Connecting a water pump to the boats 12 volt system??

[Matt341]

HI All,

Im at the stage now when Im ready to connect the water pump to the 12 volt supply. I have run the wire back to the switch area fine but im a bit (very!!) confused.

There are a total of 3x 6 switch panels, I was thinking of connecting the pump to the bilge pump switch as there is no auto bilge pump.

Wires everywhere is a recipe for confusion but I think I have sussed them out, there is a positive supply to the switches which is then carried across each panel, there is then a negative off each which seems to be connected to a gold main neg block, there are then positives feeding off each individual switch connnecting to a terminal block in which the appliance is connected into.

E.g. GPS, positive out of switch, into terminal block, GPS positive then connected to positive from switch (GPS) via the terminal block. The negative then seems to connect to an unswitched block. Im guessing its just the positive that is switched.

The bilge pump positive goes from the switch to the terminal block and there is then no positive going from the terminal block which proves there is no bilge pump, it must just be a way of keeping the wires in one place.

I was thinking of connecting the pump by connecting the negative to the main block and the positive to the terminal block matching the switch feed from the bilge pump as there is no bilge pump. (Just using this as its a spare switch)

My only concern though is that its going to be a large current draw and I have been advised that I may be better to bypass the main fused switch system for lights etc. and to connect to the battery isolation switch, 1,2,both. Any suggestions whether I should do this and if so, how?

Of course the pump will have to be switched and fused for safety and so that we can turn it off when we leave the boat.

I have some pictures of the switches/wiring if this helps.

It just seems that 4 amps is a lot to put through the main system so im thinking if it would be safer to connect it more directly to the battery but at the same time keep it safely isolated.

I look forward to advice on this.

Many Thanks
Ian

 

[Bilgediver]

HI All,

Im at the stage now when Im ready to connect the water pump to the 12 volt supply. I have run the wire back to the switch area fine but im a bit (very!!) confused.

There are a total of 3x 6 switch panels, I was thinking of connecting the pump to the bilge pump switch as there is no auto bilge pump.

Wires everywhere is a recipe for confusion but I think I have sussed them out, there is a positive supply to the switches which is then carried across each panel, there is then a negative off each which seems to be connected to a gold main neg block, there are then positives feeding off each individual switch connnecting to a terminal block in which the appliance is connected into.

E.g. GPS, positive out of switch, into terminal block, GPS positive then connected to positive from switch (GPS) via the terminal block. The negative then seems to connect to an unswitched block. Im guessing its just the positive that is switched.

The bilge pump positive goes from the switch to the terminal block and there is then no positive going from the terminal block which proves there is no bilge pump, it must just be a way of keeping the wires in one place.

I was thinking of connecting the pump by connecting the negative to the main block and the positive to the terminal block matching the switch feed from the bilge pump as there is no bilge pump. (Just using this as its a spare switch)

My only concern though is that its going to be a large current draw and I have been advised that I may be better to bypass the main fused switch system for lights etc. and to connect to the battery isolation switch, 1,2,both. Any suggestions whether I should do this and if so, how?

Of course the pump will have to be switched and fused for safety and so that we can turn it off when we leave the boat.

I have some pictures of the switches/wiring if this helps.

It just seems that 4 amps is a lot to put through the main system so im thinking if it would be safer to connect it more directly to the battery but at the same time keep it safely isolated.

I look forward to advice on this.

Many Thanks
Ian

To quote the robot in Short Circuit the movies......." INSUFFICIENT DATA"


Please advise what pump? What current rating? What is current rating of bilge pump breaker or fuse?

 

[ColinS]

4 amps is not a lot in boat terms. A 25 watt masthead Tri-colour bulb draws 2 amps at 12 volts. It all depends on the wire sizes involved.

 

[fireball]

If you have a spare switch then I'd use that - as ColinS says - 4amps is not a lot in boat terms ...
You don't say if it is a bilge pump or fresh water pump you're attaching - I assume the later - so you don't want it on when you switch the boat off - far better (IMHO) to run the domestics through the one keyswitch so you KNOW you have turned everything off when you turn that master switch.

A water pump won't be drawing continuously anyway (or shouldn't) so 4amps will be in bursts and not continuous - as long as the wiring is thick enough it will be fine.

 

[Trundlebug]

Your switch panel should be fitted with a fuse for each switch. All you need to do is ensure the fuse for your bilge / water pump switch is sufficient to cope with the rated / quoted current draw for the pump you intend to fit.

I wouldn't worry about the current through the switch, or panel overall, it should be fine - and the panel will have been designed for this use.

As long as you use the correct rating of wire (that is, the right cross sectional area of copper such as 2 sqmm) everything will be fine. Usually, water pumps don't run for long anyway so although the current drawn will be 4-6A, it won't be for long enough to get the wire hot or cause any problems.

 

[Stemar]

I think there's enough information to make a start

If the pump draws 4 amps, I'd expect the existing wiring to be up to the job. Your idea of using the existing (spare) bilge pump switch seems sound, too. I assume these panels have fuses or circuit breakers. If the exisiting fuse is rated at 8amps or more, then I'd go ahead. If it's less, or you can't find the fuse, then you need someone who knows what they're doing to help you.

Here's what I'd do (apologies if this is a bit Granny/eggsucking!)

1. Work out where my wiring has to go & measure the length
2. If the length is less than about 4m, use 8amp cable, if more I'd use 10amp. Too small is a problem, too big just costs a bit more. Buy the wire. I used a sheathed twin cable for mine, 'cos it's easier to install neatly. It was 10 amp 'cos that's what the chandler had!
3. Turn off the power (battery isloator)
4. wire it up:
[battery +ve] - [isolator] - [fuse] - [switch] - [+ve connector in panel]: Existing wiring
[+ve connector in panel] - [pump]: red wire
[pump] - [-ve connector in panel]: black wire (if your colours are different, it doesn't matter too much, but I'd label them)
[-ve connector in panel] - [battery -ve]: Existing wiring.
5. Power back on
6. Test pump.

If it's all OK, job done. If the fuse blows or the pump is a bit unenthusiastic, you'll probably need help to track down the problem.

I live too far away to give hands-on assistance, but would be happy to help via PM or email.

 

[KenMcCulloch]

Hello Ian
I think you have assumed that everyone has read your previous posts about installing a pressurised water system, which is presumably what the pump is for? If so then using the unused 'Bilge Pump' switch and fuse on your main panel should be fine. (You describe them as switches but you don't mention fuses; it may be that the panels are fitted with miniature circuit breakers in which cases additional fuses are not required.) Just make sure that the cable you use and the rating of the circuit breaker or fuse are matched and adequate for the load your pump represents.

Incidentally if you do install an automatic bilge pump it's common practice to wire that independently of the distribution board and battery switches so that it remains active even when everything else is switchjed off.

 

[Matt341]

Thank you everyone for the replies, sorry that I didnt explain in more detail.

The switch boards were all replaced in the last few years as well as the wiring I believe, they are made by Aqua marina and are fused, on the rear the positive wire goes through the fuse and then to the switch.

When I turn the bilge pump switch on the switch doesnt light up like the others so im assuming there is no fuse in place, the previous owner did say that only the switches which are used, e.g. cabin lights, running lights etc. have fuses in them as he was trying to prevent un used switches being turned on. So although the fuse holder is in place there is no fuse in the Bilge Pump switch. I will also change the description to say water pump not bilge pump.

The pump is a fresh water Jabsco, max draw - 4amp. My only concern is that I dont want the lights to dim every time the pump is operate but this may be un avoidable.

So im right in thinking that it will be fine to connect the neg to the main neg block and the positive to the spare bilge pump switch. This is as long as the wiring is thick and I have a suitable fuse in place.

I want to ensure that the pump can be isolated with the isolation switch so think that this is the best way by connecting it to the fused switches etc.

Sorry for the confusion and many thanks again, hope this information is more helpful.

Ian

 

[VicS]

Some vague statements about fuse ratings and cable sizes in some of the above posts.

You need to know.

• The maximum current consumption, in amps, of the pump while running.
  
• The recommended fuse or mcb rating to allow for the high current when first switching on
  
• The total cable run distance ... there and back.. in order to determine a cable size that will not result in excessive (>3%) volts drop.

The cable size must be large enough to safely carry the current equal to the fuse/mcb rating. That's the minimum size you can safely use. (It is likely to be 1.0mm² or 1.5mm²)

The cable size must also be large enough for there to be no excessive volts drop (3% is a common maximum figure used) along its length.
There is a table HERE to give you a suitable cable size based on total run length and current
(Sorry its American and therefore uses quaint old feet and gives the result in American wire gauge, AWG, but there is a link on the page to a conversion table in order to convert to mm²)

It is very unlikely that you will arrive at a cable size of less than 14AWG (2.0mm²) or even 12AWG (3.0mm²).


As far as the source of the supply is concerned a spare switch and fuse or mcb intended for a bilge pump would seem ideal. A bilge pump will probably have a higher current rating so check and adjust the fuse/mcb as necessary. An automatic bilge pump would be better fed directly from the battery anyway .
The cables supplying the switch panel must be heavy enough to safely carry the maximum load that they are likely to be called upon to carry, they must also be heavy enough to carry that load without exceeding the 3% volt drop. So again the table in the above link should be entered with the total cable run (there and back) between battery isolator and panel and with the maximum likely load to obtain a minimum size for them.
If you have a lot of power hungry items fed from the panel you could end up with quite a sustantial cable size... doubling up on a lighter cable could be an option.

 

[Cliveshep]

Bilge pump and pressurised water system

VicS has set you on the right path as usual, get the wire size right and there is no need for your lights to dim when you run a tap. However, I'll add my two-penn'orth here - you say you have no bilge pump? I'd counsel install an automatic bilge pump independant of the battery master switch and leave it ON, (but run through a fuse of course). It'll only draw power when comes on if needed to pump out the boat, assuming your batteries are up to scratch!

As for the pressurised water system, use a dash panel switch by all means, but I'd suggest that, assuming you have a battery master switch you turn off when you go home it is not necessary to put a switch on the dash board as the first thing you'll probably do, (well , I do anyway,) is to come aboard, turn on power and gas and put the kettle on whilst sorting out everything else. For this reason we never turn off the water pump, it is always on and is shut down only by the master switch. When we're aboard it is left on, unless there is a leak the pump will only come on when it senses the pressure drop caused by the opening of a tap. We only turn off our pump when blowing down the system with an air line as part of winter layup.

Therefore, the only time you might want power on but water off is when winterising, so the switch can go anywhere convenient but not necessarily on the dashboard if there is no free circuit. Just make sure it is fused!

Save the bilge pump circuit for a bilge pump!

 

[mitiempo]

Ian
I would just like to point out that the fuse on the panel (or on any feed lines to the panel) is sized for the wire gauge you are using, not the item being installed. The reason for a fuse (or breaker) is not to protect the pump but the wires leading to it. Ideally every wire on a boat is protected by a fuse or breaker of the appropriate size for that wire. See this link for a detailed explanation. http://bluesea.com/viewresource/95
Here's another link to find wire size (also in the "quaint" ft and awg wire measurement) but it's easier to use - just set to 2,3,5, or10% loss, plug in return distance and amps to be carried and it calculates wire size. http://boatstuff.awardspace.com/awgcalc.html
Remember in DC wiring the distance from the panel and back is used for calculation. Hope this helps.
Brian
Victoria B.C.

 

[Matt341]

HI All,

Thanks for the advice. Im going to get it done on the weekend so hopefully we will have hot running water soon.

I just have a few questions, why does the wire need to run there and back?? I thought for 12 volt that the pos/neg would connect to the switch panel and then run along with the other wiring to the bow and the pos/neg connect to the pump wires??

I was thinking about using heavy duty 240 cable, I have plenty spare and of course just wouldnt use the earth. Should this be ok?

Thanks for the links, I will use the chart to calculate the fuse needed. Im guessing 5 amp as the peak pump is 4amp.

Many Thanks
Ian

 

[Stemar]

A car has metal bodywork that is earthed to the battery, and almost everything is earthed though its casing to the bodywork which carries the return, so you only need the one wire. Boats tend not to conduct electricity, so another way of the electons back home to the battery has to be found, hence the return wire. (actually the electrons are negative, so go the other way, but the idea's the same)

As for using 240v cable, it would work, but, if you're talking about mains cable, the conductors are pretty thick, which means they can develop metal fatigue from vibration and fail. I'm from good Yorkshire stock on my father's side and have Jewish blood from my mother's, so I can give lessons on tightness to anyone, but I'd prefer to buy the proper stuff.

OTOH, mains flex that you'd use for a fire would be fine from an electrical point of view, but a bit bulky because of the unused 3rd wire. I think I'd sooner have a twin cable - it won't break the bank!

 

[Matt341]

Thanks for the reply,

I am a little confused now though, where should the returning wire connect? I had a look at the electrics on the weekend and it seems there arent any returning wires even though she was rewired by a marine eletrician in 2004, e.g. one pos/neg to each light, one pos/neg to the stereo, one pos/neg to the shower drain pump.

Is this completely necessary??

Im sure I have some 2 core wire which could be used instead of the 3 core.

Thanks
Ian

 

[Searush]

Thanks for the reply,

I am a little confused now though, where should the returning wire connect? I had a look at the electrics on the weekend and it seems there arent any returning wires even though she was rewired by a marine eletrician in 2004, e.g. one pos/neg to each light, one pos/neg to the stereo, one pos/neg to the shower drain pump.

Is this completely necessary??

Im sure I have some 2 core wire which could be used instead of the 3 core.

Thanks
Ian

I think you have been confused. There are just 2 wires, one positive, one negative. When current flows, one of the 2 wires is sometimes called the return.

 

[Matt341]

Thanks for the reply,

Yes I understand now, I thought there was something that I wasnt aware of, Boats electronics are so complicated now that I wouldnt have been surprised if there was more complication.

Hopefully it will just be a case now of connecting the 2 wires to the pos and neg, positive on the switch and negative on the main negative block.

I was concerned about where to run the wire but then after having a look behind some panels I found the main wiring for the bow cabin lights etc. so will just run the new wire with these.

Thanks again to everyone for their help, this forum is brilliant.

Ian.

 

[Bilgediver]

The pump is a fresh water Jabsco, max draw - 4amp. My only concern is that I dont want the lights to dim every time the pump is operate but this may be un avoidable.

Ian

It seems this problem has yet to be addressed. Is it possible that the electrical system has grown like Topsy. You mention there now being three panels in use.

Is it possible that the main supply tpo the three panels is still the original wire as used when the boat was new and maybe now not of sufficient size to power all the electrics. There is no reason for the lights to dim just because a pump drawing 4 amps has started.

I would suggest you look at the feeds to the panels IE the red wires from the batteries and also the negative (return ) line from theearth/negative bus connection back to the batteries as you may need to replace with a wire of larger cross section.

If you need help on this then let us know the 18 items you have connected to the three panels and the wattage on each circuit so we can check if the expected maximum currents are comfortably within the capacity of the wires presently installed.

 

[Matt341]

Thanks for your reply,

I havent yet tested the pump so dont know if the lights will dim, it was just suggested by someone down the marina that they might??!!

As she was re wired fairly recently it is very likely there wont be dimming. The cables running from the batteries are really thick and so are the feed cables for each panel.

The main draw of the power is going to be the lights, 4x10watt spots in the roof, 1x10watt above the galley, 2x10 watt reading lights, 2x10 watt lights up the bow, 1x10 watt in the wardrobe and 1x20 watt in the heads. Im glad we have a solar panel and battery charger now lol however, its unlikely these will all draw at once.

Will let you know how I get on this weekend.

We have put some massive loads off the 12 volt system so far, e.g. running a fridge compressor all night off the battery and this didnt cause the lights to dim so im thinking it should be fine.

Many Thanks again
Ian

 

[Bilgediver]

Thanks for your reply,

I havent yet tested the pump so dont know if the lights will dim, it was just suggested by someone down the marina that they might??!!

Ian

Ian it sounds like your marina friend has incorrect wiring. The way you describe your setup suggests you have no reason for concern and was done by an electrician who believes in redundancy . Some boat builders certainly scrimp in this area. One only has to look at the bell wire used by Westerly in the 70 s to see this though it does ensure longer bulb life and a warmer heads

 

[Matt341]

I dont know what the original wiring was like on our Westerly so I cant really comment, but on our previous boat, which was built in the late 70's, (wasnt a westerly), the electrics were very thin, the main pos and neg battery cables were even wired the wrong way round, e.g. the red wire went onto the neg of the battery and the black was the positive!! But then I suppose in the 70's boats were a lot simpler, on that boat we only had 3 strip lights, an old Seafarer depth sounder and the running lights, that was about the only things running off the batteries other than the engine starting.

Now that boats have 12volt fridges and 12volt pumps and other high drain items off the batteries, the electrics need to be much thicker. We have only stayed on this boat a few times but notice that with the charger off the battery voltages do drop after a night onboard, even without the water pump!! I think one of the biggest drains is likely to be the lighting as it is on for the longest time. Thankfully we also have a 30watt solar panel which will hopefully keep the batteries topped up if we are on anchor.

Thanks again
Ian