DC Distribution Panel - Spaghetti?

[samsharp99]

Hello,

 

So I recently bought a 12V fridge and like others, found out the hard way that I have pretty inadequate 12V cabling on my boat. I upgraded the long run to the fridge with 10mm² and now instead of a 6V drop as the fridge kicks in, it's now only about half a volt so the fridge works - hooray!

 

To upgrade the wiring though I had to open up the switch panel just inside the door and found it's a rats nest of thin diameter cable (much less than 10mm² - even the connection from the battery) with everything connected to screw-terminal blocks with some in-line fuse holders but essentially everything is just loosely hanging in the box. There is a switch panel (without fuse holders) - similar to this sort of thing: http://www.discountmarinesupplies.com/46221317.jpg

 

I'd like to get this sorted but does anyone have any advice on/pictures of their DC-distribution setup that could help me figure out the best way to improve it?

 

I was thinking about a covered bus-bar (http://www.amazon.co.uk/Dual-Bus-Bar-amps-Cover/dp/B000K2MABA/ref=sr_1_2?ie=UTF8&qid=1442573191&sr=8-2&keywords=dual+bus+bar), a covered fuse box () and some 16mm² cable from the battery isolator to each side of the bus bar? Does that seem sensible and a good way to tidy things up? It's not a particularly big area I have to work in (15cm x 20cm x 10cm) but if I need to make it bigger then so be it. I think the cable from the leisure batteries to the isolator is pretty substantial but then after that I think it drops down to some 6mm² (maybe 8?) to the distribution panel.

 

I have quite a lot on the DC system - the main things being the water pump, shower gulper pump, fridge, lights etc. and when some of these things kick in, I notice that my lights dim. I also want to be able to run an inverter for my box-freezer (I don't have a fitted inverter) when I'm off the shore supply.

 

Does this all seem sensible?

Edited September 18, 2015 by samsharp99

[nicknorman]

Your proposals are reasonable if a little chunky for what you need, but have you considered a pukka switch panel where the switches double as circuit breakers, thus no seperate fuses required? Companies such as ASAP-supplies do them. But perhaps you dint have room for such a panel?

 

If you fit an inverter, it would be normal to take the feed for this direct from the battery isolator (via a megafuse).

 

Ps if you are going to use screw-down terminals you should terminate the cables with ring crimps (for terminals that secure the cable by means of the screw head) or bootlaces ferrules (for terminals where the bottom of the screw crushes down on the cable).

Edited September 18, 2015 by nicknorman

[samsharp99]

but have you considered a pukka switch panel where the switches double as circuit breakers, thus no seperate fuses required? Companies such as ASAP-supplies do them. But perhaps you dint have room for such a panel?

 

There is already a switch panel there - but it only has switches & indicator lights - no fuses. I hadn't considered that...I was more concerned with upgrading the cables and tidying things up rather than replacing the existing panel - I'll have a look into it though!

[Paul C]

Do you have any pics of your existing panel, switches and wiring? You could buy something like this:

 

http://www.ebay.co.uk/itm/Marine-Circuit-Breaker-Switch-Panel-6-Way-Boat-Narrowboat-Yacht-/161806203755?hash=item25ac66bb6b

 

(they do 12 switch ones too), the selection of circuit breaker ratings are sensible and the thing "acts" as a positive bus bar in that it takes one +12V connection and distributes it to the 6x or 12x (or whatever) circuit breakers. They have 6.3mm male spade connectors on the back, so you can use female spades which are fairly standard. I'd recommend buying uninsuated ones, and applying your own insulation with heatshrink. Its worth taking a little time to get the cable lengths right, tie them up (eg lots of little cable ties, and/or a variety of other cable securing hardware and use sensible colour coding too. On our boat we had the "left" and "right" lights on a different circuit breaker, and using a 2x 6 switch panels meant that there were enough to not need too many circuit breakers needing to serve 2 (or more) items.

 

You'd need a negative bus bar nearby too.

 

Also I made a neat electrics panel which was hinged down to reveal/conceal the wiring behind, 100x quicker than screwing it into a fixed panel. It also contained a battery monitor, couple of sockets and a cut out for the solar controller display behind.

[samsharp99]

I'll try and get some pictures over the weekend when I get chance, I'm at work now but started looking at various bits and pieces over lunch to shop for and then got a bit lost and thought I'd seek some expert advice!

[Chalky]

Biggest issue is how its all fused. The fuse is there to protect the cable, not the load (stand by for regular debate). If you have a small cable (e.g. 2mm csa) attached directly to the battery then its a fire hazard. If its attached to the battery via an appropriately rated fuse / breaker then it's ok. The cable between the battery and the distribution panel is usually not protected however the current automotive standard is to fit a battery terminal fuse holder and distribute power from there.

On my own boat I have a 50mm csa cable that comes from the battery to a 350A mega fuse - just outside the battery box. The mega fuse is connected before the isolator switch. From the switch there is a 50mm csa cable that goes to a domestic distribution unit fitted with circuit breakers. All power is distributed from there.

Edited September 18, 2015 by Chalky

[mayalld]

Hello,

 

So I recently bought a 12V fridge and like others, found out the hard way that I have pretty inadequate 12V cabling on my boat. I upgraded the long run to the fridge with 10mm² and now instead of a 6V drop as the fridge kicks in, it's now only about half a volt so the fridge works - hooray!

 

To upgrade the wiring though I had to open up the switch panel just inside the door and found it's a rats nest of thin diameter cable (much less than 10mm² - even the connection from the battery) with everything connected to screw-terminal blocks with some in-line fuse holders but essentially everything is just loosely hanging in the box. There is a switch panel (without fuse holders) - similar to this sort of thing: http://www.discountmarinesupplies.com/46221317.jpg

 

I'd like to get this sorted but does anyone have any advice on/pictures of their DC-distribution setup that could help me figure out the best way to improve it?

 

I was thinking about a covered bus-bar (http://www.amazon.co.uk/Dual-Bus-Bar-amps-Cover/dp/B000K2MABA/ref=sr_1_2?ie=UTF8&qid=1442573191&sr=8-2&keywords=dual+bus+bar), a covered fuse box () and some 16mm² cable from the battery isolator to each side of the bus bar? Does that seem sensible and a good way to tidy things up? It's not a particularly big area I have to work in (15cm x 20cm x 10cm) but if I need to make it bigger then so be it. I think the cable from the leisure batteries to the isolator is pretty substantial but then after that I think it drops down to some 6mm² (maybe 8?) to the distribution panel.

 

I have quite a lot on the DC system - the main things being the water pump, shower gulper pump, fridge, lights etc. and when some of these things kick in, I notice that my lights dim. I also want to be able to run an inverter for my box-freezer (I don't have a fitted inverter) when I'm off the shore supply.

 

Does this all seem sensible?

 

This is what is behind our electric panel (there is a bulkhead in place now)

 

 

[by'eck]

10mm2 cable is about right for a 12 volt fridge typically some distance from the batteries and having a compressor with a high start up current, not to mention that with too lower voltage start-up will be refused. A diesel heater is another requiring larger cross section cable although less of an issue as they are usually located much closer to the batteries, hence less volt drop. For other lesser draw devices cable runs with 3-4mm2 cable is usually fine.

[smileypete]

Can get these for the smaller DC loads:

 

http://www.ebay.co.uk/itm/12-Way-Blade-Fuse-Box-Bus-Bar-Marine-Kit-Car-Boat-HGV-12V-24V-/221141888898

 

As mentioned the feed for the fuse board and inverter should be fused with a fuse close to (but not inside) the battery box, a suitable size 'mega fuse' or 'midi fuse' and holder should do.

 

You'll also need a reasonably decent ratcheting crimper, and some decent crimp terminals (ie to BS4579 & BS4G178, try ebay and check the description)

 

http://www.amazon.co.uk/Draper-35574-Ratchet-Action-Terminal-Crimping/dp/B0001K9TGA

 

The larger cables need ring terminals from a much bigger crimper, a good boatyard, auto electrician, or even some fellow boaters may be able to help out here.

 

Fuses must protect the cable they feed from overload, plus some items like pumps may require a specific fuse size.

 

A reasonable rule of thumb for sizing cables for most DC loads is 'amps divided by three' to get the cable size required in mm^2. On a 12V boat this usually does for loads up to 5 metres away from the batts, above this increase the cable size pro rata. (But there are important exceptions to the above guide - eg 12V fridge of course!)

 

The best value cable for small loads may be 'tri rated' cable from electical suppliers or the usual online places. For cable for heavy DC loads welding cable can be a good option. For harsh conditions eg excessive damp, salt atmosphere, cable with tinned copper strands is much preferable thought pricier.

 

cheers, Pete.

~smpt~

Edited September 19, 2015 by smileypete

[Scholar Gypsy]

I'd encourage you to do a wiring diagram, which will enable you to work out what each wire does and where it goes. I finally got around to this last year, 20 years after the boat was stretched ...

[Arthur Brown]

Work out what electrical system you have, and decide what needs improving. Draw a decent diagram of what you want to have then start to pull wires in using, where necessary, the old wires as pull wires.