Grundfos SP-G, Installation And Operating Instructions Manual

Page: 8 / 21

8
The cross-section (q) of the cable should meet the following
requirements:
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 GRUND-
FOS 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
s
).
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
s
) of the cables.
If GRUNDFOS submersible drop cables are not used, the cross-
section 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 110 and 111,
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.
Lx =
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:
L =
where
L = Length of submersible drop cable [m]
U = Nominal voltage [V]

U = Voltage drop [%]
I = Rated maximum current of the motor [A]
cos

= 0.9

= Specific resistance: 0.02 [

mm²/m]
q = Cross-section of submersible drop cable [mm²]
sin

= 0.436
Xl = Inductive resistance: 0.078 x 10
-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,
determine the correct direction of rotation as follows:
1. Start the pump and check the quantity of water and head
developed.
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
developed.
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.
Check the direction of rotation as described in section
4.5.1 Checking of direction of rotation.
Fig. 8
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.
q [mm²] I
s
[A] q [mm²] I
s
[A]
1.5 18 50 153
2.5 25 70 196
4 34 95 238
6 43 120 276
10 60 150 319
16 80 185 364
25 101 240 430
35 126 300 497
Mains
Cable/connection
GRUNDFOS 6", 8", 10" and 12" motors
L1 U
L2 V
L3 W
PE PE
T
M
00
13
64
50
92
Connection GRUNDFOS 6" motors
U1 Brown
V1 Blue
W1 Black
W2 Brown
U2 Blue
V2 Black
PE Yellow/green
L2 L3
M
L1 PE
U V W PE
3
length of drop cable
permissible voltage drop in %

q
U x

U
I x 1.73 x 100 x (cos

x + sin

x Xl)