Lightning Protection; Cable Sizing - Grundfos SP Serie Montage- Und Betriebsanleitung

5.2.3 Required motor starter settings
For cold motors, the tripping time for the motor starter must be
less than 10 seconds at 5 times the rated maximum current of the
motor.
If this requirement is not met, the motor warranty
Caution
will be invalidated.
In order to ensure the optimum protection of the submersible
motor, the starter overload unit should be set in accordance with
the following guidelines:
1. Set the starter overload to the rated maximum current of the
motor.
2. Start the pump and let it run for half an hour at normal
performance.
3. Slowly grade down the scale indicator until the motor trip point
is reached.
4. Increase the overload setting by 5 %.
The highest permissible setting is the rated maximum current of
the motor.
For motors wound for star-delta starting, the starter overload unit
should be set as above, but the maximum setting should be as
follows:
Starter overload setting = Rated maximum current x 0.58.
The highest permissible start-up time for star-delta starting or
autotransformer starting is 2 seconds.

5.3 Lightning protection

The installation can be fitted with a special overvoltage protective
device to protect the motor from voltage surges in the electricity
supply lines when lightning strikes somewhere in the area, see
fig. 10.
L1
L2
L3
PE
825045
Three-phase
Fig. 10 Fitting an overvoltage protective device
The overvoltage protective device will not, however, protect the
motor against a direct stroke of lightning.
The overvoltage protective device should be connected to the
installation as close as possible to the motor and always in
accordance with local regulations.
Ask Grundfos for lightning protective devices.
Submersible motors, type MS 402, however, require no further
lightning protection as they are highly insulated.
Ask for a special cable termination kit with a built-in overvoltage
protective device for Grundfos 4" submersible motors (part no.
799911 / 799912).

5.4 Cable sizing

Make sure that the submersible drop cable can withstand
permanent submersion in the actual liquid and at the actual
temperature.
Grundfos can supply submersible drop cables for a wide range of
installations.
The cross-section (q) of the cable should meet the following
requirements:
1. The submersible drop cable should be sized 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.
L
N
PE
825017
Single-phase
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
2
q [mm ] I [A]
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-
section should be selected on the basis of the current values of
the actual cables.
Re 2:
The cross-section of the submersible drop cable
must be large enough to meet the voltage quality
Note
requirements specified in 5.1 General.
Determine the voltage drop for the cross-section of the
submersible drop cable by means of the diagrams on pages
157 and 158, 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 formulas:
Single-phase submersible motor
× Δ
U U
L
= ------------------------------------------------------------------------------------------------- -
ρ
⎛
× × × ϕ ×
I 2 100 cos sin
q -- - +
⎝
Three-phase submersible motor
×
U
L = --------------------------------------------------------------------------------------------------------- -
⎛
× × ×
I 1.73 100 cos
⎝
where
L = Length of submersible drop cable [m]
U = Nominal voltage [V]
ΔU =
Voltage drop [%]
I = Rated maximum current of the motor [A]
cos ϕ = 0.9
ρ =
Specific resistance: 0.02 [Ωmm
q = Cross-section of submersible drop cable [mm
sin ϕ = 0.436
Xl = Inductive resistance: 0.078 x 10
).
s
2
q [mm ] I [A]
s
50 153
70 196
95 238
120 276
150 319
185 364
240 430
300 497
⎞
ϕ ×
XI
⎠
ΔU
ρ
⎞
ϕ × ϕ ×
q -- - + sin XI
⎠
2
/m]
2
]
-3
[Ω/m]
11