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: Feb 2004
Posts: 14,676
Likes: 63
Super Hero
Offline
Super Hero
Joined: Feb 2004
Posts: 14,676
Likes: 63

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


If you don't inspect ... don't expect.
Joined: Feb 2007
Posts: 292
Likes: 14
Master
Offline
Master
Joined: Feb 2007
Posts: 292
Likes: 14
Originally Posted By: Geoff Hannis

Here is another good reference document:- HTM 06-01. smile
This document is a good guide but is now outdated and in the process of being updated.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.

Joined: Feb 2004
Posts: 14,676
Likes: 63
Super Hero
Offline
Super Hero
Joined: Feb 2004
Posts: 14,676
Likes: 63

Those are all good points, Mike. smile

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? think

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.

Joined: Feb 2007
Posts: 292
Likes: 14
Master
Offline
Master
Joined: Feb 2007
Posts: 292
Likes: 14
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.

Joined: Feb 2004
Posts: 14,676
Likes: 63
Super Hero
Offline
Super Hero
Joined: Feb 2004
Posts: 14,676
Likes: 63

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. smile


If you don't inspect ... don't expect.
Joined: Feb 2007
Posts: 292
Likes: 14
Master
Offline
Master
Joined: Feb 2007
Posts: 292
Likes: 14
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.

Joined: Feb 2004
Posts: 14,676
Likes: 63
Super Hero
Offline
Super Hero
Joined: Feb 2004
Posts: 14,676
Likes: 63

Yes; we should call them GFCIs! whistle

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. smile

Joined: Feb 2014
Posts: 23
Angie98 Offline OP
Dreamer
OP Offline
Dreamer
Joined: Feb 2014
Posts: 23
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?

Joined: Feb 2004
Posts: 14,676
Likes: 63
Super Hero
Offline
Super Hero
Joined: Feb 2004
Posts: 14,676
Likes: 63

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). smile

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).

Originally Posted By: Clinical Engineering Handbook (Dyro)

Electrical power systems have traditionally been regarded as falling within the province of the facilities engineering profession. However, there are several reasons for clinical engineers to be knowledgeable in this area ...

Clinical engineers should take active roles in the designs of healthcare facilities, including contributions to the design of electrical power systems. They should also adopt a broad view of their roles and should apply their expertise to the entire spectrum of technological systems supporting patient care.



Joined: Feb 2004
Posts: 14,676
Likes: 63
Super Hero
Offline
Super Hero
Joined: Feb 2004
Posts: 14,676
Likes: 63

See also this earlier thread ...

Originally Posted By: Geoff Hannis

... this is indeed an interesting thread, and worthy of resurrection, surely? Especially as it ties in with recent discussions about theatre isolated power systems, isolation transformers on theatre stack carts, and other such intriguing matters ...


Page 2 of 3 1 2 3

Moderated by  DaveC in Oz, RoJo 

Link Copied to Clipboard
Who's Online Now
0 members (), 418 guests, and 292 robots.
Key: Admin, Global Mod, Mod
Newest Members
diodoled, Al BMET, Eng_VPG, Graham Oliver, Jawad
10,188 Registered Users
Forum Statistics
Forums25
Topics11,073
Posts73,785
Members10,188
Most Online5,980
Jan 29th, 2020
Powered by UBB.threads™ PHP Forum Software 7.7.5