FAQ [Health Devices Aug-Sep 1993;22(8-9):419+]
Leakage Current Measurements Made on an Isolated
The leakage current of a device for use in
our operating room (OR) exceeds commonly accepted levels for patient care
devices when tested on a grounded system. However, when tested on the OR's
isolated power system, its leakage current is reduced to acceptable levels. Is
it safe to operate the device from the OR's isolated power system?
In a word, no—for two major reasons.
The first, and more important, reason is that a leakage current measurement made on a device operated from an isolated power system does not indicate the leakage current of the device itself; it indicates the leakage current of the device as "tempered" by the power system to which it is connected.
Consider two examples. A device with an inherently low leakage current that is connected to an isolated power system that has a high leakage current will still have an acceptable reading because of the device's ability to restrict the leakage current. Conversely, a device with an inherently high leakage current connected to a well-isolated power system with a low leakage current will also have an acceptable reading because of the system's ability to restrict the leakage current from the device. Therefore, a sufficiently low leakage-current reading indicates that the device is safe to operate on that isolated power system at that time. However, an acceptable leakage current measured on one isolated power system does not ensure that the device can be operated safely on another isolated power system that may have greater leakage current. Moreover, if you continue to operate the device on the system on which you initially tested it, the leakage current measurement may exceed the expected limit if the leakage current of the system increases without your knowledge (for example, if additional devices with high leakage currents are connected to it).
In short, testing the leakage current of a clinical device on a conventional grounded power system characterizes its worst-case performance, no matter what kind of system it is operated from. Testing a device on an isolated power system characterizes a blend of the performances of the device and the power system and therefore does not provide a reliable indication of what its performance is likely to be in the future. (Incidentally, the installed isolated power distribution system in the OR is not intended to be a substitute for a dedicated isolation transformer, which may be added to a device, or assembly of devices, to alleviate high leakage current.)
The second major concern is a legalistic one. Paragraph 7-126.96.36.199(b) of the National Fire Protection Association's (NFPA) Standard for Health Care Facilities (NFPA 99-1993) specifies that the leakage current test for devices related to patient care "shall be performed with the appropriate connection to a properly grounded ac power system" (italics added for emphasis).
The leakage current measurements on
devices normally operated on isolated power systems should be made with the
device powered from a conventional grounded power distribution system. If, for
convenience, a technician prefers to test the equipment in the room where it is
normally used and no grounded service is available in or near the space, it is
acceptable to temporarily ground one side of the isolated power system for the
purposes of the measurement. This should be accomplished with an appropriate
adapter (plugged into another outlet on the system), and the line isolation
monitor (LIM) alarm should be silenced for the comfort of those in the vicinity;
the adapter should be removed after the measurement has been taken.
Powering Lasers (or Other Devices with Special
Electrical Requirements) in the OR
In providing power for a device, such as a
laser, that requires that a special branch circuit be installed, is it permitted
to install the branch circuit from the grounded power distribution system in an
operating room (OR) where power to receptacles is provided from an isolated
Yes. As we interpret the relevant national
codes, installation of grounded power is permitted in ORs where the use of
flammable inhalation anesthetic agents has been prohibited. (However, we know
that in at least one municipality the local code was more stringent and did not
permit this relaxation.)
Where a mix of grounded and isolated power exists in the same room, codes call for outlets powered from a grounded circuit to be labeled so that users who wish to choose one outlet or the other can readily identify which is which.
Electrical Outlets in Anesthetizing
What issues affect the selection of
electrical outlets for anesthetizing locations?
Currently, no requirements call for the installation of a particular style or type of outlet in operating rooms (ORs) in which the use of flammable inhalation anesthetizing agents has been prohibited. The only restriction in the National Electrical Code
(NEC-1993) is that the outlets be listed for hospital use. This has commonly
been interpreted, in the case of parallel-blade outlets, to imply that Hospital
Grade outlets be installed.
At one time, locking-type outlets were considered appropriate, even though they might not have been required to meet the restrictions applied in flammable anesthetizing locations, to discourage both using OR equipment outside the area and bringing devices from other areas into the OR. Recently, that practice has been abandoned, in part because enhanced equipment management procedures have reduced the risks that otherwise would have occurred with moving equipment between departments.
Wherever specially configured outlets are used, adapters tend to proliferate. In general, the use of adapters should be avoided, except where absolutely necessary, because of the disadvantages associated with their use: they are one more item that needs to be followed on a preventive maintenance program, they may not be available at a time when they are critically needed, they introduce one more link in the power distribution and grounding circuit subject to failure, they are more likely to be subject to physical abuse, and they frequently can add to the strain on an outlet.
Other than the possible exception of one or two devices that may be "permanently" residing in an OR for which a designated receptacle/plug combination may be appropriate, we encourage hospitals to use one outlet type in ORs. Further, it is appropriate and desirable that the outlet be of the conventional, parallel-blade type.
What policies should we follow concerning
the use of extension cords in the hospital?
There is no across-the-board prohibition on
the use of extension cords in the hospital, although Paragraph 7-188.8.131.52(b) in
NFPA 99-1993 is widely interpreted as prohibiting the use of extension cords in
the operating room. In general, this restriction is probably justified. The cord
connector-plug junction is likely to lie on the floor and be subjected to
physical abuse and liquid spills.
A specific exception to this restriction (Exception No. 4 in the above mentioned paragraph in NFPA 99-1993) permits a cluster of receptacles fed by a single power cord to be mounted on a unit, such as a mobile cart, provided that certain provisions are adhered to. For example, the cord must be of adequate ampacity, and the assembly should be included in a periodic inspection program. We usually also advise that users be aware that a failure in one device may mean that the operation of several devices plugged into the cluster may be affected and that users judge whether this affects their decision to use the cluster. Judicious use of this approach in the OR can reduce the number of power cords lying on the floor and, therefore, reduce the tripping hazard.
The Joint Commission on Accreditation of Healthcare Organizations (JCAHO) calls for hospitals to have a policy on the use of extension cords in their institutions. We suggest the following considerations in drawing up such a policy:
- Extension cords used in a patient care area should
be made of good-quality components and be of adequate ampacity for the
- They should be tagged or otherwise identified and
incorporated in a periodic inspection program.
- They should never be placed under rugs.
- They should not be used routinely to alleviate
problems that result from a shortage of adequate outlets. Necessary steps
should be taken to add outlets to eliminate the need to use extension cords.
- They should be available in designated areas for
use during emergencies, such as during loss of power where emergency power
may be available only remotely from the bedside.
- They should not be used in public lounges, nursing
stations, etc. Device power cords should be lengthened, where necessary, to
avoid the use of extension cords.
- Electrical Safety Analyzers [11-399]
- Extension Cords, Electrical, Multioutlet [17-603]
- Isolated Power Systems [15-817]
- Lasers [12-296]
- Leakage Current Meters [12-311]
- Receptacles, Explosion-Proof [15-857]
- Receptacles, Hospital Grade [15-859]