power meter too close to network enclosure?

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mulac

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#295624 10-Apr-2022 20:55

Looking for some advice please.

My place has a recessed network enclosure (metal) inside a stud space, with the power meter also in a metal recessed box in the next stud space over.

I know you shouldn't run Ethernet and power within a foot of each other, so wonder if this might not be a good setup either. I hav Vector coming in a few weeks so it could be a good opportunity to have it moved. The OTP is in the network enclosure so I can't DIY move that.

Any experience here? Thanks all!

Jase2985

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#2899623 10-Apr-2022 20:55

its fine as its on the other side of the stud.

cyril7

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#2899624 10-Apr-2022 21:12

Don't know where you got the foot figure from, it has no reference and no registration in my knowledge.

As Jase says there is a 50mm or a solid barrier, that's it.

Also TNV cables in a metre box need to be double insulated, again to meet the barrier requirements, and that's about it.

There is a rule of thumb to clear heavy load electrical machines by at least 300mm to mitigate interference, but that's not safety related.

Cyril

mulac

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#2899630 10-Apr-2022 21:43

I read the foot (or maybe 300mm) distance between TPS and CAT6 running parallel, but it may not be corrext.

Thanks for the information, I was certainly questing potential interference rather than safety.

If there's no expected interference then I'll leave it where it is, thanks for the help and detailed reponses!

cyril7

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#2899672 11-Apr-2022 08:21

Hi as far as interference goes, and to be clear the electrical standards (AS/NZ3000 etal) only address safety, although they do mention in passing that close placement of TNV and LV should be limited to just a few meters to mitigate interference.

So as for interference, the network box I assume is a metal one and as such should be earthed as there is sure to be a power outlet in it, so it must by law be earthed, this metal case now creates a faraday shield for much of the interference, that is also earthed.

It actually takes a lot of interference, typically way more than the energy passing through your home to significantly interfere with cat5/6 cables carrying ethernet traffic.

Firstly, the ethernet signal for GigE is based on a spectral energy peak at around 70MHz, by 100MHz any significant side lobes are deminished, and the same goes for anything below around 40MHz. This is miles away from the mains 50Hz and still miles away from any significant harmonics of the 50Hz.

Next the data cabling is of a balanced design, and the coupling transformers in each interface of the ethernet connections will have a common mode rejection (CMRR) of at least 30dB if not more, so any interference (that by nature will be common mode) is immediatly and significantly nulled. Further the coupling transformers and the input circuit that follows will not respond to typically anything below around 10MHz, so any signal that does break through the CMRR is not going to cross the transformer and infiltrate the input circuit much futher.

As you can see the 50Hz and its direct harmonics are not really an issue, and when coupling cables together it only takes a few millimeters of distance to significantly drop the level of coupling, so a 50mm stud is actually a lot of space, unless of course your meter box has a 10kW rotating motor in it, then you might have an issue, but it does not.

A real threat of interference to ethernet cables is switch mode power supplies that might be encounted in a ceiling space to power LED or Halogen lighting, these often operate in the high kHz to low MHz and typically have spectral harmonic outputs well into the low MHz. As part of their design they are required to meet emission standards both directly from the body of the supply but also of conducted emissions that traverse the AC and DC leads leading from them. But still significant levels of potentially distructive interference (to ethernet signals) can exist in the close proximity of the supply and the AC and DC leads close to the supply, so in those cases I always recommend a good 300mm of clearance.

Cyril

raytaylor

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#2899852 11-Apr-2022 14:42

My place has a recessed network enclosure (metal) inside a stud space, with the power meter also in a metal recessed box in the next stud space over.

Its normal common practice.

We ask for it so the electrician doesnt moan as much when we ask them to do some extra work putting in a power point and dedicated breaker or light switch for it.

Ray Taylor

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mulac

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#2899856 11-Apr-2022 14:46

This is great and clears my concerns completely. Thanks for your help, especially @cyril7 for taking the time to give such a clear and detailed answer. This is why I love GZ!