BBS standard - wiring behind walls

[Gerkin6000]

Hi everyone

 

We're fitting out our boat and are deciding whether to run the 12v wiring outside the walls in conduit or behind the walls.

 

Conduit would be great for access but expensive so I want to know if we run them behind does it also need conduit?/can the cabling sit against the insulation or does it need a certain amount of gap? I've had a look at the BSS handbook but its doesn't give much detail and cant get in touch with any of our sparkys right now. Got loads of work to do but am being held up by not knowing what to do first, walls or electrics..

 

I'd love to hear your opinions/thoughts/experiences/BSS knowledge..

 

Thanks in advance

[bottle]

Our cables are run in 38mm waste pipe (water) at gunnel height and ceiling height behind the walls.

 

low voltage dc separate to high voltage ac

[Paul C]

12V cabling doesn't need conduit but it needs to be insulated. I'm not sure if its a BSS check but it can't touch polystyrene insulation because there is a possible chemical reaction between cable insulation and polystyrene which degrades the cable insulation. (Its quite possible there will be no degradation though). Builders are well aware of this so most boats from a certain year onwards will have a channel without polystyrene (if this has been used to insulate the boat) specifically for the cables. And runs up from the channel eg for wall/ceiling lights will have a bit of the polystyrene taken away to allow for the cable run.

 

Again, not a BSS requirement but if mains cabling is in there it needs to be in a separate conduit - BUT - the insulation around the (insulated themselves) 3 cores of typical mains flex counts! So no worries here.

PS also there's 2 current ratings for cables, one in free air and one when its installed in a loom/conduit/close to other stuff etc. Just size the cable based on the latter. In fact, you'll probably size it on voltage drop concerns rather than ultimate current carrying capability, so it will be larger anyway.

[Gerkin6000]

Thanks people. We've insulated with Celotex boards so not polystyrene so wondering is it ok to touch that and the wood tongue and groove of the wall. It looks like its ok..? I think when we were looking into putting wiring in the ceiling there needed to be a 10cm or substantial gap (?) so not sure if walls are different.

[Puddlejumper]

In conduit behind paneling

[Keeping Up]

One advantage of conduit, in the future it's easy to pull out a cable or add a new one especially if you thread a length of string down through it too.

[Gerkin6000]

So from a very reliable source it's ok not to use conduit if you use double insulated twin flex cable. Theres more info but reception was bad so won't go into that. Thanks for all your helps 10 points to Paul C!

[Grace and Favour]

So from a very reliable source it's ok not to use conduit if you use double insulated twin flex cable. Theres more info but reception was bad so won't go into that. Thanks for all your helps 10 points to Paul C!

You know that you have to use multi-strand cable, (tinned is even better) - tri-rated cable is perfect for boats, and that you DO need to work out what gauge(s) of cable are required dependent upon the equipment you'll be using?

[Paul G2]

I don't know if anyone has made this clear to you, but some cables can be run in conduit and some cannot and it all has to do with heat transfer.

 

Individual cables, or cables that might be joined like a common houselhold lamp cord, should be run in conduit. It doesn't necessarily have to be expensive or industrial grade conduit. Look at the cheap plastic flex that they use in the automotive industry, and it stands up to a whole lot more abuse than the inside of your walls will ever see. Even pvc conduit isn't very expensive and, with pvc it is so nice to be able to easily replace or add a cable. You might also want to think of things like data cable or possible solar, or possible future lighting needs and add a few "futures", which are empty conduit runs that you have installed for future use.

 

When you have two or more individual cables that are combined and contained within an outer protective jacket, those cables should not be run inside conduit, the heat won't dissipate properly. Under ordinary operation, there's not a hell of a lot of heat to dissipate, and breakers/fuses should prevent any high temps in the wires, so you don't need to worry cable heat inside the walls. But this type of cable is definitely meant to be installed without conduit. When running jacketed cable inside your walls, and this goes for pvc & plastic conduit too, you need to make sure that you protect the cable to make sure that no nails or screws can enter the cable. You don't protect your cables with memory of where it is or with good intent - you protect your cables with nail guards (little steel plates) so that it is impossible to nail or screw into them.

 

Have fun with your project and always remember that stupid questions are much more preferable than stupid mistakes, so, if you don't know or aren't sure, ask.

[NorthwichTrader]

When you have two or more individual cables that are combined and contained within an outer protective jacket, those cables should not be run inside conduit, the heat won't dissipate properly.

I've just run conduit from my low-level 240v sockets up to the gunnels, which will obviously contain two 3-core cables...is this bad practice then? Would I have been better off just dangling them freely down behind the hull lining? My rationale was to keep the cables perfectly vertical to the sockets, so I'd know for all time where they were.

Just to add, someone recently mentioned that 12/24v cannot share the same channels as 240v, unless they are separated by conduit. Is this true in the first instance and, if it is, how would you manage the situation re the BSS compliance issue mentioned above?

[Gerkin6000]

Mazing! Thanks for all the info, will have to digest slowly

[NorthwichTrader]

Paul G., on 15 Mar 2014 - 8:35 PM, said:

When you have two or more individual cables that are combined and contained within an outer protective jacket, those cables should not be run inside conduit, the heat won't dissipate properly.

 

 

 

I've just run conduit from my low-level 240v sockets up to the gunnels, which will obviously contain two 3-core cables...is this bad practice then? Would I have been better off just dangling them freely down behind the hull lining? My rationale was to keep the cables perfectly vertical to the sockets, so I'd know for all time where they were.

Just to add, someone recently mentioned that 12/24v cannot share the same channels as 240v, unless they are separated by conduit. Is this true in the first instance and, if it is, how would you manage the situation re the BSS compliance issue mentioned above?

My apologies for bumping my post, but I'm in the final stages of filling the screws on the hull sides, and the above info. casts some surprising doubt on what I've done????? Edited March 18, 2014 by NorthwichTrader

[Paul C]

My apologies for bumping my post, but I'm in the final stages of filling the screws on the hull sides, and the above info. casts some surprising doubt on what I've done?????

 

As mentioned before, cables have a current rating for their size, for when they're installed in conduit.

[smileypete]

I've just run conduit from my low-level 240v sockets up to the gunnels, which will obviously contain two 3-core cables...is this bad practice then? Would I have been better off just dangling them freely down behind the hull lining? My rationale was to keep the cables perfectly vertical to the sockets, so I'd know for all time where they were.

Just to add, someone recently mentioned that 12/24v cannot share the same channels as 240v, unless they are separated by conduit. Is this true in the first instance and, if it is, how would you manage the situation re the BSS compliance issue mentioned above?

 

Probably best to run the cables horizontally and vertically, and within 6" of floor where possible (or gunnel I s'pose), at least that's roughly what's done in houses. Running them diagonally is just asking for a stray nail or screw to be put into them.

 

I doubt heating will be a problem if 2.5mm² is used on a 16A supply and the cables aren't buried within insulation.

 

ETA: There's an electrician's forum on the web somewhere, where you may get a more definitive reply, esp if they've done boat wiring.

 

cheers, Pete.

~smpt~

Edited March 18, 2014 by smileypete

[NorthwichTrader]

 

As mentioned before, cables have a current rating for their size, for when they're installed in conduit.

Thanks, Paul C, but it was this below statement that has caused me some confusion in that principle...

 

"Paul G., on 15 Mar 2014 - 8:35 PM, said:

When you have two or more individual cables that are combined and contained within an outer protective jacket, those cables should not be run inside conduit, the heat won't dissipate properly."

[Paul G2]

My apologies for bumping my post, but I'm in the final stages of filling the screws on the hull sides, and the above info. casts some surprising doubt on what I've done?????

 

Sorry, I was actually going to answer this a couple of hours ago and opted for a nap instead.

 

Bottom line is probably "Don't sweat it!" If you just made short vertical runs inside the conduit and the rest of the cable is in the open (behind the wall) as it should be then you shouldn't have any problem. I can't for the life of me think of the what they call it right now, but there is a fitting that goes in the top, open end of the conduit that stops the cable from abrading against the sharp edge of the conduit. Did you use those fittings, or do anything to keep the wire from being cut on that edge?

 

As far as mixing 12/24V and 240V runs goes, the outer jacket on the bundled cable is the conduit, technically speaking, so I don't think you have any real separation worries. Keeping the systems separate is probably a good idea just in the very off chance you have a melt-down event you will have a better chance of only destroying one system instead of two, but that's about the only practical benefit. Wires don't ordinarily go bad, connections go bad and connection points are where access and identification are necessary. An electrician is not ordinarily going to need to dig into your wall and identify a particular wire.

 

Knowing where your wires are is always nice - not quite a proper substitute for nail guards, but probably more than adequate for those few runs you are talking about. What you have to worry about, from the protect-your-wires-from-nails-and-screws category, is where you have a cable(s) running through a hole in the wood framing. It's really easy to inadvertently do that. I wouldn't take anything apart just to go back and install nail guards, Your best bet would probably be to just make some real good notes on your plans about where your wires are and be careful about where you screw into your walls. (If you already have most of your screwing done and your electrical systems all work then it means your screws have probably missed the wires.)

 

I hope I answered your question. I know absolutely nothing about the BSS, but I doubt they re-wrote the rule book and they probably just follow good electrical wiring practices. If you have any doubts about what you did, you should check with a boat electrician over there. I'm sure I've seen some local sparky's on the forum here.

[NorthwichTrader]

Thanks, Paul, a kind and thorough explanation, thanks very much!

Re the conduit, I scraped the cut edges with a Stanley blade to smooth off the sharp edges. I figured if they couldn't cut my finger they'd be fit for purpose!

Thanks again,

Stuart

[Paul G2]

 

Probably best to run the cables horizontally and vertically, and within 6" of floor where possible (or gunnel I s'pose), at least that's roughly what's done in houses. Running them diagonally is just asking for a stray nail or screw to be put into them.

 

I doubt heating will be a problem if 2.5mm² is used on a 16A supply and the cables aren't buried within insulation.

 

ETA: There's an electrician's forum on the web somewhere, where you may get a more definitive reply, esp if they've done boat wiring.

 

cheers, Pete.

~smpt~

 

Actually, you'll find that most horizontal runs in residential construction are drilled at a height level with the apprentice electrician's gut. Not only is that a good height, out of the way of both switches and receptacles, it's also that drilling holes all day long is tiring and the easiest way to push the drill through the wood is to hold it with your hands whilst leaning against the drill motor a bit and pushing with your tummy.

 

Putting jacketed cables midst insulation is not a problem. If the cables are sized properly, very little heat is generated and being surrounded by insulation is not a problem - rock wool insulation, anyway. I don't think you'd want your cables embedded in sprayfoam.