Electrical Definitions

[alans552007]

I was wondering if anyone could tell me the definitions / difference between latching contacts and holding contacts ?

 

[charlie b]

Just a guess:

(1) The term "holding" tells me that the contact stays in position only for as long as power is available to the associated coil. Lose the power, and the contact opens.

(2) The term "latching" tells me that the contact gets put into position by the action of one coil, and it is held in place by some mechanical locking device. In order to change the position of the contact, you need to apply power to a second coil, in order to unlock the locking device.

Welcome to the forum.

 

[K8MHZ]

Just a guess:

(1) The term "holding" tells me that the contact stays in position only for as long as power is available to the associated coil. Lose the power, and the contact opens.

(2) The term "latching" tells me that the contact gets put into position by the action of one coil, and it is held in place by some mechanical locking device. In order to change the position of the contact, you need to apply power to a second coil, in order to unlock the locking device.

Welcome to the forum.

I disagree. A holding coil is energized by the amount of current flowing through it's coils as determined by an outside load, typically a starter motor. As the load decreases, so does the energy in the coil and the relay opens.

A latching coil shunts current from the load side to the coil input and uses the energized output to hold in the coil. The only way to open a latched relay is to open the circuit the relay is controlling.

 

[hillbilly]

Just a guess:

(1) The term "holding" tells me that the contact stays in position only for as long as power is available to the associated coil. Lose the power, and the contact opens.

(2) The term "latching" tells me that the contact gets put into position by the action of one coil, and it is held in place by some mechanical locking device. In order to change the position of the contact, you need to apply power to a second coil, in order to unlock the locking device.

Welcome to the forum.

That's a accurate description,,,

A holding relay is a common way to use a momentary contact (MC) pushbutton to "hold in" a magnetic motor starter.
You use the momentary pushbutton to energize (pull in) the coil on a small multi-pole (control) relay, then use a normally open (NO) contact on the same small relay to "hold" (keep supplying power to) the smaller relay's coil and another NO contact on the small relay to pull in (energize) a larger, motor starter coil.
As long as the small relay has power to it's coil, the contact(s) stay closed, continues powering the small relay coil..."holding" it closed.
This allows the other NO contact on the small relay to continue supplying power to the larger (starter) relay coil.
To stop the motor, all that is required is to break the power source to the smaller relay coil.
This is usually accomplished by installing a Normally closed (NC) pushbutton in the circuit feeding the smaller relay coil.
I hope that's clear enough.
It's kinda like pushing a doorbell....As long as you "hold" the contacts closed, the bell will ring.

A latching relay is just as Charlie describes.
All I can add is that the application of power to the relay coil(s) to get it to shift positions is "momentary"...usually thur a Normally open contact.
Kinda like switching on a light.
The switch acts like a latching relay.
The difference is the relay uses a magnetic coil(s) to switch the contacts, and you use your finger to "flip" the switch.

I'm not familiar with the other poster's description:wink:.

steve

ps....I have no idea why that "red face" is at the top of this post.

 

[billsnuff]

relating to PLC

relating to PLC

latch:

http://www.toolingu.com/definition-450310-40027-latching-relay.html

hold:

http://books.google.com/books?id=o7...&hl=en&sa=X&oi=book_result&resnum=7&ct=result

 

[brian john]

I agree with Charlie except it is not necessary to utilize two coils. One coil can be utilized with clearing contacts one powers the contactor closed and the clearing contacts remove power somewhere in the movement of the contactor inertia completes the closing, reverse the procedure to open the contactor.

ASCO lighting contactors are a good example of this. Single Coil that is.
GE use to utilize a two coil contactor, have not installed/seen one for years.

 

[Smart $]

I agree with Charlie except it is not necessary to utilize two coils. One coil can be utilized with clearing contacts one powers the contactor closed and the clearing contacts remove power somewhere in the movement of the contactor inertia completes the closing, reverse the procedure to open the contactor.

ASCO lighting contactors are a good example of this. Single Coil that is.
GE use to utilize a two coil contactor, have not installed/seen one for years.

Both types exist and available [new ] for purchase.

 

[K8MHZ]

latch:

http://www.toolingu.com/definition-450310-40027-latching-relay.html

hold:

http://books.google.com/books?id=o7...&hl=en&sa=X&oi=book_result&resnum=7&ct=result

Those seem to be the same thing.

I may be wrong, but a holding relay will open when the signal used to close it is removed, whereas a latching relay will not and stays closed so long as the controlled load's power is available.

The only definition I could find on holding relays were those that described solenoids used on automotive engine starter motors.

 

[Smart $]

Those seem to be the same thing.

I may be wrong, but a holding relay will open when the signal used to close it is removed, whereas a latching relay will not and stays closed so long as the controlled load's power is available.

The only definition I could find on holding relays were those that described solenoids used on automotive engine starter motors.

Actually, a feature common to many latching relays is the ability to not change contact status upon power failure.