Product Manual

Cables
SQ, SQE, CU 331, and SP
21
142
21. Cables
Cables for Grundfos 4" submersible motors are
available with or without plugs. The submersible drop
cable is chosen according to application and type of
installation.
Standard version: Max. liquid temperature 140 °F (60
°C).
Hot water version: Max. liquid temperature 158 °F (70
°C), for short periods up to 194 °F (90 °C) (for MS
only).
Tables indicating cable dimension in borehole
The tables indicate the maximum length of drop cables
in meters from motor starter to pump at direct-on-line
starting at different cable dimensions.
If star/delta starting is used the current will be reduced
by (I x 0.58), meaning that the cable length may be
longer (L x 1.73) than indicated in the tables.
If for example the operating current is 10 % lower than
the full-load current, the cable may be 10 % longer
than indicated in the tables.
The calculation of the cable length is based on a
maximum voltage drop of 1 % to 3 % of the rated
voltage and a water temperature of maximum 86 °F (30
°C).
In order to minimize operating losses the cable cross
section may be increased compared to what is
indicated in the tables. This is economical only if the
borehole provides the necessary space, and if the
operational time of the pump is long, especially if the
operating voltage is below the rated voltage.
The table values are calculated on the basis of the
formula:
Max. cable length of a single-phase submersible
pump:
Max. cable length of a three-phase submersible pump:
where
U = Rated voltage [V]
ΔU = Voltage drop [%]
I = Rated current of the motor [A]
q = Cross-section of submersible drop cable [in
2
]
X
L
= Inductive resistance: 0.024 x 10
-3
[Ω/ft]
cos φ = Power factor
sin φ =
ρ = Specific resistance: 9.5 X 10
-6
[Ω in
2
/ft]
Example
L = 370 ft
Cable dimensions at 1 x 220 V, 60 Hz
Maximum cable length in feet from motor starter to pump.
3
3
Motor size: 40 Hp, MMS 8000
Rated current: 64.0 A
Rated voltage: 3 x 460 V, 60 Hz
Starting method: Direct-on-line
Power factor: cos φ = 0.85
Voltage drop: 3 %
Cross-section: 0.025 in
2
sin φ:0.53
Motor Hp I
n
[A]
0.002
in
2
0.004
in
2
0.006
in
2
0.009
in
2
0.016
in
2
4"
0.33 3.3 315 522 833 1243 2047
0.50 4.4 239 397 630 938 1548
0.75 6.6 157 262 417 620 1020
1.00 7.7 121 203 321 482 797
1.50 9.0 98 164 259 387 643
L
U U
I2 100 cos

q
---
sin X
L
+



-----------------------------------------------------------------------------------------------
ft=
L
U U
I 1.73 100cos

q
---
sin X
L
+



------------------------------------------------------------------------------------------------------- -
ft=
1 cos
2
–
L
460 3
64.0 1.73 100 0.85
0.0000095
0.025
------------------------------
 0.53 0.024 10
-3
+



------------------------------------------------------------------------------------------------------------------------------------------------------------------- -
=