Could somebody explain to me what is Break-Before-Make or Make-Before-Break in electrical application. I can use relay very well, I realize it's about the time sequence, one relay or several? Or adding timer to delay? Thanks
Make mean close and break mean open the contacts.
This term is used in switches,relays and limit switches where two or more sets of contacts are used.
When such a device is actuated mechanically or electrically the normally closed and normally open contacts will change the status.
At the time the N.O.contact switches to closed status, the N.C contact is still in closed status for a brief moment and when the switching mechanism is fully operated the N.C contact opens.
This is make before break.
The other one is just opposite.
It is not necessary that the condition should exist when the device is released. That means could be one way also.
In case of a normal power loss, the building is supply through gensets. When normal power returns, there is two ways to transfert back.
1: Break before make
The genset's breakers will open before the normal power breaker is closed. There will be a short interruption.(may have problems with motors, may have to restart some equipment etc..)
2: Make before make
The gensets synchronize with normal power. When done, the normal power breaker will close and after, the genset's breakers will open. This way there will be no power interruption .
The "Break-before-make" is the standard relay configuration. The normally closed contacts open before the normally open contacts close when the coil is energised and the normally open contacts go back open before the normally closed contacts go back closed when the coil is deenergised.
The "Make-before-break" contact relays were designed to prevent a "race" circuit which is sometimes difficult to pinpoint. This was first used by the Clark Controller company in their overhead crane control systems where continous operation was vital.
These terms apply to relays and selector switches which connect one input to two or more inputs. Most relays are "break before make", i.e. when the contact changes position, it is for a moment "in the gap" between its counterparts, making contact to none of them. There are a few applications where this is unwanted. Then special "make before break" switches are used. The moving contact touches the new position counterpart before loosing contact to the first one. Note that this means to short circuit the inputs for a little amount of time.
There are not too much applications for this. To construct one imagine a digital thermometer using thermocouples. Most of these meters show fullscale or overtemperature when no thermocouple is connected. After reconnecting, some need a considerable time until they show a correct result again. You might use a "make before break" selector to avoid the overload and minimize the adaption time when you switch thermocouples.
Another application a selector for audio sources that makes no noise when switching.
This simply refers to the order in which electrical contacts sequence, typically in something like a relay with Form C contacts. Form C means there is a common terminal with a normally open (NO) contact and a normally closed (NC) contact. In 'make before break' the concept is typically that continuity is not lost. That is, when the relay is energized, the NO contact will always close before the NC contact opens, so that one circuit is connected before the other is disconnected from a common terminal.
In 'break before make' the concept is typically that even the briefest of momentary shorts must not occur between circuits connected on the NO and NC contacts. So when the hypothetical 'break before make' relay energizes the NC contact will open before the NO contact closes. Relays are specifically designed and designated to perform in this fashion.
The make/break before functions you describe are commonly found in rotary switches. You may find diagrams in parts catalogs, electrical fundamentals/principles textbooks.
I remember this from my telco days where a circuit had to been in a new state before the old one was let go. Consider switching a phone line from one cable to another, it would have to be connect to the new cable before it was removed from the old cable or the call would drop.
Using a form C relay...
Make before break is a contact arrangement where, the NO contacts are guaranteed to close (make) before the NC contacts open (break).
Break before make is a contact arrangment where, the NO contacts are guaranteed not to close (make) befor the NC contacts open (break).
Simple. Let's use a SPDT switch as an example. In break before make ( the usual case ) the NC contact breaks contact with the common terminal before the NO contact makes contact with the common terminal. This is handled mechanically by seperation when the switch is actuated.
In make before break there is an interval where all three are connected together before the NC would break contact. This is often a requirement with inductive things where an open circuit would product destructive arcing. To simulate BBM: OFF1 <delay> ON2. To simulate MBB: ON2 <delay> OFF1
Hope this makes sense. Unplanned for MBB can make outputs very unhappy.
It applies to parallel connections, for example, and transfer switch between two separate power supplies. In break before make, the first connection is opened before the second is made. For example, if you had power supplies which were out of phase with each other, you would want break before make. In an application where a momentary outage is unacceptable, and the power supplies are in phase, you would consider make before break, in which both supplies are momentarily connected in parallel before the first is removed.
These are contact configurations in relays or contactors containing several contacts. Typically these are found as contact options in contactors. When a contact breaks it is open. When a contact is made, it is closed.
Make before break is where a contact closes before a related contact in the same relay opens. This is accomplished by designing the contacts to require a longer stroke before opening, or conversely to close sooner in the stroke. This is used where it is important that there is no point in the relay transition where neither circuit is closed.
Break before make is where there is a point during the transition where neither contact is made (closed). This is the normal contact configuration for most applications.
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Michael Griffin
London, Ont. Canada
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Responding to Quingye's Wed, Dec 11, 4:10pm, query:
The most succinct definitions in the literature, besides those in old faithful, yep you guessed it, the IEEE Std 100-1992, are the those in Struthers-Dunn's handbook "Relay Engineering." It lists the following terms:
Break-before-Make... the moving contact, in transferring from one position to the other, interrupts (opens) an established circuit, before establishing (closing) a new one.
Make-before-Make... the moving contact, in transferring from one position to the other, establishes (closes) a new circuit before interrupting (opening) the circuit previously established.
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