Section I. AVOIDING ELECTRICAL HAZARDS
Electrical shocks do not just happen--they are caused. Generally, they are the
result of carelessness or ignorance. The radiology specialist operates elaborate
electronic equipment. The maintenance of this equipment is not his responsibility.
However, he must understand the basic principles of electrical protection so he can
recognize potential hazards and take actions to have them eliminated before an
accident does occur.
FUSES--MACHINE PROTECTION ONLY
Fuses and circuit breakers are protective devices that open the circuit when
current flow becomes excessive. However, a fuse does not offer any protection for the
x-ray specialist or the patient. It protects only the equipment. This point must be
remembered so you will not have a false sense of security when you work around fused
electrical circuits. The circuit shown in figure 4-1 has a 15-ampere fuse. If the currents
through resistors 1, 2, and 3 are added, they total 14.5 amperes. This is close to the
maximum current carrying ability of the 15-ampere fuse. Figure 4-2 shows the same
circuit with an additional parallel branch--a human body. Let us assume that the
electrical resistance of the body is 11,000 ohms. The current through the body as
determined by Ohm's law is
I = E or
equals 0.01 amperes.
Therefore, connecting the human body has increased the total current through the fuse
from 14.5 to 14.51 amperes. Obviously, not enough to burn out the fuse and open the
current--but enough to kill.
a. Fuse Ratings. The rating of a fuse for a particular circuit is based on the
amount of current that the circuit is designed to carry under normal operating conditions.
If a fuse burns out, it should be replaced with a fuse of the same rating. Under no
conditions should the fuse be replaced with one that has a higher rating. Furthermore, if
the replaced fuse burns out again, turn off the equipment and initiate actions to have the
equipment repaired. The same holds if a circuit breaker repeatedly opens the circuit.
b. Fuse Overloads. Electrical fires are frequently caused by circuit overloads.
For instance, if someone replaces a 15-ampere fuse with one rated at 30 amperes, the
current in the circuit would have to double before the fuse would burn out. Besides
damaging the equipment, the increased current could generate enough heat to cause a