GE Multilin 469, Instruction Manual

Page: 83 / 338

CHAPTER 3: INSTALLATION
469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUAL 3–21
FIGURE 3–23: Reduced Wiring RTDs
The Hot line would have to be run as usual for each RTD. The Compensation and Return
leads, however, need only be run for the first RTD. At the motor RTD terminal box, the RTD
Return leads must be jumpered together with as short as possible jumpers. The
Compensation leads must be jumpered together at the 469.
Note that an error is produced on each RTD equal to the voltage drop across the jumper on
the RTD return. This error increases with each successive RTD added.
V
RTD 1
= V
RTD 1
V
RTD 2
= V
RTD2
+ V
J 3
V
RTD3
= V
RTD3
+ V
J 3
+ V
J 4
, etc.
This error is directly dependent on the length and gauge of the wire used for the jumpers
and any error introduced by a poor connection. For RTD types other than 10
Ω Copper, the
error introduced by the jumpers is negligible. Although this RTD wiring technique reduces
the cost of wiring, the following disadvantages must be noted:
1. There will be an error in temperature readings due to lead and connection resistances.
This technique is
NOT recommended for 10 Ω Copper RTDs.
2. If the RTD Return lead to the 469 or any of the jumpers break, all RTDs from the point
of the break will read open.
3. If the Compensation lead or any of the jumpers break, all RTDs from the point of the
break will function without any lead compensation.
Two-Wire RTD Lead Compensation
An example of how to add lead compensation to a two wire RTD may is shown in the figure
below.
808 7 22A2.CDR
Hot
Compensation
R TD R eturn
Compensation
Hot
Hot
Compensation
R TD R eturn
A1
A2
A3
A4
A5
A 6
A7
A8
L1
L2
L3
L4
L5
L 6
L7
No connection
4 69
J1
J2
Motor Control
Terminal Box
Motor
R TD1
+
–
R TD2
+
–
R TD3
+
–
J3
J4