12v wiring - confusing

[charlie-uk]

I've been reading many posts and I'm still unclear.

 

Should I use 1.5mm/21amp wire for LED lights and 2.5mm/30amp wire for the cigarette lighter sockets (for appliances, fridge, computer, etc) and also the front headlight?

 

Could this cable be used (http://ebay.eu/1qBwQbE), maybe 1mm for LED lights and 3mm for the rest?

 

Does using too thick cable cause you lights to be dim?

 

Is red (positive) and black (negative) the general standard?

 

Can it pass through the same conduit as the 240v cable?

 

How far does it need to away from the water and gas pipes?

 

Can lights be connected in a chain (if that's the right term)?

 

 

 

 

[dmr]

Its volt drop rather than current handling capacity that matters in boats (because the cable runs are long).

 

6mm is about the minimum for most things, thicker for the fridge, though you could get away with thin stuff for LED lights.

 

THIN wires makes the light dim....due to voltage drop, Thick wires merely make your bank account empty

 

Red and black is the accepted standard

 

12v and 240 volt cables must NOT share a conduit.

 

Not sure about gas and water somebody else will tell you that. Gas should be visible throughout the boat for BSS inspection, not in a conduit..

 

You can "chain" the lights, and 12 volt sockets, but they must be connected in "parallel" rather than series.

 

...............Dave

[alan_fincher]

12v and 240 volt cables must NOT share a conduit.

 

True I believe if they are indivual insulated cables, but if a sheathed cable like those depicted is used the sheath counts as an extra layer of insulation, and it is OK to run 12V and 240V through the dame ducting.

 

So cable like that shown for 12v could share the same routing as 240V if that were done in sheathed Arctic cable.

[Tony Brooks]

I think that you need a 30 mm separation between electrical cables and gas/fuel pipes UNLESS one or the other is in trunking.It seem the outer sheath used on two or three separate conductor cables is considered a duct.

[charlie-uk]

I'm struggling to find online 2 core 6mm 12v cable. I suppose I could buy separate cables and use oversheathing.

 

Links to products would be appreciated.

[Tony Brooks]

I'm struggling to find online 2 core 6mm 12v cable. I suppose I could buy separate cables and use oversheathing.

 

Links to products would be appreciated.

 

I am concerned. DMR told you that the cable size is arrived at after calculating voltdrop and went on to say that typically 6 sq mm conductor cross sectional area is a typical the minimum. I happen to disagree with that because each boat is different and even each circuit is different but ignoring that you seem to have jumped straight into looking for 6 sq. mm. CCSA cable. That is not the way to do it.

 

As has been said over large cable is not an electrical problem but might be a financial one. Undersized cables MIGHT just result in dim lamps but could just as well result in motors burning out and horns not working. It will not take many water pump replacements to negate any saving made by using undersized cables.

 

The reason you are having difficulty in finding twin 6 sq. mm. CCSA cable is that boats are normally wired using separate cables that are then bundled together and suitably supported along the length. In the majority of cases you do not need twin cable.

 

I feel that you would do well to steep back for a while and study the electrical notes on my website and see if you can find a download of The 12 volt Bible.

 

 

[David Mack]

I've been reading many posts and I'm still unclear.

 

Should I use 1.5mm/21amp wire for LED lights and 2.5mm/30amp wire for the cigarette lighter sockets (for appliances, fridge, computer, etc) and also the front headlight?

 

Could this cable be used (http://ebay.eu/1qBwQbE), maybe 1mm for LED lights and 3mm for the rest?

 

Does using too thick cable cause you lights to be dim?

 

Is red (positive) and black (negative) the general standard?

 

Can it pass through the same conduit as the 240v cable?

 

How far does it need to away from the water and gas pipes?

 

Can lights be connected in a chain (if that's the right term)?

 

 

 

 

If you need to ask so many basic questions you need to ask yourself whether you are competant to wire a boat, or whether you would be better getting someone else in to do it.

[charlie-uk]

Thanks for the link to your site Tony, it looks packed with info.

 

The more I learn about 12 volt power, the more confusing it seems to become.

[Murflynn]

I endorse everything Tony has said.

 

Newbies should realise that they will not find definitive answers on technical matters on this forum. This is a place for discussion, it should not be used as the prime source of information. There are several sources of information for wiring boats. I would also suggest Nigel Calder's and Alastair Garrod's books (can't remember the correct titles just now).

 

Once the OP understands the basics, that is the time to come on the forum and try to iron out any particular issues that may arise.

[Arthur Brown]

In a trunk or conduit, all cables should be insulated to the highest voltage intended to exist in that trunk.

 

Forums are a poor place to learn! You have little idea who you are learning from whether they really know, or just say they do! I've met some really wise people on here with years of real world knowledge, I've also met some who can't spell their own name. It's really up to you to learn bits, buy books and learn things from people and work out who's information is best.

Edited May 22, 2016 by Arthur Brown

[charlie-uk]

It is clear to me now that this subject cannot be answered in a few posts. Any more suggestions as to where I could learn?

[Tony Brooks]

River Canal Rescue run boaters' electrical courses. They were based on the course I used to run for them but that's a few years go now. I don't know how much they will help in wiring a boat for someone with apparently very little basic knowledge though. Unless they have changed it the course notes are the ones on my website.

 

If any members have attended a recent course perhaps they could give their opinion.

 

I tend to use a book called The Marine Electrical and Electronic Bible by John C Payne (Adlard Coles) but that may be a bit heavy going for a beginner and covers far too much for a typical inland boater.

 

There are a host of paid for books, some good and some not so good.

 

It really is a case of devoting a bit of time to study.

 

At present DO NOT get involved in any boat wiring for 24V AC because that can kill, all the 12 or 24 volt stuff can do is set fire to your boat.

[charlie-uk]

The simple solution I guess is .... Hire an electrician

[Chewbacka]

I would suggest that you read buy this book to give you an overview of your boat's systems as this gives a lot of general advice. I found it very usefull when planning my self fit-out.

https://www.amazon.co.uk/Narrowboat-Builders-Book-Graham-Booth/dp/1870002717

 

I would also download the BSS check list to ensure any work you plan and later carry out will not fail a future BSS check

http://www.boatsafetyscheme.org/media/194782/2013ecp_private%20_boats_ed3_public_final.pdf

Note - if you plan to live on your boat as a residence rather than a leisure boat, then slightly different rules apply to the BSS examination requirements.

 

If you want to be fully compliant with best practice you will need to read the British standards that apply to recreational craft which can be accessed for free, I wont look up the link just now as I suggest you have a fair bit of basic study to do before you start reading those - they are not an easy read, but essential if you are fitting out a sailaway and wish to self cert and apply the CE mark.

 

When you have read the above links, then you can decide if DIY is wise for you and safe for your passengers or if you should pay for the work to be done.

Edited May 22, 2016 by Chewbacka

[W+T]

If you need to ask so many basic questions you need to ask yourself whether you are competant to wire a boat, or whether you would be better getting someone else in to do it.

 

 

If you dont ask you dont learn.

 

I am about to wire my cruiser and got my voltdrop between 0.27 - 0.32 using 2mm and on the 3mm for horn multi point use/ USB/charger etc

 

As Tony says it will be differnt for all boat as all runs set out are different lengths of cable.

 

good info here http://www.12voltplanet.co.uk/cable-sizing-selection.html

 

 

And fit cables above gas lines,

Edited May 22, 2016 by W+T

[Keith M]

The simple solution I guess is .... Hire an electrician

 

if you hirer a electrician ask them two question

 

1. Have they passed the BMET exam?

2 Have they got a copy of the Fifth edition of the BMEEA Code of Practise.

 

If the answer to both question is yes they should be OK

 

If one of the answer is no look for another sparks

 

Keith

[dmr]

 

I am concerned. DMR told you that the cable size is arrived at after calculating voltdrop and went on to say that typically 6 sq mm conductor cross sectional area is a typical the minimum. I happen to disagree with that because each boat is different and even each circuit is different but ignoring that you seem to have jumped straight into looking for 6 sq. mm. CCSA cable. That is not the way to do it.

 

As has been said over large cable is not an electrical problem but might be a financial one. Undersized cables MIGHT just result in dim lamps but could just as well result in motors burning out and horns not working. It will not take many water pump replacements to negate any saving made by using undersized cables.

 

The reason you are having difficulty in finding twin 6 sq. mm. CCSA cable is that boats are normally wired using separate cables that are then bundled together and suitably supported along the length. In the majority of cases you do not need twin cable.

 

I feel that you would do well to steep back for a while and study the electrical notes on my website and see if you can find a download of The 12 volt Bible.

 

 

 

Tony,

 

My 6mm suggestion was a late at night off the cuff response to emphasise that 1mm and 1.5 mm cables are not the way to go. I am actually happy with 4mm and even 2.5mm if the volt drops work out ok. Any thinner than that and I feel they start to lack strength and can get kinked etc, though I will use 1.5 inside the wiring cabinet for warning lights etc.

 

The correct approach is of course to get a good estimate of maximum current, including switch on surges for fridges etc, then to select cables based on volt drop. Also consider any possible future additions on the same cable run!. In addition to cable sizes the knowledge and experience to fit suitable terminations correctly is vital, and getting this wrong will cause more trouble than slightly under sized cables. A problem with thicker cables is that it can be more challenging to do fit connectors/terminations. An electrical training course sounds a good idea.

 

Thicker twin cables are a pain, separate wires are indeed the way to go.

 

..............Dave

[ditchcrawler]

The simple solution I guess is .... Hire an electrician

Another word of warning, I am a time served electrician and I can assure you that a lot of electricians dont have a clue about DC or 12 volt systems

 

if you hirer a electrician ask them two question

 

1. Have they passed the BMET exam?

2 Have they got a copy of the Fifth edition of the BMEEA Code of Practise.

 

If the answer to both question is yes they should be OK

 

If one of the answer is no look for another sparks

 

Keith

So don't listen to anything I say

[Tony Brooks]

Another word of warning, I am a time served electrician and I can assure you that a lot of electricians dont have a clue about DC or 12 volt systems

So don't listen to anything I say

 

or what I say.

 

 

 

Tony,

 

My 6mm suggestion was a late at night off the cuff response to emphasise that 1mm and 1.5 mm cables are not the way to go. I am actually happy with 4mm and even 2.5mm if the volt drops work out ok. Any thinner than that and I feel they start to lack strength and can get kinked etc, though I will use 1.5 inside the wiring cabinet for warning lights etc.

 

My post was in now way intend to be a criticism of what you said, at least 6 sq. mm.CCSA cable should do for many runs but possibly not all. I am very concerned that the OP seemed to just latch onto that size and think it would be fine for all circuits. I think we have educated him now.

[Arthur Brown]

Personally I think you should learn about boat wiring then do your installation. Ebay is probably the worst place to learn from -the information is put there by sellers!

 

1.5mm is OK for 15A at mains where a couple of volts dropped is not significant. for 12v a couple of volts lost is very significant so I'd doubt the use of 1.5mm flex for more than 5A even so with a 70ft boat there can be some long cables (Horn and tunnel light in particular) these may not carry much current without being fatter than the tables suggest.

[dmr]

To the OP

Don't worry too much about qualifications. Many "electricians" and "engineers" on the cut are totally self taught with no qualifications. Some are rubbish, some are brilliant. If you are a DIY type person then don't be put off. Read up about cable sizes, post a detailed plan here and ask the forum to comment on that. Find a friendly boater who understands this stuff to have a quick look at what you are doing and confirm it is up to scratch. If you are fitting out a brand new boat to sell then it needs to be totally correct, if you are trying to gets some lights on an old plastic cruiser liveaboard then it needs to be safe, but not a work of art. The wiring on many old boats is terrible, you can most likely do better.

 

.............Dave

[Bod]

Read this site, it was written by an acknowledged expert, who had his own narrowboat.

 

http://www.smartgauge.co.uk/cable_type.html

 

Many on here knew him as Gibbo.

 

Bod

[Murflynn]

I don't like the way the equations are expressed in Gibbo's solution.

If we allow a maximum volt drop of 1volt in a 12v system, then the cable size in sq.mm. is:

0.018 x (return length of cable in metres) x (current in amps)

[George94]

This is an excellent volt drop calculator:

 

http://www.midsummerenergy.co.uk/solar_panel_information/voltage-drop-calculator.html/

[Chewbacka]

Deleted

Edited May 27, 2016 by Chewbacka