is used where we only need to break a single line in a 120V single-phase supply, providing that it is connected to an ungrounded-circuit conductor.\r\n\r\n\"\"\r\n

Single-pole, double-throw (SPDT)<\/h3>\r\nThis switch connects a single-line conductor to either of two possible switch legs. A common household example of this is in a three-way switch loop, which allows control of a single load (usually a light) from two different locations.\r\n\r\nIn industrial settings, it is commonly used as a Hand \u2013 Off \u2013 Auto selector switch.\r\n\r\n[caption id=\"attachment_44\" align=\"aligncenter\" width=\"1024\"]\"\" Single-pole, double-throw[\/caption]\r\n

Double-pole, double-throw (DPDT)<\/h3>\r\nThe most common application of these devices is as a 4-way switch, which is used in conjecture with two three-way switches to allow for control from three or more locations. As a general rule, a light can be controlled from any number of locations, providing you start and end your switching with three-way switches and use as many 4-way switches in between as necessary.\r\n\r\n[caption id=\"attachment_44\" align=\"aligncenter\" width=\"1024\"]\"\" Double-pole, double-throw[\/caption]\r\n

Double-pole, single-throw (DPST)<\/h3>\r\nThis switch looks like a standard SPST switch from the outside but inside, instead of interrupting only one current-carrying conductor, it interrupts two. This makes it suitable for controlling and isolating loads that operate at 240V single-phase.\r\n\r\n\"\"\r\n

Triple-pole, single-throw (3PST)<\/h3>\r\nThese are used to interrupt current to [pb_glossary id=\"205\"]three-phase circuits[\/pb_glossary] and motors. With a single external handle, three current-carrying conductors can be opened or closed at once. The switches often come with housing for the mounting of fuses to provide overcurrent protection. The switch must be horsepower rated if it is used to interrupt current to a motor.\r\n\r\n\"\"\r\n

Isolating switch<\/h3>\r\nAn [pb_glossary id=\"234\"]isolating switch[\/pb_glossary] is connected upstream of a [pb_glossary id=\"243\"]power circuit[\/pb_glossary] and is NOT horsepower rated and so it is not meant to interrupt current flow. Isolating switches are not meant to control motor loads. Rather once a motor has been properly shut off, an isolating switch can be used for lockout purposes. An isolating switch can have any number of pole contacts, but to be used for lockout purposes it must provide only a single throw option.","rendered":"

Click play on the following audio player to listen along as you read this section.<\/p>\n

https:\/\/media.bccampus.ca\/id\/0_hh6o9v8q?width=608&height=80&playerId=23449753<\/p>\n

Pilot Devices Overview<\/h1>\n

These are some of the most basic control devices that we use to start and stop our motors. They can be provided with fuses<\/a> for overcurrent<\/a> protection, and if a switch<\/a> is horsepower rated, it is designed to make and break line current to a motor.<\/p>\n

Pushbuttons<\/h2>\n

Pushbuttons<\/a> are momentary contacts<\/a> that come available as either normally open (NO)<\/a> or normally closed (NC) contacts<\/a>, although many pushbuttons come with both NO and NC sets of contacts.<\/p>\n

When you depress the button, you change the state of the contacts, and when you release the button, a spring returns the contacts to their original state.<\/p>\n

These are ideal for use in low-voltage control circuits<\/a>.<\/p>\n

\"\"
Pushbuttons<\/figcaption><\/figure>\n

Switches<\/h2>\n

Switches are identified by the number of conductors (poles) they connect to, and the number of positions (throws) they can switch to. Switches are also rated for voltage<\/a> and power<\/a> and must be operated within their limits.<\/p>\n

Single-pole, single-throw (SPST)<\/h3>\n

This switch is used where we only need to break a single line in a 120V single-phase supply, providing that it is connected to an ungrounded-circuit conductor.<\/p>\n

\"\"<\/p>\n

Single-pole, double-throw (SPDT)<\/h3>\n

This switch connects a single-line conductor to either of two possible switch legs. A common household example of this is in a three-way switch loop, which allows control of a single load (usually a light) from two different locations.<\/p>\n

In industrial settings, it is commonly used as a Hand \u2013 Off \u2013 Auto selector switch.<\/p>\n

\"\"
Single-pole, double-throw<\/figcaption><\/figure>\n

Double-pole, double-throw (DPDT)<\/h3>\n

The most common application of these devices is as a 4-way switch, which is used in conjecture with two three-way switches to allow for control from three or more locations. As a general rule, a light can be controlled from any number of locations, providing you start and end your switching with three-way switches and use as many 4-way switches in between as necessary.<\/p>\n

\"\"
Double-pole, double-throw<\/figcaption><\/figure>\n

Double-pole, single-throw (DPST)<\/h3>\n

This switch looks like a standard SPST switch from the outside but inside, instead of interrupting only one current-carrying conductor, it interrupts two. This makes it suitable for controlling and isolating loads that operate at 240V single-phase.<\/p>\n

\"\"<\/p>\n

Triple-pole, single-throw (3PST)<\/h3>\n

These are used to interrupt current to three-phase circuits<\/a> and motors. With a single external handle, three current-carrying conductors can be opened or closed at once. The switches often come with housing for the mounting of fuses to provide overcurrent protection. The switch must be horsepower rated if it is used to interrupt current to a motor.<\/p>\n

\"\"<\/p>\n

Isolating switch<\/h3>\n

An isolating switch<\/a> is connected upstream of a power circuit<\/a> and is NOT horsepower rated and so it is not meant to interrupt current flow. Isolating switches are not meant to control motor loads. Rather once a motor has been properly shut off, an isolating switch can be used for lockout purposes. An isolating switch can have any number of pole contacts, but to be used for lockout purposes it must provide only a single throw option.<\/p>\n

definition<\/span>