Motor Control - Three Wire Control
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Posts: 46,084
General Topic: Motor Control Wiring
Subtopic: Systems/Methodology>Start/Stop>R emotes
Subject: Three Wire Control
Three wire control for remote (or cover mounted) Start Stop "buttons"
encompasses many areas. Those listed below are just a sampling:
1. Design Goal for safety
a. Direct Safety Concerns
1) Personnel, product and system safety and integrity
2) Prevent unexpected start-ups after
unexpected power-down
3) Multiple operators for supervision and
operations convenience
4) Ease of implementation; thus reasonable
for initial implement ion, present update and
future expansion
b. Indirect Concerns
1) OSHA / NIOSHA
2) N.E.C. / U.L.
2. Cost Effectiveness in wiring methods
3. Expandable system
4. Simplified implementation
5. Universal application regardless of manufacturer
Three wire control, when viewed as a wiring method, is simplicity itself.
Since all larger implemetations are merely an expansion of two stations
(one start, one stop), a simple ASCII diagram should more than suffice for
a basic understanding, It is presumed that the reader understands and
accepts the concept of self-latching relays thru circuitry.
Simplified Diagram
self-latching STOP
( - ) coil ( + ) ____
| | ( 1 )
* *
( 3 )
| |
N.C.
|
* (1)
| START
|
* ( 2 ) __
| | /
| | ( 1 ) ___/ *_____ ( 3 )
( - ) ( + )
* ( 3 )
control voltage
STOP operators are normally closed (open to stop), and START operators are
normally closed (close to start). Both are generally momentary operators,
except under certain conditions (range control, selector switches, etc. ).
The safety facet occurs when one realizes that manual intervention is
required to START or STOP the controlled (industrial) process. Therein,
should a power failure occur, the latching coil will drop out, and power
will NOT be re-applied to the circuit, until a START operator is activated;
ergo, this is a FAIL-SAFE method and design.
Two wire control will permit re-activation upon re-application of the power.
There are obvious dangers with this sort of system, and these systems are
normally used ONLY under emergency circumstances (overcome a mechancal
stop, or promote slight mechanical movement while supervision is taking
place (see: jogging, plugging, and over-ride systems).
This is merely provided as a general overview to a specific wiring method
and safe design practice; therein it is wholly incomplete. Please contact
the manufacturer of the devices employed for specific wiring diagrams and
specific recommendations. See also the National Electic Code (U.S.A) or
documents provided by other authorized and pertinant electrical code and
supervision agencies worlwide. Please remember that the onsite inspector
for all electrical systems has the LAST SAY as to the approval of any
system which is installed in an automated industrial or commercial process.
Regards,
Bruce V. Bates
bvbates@u...
Subtopic: Systems/Methodology>Start/Stop>R emotes
Subject: Three Wire Control
Three wire control for remote (or cover mounted) Start Stop "buttons"
encompasses many areas. Those listed below are just a sampling:
1. Design Goal for safety
a. Direct Safety Concerns
1) Personnel, product and system safety and integrity
2) Prevent unexpected start-ups after
unexpected power-down
3) Multiple operators for supervision and
operations convenience
4) Ease of implementation; thus reasonable
for initial implement ion, present update and
future expansion
b. Indirect Concerns
1) OSHA / NIOSHA
2) N.E.C. / U.L.
2. Cost Effectiveness in wiring methods
3. Expandable system
4. Simplified implementation
5. Universal application regardless of manufacturer
Three wire control, when viewed as a wiring method, is simplicity itself.
Since all larger implemetations are merely an expansion of two stations
(one start, one stop), a simple ASCII diagram should more than suffice for
a basic understanding, It is presumed that the reader understands and
accepts the concept of self-latching relays thru circuitry.
Simplified Diagram
self-latching STOP
( - ) coil ( + ) ____
| | ( 1 )
* *
( 3 )
| |
N.C.
|
* (1)
| START
|
* ( 2 ) __
| | /
| | ( 1 ) ___/ *_____ ( 3 )
( - ) ( + )
* ( 3 )
control voltage
STOP operators are normally closed (open to stop), and START operators are
normally closed (close to start). Both are generally momentary operators,
except under certain conditions (range control, selector switches, etc. ).
The safety facet occurs when one realizes that manual intervention is
required to START or STOP the controlled (industrial) process. Therein,
should a power failure occur, the latching coil will drop out, and power
will NOT be re-applied to the circuit, until a START operator is activated;
ergo, this is a FAIL-SAFE method and design.
Two wire control will permit re-activation upon re-application of the power.
There are obvious dangers with this sort of system, and these systems are
normally used ONLY under emergency circumstances (overcome a mechancal
stop, or promote slight mechanical movement while supervision is taking
place (see: jogging, plugging, and over-ride systems).
This is merely provided as a general overview to a specific wiring method
and safe design practice; therein it is wholly incomplete. Please contact
the manufacturer of the devices employed for specific wiring diagrams and
specific recommendations. See also the National Electic Code (U.S.A) or
documents provided by other authorized and pertinant electrical code and
supervision agencies worlwide. Please remember that the onsite inspector
for all electrical systems has the LAST SAY as to the approval of any
system which is installed in an automated industrial or commercial process.
Regards,
Bruce V. Bates
bvbates@u...