Patients rely on medical practitioners to keep them safe, including using medical devices and equipment that can be operated without worries over hazards. Leakage current can cause unintended consequences for medical devices, patients, and caregivers, and in the worst-case scenario, it can cause injuries or even be fatal. Understanding leakage current and your requirements as a medical device manufacturer will keep you compliant and end users safe. Here’s everything you need to know about leakage current and what might apply to your medical device and power supplies.
What is leakage current?
Leakage current is an electrical current that isn’t flowing along an intended circuit. Instead, it’s moving along an unwanted path or is flowing when the power should be off. Any device or system using electricity may have leakage current. Medical devices with leakage current can waste energy via “vampire power” or cause circuit breakers to trip. Leakage current can cause overvoltage, radio frequency (RF) noise, electrical shock, or fire. The current, when it’s leaking, will flow to the easiest path to the ground. In some cases, this can be a human body.
What causes leakage current?
An unintended current is frustrating at best and dangerous at worst, so we need to understand the cause of the leakage current to try and correct it.
Leakage current in electronics can be caused by having too high a voltage, insufficient grounding or insulation, undesired capacitor-discharge, an unwanted flow across a transistor, or environmental conditions, like temperature.
What are the types of leakage current in medical equipment?
Medical devices have three types of leakage current: Earth, touch, and patient.
Earth leakage current takes the path of least resistance and heads toward the ground. It is also known as earth line leakage or earth leakage.
Touch leakage current is when the current flows through a body if someone touches the outside of a device. This happens when the device isn’t properly grounded. Touch leakage current is also known as enclosure or chassis leakage.
Patient leakage current is when a current flows from a patient-connected device (like the electrodes from an EKG) to the ground.
What are the types of leakage current in power supplies?
The most common path of an unwanted current in power supplies moves from the Y-class electromagnetic interference (EMI) capacitors to the ground. In medical device standards, leakage current and EMI levels are regulated as part of a balancing act – they both need to be mitigated to a proper degree and need to be considered in tandem.
Y class safety capacitors, also known as Y capacitors, are used to suppress the EMI that is created by a power supply. They are placed on the primary side of the power supply, between the AC line and the ground.
Electrical noise is also called electromagnetic interference (EMI). When switching currents and voltages, EMI is an unwanted byproduct. EMI is unavoidable in a switching power supply and can interfere with electrical signals, causing problems with other devices. Y capacitors work to filter EMI.
Any electrical device run by AC power could have leakage current, including a PC-based power supply unit (PSU). However, the most common path is from these Y-class EMI filter capacitors to the ground.
How much leakage current is acceptable?
The amount of acceptable leakage current depends on the location of use, medical device classification, contact with patients, type of leakage current, and test conditions.
Location of use
Depending on where you are seeking regulation for your medical device, different standards for leakage current may apply. For example, one of the most widely used standards is IEC 60601-1 for medical electrical equipment, which is recognized in the United States, the EU, and Canada, and has harmonized standards in other countries as well. This standard includes strict limits on leakage current allowed in medical electrical equipment.
Medical device classification
Different medical device classifications come with different requirements. For example, PC-based power supplies under 60601-1 standards are categorized as a component of a movable or stationary device. Class I devices need to have both sufficient insulation and a protective earth grounding to guard against electrical shock to meet regulatory standards.
Contact with patients
The end application determines what the maximum leakage current can be on a medical device. Is the device connected to a patient or not using an applied part? If so, how is the applied part connected?
An applied part is defined as a part of the medical electrical equipment that needs to come into contact with a patient. There are three different applied part types: B, BF, and CF.
Type B (body) applied parts operate in the vicinity of the patient but don’t make direct electrical contact (X-ray machines). Type BF (body floating) parts make direct contact (ultrasound). Type CF (cardiac floating) makes contact with the heart (defibrillators).
When it comes to power supplies, they should never be in direct contact with a patient. However, they might be connected to accessories that are in direct contact. Any accessories that are connected to devices that connect to patients fall under the same leakage current safety standards as the medical equipment itself.
Type of leakage current
Power supplies may have earth leakage current or touch leakage current.
Test conditions
Specified testing methods determine allowable leakage current limits under certain conditions. The two most common test conditions are normal condition (NC) and single-fault condition (SFC). Normal conditions exist when all the means that protect against hazards are intact. In a single-fault condition, it means that there is one means that works to reduce risks that are either abnormal or defective.
Why is mitigating leakage current important?
Both patients and caregivers are vulnerable to leakage currents, but mitigation measures are especially important for patients. Caregivers can usually move quickly away from the source of shock, but patients may be more prone and vulnerable to harm from leakage current due to being under anesthesia or being immobile.
Is a commercial or medical power supply better for leakage current?
See our blog on leakage current requirements for a chart breaking down standards for medical and commercial power supplies. One of the most important things to note is that power supply standards that aren’t medical-grade allow for seven times as much leakage current in single-fault conditions compared to medical-grade power supplies.
Each type of leakage current that may occur with a medical device – earth, touch, and patient – needs to follow rigorous means of protection (MOP) standards. For some standards, the “patient vicinity” can be as far as six feet away from the patient.
When designing and using medical devices, using medical-grade power supplies is crucial. RAM Technologies offers compliant PC-based power supplies that can help you maintain compliance and mitigate risks from leakage current. Start the conversation with us today.
More Resources:
Custom Power Supply Cables for Medical Devices
Different Power Supply Sizes and Why They Matter
We Answer Your Power Supply Questions
