Electrical - Busbars and Fuse Boxs and Lights oh my!

[Abestea]

Hi,

I have been attempting to learn a little bit about the wiring within my Sigma 33 so i can wire up a new mast head light and a depth gauge. When i examined the current state, there are fuses attached to both the +ve and -ve wires. I am more used to car elecrics which only have one fuse. Is this normal in boats?

Plus my researching has determined that all books talk about having a bus bar. On the boat the +ve fusebox and -ve fuse box has wires connecting the separate fuses together. In almost a rudimentary +ve and -ve busbar attached directly. Is this ok to have or should i install two separate busbars and have connecting wires.

I am thinking this may be a better option as i may want to add further electrical equipment and the busbars would be more sensible.

Oh and why do my port lights have two +ve and two -ve wires foing to each light where the starboard side lights have only one +ve and one -ve wire going to each light? Is this a starboard/port parallel circuit and the lights on each side are in series?

When it comes to electricity i am not a bright spark!

thanks

 

[VicS]

Unusual to find fuses on both positive and negative I would have thought. Unnecessary and a bit of a pain at times I suspect.

Nothing particularly wrong with linking the fuses together in the way you describe, if I understand you correctly.

If you want more equipment requiring more fuses then the simplest is to wire in the same way but remember that at one point one wire will be carrying all the load so some fairly heavy cable may be needed.

I think I may be able answer your question about the wiring of the lights. The +ve & -ve supply goes to the lights on the port side and then on from there to the starboard side lights. Hence two pairs of wires on the port side and only one on the starboard. Port and starboard are wired in parallel.

As an elementary introduction to the electrics I think you will find The Boat Electrical notes on the TB training website very useful. They start at the beginning assuming you know nothing!

Regarding the wiring the mast head light you may find one of these cable size calculators useful

http://www.unlimited-power.co.uk/cable_sizing.html

http://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html

(note the cable run length is there and back, so its 80ft up and down a 40ft mast)

 

[whipper_snapper]

[ QUOTE ]
On the boat the +ve fusebox and -ve fuse box has wires connecting the separate fuses together. In almost a rudimentary +ve and -ve busbar attached directly. Is this ok to have or should i install two separate busbars and have connecting wires.

[/ QUOTE ]

The usual arrangement is a -ve busbar, but a +ve distribution 'post'. That is because, in most arrangements, there are many fewer and thicker +ve wires attached to the +ve post/busbar - there will be a main 'in', a feed to a switch board, and 1 or 2 feeds to other things. Whereas the -ve busbar takes the -ve from every circuit.

Having a single, (often insulated) post for the +ve is therefore easier and safer as you don't have pos and neg uninsulated busbars in the same space, just waiting for a screwdriver, spanner, or floating wire to short them.

 

[Abestea]

Thanks VicS. Had a quick skim through the websites and they look like they will be very useful. Would spend longer but need to go to work. Boo! /forums/images/graemlins/mad.gif

I initially stumbled on the double fuses when i tried to work out what the fuses were for. I was quite bemused by it.

The overloading is my biggest worry. I once wired up a stereo in a ford capri only to see flames appear in the dashboard through where the stereo uset to go as i had fitted it lower down. OK it was 18 years ago but, I most certainly do not want to repeat this on the boat.

Whipper_snapper: my fears exactly with exposed busbars. I am currently cringing as the fusebox is currently exposed. Anything bouncing around down there in the alcove where it is could cause major problems.

 

[stephenh]

“…why do my port lights have two +ve and two -ve wires going to each light where the starboard side lights have only one +ve and one -ve wire going to each light?”

Are the wires all of a similar size ? – Not two thinner wires going to the port light ?

One of the classic ways of repairing a known (metered) fault in wiring circuits, which can be very hard to find, is to run completely new wiring in and abandon the old, faulty stuff. Cheaper in the long run…

A good sparks would have stripped out the old but this is not always possible, at least it should be cut back and isolated.

It sounds like someone in a hurry, ( and who is perfect?) – try testing each combination , labelling the wires this time !

Good luck

A book to be recommended is ‘Electrics Afloat’ by Alastair Garrod.

 

[Cerddinen]

You should look carefully at the bus bar on the Sigma 33. On mine it was located slightly forward of the switch panel outboard of the chart table. Why do I know where it was? Because at 23.30 on a pretty miserable May night we lost all electrical power shortly after rounding Portland Bill heading west. No lights, no VHF, no GPS. We sailed the rest of the night by holding a torch beam on the compass. Back in harbour the fault was easily found: all the negative leads were clamped to the bus bar. The return from the bus bar to the batteries - the single most critical lead - was not clamped to the bus bar. Instead, it was held in place by a wood screw passing through the bus bar and held by a few threads into a wooden panel. This had worked loose (which is not surprising) and cut every circuit on the boat. I still cannot believe that any boatyard could see this as an acceptable practice.

 

[Dave_Seager]

I have a Princess 32 dating from about 1974. The original wiring includes both +ve and -ve fuse boxes, twelve circuits are fused so there are 24 fuses in all. Later additions have been made using a -ve bus bar and +ve fuse box.
Incidentally, the Boat Safety Scheme used on inland waterways requires fuses to be fitted with insulating covers.
Regarding your navigation lights, as others have said, it is probably because the wiring is looped into one light and then feeds the other.

 

[halcyon]

The fuses in pos and neg was a Lloyds requirement, so was probably built to full Lloyds spec. It was also possible to have both pos and neg cables switched as well, so two pole switches were used.

Brian