Medical power connections

Changing regulations are placing new requirements and demands on designers of hospital-grade devices

BY RALPH BRIGHT
Interpower
Oskaloosa, IA
http://www.interpower.com

For obvious reasons, selecting power-based products such as power strips, sockets, and power-entry modules for use in medical applications is serious business. New technologies and ever-changing requirements demand that medical equipment meet special requirements.

Power strips

New regulations for manufacturing medical power strips have led to a great need for further technological development to meet rigorous safety standards. Specifying power strips for medical applications that will meet agency requirements for direct patient contact applications can create a difficult challenge.

This is especially true for engineers and specifiers, who must meet additional stringent requirements with the purpose of ensuring the protection of patients during the use of equipment in their facilities and in the field. Currently, specifying power strips to be used in conjunction with equipment for direct patient contact applications can be especially difficult.

New guidelines

A few years ago, Underwriters Laboratories (UL) contacted medical power-strip manufacturers, outlining a new stance regarding power-strip approval for medical use. Essentially, UL mandated that medical power strips approved under standards UL 544 or UL 2601-1 were no longer eligible to carry the UL mark of endorsement. Furthermore, power strips approved under UL 1363 or UL 1449 could not be referenced as appropriate for medical applications, even if they were using medical-grade sockets.

UL felt that power strips using these approvals and references for medical use were misleading the public, suggesting that these items were actually medically approved and acceptable for use under the UL medical guidelines. At the time, this left the market empty of truly medically approved power strips and left some medical equipment manufacturers with the problem of finding alternatives that would meet the new requirements.

Key elements to consider when specifying or identifying a power strip with medical approval under the new UL guidelines are:

Compliance with one or more of the following safety standards:

-UL 60601-1

-IEC 60601-1-1

-EN 60601-1

-CAN/CSA C22.2 No.601-1-M90

-CAN/CSA C22.2 No.601.1S1-94

-CAN/CSA C22.2 No.601.1B-98

Products or literature displaying the medical approval symbol.

On NEMA strips, outlet covers that can only be opened with the use of tools—for patient safety—as required by UL in order to prevent the inadvertent connection of equipment with standard mains plugs by unqualified personnel.

Verification that leakage current and other critical specifications meet both the medical standards and your requirements—if there are no leakage-to-current specifications, strips may not be approved for medical use.

Uses and installation

Medical strips are approved for use as a component in medical rack systems, carts, dental chairs and equipment, laboratories, computer systems, rack-mount cabinets, and more. Installation may be fixed or portable and the system may be easily moved from one place to another while connected to the supply.

Regulated solutions

Some strips feature a safety connector lock on the inlet for a secure and reliable power connection. Locking the cord to the inlet prevents accidental power loss to critical equipment.

This locking interconnection system is essential for customers to ensure patient safety. Such units also have a guard attached to the circuit breaker to prevent accidental tripping of the switch.

Some power strips are approved by UL for medical use in both the US and Canada and carry the medical approval symbol on their labels. Medical power strip specifications should also include typical leakage current values, for which UL has set a limit of 500 mA.

Cords and cordsets

Cords used with North American medical equipment must be hospital-grade. What makes the cord hospital grade? The plug.

Commonly known as hospital-grade plugs, they are subject to special requirements contained in the following standards:

Medical equipment: UL 60601-1 and CAN/CSA C22.2 no 60601-1

Power supply cords: UL 817 and CAN/CSA C22.2 no 21

Attachment plugs: UL 498 and CAN/CSA C22.2 no 42.

The hospital-grade plug pattern conforms to the NEMA 5-15 standard. However, there are differences:

The blades are usually solid instead of folded brass

The blades are normally nickel-plate.

The plug includes a cable retention device or strain relief to prevent any stress to the plug’s internal connections. It is imperative that the ground connection be reliably maintained to protect the patient and medical staff. Although many hospitals prefer that the plug be clear so that internal connections can be inspected visually, the UL and CSA standards do not mandate clear plugs nor do they provide any restrictions on color. Gray is another common color for hospital-grade plugs and cords.

Approvals

Hospital-grade power cords and cordsets should carry the “green dot” to signify they have been designed and tested for grounding reliability, assembly integrity, strength, and durability. They should comply with UL 817 and CAN/CSA C22.2 no 21 as hospital-grade power cords and cordsets.

Specifically, UL 60601-1 Sections 57.2 and 57.3 require that “patient care equipment” used in the “patient vicinity” must use hospital-grade attachment plugs. “Patient care equipment” and “patient vicinity” are defined in UL 2601-1 sections 2.12.100 and 2.12.101.

Section 6.5 of UL 60601-1 also requires that non-detachable power-supply cords—those without the common IEC 60320 C13 connector—must use flexible cable where the conductor insulation meets IEC 60227, (for example, brown, blue, and green/yellow color coding). There are no specific maximum lengths for cords noted in the standards listed above, yet the equipment must pass the leakage current test requirements set forth in UL 60601-1 and CAN/CSA C22.2 no 60601-1. Cord length has an effect on leakage current within a system.

Low-leakage current

Leakage current flowing between line and ground in electrical equipment can, under certain circumstances, present a lethal shock hazard to users. The shock hazard is usually a function of the amount of leakage current, accessibility of a “hot” surface to the user, and whether or not the user is well grounded.

In patient-connected medical equipment, the susceptibility of the patient to serious injury or death is increased. This is due to the low-impedance path between the patient and equipment, and the high probability that the patient will complete the fault circuit.

Low-leakage currents require special constructions in some components. The use of a low-leakage filter in the 5–µA range at 250 Vac is desirable. In addition, fusing of both line and neutral connectors may be required (for example, double fusing).

International requirements

Medical equipment used in Australia must meet AS/NZS 3200. There are no special requirements for plugs, only preferences. All Australian plugs must be approved to AS/NZS 3112. In Australian medical applications, it is preferred by hospitals to have a clear, transparent plug and orange, flexible cable. These plugs and connectors must carry one of the many Australian approvals.

Danish hospital-grade plugs and sockets are recommended to accommodate medical applications and specifications added to the SB 107-2-D1 standard, which was published at the end of 2003. These sockets should be designed to prevent normal equipment from being connected and disrupting the mains circuit in specific medical settings.

International markets, including European medical equipment used in these markets, typically must meet EN/IEC 60601-1. At this time, there are no special performance or construction requirements for plugs and sockets used in these applications. ■

Medical Power Connections

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