Separate Control
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Re: Separate Control
I'll be interested in the responses to this post. I had something come up last week. I think the answer may be the difference between a dry contact and a powered contact. The dry contact does not impose an electrical signal from an outside source. The powered contact receives a signal from an outside source to energize the coil and change the state of the contact. I am still confused on what a dry contact is and how it works physically, which is why I'll be interested in the responces you get. Thanks.
I'll be interested in the responses to this post. I had something come up last week. I think the answer may be the difference between a dry contact and a powered contact. The dry contact does not impose an electrical signal from an outside source. The powered contact receives a signal from an outside source to energize the coil and change the state of the contact. I am still confused on what a dry contact is and how it works physically, which is why I'll be interested in the responces you get. Thanks.
stew
Senior Member
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- federal way,washington
Re: Separate Control
Steve in my experience separate control refers to the control voltage supply. with an integral control you are using one leg og the input voltage for your coil voltage and with separate control your control voltage comes from a separate source such as a step down transformer which may or may not be tapped off the input supply.When you dont want high voltage out in the pusbutton circuits you use separate control voltage say at 110 or 24 volts for coil and pushbutton circuits.
Steve in my experience separate control refers to the control voltage supply. with an integral control you are using one leg og the input voltage for your coil voltage and with separate control your control voltage comes from a separate source such as a step down transformer which may or may not be tapped off the input supply.When you dont want high voltage out in the pusbutton circuits you use separate control voltage say at 110 or 24 volts for coil and pushbutton circuits.
- Location
- Wisconsin
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- PE (Retired) - Power Systems
Re: Separate Control
A standard Square D NEMA contactor is expected to have the coil powered from the supply lines, this is often called Line Voltage control. Square D factory wires one side of the coil to L2. This arrangement is most common with 120V or 240V single phase systems, although there are times when 480V control is used.
Separate control intends for the coil to be powered separately from the powerline. For example, the coil power might come from a 480V to 120V control power transformer. In this case the Square D form S device does not have any factory wiring between L2 and the coil.
To field convert a device:
remove the wire on L2 and you now have a form S circuit.
add a wire from the coil (or overload relay) to L2 and you now have a line voltage (non-form S) circuit.
For more info try: Square D wiring diagrams.
[ June 21, 2004, 05:53 PM: Message edited by: jim dungar ]
A standard Square D NEMA contactor is expected to have the coil powered from the supply lines, this is often called Line Voltage control. Square D factory wires one side of the coil to L2. This arrangement is most common with 120V or 240V single phase systems, although there are times when 480V control is used.
Separate control intends for the coil to be powered separately from the powerline. For example, the coil power might come from a 480V to 120V control power transformer. In this case the Square D form S device does not have any factory wiring between L2 and the coil.
To field convert a device:
remove the wire on L2 and you now have a form S circuit.
add a wire from the coil (or overload relay) to L2 and you now have a line voltage (non-form S) circuit.
For more info try: Square D wiring diagrams.
[ June 21, 2004, 05:53 PM: Message edited by: jim dungar ]
hbiss
EC, Westchester, New York NEC: 2014
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- Hawthorne, New York NEC: 2014
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- EC
Re: Separate Control
I am still confused on what a dry contact is and how it works physically
It's really quite simple. Keep in mind that dry or wet (powered) contacts are usually incorporated into some device or assembly with the wiring brought out to screw terminals hence the mystery.
Consider a simple example- a wall switch and light. The switch, all by itself with nothing connected to it is a dry contact. Wire it into a circuit the normal way and the lamp would be considered to be connected to a wet contact via the switch leg and neutral.
So, a dry contact will provide no voltage across its terminals, only continuity when closed.
A wet contact is simply a dry contact with one side connected to a voltage. The other side and the other side of the supply voltage are the "switch" contacts or wet contact terminals. When the contacts are closed there will be a voltage across the terminals.
-Hal
I am still confused on what a dry contact is and how it works physically
It's really quite simple. Keep in mind that dry or wet (powered) contacts are usually incorporated into some device or assembly with the wiring brought out to screw terminals hence the mystery.
Consider a simple example- a wall switch and light. The switch, all by itself with nothing connected to it is a dry contact. Wire it into a circuit the normal way and the lamp would be considered to be connected to a wet contact via the switch leg and neutral.
So, a dry contact will provide no voltage across its terminals, only continuity when closed.
A wet contact is simply a dry contact with one side connected to a voltage. The other side and the other side of the supply voltage are the "switch" contacts or wet contact terminals. When the contacts are closed there will be a voltage across the terminals.
-Hal
stew
Senior Member
- Location
- federal way,washington
Re: Separate Control
I dont wish to confuse the issue but if you put a voltmeter across a lite switch when it is in the off position you read circuit voltage. When you close the switch you then read 0 volts.
I dont wish to confuse the issue but if you put a voltmeter across a lite switch when it is in the off position you read circuit voltage. When you close the switch you then read 0 volts.
Ed MacLaren
Senior Member
Re: Separate Control
It is physically a component of a fire alarm panel, but is electrically a component of a motor starter control circuit.
Ed
An example of a "dry contact" is the auxilliary relay contact supplied in many fire alarm panels that is used, for example, to shut down a supply fan.
It is physically a component of a fire alarm panel, but is electrically a component of a motor starter control circuit.
Ed
Re: Separate Control
Contacts are usually called wet or dry when you are talking about two separate pieces of equipment. Consider an elevator control panel and a fire alarm control panel. The fire alarm panel has a contact to shut down the elevator. The elevator panel has an input to shut it down that consists of two terminals.
The contact in the FACP panel would be a dry contact if both its terminals are not connected to anything. It could be a relay contact for example. The FACP can engage the relay and close the contacts, but the contacts aren't connected to anything else in the fire alarm control panel.
For this dry contact to be used by the elevator panel, the elevator panel would have to put a voltage on one of its input terminals. When the FACP contact closes, the voltage appears at the other elevator panel input terminal.
For a wet contact, the FACP would apply power to one side of the contact. Then the input to the elevator panels may be another relay that engages when the FACP contact closes.
Thats not as clear as I hoped when I started, but I hope that helps.
Steve
Contacts are usually called wet or dry when you are talking about two separate pieces of equipment. Consider an elevator control panel and a fire alarm control panel. The fire alarm panel has a contact to shut down the elevator. The elevator panel has an input to shut it down that consists of two terminals.
The contact in the FACP panel would be a dry contact if both its terminals are not connected to anything. It could be a relay contact for example. The FACP can engage the relay and close the contacts, but the contacts aren't connected to anything else in the fire alarm control panel.
For this dry contact to be used by the elevator panel, the elevator panel would have to put a voltage on one of its input terminals. When the FACP contact closes, the voltage appears at the other elevator panel input terminal.
For a wet contact, the FACP would apply power to one side of the contact. Then the input to the elevator panels may be another relay that engages when the FACP contact closes.
Thats not as clear as I hoped when I started, but I hope that helps.
Steve
Re: Separate Control
Back to the separate control:
As always, thanks for the responses. Thats what I thought separate control was, but the Square D catalog makes it sound like there is something more than a jumper that is differnet on separate control. For example, they say "you must order separate control for 24 volt coils".
But if its just a matter of changing a jumper, I can't go wrong specifying the contactor. The electrician can always change it in the field.
STeve
Back to the separate control:
As always, thanks for the responses. Thats what I thought separate control was, but the Square D catalog makes it sound like there is something more than a jumper that is differnet on separate control. For example, they say "you must order separate control for 24 volt coils".
But if its just a matter of changing a jumper, I can't go wrong specifying the contactor. The electrician can always change it in the field.
STeve
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
Re: Separate Control
I dont wish to confuse the issue but if you put a voltmeter across a lite switch when it is in the off position you read circuit voltage. When you close the switch you then read 0 volts.
That's not what I was talking about. A switch not connected to anything (or for Steve if you are holding it in your hand in the supply house
) is a dry contact.
-Hal
I dont wish to confuse the issue but if you put a voltmeter across a lite switch when it is in the off position you read circuit voltage. When you close the switch you then read 0 volts.
That's not what I was talking about. A switch not connected to anything (or for Steve if you are holding it in your hand in the supply house
) is a dry contact. -Hal
Ed MacLaren
Senior Member
Re: Separate Control
Ed
How would one make use of the dry contact without "connecting it to something"? (See sketch above).
Ed
- Location
- Wisconsin
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- PE (Retired) - Power Systems
Re: Separate Control
Back to separate control.
Steve,
Square D does not consider a line voltage of 24V so they have the requirement of adding form S.
To be safe always order devices, from Square D, as form S. This way if the coil doesn't work the installer can add a wire.
To be iffy always order them as line voltage and hope the installer remembers to remove the coil connection.
Back to separate control.
Steve,
Square D does not consider a line voltage of 24V so they have the requirement of adding form S.
To be safe always order devices, from Square D, as form S. This way if the coil doesn't work the installer can add a wire.
To be iffy always order them as line voltage and hope the installer remembers to remove the coil connection.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: Separate Control
Ed,
Strictly speaking, once a dry contact is wired with a supply it is no longer dry (the descriptor is no longer valid). But, in general terms, an installed dry contact is a contact that receives it's voltage from an external power supply.
Ed,
Strictly speaking, once a dry contact is wired with a supply it is no longer dry (the descriptor is no longer valid). But, in general terms, an installed dry contact is a contact that receives it's voltage from an external power supply.
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