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Volt Drop Table

Current carrying capacities and associated voltage drops for twin and multicore P.V.C insulated cables, non- armoured (copper conductors).


BS6006 & BS6346

Conductor operating temperature 70°C

Conductor cross sectional area
Installation methods A to C† of table 9A ('enclosed')
Installation methods E to H of table 9A ('Clipped direct')
Installation method K of table 9A ('Defined conditions')
One twin cable. With or without protective conductor single phase
a/c. Or d/c.
One three-core cable, with or without protective conductor, or one four core cable phase one
One twin cable. With or without protective conductor single phase
a.c. Or d.c.
One three-core cable, with or without protective conductor, or one four core cable phase one
One twin cable. With or without protective conductor single phase
a.c. or d.c.
One three-core cable, with or without protective conductor, or one four core cable phase one
 
Current carrying capacity
Volt drop per amp per metre
Current carrying capacity
Volt drop per amp per metre
Current carrying capacity
Volt drop per amp per metre
Current carrying capacity
Volt drop per amp per metre
Current carrying capacity
Volt drop per amp per metre
Current carrying capacity
Volt drop per amp per metre
1
2
3
4
5
6
7
8
9
10
11
12
13
mm²
A
mV
A
mV
A
mV
A
mV
A
mV
A
mV
1.0
14
42
12
37
16
42
13
37
        
1.5
18
28
16
24
20
28
17
24
        
2.5
24
17
21
15
28
17
24
15
        
 
4
32
11
29
9.2
36
11
32
9.2
        
6
40
7.1
36
6.2
46
7.1
40
6.2
        
10
53
4.2
49
3.7
64
4.2
53
3.7
        
16
70
2.7
62
2.3
85
2.7
70
2.3
        
                         
25
79
1.8
70
1.6
108
1.8
90
1.6
114
1.8
95
1.6
35
98
1.3
86
1.1
132
1.3
115
1.1
139
1.3
122
1.1
50
        
163
0.92
140
0.81
172
0.92
148
0.81
 
Ac / Dc
  
Ac / Dc
  
70
        
207
0.65/0.64
176
0.57
218
0.65/0.64
186
0.57
95
        
251
0.48/0.46
215
0.42
265
0.48/0.46
227
0.42
 
120
        
290
0.40/0.36
251
0.34
306
0.40/0.36
265
0.34
150
        
330
0.32/0.25
287
0.29
348
0.32/0.25
302
0.29
185
        
380
0.29/0.23
330
0.24
400
0.29/0.23
348
0.24
240
        
450
0.25/0.18
392
0.20
474
0.25/0.18
413
0.20
300
        
520
0.23/0.14
450
0.18
548
0.23/0.14
474
0.18
400
        
600
0.22/0.11
520
0.17
632
0.22/0.11
548
0.17

† For installation Method C, the tabulated values are applicable only to the range up to and including 35mm². For larger sizes in this installation method, see ERA report 69-30. For cables in ducts in the floor of a building, the ERA ratings must be adjusted by the appropriate factor for the ambient temperature.

The current carrying capacities in columns 6 and 8 are applicable to flexible cables to BS 6004 Table 1(b) where the cables are used in fixed installations.



Correction Factors

For Ambient Temperature

Ambient temperature 25°C 35°C 40°C 45°C 50°C 55°C 60°C 65°C
Correction factor 1.06 0.94 0.87 0.79 0.71 0.61 0.50 0.35


Sample Formulae for the Volt Drop Table

FORMULA = LENGTH X VOLT DROP X AMPS = VOLT DROP OVER LENGTH
1.0 mm TWIN CABLE FORMULA = 42 MV PER AMP PER METER      
10 metres at 5 amp with 1.0mm twin =
 10 x 5 x 42 =
2100 mv
1000
 2.1 volts
20 metres at 5 amp with 1.0mm twin =
 20 x 5 x 42 =
4200 MV
1000
 4.2 volts
30 metres at 5 amp with 1.0mm twin =
 30 x 5 x 42 =
6300 MV
1000
 6.3 volts
50 metres at 5 amp with 1.0mm twin =
 50 x 5 x 42 =
10500 MV
1000
 10.5 volts
75 metres at 5 amp with 1.0mm twin =
 75 x 5 x 42 =
15750 MV
1000
 15.7 volts
100 metres at 5 amp with 1.0mm twin =
 100 x 5 x 42 =
21000 MV
1000
 21 volts
 
1.5 mm TWIN CABLE FORMULA = 28 MV PER AMP PER METER      
10 metres at 5 amp with 1.5mm twin =
 10 x 5 x 28 =
1400 MV
1000
 1.4 volts
20 metres at 5 amp with 1.5mm twin =
 20 x 5 x 28 =
2800 MV
1000
 2.8 volts
30 metres at 5 amp with 1.5mm twin =
 30 x 5 x 28 =
4200 MV
1000
 4.2 volts
50 metres at 5 amp with 1.5mm twin =
 50 x 5 x 28 =
7000 MV
1000
 7.0 volts
75 metres at 5 amp with 1.5mm twin =
 75 x 5 x 28 =
10500 MV
1000
 10.5 volts
100 metres at 5 amp with 1.5mm twin =
 100 x 5 x 28 =
14000 MV
1000
 14.0 volts
 
2.5 mm TWIN CABLE FORMULA + 18mv PER AMP PER METER      
10 metres at 5 amp with 2.5mm twin =
 10 x 5 x 17 =
850 MV
1000
 0.85 volts
20 metres at 5 amp with 2.5mm twin =
 20 x 5 x 17 =
1700 MV
1000
 1.7 volts
30 metres at 5 amp with 2.5mm twin =
 30 x 5 x 17 =
2500 MV
1000
 2.5 volts
50 metres at 5 amp with 2.5mm twin =
 50 x 5 x 17 =
4250 MV
1000
 4.2 volts
75 metres at 5 amp with 2.5mm twin =
 75 x 5 x 17 =
6375 MV
1000
 6.3 volts
100 metres at 5 amp with 2.5mm twin =
 100 x 5 x 17 =
8500 MV
1000
 8.5 volts
 

MINIATURE CIRCUIT BREAKERS FOR USE IN CONJUNCTION WITH MOTOR STARTERS AND TRANSFORMERS

 
Table 2-1 phase 240V AC DOL starting
Motor starters
In general miniature circuit breakers can give only short circuit protection to motor loads due to high starting currents which may be encountered: typically 3 to 12 times full load current (FLC)

Assumptions
The tables give recommended mcb ratings for motors up to 37kW based on the following assumptions:

Direct on-line starting
starting current = 7 x FLC
run up time =
6 seconds, motors < 3 kW
10 seconds, motors < 22 kW
running currents = average values only
(individual manufacturers figures may vary)
four pole motors i.e. speed approx.
1500 rev/min.

For Higher inertia loads i.e. hoists and fans run up times maybe considerably longer than those assumed above. The rating of the mcb must take account of the greater run-up time and starting current. The required mcb rating can be determined by reference to time/current curves (consult us)

Star/ delta starting
Since, during the changeover from star to delta, a high current surge in the order of DOL values may be met, the mcb rating selected should be the same as that
recommended for DOL starting
KW
Hp
Running
C60H
C60HC
C60HD
NC100C
NC100D
0.12
0.166
0.55
2
1
1
    
0.18
0.25
0.7
2
1
1
    
0.25
0.33
0.87
2
2
1
    
0.37
0.5
1.35
4
2
2
    
0.55
0.75
1.55
4
2
2
    
0.75
1
1.93
6
4
2
    
1.1
1.5
2.5
6
4
4
    
1.5
2
3.5
10
5
6
    
2.2
3
4.8
16
10
10
10
10
3
4
6.4
16
16
10
16
10
3.75
5
7.8
20
20
16
20
16
4
5.5
8.1
25
20
16
20
16
5.5
7.5
11
25
25
16
25
16
7.5
10
14.4
32
25
20
25
20
9.33
12.5
17.3
40
32
20
32
20
11
15
21
50
40
25
40
25
13
17.5
25
63
50
32
50
32
15
20
28
63
50
40
50
40
18.5
25
35
  
63
50
63
50
22
30
40
  
63
50
63
50
30
40
54
    
63
80
63
37
50
65.5
      
100
80
Table 2-1 phase 240V AC DOL starting
KW
Hp
Running
C60H
C60HC
C60HD
NC100C
NC100D
0.12
0.166
0.95
2
2
1
    
0.18
0.25
1.5
4
2
2
    
0.25
0.33
1.7
6
2
2
    
0.37
0.5
3
10
6
4
    
0.55
0.75
4.5
16
10
6
10
  
0.75
1
5.5
16
16
10
16
10
1.1
1.5
8.5
20
20
16
20
16
1.5
2
10.5
25
25
20
25
20
2.2
3
15.5
32
32
25
32
25
3
4
20
40
40
32
40
32
3.75
5
24
50
50
40
50
40
5.5
7.5
34
63
63
50
63
50
6.3
8.5
36.5
  
63
63
63
63
7.5
10
45
    
63
80
63
11
15
66.5
      
100
80

 
VA
Primary
in (A)
C60H
C60HC
C60HD
NC100C
NC100D
Transformers
High inrush currents are also produced when transformers are switched on. Typically 10-15 times full load current.

Assumptions
The tables give recommended mcb ratings for single phase transformers up to 12500 VA and three phase transformers up to 30000 VA on the following formula.

Mcb rating
15 x normal current of transformer
min instantaneous tripping
cc efficient of mcb
500
0.7
4
2
1
    
750
1.04
6
4
2
    
1000
1.39
6
4
2
    
2000
2.78
10
10
6
10
  
5000
6.95
32
16
10
16
10
10000
13.89
50
32
20
32
20
15000
20.84
  
50
32
50
32
20000
27.78
  
53
40
63
40
25000
34.73
    
50
80
50
30000
41.67
    
63
80
63
Table 4 - 1 phase transformers 240V AC supply
VA
Primary
in (A)
C60H
C60HC
C60HD
NC100C
NC100D
50
0.21
1
        
100
0.42
2
1
1
    
250
1.04
6
4
2
    
500
2.08
10
6
4
    
1000
4.17
20
10
10
10
10
2500
10.42
40
25
16
25
16
5000
20.84
  
50
32
50
32
10000
41.67
    
63
80
63

Ohms Law

IF YOU KNOW NEED TO KNOW
 
VOLTS ÷ RESISTANCE = AMPS
VOLTS ÷ AMPS = RESISTANCE
VOLTS x AMPS = WATTS
WATTS ÷ AMPS = VOLTS
WATTS ÷ VOLTS = AMPS
AMPS x RESISTANCE = VOLTS

CABLE LENGTH
RESISTANCE
x
CURRENT
DRAWN
=
VOLT DROP
------------------
-----------
Ohms
AMPS OR M/AMPS
 

Copyright ©2010 KT Assemblies Ltd. E&OE - accuracy is maintained where possible but weights and descriptions on this site are intended for guidance only.