conduit through sprayfoam/celotex

[DanMax&Belle]

Hi All,

 

I followed advice from CW when ordering my boat and got 25mm of spray-foam on all internal surfaces above the bilges. I am now looking at the wiring looms for my LEDs.

 

I intend on using conduit (not sure which - that's basically my question) but i imagine something like this..

 

https://www.google.co.uk/search?q=20mm+conduit&espv=2&biw=1366&bih=643&source=lnms&tbm=isch&sa=X&ei=puOSVJ6IO8Ou7AbZnICgDg&ved=0CAcQ_AUoAg#facrc=_&imgdii=_&imgrc=-pX5wtCG84khWM%253A%3Btg3byMK0xQVrdM%3Bhttp%253A%252F%252Fcpc.farnell.com%252Fproductimages%252Ffarnell%252Fstandard%252F42405771.jpg%3Bhttp%253A%252F%252Fcpc.farnell.com%252F1%252F1%252F54260-20mm-steel-pvc-conduit-10m-cb02640-elkay.html%3B193%3B200

 

 

and circular junction boxes above each LED position.....

 

https://www.google.co.uk/search?q=circular+junction+box&espv=2&biw=1366&bih=643&source=lnms&tbm=isch&sa=X&ei=QOSSVKu7C4_B7AbRpIGgDg&ved=0CAcQ_AUoAg#facrc=_&imgdii=xvVlMt2NQhk9UM%3A%3BKeJ1IqoG71oYnM%3BxvVlMt2NQhk9UM%3A&imgrc=xvVlMt2NQhk9UM%253A%3B9_aCDDsH1j-ZwM%3Bhttp%253A%252F%252Fimg.weiku.com%252Fb%25255C001%25255C362%25255C195Junction_Box_2_way_.jpg%3Bhttp%253A%252F%252Fwww.seekpart.com%252Fvalves-fittings%252Fpipe-fittings%252Fpvc%252Bjunction%252Bbox.html%3B640%3B480

 

 

to house the wiring then to use cut to size Celotex boards and expanding foam (as filler/adhesive) to make the additional 50mm (aprox- does vary through out the boat) to bring level with the battons.

 

Any recommendation on the best conduit to use and why? I imagine ability to withstand fire is one property, any others....?

 

Many thanks!!

Edited December 18, 2014 by DanMax&Belle

[nicknorman]

Not really answering your question but why use conduit when the wiring is between the lining and the foam? Conduit is needed to protect wiring from impact, chafing etc but the lining does the same job, provided care is taken to avoid sharp edges of battens etc from damaging the cable. One other advantage of conduit is the ability to add more cables fairly easily afterwards, but I wonder how likely it is that you would want to add more wires in the ceiling along the route of the conduit and the existing lighting holes?

 

So what you propose is not wrong, I just wonder whether the effort is justified? Certainly, conduit for the main wiring paths (along the gunnel etc) but not, I suggest, to each overhead light.

[b0atman]

Why withstand fire ?

[Murflynn]

conduit is useful if you want to replace or add cables in the future, providing there are adequate access locations.

[bottle]

The only 'conduit' I have is 32mm waste pipe run at gunwale and roof corners.

 

In the engine room, flexible conduit of the type can that can be fitted after the cable is run.

[Sierra2]

For wires you are very unlikely to ever need to change, just run over rated wires and encase them in spray foam. In the event you do need to add more wires down the line, just score a groove in the spray foam and use some tape to hold the wire(s) in place, in the groove while you replace the ceiling pannels. If you wanted to add diffrent lights in different places later on, the conduit would be in the wrong place and useless.

 

Chaz

Edited December 18, 2014 by Sierra2

[DanMax&Belle]

Not really answering your question but why use conduit when the wiring is between the lining and the foam? Conduit is needed to protect wiring from impact, chafing etc but the lining does the same job, provided care is taken to avoid sharp edges of battens etc from damaging the cable. One other advantage of conduit is the ability to add more cables fairly easily afterwards, but I wonder how likely it is that you would want to add more wires in the ceiling along the route of the conduit and the existing lighting holes?

 

So what you propose is not wrong, I just wonder whether the effort is justified? Certainly, conduit for the main wiring paths (along the gunnel etc) but not, I suggest, to each overhead light.

Hi Nick,

 

Thanks - very valid point. I am not planning on adding wires (I guess you never are), especially in the ceiling though.

 

In the event of a wire overheating is there merit in having the wire protected (?) in conduit? i guess it would have to be metallic conduit?

 

thanks

Why withstand fire ?

thanks b0atman - overheating cables(?) I understand that overheating wires are the main cause of electrical fires?

conduit is useful if you want to replace or add cables in the future, providing there are adequate access locations.

as per Nicks point i dont think i will add wires in the same place as the lighting loom , if i really need to then all i would need to do is remove the T&G and add more wires/conduit(?)

[Machpoint005]

>> - overheating cables(?) I understand that overheating wires are the main cause of electrical fires?

 

Certainly with mains, but on a 12v system?

[DanMax&Belle]

For wires you are very unlikely to ever need to change, just run over rated wires and encase them in spray foam. In the event you do need to add more wires down the line, just score a groove in the spray foam and use some tape to hold the wire(s) in place, in the groove while you replace the ceiling pannels. If you wanted to add diffrent lights in different places later on, the conduit would be in the wrong place and useless.

 

Chaz

Good point Chaz - i agree i don't think i would likely need to add wires in the same place in the future. holding wires in place against sprayfoam (which i understand is flamable is it not?) seems no best practice (i totally accept i am not qualified to make that assumption).

 

Certainly with mains, but on a 12v system?

ok - fair enough well this question is only with regards to LED lighting so fair enough.

[nicknorman]

- overheating cables(?) I understand that overheating wires are the main cause of electrical fires?

 

I don't think that is true for boats, but obviously it is a possible cause. I would suspect that solid fuel stoves are the primary culprit. Normally with 12v systems the voltage drop is the primary consideration when selecting cable thickness, and consequently the cable is subject to much lower current than it could take from a thermal point of view. Cabling should of course be protected by appropriate fusing near the power source (batteries) so that under a fault condition, the fuse will blow before the cable overheats. Even though as I said volt drop is normally the primary consideration, it is worth checking the selected cable's current-carrying capability from a thermal point of view, bearing in mind that the cable's environment (in free air, buried in foam etc) has a major impact on its thermal rating.

 

If you have LED lights the current demands are low, the fusing can be small and the selected cable will probably be over-rated simply because cable of the correct (minimum) rating is too thin, difficult to connect and mechanically fragile.

[lewy]

For wires you are very unlikely to ever need to change, just run over rated wires and encase them in spray foam. In the event you do need to add more wires down the line, just score a groove in the spray foam and use some tape to hold the wire(s)

Chaz

pvc cables should not come into contact with foam insulation

 

Commonly used PVC plasticisers tend to exhibit solubility in polystyrene and polyurethane insulating materials, As a result of this there will be migration of plasticiser from the PVC compound where there is a direct contact between the two materials, this causes the PVC on the cable to become harder and more brittle.

[DanMax&Belle]

I don't think that is true for boats, but obviously it is a possible cause. I would suspect that solid fuel stoves are the primary culprit. Normally with 12v systems the voltage drop is the primary consideration when selecting cable thickness, and consequently the cable is subject to much lower current than it could take from a thermal point of view. Cabling should of course be protected by appropriate fusing near the power source (batteries) so that under a fault condition, the fuse will blow before the cable overheats. Even though as I said volt drop is normally the primary consideration, it is worth checking the selected cable's current-carrying capability from a thermal point of view, bearing in mind that the cable's environment (in free air, buried in foam etc) has a major impact on its thermal rating.

 

If you have LED lights the current demands are low, the fusing can be small and the selected cable will probably be over-rated simply because cable of the correct (minimum) rating is too thin, difficult to connect and mechanically fragile.

Great - That's pretty much cleared it up for me and answered all my questions. thanks Nick. Thanks all

 

Hope this is useful to other fitouters!

 

Dan

pvc cables should not come into contact with foam insulation

 

Commonly used PVC plasticisers tend to exhibit solubility in polystyrene and polyurethane insulating materials, As a result of this there will be migration of plasticiser from the PVC compound where there is a direct contact between the two materials, this causes the PVC on the cable to become harder and more brittle.

lewy - interesting. How likely is my "standard" multistrand cable going to be PVC? alot of the conduit i was considering was either PVC or PVC coated...

[frangar]

pvc cables should not come into contact with foam insulation

 

Commonly used PVC plasticisers tend to exhibit solubility in polystyrene and polyurethane insulating materials, As a result of this there will be migration of plasticiser from the PVC compound where there is a direct contact between the two materials, this causes the PVC on the cable to become harder and more brittle.

This is more common with polystyrene. Spray foam tends to be ok.

 

Cheers

 

Gareth

[DanMax&Belle]

This is more common with polystyrene. Spray foam tends to be ok.

 

Cheers

 

Gareth

lewy - this is what i understood too. Sprayfoam is ok with PVC but polystyrene is not...

[nicknorman]

lewy - this is what i understood too. Sprayfoam is ok with PVC but polystyrene is not...

That is certainly my understanding too. Our boat is built / fitted out by a reputable boatbuilder who has built over 200 boats and certainly our ceiling wiring is in contact with the spray foam. I have never heard of it being a problem.

[bottle]

Sprayfoam OK

 

Polystyrene NOT OK

 

Is the way I understand it.

 

DanMax

 

If you select cable of suitable size for halogen lighting and then fit LEDs you will have more than enough headroom for safety.

[nb Innisfree]

I thought modern PVC cable didn't suffer from leeching.

[Guest]

The wiring on my boat has caught no harm where it is in contact with spray foam.

[Detling]

My guess is that at some time you will want more wires, I have added TV aerial, Radio Aerial and Solar panel wiring into my ceiling in the last two years next project is some form of external aerial for my internet wifi / mifi router so yet another wire needed.

[Sierra2]

Lighting is the only factor you may want to change. Solar, antennas can all be planned in advance (even if not installed at fit out)

 

Until the boat is fitted out its hard to gauge exactly where and how bright every light should be (even with dimmers), thus it's the only wires that need to be moved or added normally.

 

Click on my link below and then the 'photos by page' for my recent electrics

[blackrose]

For wires you are very unlikely to ever need to change, just run over rated wires and encase them in spray foam.

 

My understanding is that the current carrying capacity of electrical cables is rated in "free air" conditions, and that encasing cables in foam seriously reduces their current carrying capacity because they get hot?

Edited December 20, 2014 by blackrose

[nicknorman]

My understanding is that the current carrying capacity of electrical cables is rated in "free air" conditions, and that encasing cables in foam seriously reduces their current carrying capacity because they get hot?

 

Yes that's true, however for most narrowboat domestic 12v electrical installations, the "current carrying capacity" is not the design criteria, rather it is volt drop. So normally, such cables are operating well below their thermal limits even if they are encased/trucked/bundled. It might be a different matter for 240v where thermal limits are normally the criteria.

[Guest]

Yes that's true, however for most narrowboat domestic 12v electrical installations, the "current carrying capacity" is not the design criteria, rather it is volt drop. So normally, such cables are operating well below their thermal limits even if they are encased/trucked/bundled. It might be a different matter for 240v where thermal limits are normally the criteria.

Aye when carrying 12V over a distance, and when compyling with the volt drop requirements, the current and thermal limits don't normally matter. I was careful to keep the 240V cables on my boat in free air.

[ditchcrawler]

Clip on lid plastic trunking makes life reasonably easy for adding cables at a later date.