Electrical connections for dummies

[eddystone]

I tend to go a bit gaga faced with 12V systems on yachts, including my own. Couple of questions:

1. I know you can get spade extension terminals, like a little Xmas tree, but how to extend the negative connection block behind the switch panel? Mine is like a bar with holes in it and it's rammed full.

2. I want to fit a red/white chart light on a "wand" could I take a spur off the wires leading to a light fitting above the chart table?

3. Want to fit a surface mounted 12V/USB dual charging socket above the chart table - could i solder the wires to the ones coming out of the 12V socket on the switch panel?

4. Need to fit a new bulb into the bulkhead compass (Plastimo) It has in incredibly thin twisted 2 ply flex. Is this uni polar or is there a positive and negative? And should I step this up to a thicker cable with a connector to go into the back of the compass switch on the panel?

 

[ChromeDome]

1. Replace the current bar or extend by adding another somewhere, using a proper capacity wire between the bars.

2. and 3. Yes. The same switch and fuse will then cover them. Mind the combined draw on the sockets, the fuse must be big enough to cope (USB standard is ½ ampere at 5 volts which isn't a lot, but many modern devices can take several times that.
4. Thin cable indicates a very low consumption and the lamp might be an LED. If so, it will work only if the polarity is correct. If not straightforward by the existing connection, a multimeter will show which wire is positive and negative

 

[Trident]

Too many extensions is a bad idea - better for the negative to wire the panel to a small negative busbar and then make all the connections individually to that

If the fuse ratings work then yes you can spur off another light cable but as most chart table wands have their own switch I would connect it separately with an inline fuse if you are out of switches on the panel

I would not solder anything really on a boat as solder can be brittle and crack with movement . For another USB socket again think about how is it fused and if its running off the wiring to another socket can both be used at once and still be within the safe sizing of the wire and the fuse? Again a pos and neg busbar behind the panel with correctly sized wires and fuses may be a better way and allows you to individually size inline fuses to each load

The compass flex is twisted by design

 

[pmagowan]

Boats have quite a lot of vibration and are a hostile environment. I wouldn't use the spade terminals, go for the rings and screw/bolt arrangement. You can put multiple on one screw but you are better to have a larger bar if you find you are piling them on top of each other.

Always size fuses for the wire that it is protecting. ie big fuse for large diameter wire that will carry heavy load. The idea is that the fuse melts before the wire does. Fuse must be small enough to melt first but large enough to carry expected load. If the difference between these things is too small then you need a bigger wire.

A bus bar or distribution bar generally has a large cable going in supplying either a connection to positive or negative of the battery. You then have small wires to individual loads. In general the positive is fused.

 

[Tranona]

Wago connectors are your friend for this sort of thing.
12voltplanet.co.uk/wago-221-compact-splicing-connector.html

photo shows some examples behind my distribution panel