WHITE PAPER
Safety Considerations with Overcurrent
Protection Provided in Medical Grade Power
Strips Used in Patient Care Areas
Written by: James W. Forte, P.E.
Overcurrent protection is an important safety feature of Medical Grade Power Strips.
It is provided to protect the circuit from overloads as well as short circuits, disconnecting the power strip should any of these events occur. This reduces the risk of fire,
electric shock, or injury to persons.
The Standard for Medical Electrical Equipment,
UL60601-1, is used to evaluate Medical Grade
Power Strips. This Standard is based on the
European Standard, EN60601-1. This European
Standard requires circuit breakers in both the line
and the neutral of a Medical Grade Power Strip
because the attachment plugs used in Europe
are not polarized. In other words, when you plug
in a European Medical Grade Power Strip, you
do not know which “leg” will be connected to the
line conductor and which will be connected to the
neutral conductor. When the US Standard was adopted, the European circuit breaker requirement
was adopted as well.
However, in North America, we use a polarized
plug. We always know which “leg” is connected to
the line (ungrounded) conductor and which is connected to the neutral (grounded) conductor. Since
our grounded neutral is at zero volts, the neutral
is not a shock hazard.
There are currently Medical Grade Power Strips
on the market here in North America that
use individual circuit breakers in both the line
(ungrounded) and neutral (grounded) conductors.
An example of what this looks like is shown in
Figure 1.
FIGURE 1
Circuit Breakers
These individual circuit breakers operate completely independent of one another. During an
overload or short circuit, these independent
circuit breakers are going to be in a race to see
which will trip first. As such, there is a 50%
chance that the circuit breaker in the neutral
(grounded) conductor will operate first. Any equipment connected to the power strip will appear to
be in an unpowered state, but the live parts inside
the equipment will still be energized. If a person
were to go inside the equipment in an attempt
to make repairs, they could receive an electric
shock. Legrand Medical Grade Power Strips use
a single pole circuit breaker in the line conductor.
Due to the polarized plug, our circuit breaker will
always disconnect the line conductor only and will
not create a shock hazard.
It is true that Medical Grade Power Strips with
individual circuit breakers in both the line and
neutral comply with existing safety standards.
However, individual circuit breakers are not allowed by the National Electrical Code (NFPA70)
due to the increase in risk of electric shock that
it creates. NFPA70, Section 240.22 states that no
overcurrent device shall be connected to a neutral
conductor unless the overcurrent device disconnects all conductors of the circuit, including the
neutral, and is designed so that no pole can operate independently.
Legrand Medical Grade Power Strips, being designed for the North American market, use a single circuit breaker in the line conductor only. They
comply with UL60601-1 with the single circuit
breaker because we provide the following warning in the installation instructions: “This product
incorporates over current releasing only in the ungrounded phase conductor. This product must not
be used in countries other than the United States
and Canada.” They also comply with National
Electrical Code Section 240.22 and therefore do
not increase the risk of electric shock.
Protect your patients and staff by
ensuring that your Medical Grade
Power Strips comply with National
Electrical Code Section 240.22.
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