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The cross-section (q) of the cable should meet the following re-
quirements:
1. The submersible drop cable should be dimensioned to the
rated maximum current (I) of the motor.
2. The cross-section should be sufficient to make a voltage drop
over the cable acceptable.
Use the largest of the cross sections found under points 1. and 2.
Re 1: The following table specifies the current value of Grundfos
submersible drop cables (i.e. the maximum current tolerated by
the drop cable) at an ambient temperature of maximum 30°C.
Please contact Grundfos if the ambient temperature lies above
30°C.
When sizing the submersible drop cable, make sure that the rated
maximum current does not exceed the current value (I
For star-delta starting, however, size the cables so that 0.58 x the
rated maximum current of the motor does not exceed the current
value (I
) of the cables.
s
I
[A]
q [mm²]
s
1.5
18.5
2.5
25
4
34
6
43
10
60
16
80
25
101
35
126
If Grundfos submersible drop cables are not used, the cross-sec-
tion should be selected on the basis of the current values of the
actual cables.
Re 2:
Note: The cross-section of the submersible drop cable must be
large enough to meet the voltage quality requirements specified
in section 4.1 General .
Determine the voltage drop for the cross-section of the submersi-
ble drop cable by means of the diagrams on pages 99 and 100,
where
I =
Rated maximum current of the motor.
For star-delta starting
I = rated maximum current of the motor x 0.58.
Lx =
Length of cable converted to a voltage drop of 1% of the
nominal voltage.
length of drop cable
Lx =
permissible voltage drop in %
q =
Cross-section of submersible drop cable.
Draw a straight line between the actual I-value and the Lx-value.
Where the line intersects the q-axis, select the cross-section that
lies right above the intersection.
The diagrams are made on the basis of the formula:
U x ¡U
L =
Î
I x 1.73 x 100 x (cosÓx
q
where
L =
Length of submersible drop cable [m]
U =
Nominal voltage [V]
¡U =
Voltage drop [%]
I =
Rated maximum current of the motor [A]
cosÓ= 0.9
Î=
Specific resistance: 0.02 [¶mm²/m]
q =
Cross-section of submersible drop cable [mm²]
sinÓ= 0.436
Xl =
Inductive resistance: 0.078 x 10
82
).
s
I
[A]
q [mm²]
s
50
153
70
196
95
238
120
276
150
319
185
364
240
430
300
497
+ sinÓx Xl)
-3
[¶/m]
4.5 Connection of motor
Three-phase submersible motors must be protected, see section
4.2 Motor protection .
For electrical connection by means of the CU 3, see the separate
installation and operating instructions for this unit.
When a conventional motor starter is being used, the electrical
connection should be carried out as described below.
4.5.1 Checking of direction of rotation
Note: The pump must not be started until the suction intercon-
nector has been completely submerged in the liquid.
When the pump has been connected to the electricity supply, de-
termine the correct direction of rotation as follows:
1. Start the pump and check the quantity of water and head de-
veloped.
2. Stop the pump and interchange two of the phase connections.
In the case of motors wound for star-delta starting, exchange
U1 by V1 and U2 by V2.
3. Start the pump and check the quantity of water and head de-
veloped.
4. Stop the pump.
5. Compare the results taken under points 1. and 3. The connec-
tion which gives the larger quantity of water and the higher
head is the correct connection.
4.5.2 Grundfos motors, direct-on-line starting
The connection of Grundfos submersible motors wound for direct-
on-line starting appears from the following table and fig. 8.
Mains
Grundfos 6", 8", 10" and 12" motors
L1
L2
L3
PE
Check the direction of rotation as described in section
4.5.1 Checking of direction of rotation .
Fig. 8
L1
U V W PE
4.5.3 Grundfos motors, star-delta starting
The connection of Grundfos submersible motors wound for star-
delta starting appears from the following table and fig. 9.
Connection
U1
V1
W1
W2
U2
V2
PE
Cable/connection
U
V
W
PE
L2 L3
PE
M
3
Grundfos 6" motors
Brown
Blue
Black
Brown
Blue
Black
Yellow/green
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