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Topic Title: Mixing 24V control and Ethernet/CAT 5 and LV mains in same enclosure
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Created On: 19 April 2014 01:51 PM
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 19 April 2014 01:51 PM
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justinneedham

Posts: 17
Joined: 21 January 2005

I have been approached by a potential customer with a view to installing Home automation (Loxone system) in new build.

One issue which immediately question is the "Miniserver" which is DIN-rail mounted controller for use inside mains enclosure/Consumer unit. This provides 230V switched outputs, and is provided with 24V DC switched inputs (suggested connectivity being via Cat5e/6/7 cable from room-mounted push-buttons) and also Ethernet, all into the same enclosure.

I'm struggling to make complete sense of the implications of this with regard to "Requirements for Basic Protection". I would assume that Cat5e/6/7 cable isn't necessarily insulated to LV standards, and in any case, the various switches and accessories connected to the 24V side themselves have no CPC.

It seems hard to see that a manufacturer in mainstream production hasn't covered these issues, but I am unable to find any reference to such in their on-line documentation and there seems to be to me several unanswered questions.




 19 April 2014 02:38 PM
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Fm

Posts: 668
Joined: 24 August 2011

At some point in smaller control panels lv and elv enter on the gland plate, i wouldnt see a problem with it, keep them away from each orher, dont untwist the cat 5
Diffent on a mcc or similar, with separate power and instrumentation
 21 April 2014 11:14 PM
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AJJewsbury

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I'm struggling to make complete sense of the implications of this with regard to "Requirements for Basic Protection"

I'd hope that the 24V/CAT5 side would be PELV or SELV (or near equivalent) - so if you provide basic protection via section 414.2 you don't have to worry about providing basic protection via other means (e.g. references to sections 416 & 417), just as long as you keep it separate from the mains side. Same idea as door bell transformers or mains fed intruder alarms.
- Andy.
 23 April 2014 04:59 PM
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justinneedham

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Originally posted by: AJJewsbury
so if you provide basic protection via section 414.2 you don't have to worry about providing basic protection via other means (e.g. references to sections 416 & 417), just as long as you keep it separate from the mains side. Same idea as door bell transformers or mains fed intruder alarms.
But 414.4.1 (ii)"protective separation from live parts of circuits not SELV or PELV provided by double or reinforced insulation or by basic insulation and protective screening.." The "Server" is DIN rail mounted inside CU, live contacts out, live inputs fed from respective MCB. There would be no "protective screening" between SELV contacts/CAT5 and single-insulated mains low voltage. Separation of a few CM within the CU, but no barrier as such. Loxone [IMG][/IMG]
 23 April 2014 05:12 PM
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AJJewsbury

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The "Server" is DIN rail mounted inside CU, live contacts out, live inputs fed from respective MCB. There would be no "protective screening" between SELV contacts/CAT5 and single-insulated mains low voltage. Separation of a few CM within the CU, but no barrier as such.

Ah, with you now! I'd pictured it rather like a DIN rail mounted bell transformer where you often have a cover for the terminals so the cable sheaths can be taken right into the unit.

Is the "few cm" in the enclosure sufficient for "physical separation" of the PELV/SELV and mains sides - 414.4.2 (v) ?

Or could you used insulated & sheathed single-core cables for the mains in the vicinity of the ELV side (providing double/reinforced insulation as per 412.2.4)?

- Andy.
 23 April 2014 05:37 PM
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justinneedham

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Hi Andy, thanks for coming with me on this one.
I am unhappy about the physical separation distance. In the picture last post, the green front extends through CU so is the height of MCB. Thius I'd guess ~4cm between 24V side and mains terminals (the row on bottom left in red).

You suggest " insulated & sheathed single-core cables". I guess that's one way, but inconvenient as the house will be conventionally wired in T&E.

Might one over-sleeve the SELV side to comply? (or over-sleeve T&E cables where they are stripped back)?
 23 April 2014 06:17 PM
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OMS

Posts: 19663
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Stick the controller in its own din rail enclosure - put terminal blocks on the din rail where the controller would have sat (ie in the MCB dist BD) and wire the 230V side in insulated and sheathed cables ?

Or use the 230V side to switch relays and keep the 230V away from the controller completely

In practice however, depending on how you route relevant cables, it's not that difficult to maintain seperation such that a cross over faut isn't credible - ie cables cannot physically touch

Regards

OMS

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Failure is always an option
 23 April 2014 09:23 PM
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justinneedham

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Hi OMS.
The controller can't be separated from the SELV since they are both in one unit.

The relays would work I guess, but this server really is just relays anyway. I'm questioning the way they would be wired up. Also adds a "layer" and some more space.

So provided one could proceed by ensuring a cross-over couldn't occur with the cable lengths available, then that's probably the most straightforward way to go.

Failing that being possible, I am interested in the idea of over-sleeving the T&E cores, or over sleeving the SELV side. That would be "site applied insulation". Would need to make a good job of it 414.2.1.2. Would I be right in thinking we could accept that?
 24 April 2014 10:08 AM
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OMS

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Originally posted by: justinneedham

Hi OMS.

The controller can't be separated from the SELV since they are both in one unit.

I appreciate that - it's why I suggested a seperate enclosure into which you only take insulated and sheathed 230V cabling or you only have "SELV" by the use of relays.


The relays would work I guess, but this server really is just relays anyway. I'm questioning the way they would be wired up. Also adds a "layer" and some more space.

Indeed - but it fully addresses your concerns

So provided one could proceed by ensuring a cross-over couldn't occur with the cable lengths available, then that's probably the most straightforward way to go.

It would be - and is usual practice. I'd hazard a guess that for thousands of HA installers, the issue never crosses thier minds.

Failing that being possible, I am interested in the idea of over-sleeving the T&E cores, or over sleeving the SELV side. That would be "site applied insulation". Would need to make a good job of it 414.2.1.2. Would I be right in thinking we could accept that?

Oversleeving is a common practice and easy to achieve with heat shrink for example. Personally, I would sleeve the 230V side rather than the 24V or comms side, but depends on what quantity of each cable type you have.

In practice however, it's not that difficult to achieve seperation just by physical routing of cables



Regards

OMS

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Failure is always an option
 24 April 2014 01:59 PM
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AJJewsbury

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In practice however, it's not that difficult to achieve seperation just by physical routing of cables

I'd agree with that - with most of the alarm panels I've worked with (which for some reason seem to prefer to have most of the zone terminals next to the mains transformer ) - it's usually easy enough to use a few small cable ties keep the ELV side bunched together and well away from the mains wiring - although it can significantly restrict your choice of cable entry points. If you're obliged by the layout into a 'rat's nest' mix of LV and ELV then oversleeving the mains side would seem easier.

What are people's thoughts on using PVC sleeving to the same standard as we use for G/Y c.p.c. sleeving for T&E (BS EN 60684 according to 543.3.100)? Readily available in live colours, and presumably acceptable as one layer of basic insulation (since it normally insulates the c.p.c. from the screw heads of live terminals)

- Andy.
 16 July 2014 10:25 PM
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JP1000

Posts: 9
Joined: 03 June 2009

I also have a need to install this Loxone product .

If I was to use a cat7 cable that has both insulation and sleeve that can withstand a test voltatge of 1000v , would I be right in saying that I can meet the requirements of both basic protection and and SELV (provided I have a power source that is BS EN 61558-2-6 compliant.

-JP
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