By Kevin Cheong, P.Eng.
HEALTH CARE: Electricity and ClinicsEngineering
Electrical systems for hospitals are subject to a number of requirements that are more stringent than those for other buildings. One reason is that there is a much greater likelihood that people will ...
Electrical systems for hospitals are subject to a number of requirements that are more stringent than those for other buildings. One reason is that there is a much greater likelihood that people will be incapable of taking care of themselves if they are very feeble, sedated, unconscious, or mentally ill. There is also a greater likelihood that their skin continuity is compromised. Our skin provides our most basic electrical insulation from shock hazards. The special criteria are primarily for emergency power and the prevention of electrical shocks.
A change is impending in the way medical clinics and possibly even doctors’ and dentists’ offices are constructed with respect to their electrical systems. The Canadian Standards Association has begun to recognize that many procedures traditionally associated with hospitals are being performed in clinics. Standard CSA Z32-99 should be applied to these types of facilities once the 2002 Canadian Electrical Code comes into effect. While the new electrical code has been out for a while, it is not yet enforced.
There is normally a lag between when a new standard or code is published and when it comes into effect. The idea is to allow people to get a copy, familiarize themselves with it, and if necessary make amendments. In the case of somewhat obscure standards that are only enforced because they are referenced by the building or other codes, the lag can be years. The updates to less frequently used standards often are not picked up until the next version of the code comes out.
In the case of CSA Z32-99, the standard has been out for years; hence the ’99 nomenclature. The predecessor codes Z32.2 and Z32.4, weren’t drastically different.
What has changed is that the referring Canadian Electrical Code requirements will be applied to areas outside hospitals. Section 24 has been changed from “hospitals” to “health care facilities.” Medical clinics are specifically listed in the notes. A health care facility is defined as “. . . a set of physical infrastructure elements that are intended to support the delivery of specific health-related services.” This vague definition makes it unclear if a particular location should be considered a “health care facility” or not. CSA Z32 is a standard (guideline) rather than a code (mandatory).
What’s critical about having to apply the Z32 standard in the new types of medical facilities is that it includes test procedures that the requirements are met. For example, CEC rule 8-102 (1) (c) requires that the voltage drop for a branch circuit not exceed 3% for all installations, not just hospitals. The difference is that the voltage drop is put to the test in a hospital, whereas it is not for a normal building.
The voltage drop at the receptacle is tested with an 80% load applied. If you were to test a typical home or office plug, it would more than likely fail. The intent of the criterion is to ensure medical equipment has as stable a source of power as possible. In practice this involves using larger wiring than the minimum allowed. In some long runs we have seen wiring three sizes larger. At a minimum the Electrical Code requires that the wire be at least one size larger than normal (#12 AWG vs. #14 AWG, CEC 24-102(2)).
Another test is applied to ensure that there is very little difference in voltage between the ground pins of the various receptacles and other exposed conductive surfaces that could provide a path to ground. If a significant difference in potential existed between two grounded surfaces, a current could be created in a person touching two surfaces. While it takes tens of volts to break even wet skin, it takes considerably less to break compromised skin. The childhood experiment of licking a nine-volt battery can demonstrate how little voltage is required. It is also important to remember that it only takes about 10 milliamps to make it impossible to let go, and about 100 milliamps to kill because this is all that is required to disrupt the sinus rhythm of the heart (assuming the current passes through the heart). This is why Class A ground fault breakers and receptacles trigger at six milliamps.
In order to comply with the voltage difference criterion, the standard requires an increase in the size of the bond wires and the number of things that are solidly bonded (bonding is the term used for the interconnection of pieces of equipment that should not be energized to ground). In fact, the Electrical Code requires that the bond be insulated (or otherwise isolated), and as large as the phase conductors. Neither of these conditions can be met by normal wiring.
The term “patient outlets” as referred to in the standard does not necessarily mean all the outlets in a room because the intent is to provide the special treatment only for outlets that could serve a piece of medical equipment that is connected to a patient. The standard specifically allows that “housekeeping” outlets will be exempt from the requirements, but these are required to be clearly identified. The term “patient outlet” may, however, be required for the wiring in dentists’ or doctors’ offices.
Whether a particular local authority feels that the various patient outlet requirements need to be applied will likely depend on the conductivity between the drill or other device touching a patient and the power source, or on how reduced the patient’s resistance to a shock is, or on how capable of response the patient will be.
The last significant test is for pin retention, where the force required to pull a standard plug, albeit from each pin individually, is measured. The Electrical Code requires the use of “hospital grade” receptacles, which are of a significantly higher quality than standard “commercial grade” receptacles. Hospital grade receptacles are also considerably more expensive.
While it could be argued that Z32 is only a standard and therefore can be applied with some discretion, most of the above requirements, other than testing, are in the Electrical Code. Therefore all the testing in the standard does is confirm that you have met the requirements in the code. Omitting the testing on the basis that it is not in the code is similar to not reading the code on the basis that it might have a requirement you have not met. Ignorance provides a very poor defence for negligent work. On the bright side, typically the testing accounts for only a small amount of the additional cost of outfitting a space to meet the patient care area requirements.
Having worked to these requirements and this standard for years designing electrical systems for hospitals, I think it will be very interesting to see how they will be applied to the other areas. I have seen wide variations in how codes and standards are enforced in geographically close areas. Trying to take a stringent standard such as Z32-99, or even just section 24 of the CEC (Patient Care Areas), and suddenly to apply it to every dental or medical office or clinic will be a challenge for all.
Kevin Cheong, P.Eng. is an electrical engineer with Robert Freundlich Associates of Vancouver.