New BSS Requirement: 25mm2 cables.

[huldah]

I had my BSS inspection and the surveyor told me that in future all battery cables will have to be 25mm2. I have not been able to find more details, however, the following are my own thoughts.

Does this refer to new boats and those being rewired or updated?

Is this because damaging a thinner wire that is not fused could cause a fire throughout the length of wire, perhaps 20 ft or more? With a thicker wire a fire will be confined the the damaged area.

I intend to rewire Pendragon. As far as I can see this would mean terminating the 25mm2 cable in a main fuse. Each wire from this fuse to the fuse box will need to be capable of carrying the full current of the main fuse.

 

[pvb]

I had my BSS inspection and the surveyor told me that in future all battery cables will have to be 25mm2. I have not been able to find more details, however, the following are my own thoughts.

Does this refer to new boats and those being rewired or updated?

The current BSS already requires battery cables to be "approximately 25mm2" - see chapter 3 of the BSS. This applies to boats being checked for BSS compliance, whether new or old. 25mm2 is a sensible minimum size for battery cables - some installations may need heavier cable.

I intend to rewire Pendragon. As far as I can see this would mean terminating the 25mm2 cable in a main fuse. Each wire from this fuse to the fuse box will need to be capable of carrying the full current of the main fuse.

I don't understand what you're trying to say. Fuses protect wire. You'd have heavy cable as far as your main switch panel, then separately-fused circuits with smaller wire for distribution to lights, etc.

 

[TrueBlue]

The BSS people (and a lot of other quasi regulation bodies) regularly anger me -

I had a quick look at the BSS Guide - here
and there's nothing specific about cable size, other than it should be "adequate". That's not helpful, and more to the point the "examiner" - who doesn't have to have any knowledge of industry custom or practice can make it us as they go along.
Some of them do, probably through ignorance, rather than for any questionable reason.

To my mind these things should be a matter of record, rather than whatever an instructor says in a training session.

From a practical standpoint 25mm sq is probably a sensible size, but again, look at your car - if late - I bet your main cable is a lot less than 25mm.

All this minor rant doesn't help you because in the final analysis, you'll want your boat to comply, and nobody, but nobody is going to make an issue of a small point as any appeal / complaint will be rejected by the Scheme folks (unless the inspector is way, way out of line).

25mm has been bandied about ever since the scheme came it and there's been no official ruling yet.

The scheme doesn't "do retrospective" , after a lot of fuss they've made exceptions for existing installations, for the most part.

Looking at your post again; I thought the issue was that battery interconnect and starter cables should be heavy gauge = 25mm, but main bus feeds should be sized for whatever your installation's requirements are.

Apart from my feed to the 1800W inverter (25mm) the bus feed to my control cabinet is 8mm (?) not measured it, as motor industry flexible cable is measured in sq. mm.

Let's see if anyone else can help, without getting wound up by the BSS wallahs.

 

[pvb]

I had a quick look at the BSS Guide - here
and there's nothing specific about cable size, other than it should be "adequate".

Look again.

 

[ProDave]

If the BSS is imposing a BLANKET ruling saying those cables must be 25mm then it's stupid, without giving the surveyor any oportunity to actually look at the real loads and cable protection.

Yes in most cases, where the battery is charged by an alternator, and is used for starting a motor, then yes 25mm would be a reasonable minimum size.

But on a little boat like mine, with only an outboard motor (without charger) the battery is just there for VHF, depth finder and lights. It's wired in about 6mm cable and FUSED at the battery appropriately.

I do hope a BSS inspection would not fail my boat and insist on stupid sized wire for the job. Thankfully it doesn't need BSS but you never know one day.

I guess to get round it I need a very short length of 25mm to a master switch right next to the battery, then I can do what I like.

 

[huldah]

I don't understand what you're trying to say. Fuses protect wire. You'd have heavy cable as far as your main switch panel, then separately-fused circuits with smaller wire for distribution to lights, etc.[/QUOTE]

I have already built a fused box including bus bars. The problem is that I may have difficulty finding room for a 25mm2 cable in the box. So a separate fuse may be required underneath the box.

 

[TrueBlue]

Oh Poo..

Look again.

What an idiot - I clicked on a tag labelled "online" - which on second examination is the older 2002 version for hire boats.

Bother, I do like to get things right.

I can't quarrel with the above, quite clear, so

apologies to all (I still like to rant about BSS and the like, if I can find an excuse...)

Frinstance my first examiner insisted that I had to have to a switch in the negative feed (??) rather than in the Positive - doesn't make sense to me, but it was done. switches everywhere, and not deemed not to be a requirement - see last note above.

 

[ProDave]

I don't understand what you're trying to say. Fuses protect wire. You'd have heavy cable as far as your main switch panel, then separately-fused circuits with smaller wire for distribution to lights, etc.

What I am trying to say is on my boat, there are only very small loads, so no need for 25mm cable anywhere.

BUT the danger of using small cable is, if a short circuit occurred, then a large current would flow and the cable would get dangerously hot. Mitigated by a suitably rated in line fuse and fuse holder right next to the battery.

This is how my boat, and probably thousands of similar small boats, and certainly many thousands of caravans are wired, that only use a 12V battery to supply small loads, and only has a small (if any) battery charger.

This is perfectly safe, arguably more safe than a larger boat that may have many metres of large cable, unfused, from the battery to the isolator.

All I was saying is the BSS seems to be written such as to ignore small installations like mine, and insist everything is wired as though the battery is going to be used for starting a fixed engine, and charged at a high rate from an alternator on that engine.

 

[VicS]

Fit a master switch and a fuse rated to support your max load near your battery. Connect that to the battery with 25mm² cable. BSS requirement met!

Wire from the fuse/switch to your distribution panel in cable that is the next size rating up to the fuse. ( negative same size)

cannot see that's not what you would want anyway.

 

[Ubergeekian]

If the BSS is imposing a BLANKET ruling saying those cables must be 25mm then it's stupid, without giving the surveyor any oportunity to actually look at the real loads and cable protection.

It seems that to pass a pass a BSS inspection, my Jouster (no reasonable offer refused) would need the same size battery cable feeding a Seafarer echo sounder, two 5W cabin lights and a 25W tricolour as someone in a 38 footer with inverter, pressurised water system, engine, fridge ...

Hooray for common sense!

 

[Bobobolinsky]

The BSS people (and a lot of other quasi regulation bodies) regularly anger me -

I had a quick look at the BSS Guide - here
and there's nothing specific about cable size, other than it should be "adequate". That's not helpful, and more to the point the "examiner" - who doesn't have to have any knowledge of industry custom or practice can make it us as they go along.
Some of them do, probably through ignorance, rather than for any questionable reason.

To my mind these things should be a matter of record, rather than whatever an instructor says in a training session.

SNIPPED

Let's see if anyone else can help, without getting wound up by the BSS wallahs.

Sorry, can't agree with your assessment of BSS examiners, there are strict requirements for admission to the course, dealing with qualifications and experience, the course itself is an intensive two week course with evening reading required (so much that the training centre is considering pre course online content. The is only one approved training provider, Evesham College, so all courses are well rehearsed and led. All the BSS examiners that I have been involved with have had more than adequate experience of the marine industry. Finally, you have to be pretty committed to spend £3K on the course and attend regular seminars

 

[VicS]

It seems that to pass a pass a BSS inspection, my Jouster (no reasonable offer refused) would need the same size battery cable feeding a Seafarer echo sounder, two 5W cabin lights and a 25W tricolour as someone in a 38 footer with inverter, pressurised water system, engine, fridge ...

Hooray for common sense!

No!
you only need 25mm² for the items listed here

As my reply above 25mm² to a master switch. It is the only one on that list that applies. BSS satisfied.

Fit a 5 amp fuse and then you can safely run power to all the other items you list in 0.75mm² except where heavier is need to avoid volts drop.

 

[ProDave]

Fit a master switch and a fuse rated to support your max load near your battery. Connect that to the battery with 25mm² cable. BSS requirement met!

Wire from the fuse/switch to your distribution panel in cable that is the next size rating up to the fuse. ( negative same size)

cannot see that's not what you would want anyway.

I would not want that, because there is some distance between the battery and the master switch. I like the master switch where it is, it's nice and accessible.

And as I say, the cable between the battery is more than adequately rated for the load, and fused to prevent danger. Common sense prevails.

Now if the BSS forced me to either move the master switch closer to the battery (and less accessible) or fit huge great thick (and almost certainly therefore un fused) leads instead, then I'm afraid the BSS is an ass.

I am all for a proper electrical engineer designing the system and choosing appropriate cables and appropriate protection (mechanical and fusing) for those cables, but alas that's not what this is about, it's all about "ticking boxes"

If the examiners are really as highly trained as you suggest, they should be able to clearly see a simple installation like mine is safe.

 

[charles_reed]

Problem is less wire overheating, but more voltage drop, increased amps and overheating of high-current consumers, such as windlasses (or in my case the keel-lift pump which draws 440 amps on start-up).

That cable size is only demanded from battery to main switch, but is probably wise for feed to bus-bar, winch etc.

 

[VicS]

I would not want that, because there is some distance between the battery and the master switch. I like the master switch where it is, it's nice and accessible.

And as I say, the cable between the battery is more than adequately rated for the load, and fused to prevent danger. Common sense prevails.

But surely you have a battery isolating switch close to the battery?

 

[No Regrets]

All this.....just for a couple of pieces of Wire.

FFS.......ROFL!

 

[VicS]

All this.....just for a couple of pieces of Wire.

FFS.......ROFL!

But a couple of pieces of wire connected to a battery capable of delivering several hundred amperes and consequently well able to set fire to your boat in the event of a fault.

 

[Ubergeekian]

But a couple of pieces of wire connected to a battery capable of delivering several hundred amperes and consequently well able to set fire to your boat in the event of a fault.

So better make the wires as big as possible, then. Especially on the live bit before the isolator.

 

[ProDave]

But a couple of pieces of wire connected to a battery capable of delivering several hundred amperes and consequently well able to set fire to your boat in the event of a fault.

Hence the FUSE close to the battery.

In the event of a short, having 25mm cables WITHOUT a fuse will not do anything to stop the boat catching fire.

I could understand this wire size stipulation if there was a maximum (very short) distance and conditions laid down for mechanical protection to prevent a short, but there are not.

So I still contest that for my boat (and many thousands like her with low power consumption) that thinner wires protected by a fuse right next to the battery is much much safer. That is after all how caravans are wired, and a boat like mine has much more in common with a caravans 12V system than it does with that of a larger boat with inboard electric start engine (which is much more like a cars electrical system)

 

[savageseadog]

I'm an electrical engineer with many years experience and would like to think I know what I'm talking about. I've no idea what the standard says and can't be bothered reading it. It is generally a good idea to use maximum size wire in every instance for low voltage DC systems. Every connection to a battery should be the minimum possible length to a fuse and maximum size. The basic issue is that a short circuit down a long length of thin wire will potentially create enough heat for a fire. The other issue is the battery could overheat and blow or catch fire. I imagine the standard is saying that the first run of cable to a fuse panel should be of minimum length and minimum 25mm sq and any size you like after the fusing (or hopefully a set of sizes/lengths for fused/breaker ratings). If the standard says anything else I couldn't imagine why.
It's not a trivial matter and it would be good to see some kind of standard or regulation set out and used.
It's always worth keeping the cable size up anyway, there is less voltage drop, less prone to damage and less prone to catch fire.