5 Sample Calculation AC Power Equipment Minimum Distance
This is a sample calculation to determine minimum distance from a feeder, transformer, or other
AC electrical source, using the Formula found in Magnetic Field Consideration Electrical Current
subsection to determine minimum distance from a feeder, transformer, or other AC electrical
source.
I (amps) = 20X
2
(meters) ÷ S (meters)
Note that the formula has 3 variables, if you have 2 of them, you can calculate the 3rd. In this
example, we calculate the minimum distance X from the source, in this case a main electrical
feeder carrying 450 amps of current in a 5 inch conduit.
Rearranging:
where:
x
Minimum distance (in meters) from the feeder lines to isocenter of the magnet
l
Maximum allowable RMS single phase current (in amps) or maximum allowable RMS line current (in amps)
in three phase feeder lines
S
Separation (in meters) between single phase conductors or greatest separation between three phase con‐
ductors
Note that the separation “S" is the spacing between the conductors and when all 3 conductors
are run in a single conduit, “S" is simply the diameter of the conduit.
S = 5 inches = 0.127 meters
The conduit should be 1.7 meters or 5.4 feet from the magnet isocenter.
In other situations, the spacing “S" may be the spacing between HV feeders, the distance
between transformer lugs, or the spacing between conduits when the phase conductors are run
in separate conduits.
What if it is too close? Keep in mind that if this is an existing condition, you should request an
EMI study
to quantify the magnitude and direction of the AC disturbances. The calculation is
worse case and does not take into account the vector direction of the AC interference. The
magnet is only sensitive to AC disturbances that are directed horizontally (magnet z-axis). Also
the calculation does not account for any magnetic shielding effect of steel conduit.
SIGNA Voyager Pre-Installation
Direction 5680008–1EN, Revision 2
172
5 Sample Calculation AC Power Equipment Minimum
Distance
