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Hi

Before I make a final decision, if I use 50mm XPS foam as my base board, what is the best way to attach all the wiring underneath?

I've seen people have a 3mm ply and glue the foam to that and others that have just glued to the foam to the supports.

If I go without the 3mm ply, I thought about using cable nail clips and push them straight into the foam, not sure how long that would last, maybe drop some glue on the nail before pushing them in.

Any thoughts.

Cheers
Building baseboards entirely of XPS foam (if I have read correctly) is an unusual thing to do - not many do it.
I would have thought that XPS foam would be insufficiently strong to prevent sagging and would therefore require support. It's moisture absorbing and warping properties are probably not well known in the hobby. I would also suggest that 3mm ply would also be insufficient.

My suggestion would be to used tried and tested methods such as ply construction and limit the use of foam to just track-beds on top of ply.

I built my boards using 12mm ply and these have lasted 25 years, including a year of storage in a Sydney garage with extremes of temperature from -5 to +40, with no impact whatsoever.

Using foam, you also need to consider how you are going to attach everything on top of it - some glues destroy polystyrene and it probably won't hold any kind of pinning.

With regards cabling, I would recommend just cutting slots like I did in the cork that I use: https://modelrailways.online/Pages/Vu/PowerFeedingwithDroppers
Run the cable through holes in the surface and do all your cable runs underneath.

Please don't bury cables in scenery: as sure as night follows day, you will need access to it. Better to access it from under the board than to have to destroy scenery to get access.

Something else to watch: some foams have chemical reactions with the shielding on cables, causing the latter to break down and short. I would suggest that XPS is a bit too much of an unknown for me to be comfortable with it.
 

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I would be tempted to consider self adhesive copper tape - Lidl are currently flogging a 10m long roll for £4.99
I wouldn't! With no disrespect, I wish people would stop recommending this rubbish!

It was a product promoted about 20 years ago by a (now defunct) UK DCC supplier IIRC and it was always underrated current-wise and people had all kinds of voltage drop issues which resulted in a plethora of 'wives tale fixes' to resolve which in turn, created further problems! Stay away from it - it's the wrong tool for the job.

Copper tape was invented for running power down walls for dolls house lighting. Use it for what it was designed for and nothing more.
 

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May I respectfully suggest that asking for advice and then ignoring it isn't generally regarded as an ideal approach ?

There are issues with support of foam and I personally, don't think 3mm ply is sufficient in any circumstances. Then there are issues of chemical interactions between foam and wire sheathing.

Even if you put wires under the boards, they are still going to have to pass through the foam to get there.

Why are you persisting with foam ? Got a 'job lot on the cheap' or something ? It is going to create a very unstable base to which you are going to have all kinds of issues attaching things to it.

In the planning of my layouts, I adopt more conventional construction methods as I tend to want them to last and not suffer warping of sagging issues. I learned the hard way many years ago!
 

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Sure, it's entirely your call.

One of the things I commonly see on layouts is people adopting methods which supposedly make scenery formation easier (ie various types of styrene/foam etc), but it is done at the expense of track-beds and usually results in uneven, variable track-beds which in turn, affect running performance for ever more.
Personally, I believe that the track bed is of the highest importance as it is the thing that will make or break a layout. I was simply trying to help you avoid problems.
One option to ensure a reliable track bed for your situation might be to place ply on top of the foam under the track.

Happy modelling!
 
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