Ferrules on flexible cable used for permanent wiring

[tinnews]

We have just bought a boat, in Belgium. One of the first things I need to start doing is to improve/replace a lot of the wiring. I have a reasonable level of experience of domestic wiring (and I'm also an Electrical Engineer with a degree although I know that doesn't always translate to any level or prectical competance).

Talking to other boat people it's a no-no to use solid cable on a boat as it apparently will fatigue and fracture over the years. So, flexible it is. Again boat people say to put 'bootlace ferrules' on all screw connections, does this agree with experience/expertise here?

Any other advice or recommendations for boat wiring would be very welcome, as would any books on the subject. An equivalent of the IEE "on-site guide" for boats would be perfect.

[Dave Plowman (News)]

It would depend on the size of the hole in the terminal. If very much larger than the cable a ferrule would be the way to go. If close to the cable size I doubt it makes much difference.

[Tim Lamb]

In message , [e-mail] writes

I think there is a lot more to learn about *stranded* cable with regard to vibration resistance and suitability for the marine environment.

ISTR that motor vehicle wiring is 40 strand rather than 7 or 29 found in some domestic flexes. Buying from a marine chandler should ensure something suitable. Corrosion resistance must be a requirement.

Vibration fractures at the screw termination may be reduced by ferrules but DO NOT solder tin the lead end.

regards

[js.b1]

Automobiles suffer extremes of thermal cycling, vibration, impact, oil, fuel, coolant. So in that respect I would suggest good quality automotive wire for SELV applications, wrapped in loom tape (not sticky) &/or suitably prepared flexible conduit.

For LV applications I would use H07RNF flex, the N is polychloroprene (neoprene) which is resistant to most things, with ratchet crimp bootlace ferrules. You would need to check H07RNF is ok in all applications, but I suspect it is - single core right up to multi- core.

Canada and others do favour tinned stranded for marine applications re corrosion, the tinning corrodes to exclude oxygen & water from the electrical connection. Remember SELV connections can suffer quite significant heating in high current draw applications which can lead to electrical fires. Additionally sparking probably does not go down well with any Propane leaks, propane being heavier than air sinks to bottom of boat and lurks out of nasal smell range until it finds an ignition source. Welding cable is extremely flexible re battery connections, it might be sheathed (like 6181Y) alternatively H07RNF is available in singles, difficulty might be getting cut lengths. Nice big crimp tool needed for battery terminals :-)

Even BS7671 17th permits flex for fixed wiring (which would make many old timer DNO staff have a fit), but suitably prepared for terminals. Now a typical switched fused connection unit has identical screw terminals for both the cord outlet & fixed wiring side. One can argue that no preparation is required for flex, alternatively I always bootlace ferrule (small conductors in particular because they can be mashed by the tighten-until-it-squeaks brigade).

A good dehumidifier for a boat is an X-Dry, they restart on power loss, some near identical clones of them now. Avoids condensation build up if it is subject to such in winter - the dessicant type avoid the low-temperature low-performance issue and produce some degree of heat by virtue of their design (350-550W when operating on the humidistat).

[John]

And also extortionate cost as well, no doubt.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember [e-mail] saying something like:

Definitely. Use a good quality automotive grade for 12/24V and the same cable if rated for mains. You can still get similarly multi-stranded mains, but it's harder to find.

Yep. It's good practice anyway.

[Dave Osborne]

Some on-line vehicle electrics and parts suppliers:

[NT]

bootlace ferules make the connection mroe robust

NT

[dom]

That's also the wisdom I received.

IIRC solder slowly shears under compression, so a screw termination of tinned multistrand wire may work loose over considerable time periods.

Regarding bootlace ferrules - they're dirt cheap from Screwfix - *but* ensure you buy ones that closely fit the bare stranded wire end.

OTOH it is ok to over-solder things like spade connectors to turn them into solid joints - popular on vehicles with old 6V electrics to reduce voltage drops.

In a marine application, I'd be giving a lot of thought to ensuring moisture can't get past grommets, and making joints that are easy to inspect for corrosion.

[Andy Champ]

x-posted to uk.rec.sailing. Some guys there who seem to know their stuff (no electrics in my boat!) and you'll soon spot the Denis equivalent.

Andy

[Gordon Freeman]

If that link doesn't work go to

then choose the PDF "Not Another Article on Boat Electrics".

[tinnews]

It's hardly the "On-site Guide" for boats is it! :-)

It's very good basic advice (make sure the wire is thick enough and keep the conenctions sound and clean) but there's not much more. I'm after things like:-

Recommended wire type and *size*. Yes, one can work out from first principles what size wire to use everywhere but some standard, default values would save a whole lot of time. (The "On Site Guide" provides exactly this for mains wiring in the house)

Typical wiring layouts - e.g. do you run a 12 volt (or 24 volt) 'trunk' down the boat and run individual connections to lights etc. from that, or do you run radial connections from the distribution panel to each light?

Should one use 'common' return wiring or is better practice to run pairs to everything?

Switching setups for inverter use.

[Nikki Locke]

Used tinned cable where possible.

Nigel Calder wrote the bible:

[tinnews]

Yes, I've just ordered that.

[Nikki Locke]

Nigel Calder's book has a table.

Normally there are loads of circuit breakers (in old boats, fuses) at the switch panel. Sensible groups of stuff are connected to each one, by wire appropriate to the trip current.

Pairs to everything. Except that you can run one pair to a series of non-essential stuff, wired in parallel - e.g. cabin lights.

Serious inverters are often wired directly to the main battery fuse or switch, as they draw far too much current to go via the regular wiring. It is not usual to share the same mains voltage sockets between an inverter and direct shore power supply (too many things could go wrong!). Some boat inverters also do battery charging, via the same 12V leads. But then I've never looked at a boat which had an inverter built-in when the boat was built, so what do I know!

[Dave Liquorice]

I'd go for radials for each appliance group. So a couple of lights in a single cabin would be one circuit not two.

Currents are high at 12v and thus significant voltage drops rather easy to gain. Your "common" would have to be a serious bit of copper... Like wise your suggested trunk above is probably not a good idea.

[Derek Moody]

Everything on a boat moves, solid -will- fatigue. Run flex with the occasional extra loop left free to slip a little so it can adapt to the vessel's requirements.

Solder if at all possible. Crimp and solder too where there might be a strain - whatever you use make sure it's *big*, you are carrying more amps than domestic wiring and everything has to run cool - fuse everything. Consider running two wires in parallel for critical systems - when all is well they'll help reduce voltage drop and in time of trouble they're less likely both to go at once. Use lots of vaseline, grease and WD40 as appropriate.

Dunno about books. Avoid running sounder, radio and radar cables in parallel if at all possible. Use stainless, marine co-ax, never TV aerial cable.

Run two wires to everything that matters - don't forget to protect (grommet) everything that runs against 'fixed' points, remember, it's all gonna move. Use *big* switches.

Oh, and keep power cables away from the compasses.

Cheerio,

[Pete Verdon]

You could also try asking on the Practical Boat Owner forum at

. Be aware that first-time posters are subject to a moderation that can take a few hours to go through.

Personally I'd avoid screw terminals as far as possible (which probably isn't completely). For permanent joints I'd use solder and adhesive-lined heatshrink, or I've recently heard of gel-filled IDC crimp blocks which are supposed to be good and are on my list to try for my upcoming electrical refit. (Waiting till winter for that, though - now is the time for sailing even if the wiring is a dangling, corroding pile of bodges and birds' nests.)

For big loads like electric windlasses, many people use welding cable, but that shouldn't be necessary for normal circuits.

Furneaux Riddall is supposed to be a good supplier, though I haven't (yet) used them myself.

Pete

[Tim Lamb]

In message , Derek Moody writes

Umm.. I have a dinghy so not speaking from nautical experience. Tinning the ends of stranded wire leads to failure if the wire is allowed to vibrate. Something to do with the outer strands taking more of their share of the mechanical load until they fracture and so on. The other issue is that solder is softer than copper and *flows* under pressure from the screw terminal leading to loose connections.

regards

[tinnews]

My experience and *lots* of other peoples experience says that soldering is a *bad* thing to do with flexible connections. They fatigue rapidly at the end of the tinned section and fracture there. Good crimped connections with no solder are much better. Another issue with crimp+solder is that the solder creeps and the crimp comes loose.