EBME Forums Forums Maintenance Technical Assistance How should we test stacks?

We currently test equipment on stack systems on an individual basis (unplugging them from the trolley).

Estates PAT test the trolley extension leads/sockets.
Is the trolley a piece of medical kit? Should it be tested to the medical kit standard?

We need a better work instruction for stacks - anyone already done this?

John.

Assuming you are referring to electrical safety testing, John, there's nothing wrong with testing each bit of kit on the stack (especially opening up and examining the mains plugs, if possible). That, and tidying up the mess of cabling normally encountered.

On the other hand, if time is short (and no doubt this will generate howls of protests from the purists amongst us), if the complete system passes OK from the main plug (the one to the isolating transformer, supposedly), why proceed further?

Works for me Geoff. Test the system as a system via the mains plug attached to the isolating transformer. Always assuming your stack has one of course!

Perhaps you missed this one, John.

Thanks for the link Geoff,

i heard from one of the techs here that there is a 'new' electrical safety testing regime that has been agreed - but he didn't have details - heard it from someone, who heard it from someone else. I want a piece of paper to look at. I've seen DB2006 (05) - no surprises there - and nothing new on safety testing procedures.

Most of the systems here do not have isolating transformers, but i think that testing the system 'as a whole' works for me - (but may not be in line with the manufacturers guidelines).

Which manufacturer ... the trolley, the isolating transformer, the camera controller, the insufflator, the recorder, the printer, the monitor, etc., etc.? As you know, they can all be made by different people! My guess is that your guess is as good (better, as in more informed) as any of theirs.

What's that ... no isolating transformers? How come?

Some stacks come with isolating transformers, but for those without, the estates manager would not approve the purchase of Isolation transformers unless we could quantify the risk in a measureable way.

Also, When does a trolley become a stack? 1 shelf , 2 shelves, 3 shelves, 2 devices, 3 devices. A lot of grey areas.

Lot's of grey Estates Managers about too, Mate.

Obviously, what matters is the "worse case" in earth continuity and "risk current", regardless of the number of shelves, size of the castors, or colour of the paint!

In previous lives I have come across many stacks in a shocking state (yes, literally), which is disappointing when you consider how, when and where they are used. But, there again, servicing of theatre kit has been known to be neglected by biomeds before, has it not? I seem to recall earlier threads about "difficulties in accessing equipment" and "out of hours servicing" etc.

John

We should define the difference between equipment Systems and equipment Stacks as I think IEC 60601 sets different limits for safety testing of systems and individual items of equipment.

An equipment system is a combination of items of equipment mounted on a trolley with only one mains lead coming from the trolley. All the other leads connect to an internal extension block that is only accessed with the use of a tool. This should only be safety tested as a complete system.

An equipment stack may also only have one mains lead coming from the trolley but all the other mains leads may be accessed without the use of a tool. This equipment can then be safety tested individually and should also be safety tested as a system in its normal configuration to ensure it complies with the limits set for system testing.

Earth bond is different perhaps but as far as I'm aware the limits specified in 60601-1 are applied consistently for an individual device or a system (whether you call it a "Stack" or a "System"). Irrespective of the number of devices in the system the limits remain fixed.

I'd be interested to see an example of where the leakage limits specified in 60601-1 are different for an individual medical device and those of a medical system made up of those devices (of the same type and class) that are typically found in a video-endoscopy "stack".

Isn't the whole point of non-conductive shielding, potential earth bonding and mains separation, i.e. additional Means of Protection (MOP) fitted to medical systems, to ensure that combined values of earth & enclosure leakages, etc, in a medical system, are reduced to less than the maximum limits specified in 60601-1?

If extra means of protection isn't required for the system, i.e. it meets 60601-1, then fine but in my experience it is very difficult to achieve a "pass" on a system comprising the elements that Geoff suggests, even if they individually meet 60601-1, since combined leakages, e.g. earth leakage and enclosure leakage (SFC - Earth O/C) can easily exceed the maximum limits specified.

There are also "systems" or "stacks" that use extra MOP on some devices on the stack, e.g. a separating transformer, with the mains of other devices in the system powered elsewhere (of course these devices should not funtionally interconnect with mains-separated devices but sometimes they do if operators have access to functional connections and alter them).