Within BS7671 there is the following clause:-

560.7.7 Safety circuit cables, other than metallic screened, fire-resistant cables, shall be adequately and reliably separated by distance or by barriers from other circuit cables, including other safety circuit cables.

Now I read this in two ways, the first is this is specifically talking about fire rated cables only… or

This is insinuating that unless I use a metallic screened fire-resistant cable I must provide separation by distance or by barriers including from other safety circuit cables. Does this mean a common dedicated medical IT final circuit trunking is not acceptable as each IT circuit in its own right is a safety circuit, therefore if I was to move away from fire rated cable I would need to ensure each IT circuit is installed in its own individual piece of containment (conduit) to give the correct level of separation or would a common galvanised trunking dedicated to the IT cabling be sufficient.

I appreciate no one will give me an answer to the question above, but can people let me know how they interpret this clause to see if I’m on the right lines.  

Can I ask how do you interpret this clause?

I think I might interpret this as an installed circuit which is used to provide safety indication or control, new or added when the others were installed, requires protection from electromagnetic interference and other forms of fault and possible damage, by the use of metallic screening or providing a suitable distance from other circuits (100mm+).


Legh

I'm not sure you can read this particular Regulation in isolation, without considering other requirements in the Regulation Group 560.7 (see note to 560.7.1), and perhaps other requirements in BS 7671?

This is to do with circuits for Safety Services, defined as:
Safety service. An electrical system for electrical equipment provided to protect or warn persons in the event of a hazard, or essential to their evacuation from a location.

Based on this I would not classify dedicated medical IT final circuit cabling as a safety service and so this requirement would not apply.

Others may have different opinions of course.

Alasdair

That might be evidence of the fact that the particular requirements of 560.7 weren't written for Medical IT systems.


And they wouldn't necessarily be, as:


(a) It's not part of Section 710; and

(b) BS 7671 doesn't specifically require any part of Medical IT systems to be classified as safety circuits - but see 710.560.6.1.1(iii) and 710.560.7 for equipment that could be designed to use or be part of a Medical IT system, if the design assessments determine.



Perhaps this is an item for future clarification through HTM 06-01 which actually contains the requirements for Medical IT Systems final circuits to be classified as safety circuits as a general carte-blanche statement?

I will start off this reply by stating that my expertise is in fields where BS7671 is generally not applicable so the following is in relation to systems design in general rather than compliance with BS7671.

However I do have considerable experience with requirements for safety systems, emergency systems, etc. so I will expand on my earlier comment.

Safety systems as defined in BS7671 are aligned with my experience and where there is reference to a safety system it is generally looking at the functionality being provided. Where there is reference to a safety circuit it is referring to the wiring of a particular sensor/alarm sounder or similar which is part of that safety system. A safety system should be designed on fail safe principles but also be designed so that a fault in one circuit will only affect that circuit, and with the fail safe principle should if possible provide fault detection (e.g. an alarm should fail to the alarm condition).

If a single fault is not to affect more than one safety system (or safety circuit) it follows that there must be separation of the cabling. However if the cable is both fire resistant and armoured or otherwise mechanically protected then neither a fire nor mechanical damage should affect multiple circuits.

(It is at this point I run into problems with the wording of 560.7.7)

The wording implies that if you don't have fire resistant metallic screened cables the only solution is separation. I can't see that there is a difference between fire resistant metallic screened cables and normal cables run in a steel pipe, since the latter will be protected from fire and mechanical damage. However if separation is required then I don't see any option but to provided it (though how much separation is needed is another debating point).

The reason for protecting the safety system cables is that they are normally relied upon during abnormal situations such as fire, explosion, flooding, earthquake (though not so much in UK) or natural disaster. Medical IT cables are not expected to have to cope with such situations but rather medical emergencies during which the normal systems will be expected to be operational.

Of course I was not part of the committee writing BS7671 so I am quite happy to have this challenged.

Alasdair

The case of a medical IT system is somewhat different.


A first-fault on the system may well simply cause an alert, but the system keeps going ... to power medical equipment that may well be keeping a patient alive (but this is not always the case). A second fault on the system (any circuit) may cause the operation of the protective device on that circuit alone. The medical IT system is not intended on its own to protect the patient from electric shock, it is used in this manner to provide continuity of supply and alert medical staff on first-fault, so first-fault doesn't take out a circuit, or the whole system.


As to the particular protection requirements for a specific installation, it's important to understand what the medical IT system is achieving (i.e. what clinical procedures are being carried out, and what the powered equipment is intended to do).


The situation is further complicated by the requirement to understand what any evacuation policy will be whilst patients are being treated, during a fire situation - so I guess you will get different answers for different situations.

But playing devils advocate as you've said When you read the BS7671 part 2 definitions  for a safety circuit it states:-

Safety service.

An electrical system for electrical equipment provided to protect or warn persons in the event of a hazard, or essential to their evacuation from a location.


But could you argue this definition still applies as it provides protection by continuing supply medical electrical equipment if there is a failure in supply or an adverse condition.

I think in reality this this needs addressing in the next version of the HTM otherwise Contractors will continue to be scared of non-complying to the regulations unless they use fire rated cabling.


so the question is if the UPS/IPS are located in adjacent fire compartment (deemed low risk)  to the area they serve  would you wire the final IT circuits in FP100 or LSF singles ???
 

No, there's a point where people have to think for themselves.


In some circumstances, your last "scenario" plays out, in others, it does not. And in this particular case, the adverse circumstances may not be fire ...


BS 7671 is not intended to replace a "designer", and in fact the standard requires one.


And in answer to the last question "it depends" is the only answer available without more detail. Fire may not be the only risk, and the particular procedures involved may (in a Group 1 location) be of a very different nature to a Group 2 location, for example.




This isn't a game of chess, but the consideration of a Standard (BS 7671) and an Industry Code of Practice (HTM 06-01) - both of which can only be cited as a whole, and which have different weight when considering what was actually done (not what could have been done).


The outcome, when adapted to reality, is not always a binary response.