Cat 6 to outbuilding

I am thinking of extending my network to an outbuilding. A lot of what I read contains dire warnings about the consequences, in part because outbuildings often should be T-T earthed - ie have the earth cpc connected to a local ground rod for the outbuilding. In my case, I can use the house earth with no issues because we have a T-NCS earth. So the risk is a lightning strike in the vicinity causing a difference in potential between the 2 ends and taking out some network kit.

So, my questions:
[1] I am thinking of using a short length of fibre between switches at one end as an optical isolator. Any comments or recommendations?
[2] Any other thoughts or experience on this situation?

Thanks for any input.

Might update a few things, but good for a look…

https://forums.thinkbroadband.com/multiuser/t/468521...

Ah, thanks for that. I found these off the back of that:
https://forums.thinkbroadband.com/multiuser/f/468098...
https://forums.thinkbroadband.com/multiuser/f/467914...

A good start, although I am not so keen on helical armouring for the fibre - depends whether I can duct this.

Seal the end of the ducts with duct sealant if you use tight buffered fibre sure to the risk of rodent damage. Loose tube construction would be good enough in ducting, you then don’t have gel mess to deal with either.

How far?

What speed do you have in the house and what do you want remotely?

Budget?

It's about 30m. I have 1000M in the house and 160M incoming FTTP. Realistically, 100M at remote end would be good enough, but for the most part, I think that if I achieve 100M, the cost to go to 1000M will be trivial. Assuming Cat 6 or Fibre.

Prefer not to do wireless and I have some trenching needed anyway, so another cable or fibre will not be a problem. Budget is not a big deal as long as I am not doing a private link between house and outbuilding via Starlink.

The main issue here is getting electrical isolation, hence looking at a very short optical link

If you are trenching then run in two fibres - just in case

I use Ubiquiti NanoStation Loco5AC wirelessly to my Garage and get a 300+Mbps link and it could be faster but I only need 15-20Mbps.

You can also get pre-terminated SWA fibre kits. I've previously used Paragon Networks to do 120m, 135m and 350m links with 4-core single-mode. I know that FS.com also do various pre-term/armoured cabling solutions, but not used their specific products in this space.

My preference is always to use single-mode as it allows far more flexibility. For example you can run Sat/Terrstrial/Radio from a FIRS-based antenna/head-end along a single core of SMF, so perfect TV in your shed (...along with perfect internet access)

Did you move ahead with this or make any progress?

Hah! The outbuilding is not yet built. The question is for the design phase. But all input appreciated.

In reply to a post by Pheasant:

Did you move ahead with this or make any progress?

OK, I have made something of a decision here. The main underground section will be in Cat6 Steel Wire Armoured cable. At the remote end, I will have a switch with an SFP connection and fibre to a Fibre-to-Copper Converter, such as the MikroTik RBFTC11.

Principal factors on this decision are that I am very happy with CAT6 and I have no functional need for fibre other than for galvanic isolation between remote buildings. I also think that SWA will be more robust during the build phase than helically armoured fibre.

Thanks for circling back with an update. 🙏

I have an outbuildings >100m from house. I used CAT5E I get 1GbE across to it no problem, with a patch panel connection at each end. The cable is available from screws and the like for not much money. It does have a separate earth spike,.

It passes through my garage, where one of the patch panels is. This is 20m .from the house, I get 2.5GbE to the garage,,along same cable, without any patch panel links. Again another earth spike.

I think 1000feet of cable was <£30.

Many people forget that UTP ethernet is already galvanically isolated at both ends between the cable and electronics, required to accommodate 1.5kV AC RMS 50/60Hz for 60 sec / 2.25kV DC for 60 sec / 10 2.4kV pulses as defined in RFC 60060. If that gets exceeded between house and outbuilding with T-NCS you will likely have more to worry about that replacing odd bits of networking kit.

In reply to a post by fleddy:

... It does have a separate earth spike,.

Again another earth spike.

Why the earth spikes? And what are you earthing? Is it cable armour? Or other parts of the kit?

Earth spikes seems to be the way to cause problems of transfer potential which is what I want to eliminate, but it depends on what your earthing scheme is.

In reply to a post by tdw42:

Many people forget that UTP ethernet is already galvanically isolated at both ends between the cable and electronics, required to accommodate 1.5kV AC RMS 50/60Hz for 60 sec / 2.25kV DC for 60 sec / 10 2.4kV pulses as defined in RFC 60060. If that gets exceeded between house and outbuilding with T-NCS you will likely have more to worry about that replacing odd bits of networking kit.

Sorry, I got carried away. My electrics are T-NS, but we are bonded as though T-NCS.

Re the isolation, how is this achieved? Are the RJ45's connected to little signal transformers or capacitors with a good voltage rating?

In reply to a post by DFScale:

Sorry, I got carried away. My electrics are T-NS, but we are bonded as though T-NCS.

Either still have a direct bond between the two ends.

Re the isolation, how is this achieved? Are the RJ45's connected to little signal transformers or capacitors with a good voltage rating?

Both, the data passes through transformers, the termination ground has a capacitor to the local signal ground. See Figure 7 in https://resources.altium.com/p/gigabit-ethernet-101-... as an example.

Even PoE is galvanically isolated, the device power supply electronics have an output transformer so again there no connection between the cable and generated supply.

In reply to a post by DFScale:

OK, I have made something of a decision here. The main underground section will be in Cat6 Steel Wire Armoured cable. At the remote end, I will have a switch with an SFP connection and fibre to a Fibre-to-Copper Converter, such as the MikroTik RBFTC11.

Sorry, I don't understand this. The MikroTik converter you show has an RJ45 port and an SFP port, and you say you will bring fibre into that (presumably with a 1000baseLX SFP). What will the other end of that fibre plug into?

Are you using the Mikrotik in effect as a sort of sacrificial lightening arrester?

It seems to me that if there's going to be fibre anywhere, then between buildings is where it would be better deployed - but I don't think I have the complete picture of what's going on here.

In reply to a post by candlerb:

Sorry, I don't understand this. The MikroTik converter you show has an RJ45 port and an SFP port, and you say you will bring fibre into that (presumably with a 1000baseLX SFP). What will the other end of that fibre plug into?

Switch with SFP connector
1000baseLX SFP
Fibre
Mikrotik convertor
CAT6

In reply to a post by candlerb:

Are you using the Mikrotik in effect as a sort of sacrificial lightening arrester?

It is not intended to be sacrificial. Just galvanic isolation

In reply to a post by candlerb:

It seems to me that if there's going to be fibre anywhere, then between buildings is where it would be better deployed - but I don't think I have the complete picture of what's going on here.

Obvs not. I have some very busy trenchwork and I am not convinced about Helical Wire Armouring for fibre vs SWA for CAT6

I would probably choose a PVC duct and non-armoured, outdoor grade fibre. But clearly you've weighed up the pros and cons for your installation, which is what matters.

+1

A lot of expense to go to for galvanic isolation with otherwise zero benefits of a fibre connection to my mind.

But I respect the OPs choice. So remains otherwise shtum 😂

There is no benefit to a fibre connection, other than galvanic isolation, since the rest of the network is limited by being CAT6. The expense looks similar to the expense of running fibre over the whole route. Fibre over the whole route confers no benefit and the disbenefit of requiring pre terminated cables.

In reply to a post by tdw42:

In reply to a post by DFScale:

Sorry, I got carried away. My electrics are T-NS, but we are bonded as though T-NCS.

Either still have a direct bond between the two ends.

Re the isolation, how is this achieved? Are the RJ45's connected to little signal transformers or capacitors with a good voltage rating?

Both, the data passes through transformers, the termination ground has a capacitor to the local signal ground. See Figure 7 in https://resources.altium.com/p/gigabit-ethernet-101-... as an example.

Even PoE is galvanically isolated, the device power supply electronics have an output transformer so again there no connection between the cable and generated supply.

Ah, thanks for this. I have taken a brief look which addresses some of the concerns, but I need a deeper look.

Spikes are incidental and separate from the 10baseT Ethernet connections. I should have mentioned that

Both buildings have mains Section 19 fuse boxes, and supply from the main property supply.

At some point I investigated having a separate 3 phase supply to the garage, as the last pole for the supply is next to the garage. I was looking at piece of 3 phase equipment for the garage.

When I installed the new supply to the "cabin", I had issues with it tripping the RCD in the house (not the 2 others the supply was going through). To try to alleviate these (and an earthing issue) I added the earth spikes. The spikes were cheap and easy, but not the solution.

Re: isolation , as tdw42 points out, Ethernet over UTP doesn't require this, having inbuilt isolation in the standard.

I have/had a stack of 10GbE and 40GbE fibre equipment but decided it would be OTT to install fibre in a domestic environment. I think this is still the case. 1GbaseT is almost free, 2.5GbaseT is cheap as chips. Even 10GbaseT is reasonable.

1GbE over UTP is perfectly adequate, utilises very cheap cable is easily installed, tested and maintained.

My only wish is that I'd pulled a second Cat 5E cable, (or Cat6) for a separate PoE WiFi. I have this everywhere else, driven by a central switch (on a UPS, together with main router). This is what I have elsewhere, as we have no phone reception and rely on WiFi/WiFi-calling/VoIP for all phone communication.

In reply to a post by fleddy:

I have an outbuildings >100m from house. I used CAT5E I get 1GbE across to it no problem, with a patch panel connection at each end. The cable is available from screws and the like for not much money. It does have a separate earth spike,.

It passes through my garage, where one of the patch panels is. This is 20m .from the house, I get 2.5GbE to the garage,,along same cable, without any patch panel links. Again another earth spike.

I think 1000feet of cable was <£30.

That's an entire 305m box, If you paid that little then it isn't Cat5e.

The specs for Cat5(e), 6(a), 7, 8 etc. state the conductors are to be pure copper, anything considerably cheaper than £100 per box these days will be copper clad aluminium (aka Counterfeit Cat5/6) and will cause no end of issues. The diameter of the conductors (AWG - lower number is thicker) is likely to be less too so resistance will be increased, on top of the increased resistance by dint of them being aluminium.

The weight of the box will be the dead giveaway, or having CCA printed on the cable (not to be confused with Cca fire compliance rating).

Edited by _KP_ (Sun 02-Mar-25 20:20:52)