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As originally asked by Luke Barratt.

need HELP. I’m an ME doing some consulting for a small ophthalmic start-up. In making an accessory for a Slit Lamp functional across multiple brands we’re really struggling to understand 60601’s application.
How is it possible that one brand of Slit Lamp with a cast aluminum chassis to which the patient has contact have infinite resistance to ground, whereas the other is actually shorted to ground?

We hired a local expert on 60601 and found that we didn’t actually get straight answer on keeping our designs compliant. The project EE is doing his best with the circuity, but not able to help me know if my machined AL components should be grounded, or left isolated.

Any thoughts / help most welcome!

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Judy Findlay
Project Leader – Medical devices
Hi Luke,

You may already have your answers, or have found someone to help, but I just thought I would clarify something you asked about earlier. The IEC 60601-1 classification (Class I and Class II) relate to grounding (see definition below), and is completely unrelated to the FDA regulatory Classifications I, II and III, which relate to risk, and which determine the regulatory process with FDA.

Also, make sure you use the 3rd edition of IEC 60601-1. There are a number of requirements (in addition to the electrical shock shock) that should be considered early in the design process.

3.13
CLASS I
term referring to electrical equipment in which protection against electric shock does not rely on BASIC INSULATION only, but which includes an additional safety precaution in that means are provided for ACCESSIBLE PARTS of metal or internal parts of metal to be PROTECTIVELY EARTHED
NOTE See Figure 3.
3.14
CLASS II term referring to electrical equipment in which protection against electric shock does not rely on BASIC INSULATION only, but in which additional safety precautions such as DOUBLE INSULATION or REINFORCED INSULATION are provided, there being no provision for protective earthing or reliance upon installation conditions
NOTE 1 See Figure 4.

All the best.
Cheers,
Judy

Yuri Sokolov, MSc, PhD, MBA
Entrepreneur, Investor, Business Advisor
Luke, as a part of product validation, your device will have to undergo regulatory testing at a Testing Lab – like UL and Intertek. Electrical safety may not be the only requirement applicable to your device, there may be other requirements, e.g. EMC, material toxicity and/or flammability, labels, marks.

If you want to sell in jurisdictions beyond the US, then there may be variations of requirements and marks, such as CE-Mark. All requirements should be defined at an early stage of development to avoid any surprises at the testing stage. Such surprises may be quite costly.

In my experience, the best course of action is to consult the Lab where you plan to have your device tested.

The process of interaction with UL is outlined at:
[http://www.ul.com/global/eng/pages/offerings/perspectives/manufacturer/prepareforulevaluation/|leo://plh/http%3A*3*3www%2Eul%2Ecom*3global*3eng*3pages*3offerings*3perspectives*3manufacturer*3prepareforulevaluation*3/8z4H?_t=tracking_disc]

Some find it easier to work with Intertek:
[http://www.intertek.com/medical/?gclid=CJWn_Pn437ICFegWMgod9wkAow|leo://plh/http%3A*3*3www%2Eintertek%2Ecom*3medical*3%3Fgclid%3DCJWn_Pn437ICFegWMgod9wkAow/4HIY?_t=tracking_disc]

Bob. Taylor
Safety Engineering Consultant at South West Product Safety Consultancy
There are many ways to crack this nut. If you want to make the equipment class II then you need 2 means of protection to ground/earth. The type of protection depends where in the equipment you are considering. I would guess that it would need to be 2 means of patient protection for this sort of equipment. I would also think the equipment would be a type B equipment as it is non-invasive I think. If you want to make the equipment class I (earthed accessible metal parts), then it must meet the requirements of protective earthing. You must remember that in 601 the patient is earthed in normal condition and can be connected to mains in single fault condition, which is possibly why the FDA want it to be class II. Also, if it is used in the home environment then it would need to be class II anyway.

Having said all this, your starting point for a medical device should always be an isolation diagram. You then might need the help of an electrical or electronics engineer and one that knows how to apply 601-1.

Paul Doolan
Technical Support Engineer at Cardiac Science
How is the equipment defined for IEC 60601, is it type B or BF? As you are looking at different slit lamps, then they may well be defined differently – you need to go back to the slit lamp documentation & go from there!

Campo Elias Pena Laiton
Service E. en Block Scientific Inc
Can you watch the IEEE maybe.

Luke Barratt
Principal at Artiflex Engineering
Daniel –

Yep, you nailed it – we know we need to know and if even the Mechanical guy is looking for answers we much be desperate! I’ll take this off line and would be interested to get you in touch with the Chief Engineer / Partner for whom I “consult”.

Thanks –

Daniel Peressotti
Senior Engineering Technologist – Electromedical and Laboratory Equipment at CSA International
Hi Luke,

Your issue deals with isolation/insulation requirements. It is essential that you identify how you are going to isolate accessible parts and patient applied parts from “live” parts. There are many ways to achieve the isolation required (i.e. BI, DI, RI). You need to speak with someone who knows the standard inside and out (like myself). However, I don’t generally help Consultants. A person claiming to be a “Consultant” should know what they are talking about (no offense).
Good luck.

Luke Barratt
Principal at Artiflex Engineering
David and Daniel – Thanks very much for this feedback. I will review the test configuration examples, that makes great sense.
At risk of revealing my abject ignorance… (oh no, wait, I already did that!) I do recognize the potential of patient being a possible path to ground and thereby not meeting the incredibly low threshold for allowable current though patient per 60601. My mechanical logic (which often fails me in the EE field) says that everything heavily grounded with straps dictating the path of least resistance is through the copper not the patient. With an isolation transformer in place do you not then couple the grounds?

Daniel, I believe I understand what you’re saying – need to meet the spec, but you can meet the spec without necessarily applying an isolation transformer (hence 1 slit lamp that’s grounded while another brand isn’t).

The Slit Lamps are Class II according to FDA guidance from 1998. I can’t find 510k’s from the equipment we’re talking about, but the designs could well be grandfathered.

Thank you again gentleman!
Luke

Daniel Peressotti
Senior Engineering Technologist – Electromedical and Laboratory Equipment at CSA International
Just a quick comment regarding Mr. McBrayer’s post. It is not necessary for all electromedical device’s to have isolation transformers. They do need to meet the applicable separation, creepage/clearance distances and the applicable leakages.

Regarding your issue, is the device with with infinite resistance from chassis to gnd Class II?

David McBrayer
CTO at Retired
Any electromedical device powered from the mains must have an isolation transformer to limit the risk of “ground fault current”. Recall, the patient is the potential “ground fault”. The amended second edition of IEC 60601-1 has examples of test configurations you may find useful.

Cheers,
David