12 volt circuits

[DHutch]

What I would definitely NOT recommend is using 13A square pin sockets to supply 12 volts, as we also have aboard. This means you would have 12 volt equipment with a 240 volt plug on, (we don't !), and the possible consequences of that should be obvious. At such point as I need to plug any 12 volt equipment in, I'll certainly change this unsatisfactory arrangement !

Yeah, absotulty!!

- Our boats 24v rings are done with the "ketle lead" type plugs/sockets

- Which is ok, however, there still 240v fittings, so i would have used somthing else, maybe 2pole speakons?

 

 

 

Daniel

[Guest]

I have said this before but anyway:

I once picked up an expensive DC fuse/switch panel in a chandlers with a view to using it on dc circuits in our boat. On careful examination the switches were actually marked "for AC only."

[bottle]

AC switches will work on DC but as I said before DC is more likely to set up an arc when the switch opens.

 

DC switches are designed to act faster and have a bigger gap when open.

 

The more a switch is used the more likely there is to be a problem.

 

The AC switches/breakers in a distribution board are not used that often so should give adequate service.

[alan_fincher]

AC switches will work on DC but as I said before DC is more likely to set up an arc when the switch opens.

 

DC switches are designed to act faster and have a bigger gap when open.

 

The more a switch is used the more likely there is to be a problem.

 

The AC switches/breakers in a distribution board are not used that often so should give adequate service.

 

Yes, I totally agree.

 

I seem to remember that some small toggle switches used to be rated for both AC and DC, but with a lower maximum allowed current for DC. (Don't know if that's still true ?)

 

But as I said, and I think you are agreeing, if you only ever throw the on-off switch when nothing is running, I can't see too many problems with using a 240 volt designed panel on 12 volts.

 

 

But what's the best accepted solution for 12 volt power outlets....

 

I've come across...

 

Car cigarette lighter style ones - which I don't much like - the plugs can spring (or get knocked) out rather easily, I think.

 

Use of old 5 amp style round pin Mmins plugs, (as were in use for domestric 240volt electrics before 13A square pins). THese seem to actually be sold, (very expensively for what they are), in chandleries for this precise purpose. Presumably same comments as above apply, if they are switched, and certainly I wouldn't want to use them for more than 5 amps.

 

So what's "normal", please ?

[bottle]

Try this Link and scroll down to Accessory plug & socket. about two thirds of the way down. Items 1 and 7

 

We used this type in our vehicles they make a 'positive' connection

Edited January 11, 2006 by bottle

[DHutch]

Theres donest really seam to be 'standard' quite a few carvans use the flat-bladed sockets like this one

- But they dont seam to allow you to get the pollarity right?

- They also use lighter-sockets a lot (with mulitple 3-way adapers etc)

 

The little round pins seam quite a good idea, although there also really 240v fittings, the prolly less used that the "kettle lead" type now-a-days.

 

 

Daniel

[Moley]

Many thanks for all the comments.

 

There's been quite a bit of talk about cable sizes. I'm going to be using mostly 2.5mm sq, and thicker where required.

 

However, I like Maffi's idea about running a main line forward to a secondary fuse board in the galley area. Is there any reason why I shouldn't use mains cable (the heavy gauge, solid core twin & earth stuff in your domestic ring main, ignoring the earth of course)?

[Guest]

Many thanks for all the comments.

 

There's been quite a bit of talk about cable sizes. I'm going to be using mostly 2.5mm sq, and thicker where required.

 

However, I like Maffi's idea about running a main line forward to a secondary fuse board in the galley area. Is there any reason why I shouldn't use mains cable (the heavy gauge, solid core twin & earth stuff in your domestic ring main, ignoring the earth of course)?

That is the way larger buildings are wired to avoid huge cables and volt drop. Fail to see why a boat would be any different.

[ChrisPy]

Many thanks for all the comments.

 

There's been quite a bit of talk about cable sizes. I'm going to be using mostly 2.5mm sq, and thicker where required.

 

However, I like Maffi's idea about running a main line forward to a secondary fuse board in the galley area. Is there any reason why I shouldn't use mains cable (the heavy gauge, solid core twin & earth stuff in your domestic ring main, ignoring the earth of course)?

BSS 'best practice recommendation' is for multi-stranded conductors.

 

'Heavy mains cable' may be only 2.5sq.mm., and is unlikely to meet the combined requirement for your DC systems. Have you done a voltage drop check?

 

All my domestic distribution DC wires are 4sq.mm, but there are several posts recommending 6sq.mm.

[bottle]

Many thanks for all the comments.

 

There's been quite a bit of talk about cable sizes. I'm going to be using mostly 2.5mm sq, and thicker where required.

 

However, I like Maffi's idea about running a main line forward to a secondary fuse board in the galley area. Is there any reason why I shouldn't use mains cable (the heavy gauge, solid core twin & earth stuff in your domestic ring main, ignoring the earth of course)?

 

I am going to be pedantic here, I think you mean a ring circuit ( the one with 13amp sockets attached) these are wired in 2.5mm sq cable. A 'ring main' is completely different. It has been discussed before and I believe that solid core is not advisable (someone will put me right)

 

 

Edit: Chris got here first must type quicker

Edited January 14, 2006 by bottle

[Guest]

Sorry didn't notice the solid cable bit. You should use multi strand to comply. I used cable called "tri-rated" which is highly flexible with many strands. It is available from decent wholesalers and is normally used for panel wiring. 2.5 may be OK fairly close to fuse board, but like Chris I used 4mm mainly.

[Moley]

Thanks folks, that's about what I reckoned, but thought it was a valid question.

 

Ade.

[bottle]

Thanks folks, that's about what I reckoned, but thought it was a valid question.

 

Ade.

 

Hi

 

All questions are valid, it's the answers that aren't.

 

As for cable size bigger is better the only limitation is the size of the holes (terminals) that they have to go in.

[John Orentas]

Hi Moley.

 

We seem to be getting into a competition here on who uses the thickest cables, using heavier conductors than are needed will not normally do any harm but that is not the same as saying the thicker the better. To use wires above 1.5mm for a light fitting is just silly and it will give you problems with installation.

 

The thing is to keep everything simple, at first sight fitting extra distribution boxes may seem sensible but when you sketch things out very little wiring is saved and you are just adding complexity. Remember there is no such thing as zero volt drop in any circuit, most appliances and fittings will have a written or assumed upper / lower voltage limit which they will be perfectly happy with, just use wire sizes which allow a comfortable margin.

 

As someone said Tri-rated flexible cables are good. You don't need 'sheathed' cable anywhere.

 

let me know if you would like any specific volt drop or other calculations.

[DHutch]

That is the way larger buildings are wired to avoid huge cables and volt drop. Fail to see why a boat would be any different.

And also there the huge number of cables invovled

- In our house the wireing from the disboard to the majority of the house goes up the underside of the stairs, and with the all pinned down in a line, theres almost enought to cover the whole width of the stairs.

- Imagine running pair of wires from every ring main, and every other lighting cicurt in the traford center back to one disboard.... the mind boggles!!

 

No boat is going to be that big, or have that many circuits.

- Our (24v) disboard is about 2/3 the way from the front of the boat, and every thing wires back to that.

 

 

Daniel

[alan_fincher]

BSS 'best practice recommendation' is for multi-stranded conductors.

 

Actually it's more than "best practice"...........

 

Latest BSS guide clearly states

 

-----------------------------------------------------------------------------------------------------

New electrical installations must use multi-stranded conductors, since solid conductors can easily break where there is high vibration or repeated flexing of a cable.

 

If solid conductor wiring is already fitted this is acceptable, as long as it’s securely supported and shows no sign of wear and tear.

-----------------------------------------------------------------------------------------------------

 

So use of solid conductors on anything new should be a fail, I believe.

[John Orentas]

Actually it's more than "best practice"...........

 

Latest BSS guide clearly states

 

-----------------------------------------------------------------------------------------------------

New electrical installations must use multi-stranded conductors, since solid conductors can easily break where there is high vibration or repeated flexing of a cable.

 

If solid conductor wiring is already fitted this is acceptable, as long as it’s securely supported and shows no sign of wear and tear.

-----------------------------------------------------------------------------------------------------

 

So use of solid conductors on anything new should be a fail, I believe.

 

 

There is still a problem here, the BSS intended to stipulate that flexible cable should be used throughout, the previous issue was worded as above (multi-stranded of course is certainly not the same as flexible).

 

I pointed out their error in plenty of time for them to modify the text for the latest issue but they chose to ignore me.

[DHutch]

There is still a problem here, the BSS intended to stipulate that flexible cable should be used throughout, the previous issue was worded as above (multi-stranded of course is certainly not the same as flexible).

 

I pointed out their error in plenty of time for them to modify the text for the latest issue but they chose to ignore me.

Yeah, i beleave you've said

[Sam]

There is still a problem here, the BSS intended to stipulate that flexible cable should be used throughout, the previous issue was worded as above (multi-stranded of course is certainly not the same as flexible).

 

I pointed out their error in plenty of time for them to modify the text for the latest issue but they chose to ignore me.

 

I'm sure they have their own advisors…… and yeah i agree you do say that quite often.

[alan_fincher]

There is still a problem here, the BSS intended to stipulate that flexible cable should be used throughout, the previous issue was worded as above (multi-stranded of course is certainly not the same as flexible).

 

I pointed out their error in plenty of time for them to modify the text for the latest issue but they chose to ignore me.

Yes,

 

I can see two further problems with it.....

 

1) How can a BSS inspector determine when any "soilid conductor" wire was added, and hence if it's original (OK, appenently), or a recent modification (not OK).

 

2) In my experience of failed cables and flexes, it is perfectly possible for a cable to look perfect outside, but to have broken conductors inside. Therefore "shows no sign of wear and tear" means nothing in this context to me, as a visually perfect cable may well be hiding broken, (or near broken) conductors.

 

Anyway, I think we all agree - you shouldn't use 2.5 mm T&E cable on a boat for either 12 volt or 240 volt circuits.

[ChrisPy]

Actually it's more than "best practice"...........

 

Latest BSS guide clearly states

 

-----------------------------------------------------------------------------------------------------

New electrical installations must use multi-stranded conductors, since solid conductors can easily break where there is high vibration or repeated flexing of a cable.

 

If solid conductor wiring is already fitted this is acceptable, as long as it’s securely supported and shows no sign of wear and tear.

-----------------------------------------------------------------------------------------------------

 

So use of solid conductors on anything new should be a fail, I believe.

there must be several versions of the 'latest BSS guide' floating about.

 

I downloaded the BSS Essential Guide second edition August 2005 yesterday. Chapter 3 page 7 states:

 

Best Practice

we highly recommend that new electrical installations be made with multi-stranded conductors ...... etc.

Edited January 15, 2006 by chris polley

[DHutch]

there must be several versions of the 'latest BSS guide' floating about.

 

I downloaded the BSS Essential Guide second edition August 2005 yesterday. Chapter 3 page 7 states:

 

Best Practice

we highly recommend that new electrical installations be made with multi-stranded conductors ...... etc.

Yeah, the latest version i know about is that that is on the BSS site, which is as you say Aug05, and its little only guidence.

 

Heres a screen shot.

 

 

Daniel

[Amicus]

If I may haul back to the AC/DC rating thing.

I'm having trouble getting my head around this question, let alone any answers. I can see the thing about switching and arcing but why would this thing, a simple busbar, be rated 300V AC and 48V DC.

http://www.bepmarine.com/showproduct.cfm?productid=1126

[Keeping Up]

If I may haul back to the AC/DC rating thing.

I'm having trouble getting my head around this question, let alone any answers. I can see the thing about switching and arcing but why would this thing, a simple busbar, be rated 300V AC and 48V DC.

http://www.bepmarine.com/showproduct.cfm?productid=1126

Now IMHO that is UTTERLY bizarre.

[Guest]

Now IMHO that is UTTERLY bizarre.

Mine too.