Home Articles Downloads Forum Products Services EBME Expo Contact
Previous Thread
Next Thread
Print Thread
Rate Thread
Page 2 of 3 1 2 3
Joined: Sep 2017
Posts: 111
Likes: 3
Savant
Offline
Savant
Joined: Sep 2017
Posts: 111
Likes: 3
Thank you Geoff,

To introduce myself, I worked for Siemens Medical from 76-98 then MDA (now MHRA) from 98 as a medical device specialist and then took a radical side-step as the radiation policy lead in the Dept of Health in 2004 so have been on an electrical holiday until I joined the mass exit from DH earlier this year. I've now set up a part-time training venture - I put a URL on the post last night but it got removed so am interested how I can get myself promoted like Eastwood Park do. I also can't create a new post as per the instructions so don't know if I'm being vetted at the mo either.

I originally conceived MEIGaN while at MDA and understand their are still ambiguities out in the field.

I agree with you on the primacy of the mains flex and sure a good programme of lead testing/replacement is key. I haven't got any views on the use of the supplementary connectors - I just literally state what they are for.

Do you work in a hospital or are you industry?

BW Ian

Joined: Feb 2004
Posts: 14,654
Likes: 60
Super Hero
Offline
Super Hero
Joined: Feb 2004
Posts: 14,654
Likes: 60

If you are the man behind MEIGaN, then I salute you, Ian. It was a much-needed document. [Linked Image]

Regarding that other stuff ... well, I suspect that Eastwood Park is one of the site's sponsors. Anyway, you'll need to deal with Huw about all that (but might I suggest using your Profile).

"Primacy of the mains flex" ... yes, I like that one. Hopefully it will catch on. Bravo!

About myself:- well, it's fifty years ago this week that I left home to make a start in the army; so, as you may imagine, I don't really "work" much these days (not in the usual sense of that word, anyway). My only involvement with the NHS (limited as it was) was via a few brief excursions as an Agency Technician. Luckily for me, most of my "biomeding" was done overseas; and the only "work" I do now is the development and maintenance of my TaskMaster computer program.

So I guess I am also on an "electrical holiday" (somewhat extended, in my case) - although I still have my multimeter(s) and what-have-you close at hand - "just in case"! smile


If you don't inspect ... don't expect.
Joined: Jun 2000
Posts: 2,410
Likes: 12
Huw Offline
Hero
Offline
Hero
Joined: Jun 2000
Posts: 2,410
Likes: 12
Originally Posted by Ian Chell
I also can't create a new post as per the instructions

There is nothing that should be stopping you from posting Ian.
If you'd like to PM me with the details / error messages etc., I'll take a look.

Joined: Feb 2007
Posts: 289
Likes: 14
MikeX Offline OP
Master
OP Offline
Master
Joined: Feb 2007
Posts: 289
Likes: 14
Originally Posted by Ian Chell
If it helps, supplementary bonding conductors are meant to act as a back up to the medical device's earth conductor in the mains flex.
Well not according to BS EN 60601-1 as section 8.6.7 states:

• The terminal shall not be used for a PROTECTIVE EARTH CONNECTION.

Joined: Feb 2004
Posts: 14,654
Likes: 60
Super Hero
Offline
Super Hero
Joined: Feb 2004
Posts: 14,654
Likes: 60

Yes; I absolutely concur with that ... even without refering to the Standard (common sense, plus a little bit of knowledge, plus occasional thought and a continuum of practised experience are all that are required).

But Fair Play to Ian; was it not he who came up with "primacy of the mains flex"? smile

See - I've used it already!

Meanwhile, what are these SEB (SBC, ECP, whatever) in medical rooms supposed to be for, then ("officially", that is)? think


If you don't inspect ... don't expect.
Joined: Feb 2004
Posts: 14,654
Likes: 60
Super Hero
Offline
Super Hero
Joined: Feb 2004
Posts: 14,654
Likes: 60

... still patiently waiting for a reply. sleep


If you don't inspect ... don't expect.
Joined: Feb 2007
Posts: 289
Likes: 14
MikeX Offline OP
Master
OP Offline
Master
Joined: Feb 2007
Posts: 289
Likes: 14
The idea is simple; to ensure items are at the same (equal) voltage (potential) with respect to each other.

Historically some have thought this was to keep voltages between conductive parts below values such as 10mV, 50mV or. 100mV. In fact it is to keep the voltage below 25V a.c. In a non-medical location this voltage would be 50V a.c. as set out in BS7671. This voltage may occur, for example, during a live fault to earth before the protective device operates.

However, some use it as a mitigation when using equipment with an applied part that is not in line with the procedure being performed, for example, using a type B rated dialysis machine for CVC dialysis, which should be CF rated. In this case the equipotential connection will keep the touch leakage down if the protective earth of the dialysis machine becomes open circuit.

The reality is that these equipotential connections should not be needed, if the electrical installation meets the required standards and the correct properly maintained ME equipment is used. In the U.K. they are rarely used but some countries use them extensively. I am not aware of higher death rates in the U.K. by comparison with countries who use them extensively. Read into that what you will.

Joined: Feb 2004
Posts: 14,654
Likes: 60
Super Hero
Offline
Super Hero
Joined: Feb 2004
Posts: 14,654
Likes: 60

... I read into that that some countries have sub-standard (that is, inherently unsafe) electrical supplies (and some are severely so); and I have seen many myself in days gone by.

Yes; Equipotential Points:- a kludge that attempts to improve electrical safety by tying a number of equipment chassis together - as a psuedo "earth" which (in an electrically "poor" environment) could still be many volts above true ground (adjacent plumbing, or whatever).

In other words, something that sometimes offers users nothing much more than a (false) sense of security! whistle

But do the users have any idea about them anyway? And do they use them?

Answers:- not much of a clue, but some may use them (without really understanding why) just because they are there! Others may use use them as they believe (or have been told at some stage) that they are some sort of "safety feature" (as in, "the more, the merrier", "belts and braces", or whatever).

Technically, I would suggest that they simply provide a parallel path to the Protective Earths of equipment power cables.

BTW, I notice only ten votes in the Poll. Pretty poor show; and hardly representative.


If you don't inspect ... don't expect.
Joined: Feb 2007
Posts: 289
Likes: 14
MikeX Offline OP
Master
OP Offline
Master
Joined: Feb 2007
Posts: 289
Likes: 14
I think the low number of respondents represents the low usage of these connections! As you say I think often where they are used it is from a "fear" point and not one of understanding.

It is the same sort of misunderstanding that has convinced some that a voltage of 0.1V is in some way harmful to patients, since this is the voltage measured by the IEC 60601-1 human body model and represents 100uA so must be dangerous. Whereas a potential of 0.1V will actually not represent any danger or lead to a current of 100uA when applied via the barrier of the skin. But... I hear you say, the skin is bypassed during medical procedures! Yes, but the voltage is not applied between two points inside the body! The source may be via a catheter but the return can only be via a B type applied part, such as the patient lying on a table top or connected to some other "earth" referenced part. In other words the voltage first has to overcome the barrier of the skin.

If you look at the work done by O. Z. Roy on 60 Hz ventricular fibrillation and rhythm thresholds and the non-pacing intracardiac catheter , which is the basis for the values in IEC 60601-1, we can see the voltages he applied where in the 50V to 110V range to get the values he measured. He needed to apply these voltages as the resistance of the fluid filled catheters was up to 2M ohm. Had he applied just 0.1V nothing would have been measured!

Just shows how if you take something out of context you can quickly get worried about noting!

Joined: Feb 2004
Posts: 14,654
Likes: 60
Super Hero
Offline
Super Hero
Joined: Feb 2004
Posts: 14,654
Likes: 60

Yes; very astute (especially the closing sentence). [Linked Image]

Unfortunately, Roy's learned dissertations do not appear to be freely available on line. But "students" who may be interested in Roy et al could make a start here (where even the brief abstracts are quite revealing).


If you don't inspect ... don't expect.
Page 2 of 3 1 2 3

Moderated by  DaveC in Oz, RoJo 

Link Copied to Clipboard
Who's Online Now
1 members (daisizhou), 435 guests, and 401 robots.
Key: Admin, Global Mod, Mod
Newest Members
MDevins, EmsR16, Fergusben1, Guilherme Gomes, Salvatore
10,173 Registered Users
Forum Statistics
Forums25
Topics11,055
Posts73,707
Members10,173
Most Online5,980
Jan 29th, 2020
Powered by UBB.threads™ PHP Forum Software 7.7.5