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Author Topic: techie sparky question  (Read 7401 times)
Amy
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« on: March 23, 2010, 02:02:27 PM »

Can anyone help me size some cable I need to fit on the boat please?

Im going to have a battery bank and inverter, charged up by a combination of 220v shore power and engine driven alternators.

As the boat is 50' long, and various mooring options might be possible, I would like to put a bulkhead mounted 16Amp three pin blue socket fitting in the wheel house to plug the shore power lead into, but also fit the same at the bow, and connect the two into the battery charger.

Given that the bow socket will be some 35' from the charger in the engine room, what size/thickness cable do i need?
To comply with regs, it must be flex cable, multistrand type, not domestic house wire.



I have found some rather nice LED resessed ceiling lights and would like to run a supply from the engine room, the full length of the ceiling, up one side of the boat and back down the other side in a ring to supply posibly up to 20 lights, 10 one side and 10 the other.

Can I do this in one circuit or is it best to do individual rooms on their own supplies?
Whichever way, will there be much voltage drop and will that effect the LEDs.
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djh
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« Reply #1 on: March 23, 2010, 02:09:56 PM »

Isn't it simpler to have a single socket and just make the shore lead 50' longer?
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« Reply #2 on: March 23, 2010, 02:14:48 PM »

No cos Im also having a backup genny which can live in a box on the foredeck and a 4' lead to plug into the front socket.

Got to think of my old age and back. Cant be lugging the jenny out every time I want to use it.
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Ted
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« Reply #3 on: March 23, 2010, 02:46:04 PM »

I would use Arctic 3 core 16A caravan hook-up cable - blue covering. Available from camping suppliers at about 1/m.
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« Reply #4 on: March 23, 2010, 03:10:13 PM »

What is the power of the inverter?  That will determine the starting point for voltage drop.  In practical terms, Ted's suggestion of 16A cable will be fine. 

Make sure that the foredeck fitting is 100% waterproof.  Salt water and electrics, especially 220v do not mix.

The blue IP44 fittings might not be good enough http://www.screwfix.com/prods/49232/Electrical-Supplies/Industrial/240V/200-250V-MK-Commando-Interlocked-Straight-Socket-2P-E-IP44#

go for proper marine fittings.

For interior lights, go for several switched circuits.  Then you have control and can turn unwanted ones off at the distrbution board.  I know that LED bulbs are lower wattage than the filament bulbs when I sailed a lot, but energy manangement is very important on yachts.  Maybe also use a thick enough cable to allow filament bulbs as you will find LEDs are give a harsh light.


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johnrae
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« Reply #5 on: March 23, 2010, 04:03:04 PM »

Don't wish to sound petty, but, it's a bulkhead plug you need on the boat, so's the travelling lead (extension) has a "free" socket end on it to connect at the boat's fitting.  If you fitted a socket on the boat the lead would have to have a plug with pins on both ends of it, which you be an accident looking for somewhere to happen.
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Justme
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« Reply #6 on: March 23, 2010, 04:13:10 PM »

Danger Will Robinson Danger



If you have a plug at each end of the boat (it has to be a plug even if its a mounted one) then unless you fit the central point with an isolator to select the end in use or for a cheaper solution a  twin socket (each socket is wired to one end of the boat only)& single plug (that is wired to the inverter/charger feed) set up then when you plug one end of the boat in the other end will have the live on the exposed pins.

As its length can be a max of 12m & the load will be the combination of the charger & the mains loads I would need to know what those loads would be. That said most boaters find that the incoming shore line is limited to 3-5-10-16 amps any way (thats where an Victron multi comes into its own).

Assuming the load is 4kw, the distance 12m (but dont forget you will get more v drop on the internal wiring & that the feed you are using will be a distance from the supply so the v might already be quite low) then to keep to less than 3% drop 1.5mm would be inspec. I would go for at least 2.5mm as its easy to get but would prefer 4mm.


If your shore line & bow to bat feed is going to add up to 42m then 4mm would be needed.
« Last Edit: March 23, 2010, 04:18:07 PM by Justme » Logged

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« Reply #7 on: March 23, 2010, 04:24:11 PM »

Hi Amy
If you are fitting a 230v supply you should really fit a galvanic isolator in the earth lead on board. It allows earth protection but stops galvanic currents flowing. You should also have an indicator to tell you that the live and neutral are the correct way around from the shore.(I think this is mandatory on the continent, but good for safety anyway) The wires in a supply lead might be crossed or the marina outlet might be wrong. Just need 2 x 230v indicator bulbs. connect one from live to earth and connect the other from neutral to earth. can have a push test button to switch them on or have them on all the time. I normally have a green one on the live and a red one on the neutral. If all is correct the green light will be on if it is wrong way around the red light will be on. It ensures that if you have a fault on board the breaker on the live wires will trip. if it is the wrong way around it wont.( the neutral wire is normally tied to earth shoreside so should only be a few volts to earth by the time it is onboard)
If you can fit the appliance inlet somewhere undercover it will last a lot longer.Get the ones with a waterproof cap and keep the pins inside greased with electrical grease to stop corrosion.
Iain
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« Reply #8 on: March 23, 2010, 04:42:06 PM »

Amy

Is the boat to be moored in UK. If so you will also need to comply with BW regs and inspection to gain the certificate of compliance. Some of their regs do seem a bit strange.
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johnrae
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« Reply #9 on: March 23, 2010, 07:46:39 PM »

Amy,

Some sensible info contain in this link, electrical info in sections 3 and 4. 
http://www.boatsafetyscheme.com/site/2ndedBSSEssentialGuide_212.asp

I presume you are aware that high current DC cables, if run as a parallel pair of single cables (for flow and return circuits), will try and force themselves apart due to the resultant magnetic fields.  Hence they must be well strapped down to prevent them "jumping" apart.

I first came upon the effect many years ago when I rewired my dads starting systems with superflexible welding cable   -   very impressive.

jack
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« Reply #10 on: March 23, 2010, 09:17:28 PM »

Hi guys

Thanks for the good advice.  My terminology might be misleading to some but I know what I mean. I wasnt going to leave a male ended plug dangling live where it might just cause a shock  Grin

Ive got a download copy of the BSS regs and have already consulted that with regard to relevant chapters. Isolation from the water and hull are vital, so im not going to be using the stell hull as the negative return for 12v systems.

Im still undecided whether to go down the 12v or 24v route for alternators and batteries.
What are the pros and cons for each?
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guydewdney
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« Reply #11 on: March 23, 2010, 09:29:11 PM »

24 more efficient - kit more expensive - need 24 ->12 'dropper' for most easily available 12v kit.

invest in some bigger wires, and stick to 12v.
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EccentricAnomaly
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« Reply #12 on: March 23, 2010, 09:52:17 PM »

Whichever way, will there be much voltage drop and will that effect the LEDs.

Worth doing the arithmetic but I think you'd need a lot of LED lighting to get significant voltage drop on moderately sensible wire. 

A small voltage drop shouldn't affect the LEDs as they should have a constant current circuit internally.  Have you selected your LED light fittings yet?  I imagine they'll be speced for a particular voltage range and current so it should be fairly easy to work out.  Remember, though, the radio interference problems Billy the Barge had with the PWM controllers on his LED lighting?
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« Reply #13 on: March 23, 2010, 10:34:46 PM »

Would suggest 24 volt every time, especially for engine cranking.  Running at 24 against 12 means 1/2 the current and hence less voltage loss in cables.  As far as equipment availabilty is concerned I think the argument isn't too strong.  Most marine and lorry equipment runs on 24 volts.  If you must use 12 volt equipment you can get very efficient switch-mode 24 to 12 convertors - not the old inefficient resistive/semiconductor reducer units of yesteryear.  Whichever way you go, you should avoid using a mix of 12 and 24, it's bound to lead to problems.

So that's 1 - 1 for 24 vs 12

jack
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« Reply #14 on: March 24, 2010, 09:58:58 AM »

Ive been rather busy late last night and early this morning.

Ive now secured the XUD9 peugeot engine ive been after and also have a gearbox to match, all at very reasonable cost compared with new prices so im much relieved over that.

Next topic to sort out is the electrical generation, storeage and conversion.

Initially I was going down the twin alternator, (backed up by shore power when available) into a large battery bank and a flippin great inverter.

As Martin is always rightly pointing out, you can only pull out a small fraction of the battery contents or you kill them quickly. I would need to spend @1000 on batts and if it were a one off investment, thats cool but everyone is telling me they might only last 5 years and thats with carefull management.

So, ........Machine mart supply a range of 240v single phase alternators for engine mounting.   Why dont I just go with one  12v or 24v alternator and mount a 240v 6kva alternator  on the engine, feed it via the victron charger to a smaller house batt bank to supply the inverter for moderate use appliances and use the  main current directly when I need the extra uumphhh?


That way im not killing batteries and Ive got up to 6Kva on hand when I need it, and I could use it to heat the calorifier when moored up as that, plus the engine cooling will heat the calorifier more quickly and reduce static engine hours.
It will make more economical sense to get as much out of the engine as possible whilst its running cos at  67hp, there is bags of power to spare.

The machinemart alternator is rated at 3000 rpm, so I could change pulley size and run the engine at 1500 to produce 50hz.

Does this make more sense?
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