Clinton FL-20A - Page 46

Page 38 - FL-20A Instruction Manual
Model FL-20A Cable Fault Locator
kHz and higher, it can be estimated that the threshold of
startle reaction is approximately equal to 1 mA per kHz of
frequency. For example, if a specic level of reaction from
current at 1 kHz occurs at 1 mA, then a similar level of reac-
tion would occur from 10 mA at 10 kHz. e same level
of reaction would occur from 100 mA at 100 kHz, and so
on. Leakage current measuring instruments, such as those
specied in ANSI C101-1992, take into account the eect
of high frequencies on the body. ese instruments pro-
duce readings that are “frequency-weighted,” and indicate
the level of possible physiological eect. e readings corre-
spond to the current magnitude in mA only at low frequen-
cies such as 60 Hz.
Electric current over 5 mA at 60 Hz can cause muscle
tetanization. Tetanization is dened as the state of continu-
ous contraction of a muscle undergoing a series of rapidly
repeated stimuli. A person with tetanized muscles may be
unable to let go of a conductive part, may be immobilized
(frozen), or may be unable to breathe while the current
ows. Tetanization lasts as long as the current ows. When
the current stops, the eect stops, and the muscle returns to
normal function. However, the eect can be fatal if breath-
ing stops long enough. If immersed in water, an immo-
bilized person could drown. In a manner comparable to
perception, tetanization occurs at a higher current threshold
for DC and for higher frequencies.
Ventricular brillation is a disorder involving disorga-
nized arrhythmic motion of the heart that aects blood cir-
culation. Unlike muscle tetanization, ventricular brillation
can be triggered by a short-duration burst of current of su-
cient magnitude. Ventricular brillation is not spontaneously
reversible in humans and, if not treated quickly with special
debrillating equipment, will continue until the person dies
(within a few minutes) from loss of circulation of the blood.
e magnitude of limb-to-limb current sucient to cause
ventricular brillation is greater than that which would cause
muscle tetanization. erefore, limits for continuous current
(e.g., lasting over ve seconds or so) are usually based on
muscle tetanization considerations.
Perception and
Startle Reaction Cont.
Muscle Tentanization
Ventricular Fibrillation