Wiring loom - warning!

damo

damo

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longkeel35.org.uk
Having just decided to bite the bullet and lift the engine to refurbish the engine compartment and stern gear, I got a nasty shock when stripping out the wiring. The cables in the engine wiring loom, which has probably been untouched for 25 years, and wrapped in spiral wrap, have spiral grooves where they have been working against each other, presumably due to vibration. Some cables were worn through and the cores were exposed: short circuits waiting to happen.

I will wrap each new cable first before bundling them when I refit, but does anyone have an easy solution for chafe protection ie material that is oil and heat resistant, flexible and cheap. Or is plastic spiral wrap on each cable first the obvious solution?
 
Self amalgamating tape is not generally fuel resistant.
I would suggest heatshrink tubing, and adequate support for the loom to limit movement and chafe, with a generous bend radius to allow for engine movement. These two are slightly contradictory aren't they?
Perhaps large unfused wires should be kept separate?
A good idea to route it where it can be checked for wear and tear.
Hope that helps.
Chris
 
The probs. with self amal. tape is that over time it deteriorates.What about glass tape? If you half lap it should last for years.Used a lot in armature winding.R/S sell it.
 
If fitted correctly and adequately supported this sort of thing should not happen.

When you re-fit them I would suggest routing them through the engine space further from the engine, with support every 300mm at most. If you replace the damaged wires, with new ones, then bundle them up into a loom, heat shrink them and then put them through some copex conduit type stuff this will not happen again.

Further more if you put conduit in, put in some pull throughs and then you will easily be able to add wires to that space for additional accessories later.

Ben
 
G'day,

When running cables to an engine I look for the area with the least amount of movement, this is the gearbox or top of the saildrive in 90% of boat engines, installing a junction box at this point also ensures cables are above minor spills and fills as well as providing good access for testing circuits.

Marking each cable at the J box and supply panel will also save time in the long run.

Avagoodweekend......
 
I used make looms for Military puposes and racing cars. If you can get the old one off and lay it onto a board, you can then draw around it and make a copy which you can sleeve in heatshrink. If it were my boat I would add spare wires to most legs to cover failures and future additions. It will be a matter of extra time (winter project?) but not much extra expense. I have been shocked by some of the boat wiring I have seen over the years. An engine bay with a nice looking loom may be the thing that sells your boat in the furture.
Allan
 
The routing of the cables is very important too. Once saw a Sadler Starlight 35 after an engine room fire - the engine had moved sufficiently in heavy weather to chafe through the main positive lead from the battery bank and the resulting dead short had burned through the tops of two batteries, set fire to the galley, set fire to the cable insulation. The only good thing was that the main battery switch still worked - as well it did.

You should fuse the battery leads and never route the main positive between engine and bearers as Sadler had done.
 
If you can afford it the best method is to use PTFE sleeving or failing that, silicon sleeving over your wires. This will typically give you protection up tp 250C and will not be affected by oil and diesel.
 
Thanks for the comments and ideas.

The wires were well-supported so I think that hundreds of hours of minute movement was what caused the chafing. I think I will sleeve them individually, then heat shrink the lot together!
 
Re: Wiring loom - 7 steps to your perfect wiring loom

I am a marine electronics engineer and from your description, I would definitely replace every wire in the loom. Spiralwrap is not good for long term as you have found out and cuts in your cable is just not safe to use and certainly not something you want to have on a boat, never mind trying to insure it.

There are plenty of trade electrical places that do flexible conduit which is like a PVC flexible pipe. You can also get this as half split for easy installation but it is better to use it whole and pull a wiring loom through it.

Also, since the cable is in such bad condition, now is your chance to replace with tinned copper which is far superior to normal copper and does not corrode in damp environments. E.g. I have seen bare copper go black in a week under cover in a RIB.

First things first:

1. Get your empty conduit and feed it from your engine instruments/key switch to your engine
2. Mark each cable either with tags or by colour coding with pvc tape
3. Thread your cables through in one go by cutting to length and then binding with insulating tape for easy pull through the conduit
4. All cables round the engine should be placed in fine conduit and cable tied to strong points to prevent chaffing.
5. Use crimp connectors to connect cables onto rings and spades for yoor instruments and sensors. Be sure that you use a ratchet crimping tool that gives a far superior squeeze.
6. Clean spade connections on engine and rings on instruments with a brass brush and then connect cables.
7. Use a protectant spray eg. wd-40 to keep moisture away from the back of instruments and sensors (great for cleaning up oil too).

Finally, around your bulkheads, be sure and seal any gaps which will reduce noise and be better for fire extinguishing systems.

Hope this helps
 
Re: Wiring loom - 7 steps to your perfect wiring loom

"Spray with WD 40"

I thought this was a no-no for electrics and associated bits, "banned" by the RN LI etc or did I mishear?
 
Re: Wiring loom - 7 steps to your perfect wiring loom

Thanks for your suggestions, although most of your recommendations I have already carried out elsewhere on the boat - tinned cable, conduit, proper crimped terminals, chafe protection etc.

The next stage was to redo the engine wiring as per what you recommend, but I was a bit shocked by what I found as you can imagine. I was intending to use conduit as much as possible, but spiral wrap is such an easy way to keep a bundle together or to attach a new cable alongside an existing loom. Are you saying that the wrap itself causes chafe?
 
Re: Wiring loom - 7 steps to your perfect wiring loom

I have seen spiralwrap on older boats that actually fused wires together by the chaffing and heat of the engineroom. Instead of the cable lying inside a conduit the wrap is very tight around the cables; this means any movement or vibration is rubbing the insulation of the cable. On a sliding scale, much better to use large cable ties to hold things together than wrap, or better to use a half split conduit to cover cables and then cable tie in place, and of course the best is to use conduit and feed cable through. BTW, black cable ties are more resistant to heat, oil and diesel.
 
Re: Wiring loom - 7 steps to your perfect wiring loom

All duly noted, and ta very much for that.

BTW I've just twigged who you are - I use your weather portal all the time. Good effort /forums/images/graemlins/smile.gif
 
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