EBME Forums Forums Maintenance Technical Assistance Endoscopy system installed on medical pendant

Here is another good reference document:- HTM 06-01.

This document is a good guide but is now outdated and in the process of being updated. Always refer to the latest version of the standards (BS 7671 in this case).

Just out of interest in the USA there is now a move to specify RCDs with a 5.6mA trip rating for medical locations.

Also remember an isolation transformer only provides protection against electric shock before a first fault to earth occurs. Once a fault has occurred then any subsequent fault would provide no protection! If each socket-outlet were protected by an individual RCD then safety is always maintained and there can be no issue from false tripping due to too many items being supplied by a single RCD.

How many devices that suffer a first fault to earth would be still working safely?

I have asked before on this forum for the number of times a LIM sounds as a result of a first fault to earth and the answer came back as almost never! The monitoring tends to operate when there is a circuit overload (drawing too much current) rather than some breakdown in equipment insulation.

Those are all good points, Mike.

So it seems that we can now look forward to an RCD at every isolated outlet. Sounds good to me; it would also help in identifying them, which would be another "plus".

Do you have any idea how the 5.6 mA value comes about?

On the last point, I suspect that any faulty equipment would just have been removed, then repaired and returned to service without any further investigation being carried out (or recorded). Also, is it normal practice for theatre staff to keep a log of LIM alarms (and the action taken to silence)? Somehow, I doubt it.

Well, the 2nd edition of 60601-1 allows 5mA earth leakage current (to allow for the BF fault of 5mA) and this single fault limit is the same for most domestic products.

I see UL943 also requires automatic testing of these devices, which tend to be rated 4-6mA Class A.

I must admit that I thought the lowest available RCD tripping value was 10 mA.

Is the 5 mA actually an "alarm" value, I wonder?

I ask as I have been unable (thus far) to find any reference to a 5 mA tripping RCD on line (aha, yet another pun)!

But see this catalogue.

No, these trip out like RCDs but you need to use the correct USA terms to be able to find them with Google!

Take a look at this NEMA GFCI information about the matter.

Yes; we should call them GFCIs!

In general (and to keep things simple) I would suggest that an GFCI protects just a single circuit (hence the low tripping value of 5 mA) whilst an RCD typically protects more than one circuit (30 mA tripping). So I believe that, for the circumstances being explored in this thread (one at each isolated outlet), GFCI (albeit apparently a "non-British" term) is the appropriate terminology.

GFCI : Ground Fault Circuit Interrupter
RCD : Residual Current Device

For further comments, opinions (and confusion) see this link.

Geoff,
Yes, we are still using the British-style 13-A (polarized) plugs (with fuse) and socket outlets. ;-)
I think you are right as they have catergories the endoscopy suite as "wet location" and they could not use IPS due to space constraint therefore the 10mA RCCB was installed.
"your hospital may have chosen the "wrong" one)! frown" >> you mean we should insist for a IPS for the Endoscopy system?

It's good to hear that you're still using the world's best arrangement(s) of mains plugs and sockets!

Regarding all the other stuff, it probably depends which Code(s) (Standard(s)) are being followed. As I have already mentioned, I like NFPA 99 myself (even though it is American).

Lastly, "wet location" (or not) is a local judgement call - again, I hope and presume, based upon the relevant Code(s) being followed.

The link I gave at the post to which you refer was really to indicate how "muddy the waters are" on these issues. NFPA 99 does encourage IPS in wet locations (as this .pdf makes clear). But it sounds like, in your case, you may have to tolerate an occasional interruption of power if certain fault conditions occur (that is, due to the lack of IPS).

See also this earlier thread ...