I need to run a 4mm twin and earth cable in a 150mm zone at a corner of a room with a network cable from the ceiling void to under the floor boards to an island in a dining room, is this advisable if I had the power say one side of the 150mm and the cat five the other side ?
Running network cable (cat 5) with twin and earth help
- Thread starter markymark2406
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Sure, no problem.
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SELV cables don't have to follow the same rules as LV cables.
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As you illustrate, 110.1.2 does, indeed, say that (with my emboldening) "The Regulations include requirements for:" followed by a list of eight things, but it presumably is not suggesting that all the regulations in BS7671 contain requirements in relation to all those 8 things.
So, in context, I suppose the question to be asked is about which of the regulations relate to the routing of SELV cables? Are you saying that the requirements are exactly the same for SELV cables as for cables carrying higher LV voltages?
Kind Regards, John
Whether it's SELV, data or LV, things such as prescribed zones, installation methods, appropriate means of support to prevent premature collapse in a fire, not permitted in locations such as protected escape routes and so on all apply.
I don't think you're right about 'prescribed zones' etc.). As secure suggested (and you disagreed), even in Amd2 a combination of 522.6.202(ii) and 522.6.204(v) means that buried and 'unprotected' SELV and PELV cables do not have to be in 'safe zones'. Is that not correct?
Some of the things you mention make sense - for example, any cable, no matter what it is carrying, can be a problem if it collapses in a fire and/or impairs escape routes (and the same can, of course, be said for plumbing, structural elements and even things like curtain tracks).
However, I think that, in general, the answer to my question is probably not that straightforward, since, even given 110.1.2, I don't think the fact that a regulation BS7671 'requires' something can (given that the regulations are not 'exhaustive' in considering all possible situations0 necessarily be taken to mean that the requirement relates to any cable/circuit, even if SELV/data/whatever (or even DC), can it?
To take just one example (of what I suspect are many), and sticking with 522.6.202, it would seem that, if taken literally, this regulation requires that a cable buried within 'safe zones' which is carrying LV (not ELV) and which does not have an outer earthed sheath/whatever or mechanical protection has to be RCD-protected, even if the "LV" it is carrying is DC!
Kind Regards, John
Are you suggesting that DC circuits don't need RCD protection "just because it's DC" ?
Not quite. I'm saying that BS7671 doses seems to only 'recognise' RCDs as a means of 'additional protection" in AC circuits .... ... (with my red) ...
... and it's certainly true that it's requirement for RCD protection of sockets (411.3.3) is prefaced by "In AC Systems" - which is why I was rather surprised that it was not the same in 522.6.202
I have personally not ever come across an RCD-protected DC circuit, but that's a different matter (and means nothing) - it's certainly theoretically possible.
Kind Regards, John
and very simple to do, Two matching windings on the core of a solenoid. As long as the currents in the windings are equal and opposing then there is no magnetic field in the core. Any leakage than results in the currents not being equal some magnetic field is created and the soleniod operates to either set an alarm contact or trip a mechanical disconnector.
It does require a centre tapped supply with the centre tap connected to whatever the DC might leak to such as the metal work of a production line
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That is how I understand it.
That does not seem at all unreasonable to me, AIUI DC is generally more hazardous than ac of the same voltage.
Indeed - and conceptually not really any different from the use of RCDs with AC with which we are much more familiar. Indeed, if I understand correctly, a "Type B" RCD will operate in response to a "constant DC" residual current (as well as AC residual currents).
Although I've spent many decades playing with equipment that uses DC supplies (from ELV all the way up to what today would be regarded as "HV"), I've never come across anything resembling a DC "electrical installation", so it's not surprising that I haven't ever encountered RCDs in DC installations!
I don't really understand that. A DC RCD will surely work just as well if, as with the familiar use of RCDs with AC installations, it is one side of the (not centre-tapped) supply that "the DC might leak to" , won't it?
Kind Regards, John
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