Basic electrical circuit - help needed!

MYStargazer

MYStargazer

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Hi folks

I've decided to rewire my 32' mobo.

I have to say that I don't really know much (yet) about it, but I'm determined to do it myself, as I want to know exactly where everything goes, and why, and I want to do a Rolls-Royce job (it's a mess at the mo with too many things inserted as an afterthought here and there).

Does anyone know of any good sites giving guidance on this? I've got the red Allard Coles Electrical and Mechanical Maintenance book, but I want to know about planning and making it happen, bus bars, circuit breakers, wire sizes, etc. Simple would be good!

Thoughts welcome.

Thanks!

S
 
I bought my bussbars from these people:

http://www.jgtech.com/Elecconect.htm

Rather than use chocblocks for connecting circuits, I terminated all the wires with crimps and use crimp connection blocks such as the type shown here:

http://bluesea.com/category/9/36/productline/190

Hence there are no bare wires held in place by the pressure of a screw, which to me seemed unreliable.

For cable sizes I just used stuff that would easily handle the current. To work out the current simply divide the watts by the volts. So for a 12V system a 10W light bulb will draw about an amp. A 20W masthead light will draw about 2 amps (well just under). So my boat is wired with 5A cable for all the interior lighting and electronics and 13A cable for all the exterior nav. lights, which will easily handle the current, and the thicker cable is generally easier to work with and a bit more robust (more and thicker copper strands). For wiring behind the instrument panel I got some reels of 17A cable from Halfords. Again it will easily handle the current but the extra thickness makes it easier to work with and the thicker copper means strands are less likely to break. Black for negative, red for positive.

Used spiral wrap to keep everything tidy. You can buy it in different sizes from Maplin in 10m lengths for a couple of quid. You can run your cable bundle along the spiral wrap (or more accurately, wrap it round the cable) and simply bring each wire out next to the relevant connector. If you have the connection block on one side and the earth buzzbar on the other then you can run the cable bundle down the middle and bring each wire out to the earth and connection block. Sorry that's much easier and more simply explained with a diagram. It's not as difficult as I just made it sound.

I ran all wires from electronics to the connection blocks, then from the other side of the connection blocks to the instrument panel. This means the instrument panel can be completely removed if necessary, without having to disconnect the boat wiring. I hope that makes sense.

Give everthing its own wiring, don't daisy chain. If you daisy chain all the instruments for example (so connect from one to the next) , because they are close to each other, and one link in the chain develops a fault, then you loose all the instruments wired after the fault. Much like one rope for one job: one wire for one job (or appliance). Much easier to fault find to.

Try not to have inline fuses behind the panel, such as the ones that may be fitted to your VHF power lead. if they blow you will have to get out the screwdriver to remove the panel, which is a pain. Replace them with panel mounted fuse holders. Don't forget a bus for your NMEA that you can easily wire new equipment in to.

To hold the wiring bundles in place I used cable ties and cable tie anchors with sticky backs (Maplin again) and stuck them to the fibreglass tucked out of view. The adhesive wasn't very good so I used a blob of epoxy. But then I have an MAB with no interior finish. If you have a smart gelcoat or headlining you may want to use another method.

If you use crimps, which I think is the preferred method, then they come in different colours; red, blue and yellow. The colour represents the max size of the cable the crimp will accept. I think red is 1.5mm, blue is 2.5mm and yellow is something like 6mm. Generally blue will do most stuff. but you make need red for small wiring on the back of instruments, and yellow for the thicker cable you run from the battery switch to your buzzbar, and for wiring from the earth buzzbar to the battery or engine block. You can get ones with holes of different sizes for the screws on the buzzbars and connection blocks and posts on the battery switch; spade terminals (male and female) for the switch panel; and inline couplers for joinging together wires. Try to use as few couplers as possible and replace coupled wire with a single piece. Wire's cheap, you should expect it to last, and its much more reliable than a join. Don't use pliers to squeeze the crimps, get a proper crimp tool, which is designed to crush the crimp to a certain thickness. If you use pliers and apply to much pressure you may crush and weaken the copper strands which could then break with flexing and age. Remember you want this wiring to last between 10 and 20 years (or more).

OK. hope that gives you some ideas.

Cheers,

Mark.
 
For 'simple' try to get a copy of 'The 12v bible for boats' by Miner Brotherton.
For more detailed information on design and installation I've always used the excellent 'Boatowners Illustrated Handbook of Wiring' by Charlie Wing. This is an American book, however, and others may recommend something more UK oriented.
 
Hi,

as a chartered engineer I suggest you take these steps:

1. draw a sketch of what you're going to do

2. draw a schematic, maybe more. Haynes manuals have them for cars and boat manufacturers produce them too.

3. Go to a showroom and look at a brand new boat with a similar amount of equipment

4. try your very best to avoid breaks in the cables / wires

5. label everything using something permanent

6. label everything twice!

7. I got a panel from a boat jumble for £15, this is cheaper than buying the switches!

8. corrosion is your enemy, silicone grease is your friend

Lastly, plan what you're going to do, make it work, then tidy it up. Once its all nice and neat and you're 100% confident it all works fine then check it again and finally passivate any exposed metal with something suitable

hopefully it'll be at least 6 months before you have to change something

If you're really clever you'll leave some 'hooks' for future changes!

Good luck
 
I would suggest that you proceed bit by bit.
Regard the electrics as 2 separate systems with 2 batteries.
The first is the engine system. The wiring connections etc will be dictated by the equipment alternator and engine electrics. Fit an isolation switch for this system.
The second system is all the domestics. Again fit an isolation switch however you will need some circuits to be on at all times so have a small fuse panel near the battery for these circuits that bypass the isolator. Bilge pump FM radio memory maybe solar charging.
Connect the negatives of both batteries together with heavy cable. Fit a Voltage Sensing Relay with emergency start provision to provide charging of the domestic battery. simple almost.
For the wiring fit conduit tubes for wiring so you can run the wires through circuit by circuit. Wire up and test each service ie nav lights before moving on to the next service. good luck olewill
 
When I re-built an 28' cruiser a number of years ago, I used lengths of rectangular electricians trunking (available from B&Q), screwed or glued/taped in place, to keep the cables together. This type has a snap-on cover and made it much easier to route the cables, especially when running the length of the boat. To allow a cable to enter/exit part way along the length, drill a hole in the underside.
I would advise purchasing trunking about 2" x 1", unless it will contain only a couple of wires.
The advantage that I discovered in subsequent years was it was much easier to add or remove cables when making additions or alterations.

As other posters have indicated, plan your layout first!

Good luck. I am sure you will be well pleased with your efforts!
 
Merlin do alot of very useful leaflets regarding wiring, types of cable, recommended methods of installation in their downloads...

http://www.power-store.com

Might be best to speak to them regarding recommended installation as your safety and the safety of the wiring is paramount.

Starting with your

Engine and domestic Batteries (split charge system)
Post type terminals
Crimped heavy duty cable - requires large crimpers
Heat shrinked connections
Rubber boots to insulate terminal
Flexible split conduit supported at least every 18 inches
Master fuses 250 and 400a (depends) - the only fuses on your boat
Tinned cable for smaller duty
standard insulated crimps
negative and positive busbars
BEP marine circuit breaker panel
Conduit to run all cables in of various sizes and stainless screws and cable ties to support all conduit

This is a start for the DC system. Your bilge pumps require a constant fused supply from the domestic battery so they are always on standby.

Your AC system will consist of a waterproof, surface mounted, a master breaker box with earth leakage trip and all cable in seperate conduit. Battery charger will have an AC spur box and the DC outputs should be fused, bypassing main battery switches so that your batteries can still be charged when all DC systems are off. If an inverter is to be installed then you can use an automatic changeover switch (merlin do it) which auto changes to inverter if shore supply is unplugged. Alternatively you can get a Victron combined battery charger and inverter that will do the same thing but will also supply more AC power to your boat combining the shore supply and it's own onverter when needed (real class ! ).

Then you have your monitoring side. AC and DC monitoring is required for ABYC safety standards so you could integrate the monitor panels with the DC panel and even use the AC panel part for AC circuit breakers.

For calculating voltage drop, remember the length of cable is the sum of the positive and negative cable runs to and from eg. light or winch.

Hope this helps but if you are in doubt, professional help would be recommended.
 
A very good book -

Electrics afloat - by Alastair Garrod - Adlard Coles

explains it all... with good illustrations... circuit layouts etc

good luck
 
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