EBME Forums Forums Maintenance Technical Assistance Continuity testing of power cables

I've searched but cannot find much useful on this one - can anyone help?

IEC62353 sets a resistance limit of 100m? For a detachable power cable up to 3 metres. Does anyone have any useful reference info for setting sensible limits for testing of longer cables?

Thanks for any help!

Hi Ryan,

Do you have any documentation that allows you to use cables longer than 3 meters?

Given that IEC 60601-1 clause 8.6.4 only permits 100 mili ohms unless the device has circuits that limit the current to maintain the required touch current limits.

So, refer to the device instructions for use to see if another value is permitted, but consider the issue of the wrong cable being used with a device that it is not intended for!

For non-medical devices EN 50699 has values for longer cables.

Hi Neil,

The short answer to that question is - no.

I've not come across any documentation that specifically permits or forbids the use of longer (than 3mtr) power supply cables on any device, IFUs/IFMs included.

I can say though that it's not uncommon for users to require leads longer than 3mtrs where I work, given the practicalities of plugging in a variety of equipment in various clinical spaces.

Hi Mike.

Thanks. Do you test using IEC 60601-1 in the field?

As I understood it, that 100 mili-ohm limit applies to earth-bond testing using a min 25A current, whereas the IEC 62353 test is at min 200mili-amps. The high current can overcome a lot of the contact-resistance at the plug and C13 connector.

In the UK sites should be following HTM 06-01 to ensure there is sufficient socket-outlets within easy reach of the medical equipment (clause 15.4). The use of extension cables should be precluded unless a full assessment following 60601-1 has been performed. There is even a separate Appendix 4 on this subject.

Field testing is done following IEC 62353, which as you mention allows a minimum of 200mA for the protective earth resistance measurement. Although 25A may overcome oxidisation it can also hide faults. Most medical electrical test equipment will meet IEC 61557-16 and therefore will use 200mA minimum, but may offer higher currents up to 25A. However, a meter such as the Rigel 288 or 62353 use a short high current pulse at the start of the test to overcome oxidisation resistance. Most manufacturers of medical equipment use the 200mA setting for field use. Using 25A accidentally on a part not intended to be protectively earthed can damage the equipment.