400 V and 230 V refer to the same lines - 400 V is the designation when it is three phase, 230 V when it is single phase. These voltages used to be 415 V and 240 V but were reduced to harmonise with Europe.
400 V lines are mostly carried on wood poles with four (or sometimes five) wires in a vertical array. At 400 V, the magnetic field depends as much on the net current as on the load current.
The maximum field shown here is produced when the ground clearance is the minimum allowed – 5.5 m. The maximum loads assumed are 200 A load current and 10 A net current but higher values might exceptionally be found.
Typical fields are lower than the maximum field because the clearance is usually higher and the loads are usually lower. This graph is for 8 m clearance, load current 50 A and net current 5 A.
Sometimes, the separate conductors are insulated and twisted together, called “aerial bundled conductors” (abc). Then the fields are even lower. The load currents make no contribution to the magnetic field, which now comes solely from the net current:
Please note the fields depend on the current that is assumed. That is, of course, true for all power lines, but is particularly important for 400 V lines, where the currents can vary greatly.
| 400 V open wire: |
400 V abc: |
 |
 |
This table gives some actual field values for the same conditions.
| |
magnetic field in µT at distance from centreline |
| maximum under line
| 10 m
| 25 m
| 50 m
| 100 m |
| 400 V |
wood pole |
vertical array 50 mm2 |
maximum |
clearance 5.5 m
single circuit
load 0.2 kA
net 0.01 kA@90° |
1.227 |
0.277 |
0.088 |
0.041 |
0.020
|
| typical |
clearance 8 m
single circuit
load 0.05 kA
net 0.005 kA@90° |
0.215 |
0.099 |
0.041 |
0.020 |
0.010 |
| abc |
typical |
clearance 8 m
single circuit
net 0.005 kA |
0.143 |
0.082 |
0.039 |
0.020 |
0.010 |
Note:
1. All fields calculated at 1 m above ground level.
2. All fields are given to the same resolution for simplicity of presentation (1 nT = 0.001 µT) but are not accurate to better than a few percent.
3. Supplies to single houses could be carried on different arrangements of conductors which could produce different fields.
