Satellite busbar for the bathroom circuits.

[Gybe Ho]

Is it legitimate to simplify a narrowboat's wiring by having a satellite busbar that is remote from the main point of fused DC distribution?

 

As I plan my future boat and design the main 24v DC circuits it occurs to me that I could run a single pair of wires 30ft down to the bedroom and branch out from there. The bathroom will have a cluster of 24v demands (Gulper-pump, 24v toilet macerator, shower extractor fan, downlight). I expect a +/- pair of 2.5mm multistrand with a 27amp capacity will cover the cumulative load given that a 24v gulper draws 1.75 amps.

 

I could extend the concept and power the main water pump under the bed and bedroom downlighters from the forward busbar but that means 6 circuits forward hanging off a single breaker back at the rear of the boat. Hmmm.

[nicknorman]

32 minutes ago, Gybe Ho said:

Is it legitimate to simplify a narrowboat's wiring by having a satellite busbar that is remote from the main point of fused DC distribution?

 

As I plan my future boat and design the main 24v DC circuits it occurs to me that I could run a single pair of wires 30ft down to the bedroom and branch out from there. The bathroom will have a cluster of 24v demands (Gulper-pump, 24v toilet macerator, shower extractor fan, downlight). I expect a +/- pair of 2.5mm multistrand with a 27amp capacity will cover the cumulative load given that a 24v gulper draws 1.75 amps.

 

I could extend the concept and power the main water pump under the bed and bedroom downlighters from the forward busbar but that means 6 circuits forward hanging off a single breaker back at the rear of the boat. Hmmm.

In principle yes. But you have to be careful that ALL the wiring downstream of the fuse, is rated at or greater than the fuse. So you couldn't have a big fuse supplying a fat cable to the satellite bus bar, from a 27A fuse, and then run thin 5A wire to the extractor fan without additional fusing.

 

We have a bussed system - a "ring main" of 12v dc fused at source at 100A, but the nodes connected to it are electronic and each output is individually fused (electronically, as well as a mechanical backup).

 

So realistically I think you would need a satellite fuse board.

 

Edited August 20, 2024 by nicknorman

[GUMPY]

33 minutes ago, Gybe Ho said:

I expect a +/- pair of 2.5mm multistrand with a 27amp capacity will cover the cumulative load given that a 24v gulper draws 1.75 amps.

Two words to consider.

 

Voltage Drop

[Tony Brooks]

33 minutes ago, Gybe Ho said:

Is it legitimate to simplify a narrowboat's wiring by having a satellite busbar that is remote from the main point of fused DC distribution?

 

As I plan my future boat and design the main 24v DC circuits it occurs to me that I could run a single pair of wires 30ft down to the bedroom and branch out from there. The bathroom will have a cluster of 24v demands (Gulper-pump, 24v toilet macerator, shower extractor fan, downlight). I expect a +/- pair of 2.5mm multistrand with a 27amp capacity will cover the cumulative load given that a 24v gulper draws 1.75 amps.

 

I could extend the concept and power the main water pump under the bed and bedroom downlighters from the forward busbar but that means 6 circuits forward hanging off a single breaker back at the rear of the boat. Hmmm.

 

not only what Nick has pointed out cable and fuse wise, but also doing that is definitely non-typical, so could lead to confusion and extra expense later on.

Just now, GUMPY said:

Two words to consider.

 

Voltage Drop

 

Quiet, I think his 2.5 sq mm CCSA is very optimistic. Probably a recipe for burned out pump and toilet motors because of the volt drop.

[David Mack]

Would it make more sense to have the positive wires run separately from the main fuse board, but to provide a satellite bus bar for the negatives? That way all the positives could be sized according to the fuse ratings and volt drop considerations, but a single fat common negative (with a cross sectional area equal to the sum of all the positives) would simplify the wiring and give a lesser voltage drop when not all appliances are turned on.

[GUMPY]

Idleness had an interesting system, there was a +/- run down each side in 16mm feeds were Teed off where needed in 2.5mm. only one 15amp fuse for each side. 

 

Cable sizes and fuse value are from memory and I sold it 22 years ago.

[jonathanA]

Going for a 24v system means volt drop isn't such a big issue, but I think 2.5mm cables to your secondary distribution board is a bit optimistic and really the point is to run some fairly beefy cables to that and reduce the overall amount of cables running back to the back of the boat. (It is usually the back)

 

In practice it usually makes sense to buy a few 100m coils of cable for a full fitout, so you probably won't save money but may reduce the size of the cable bundle running down the boat.  

It's also worth thinking about what circuits you want to be able to switch off /leave on when you leave the boat and don't want to be running up and down the boat flicking circuit breakers (well I wouldn't... )

 

[jonathanA]

Just to add if your 27A on 2.5mm is based on cable specs, you've fallen into the first trap.... ignore the current ratings for cable even on 24v its the voltage drop you need to think about.

For example in your bathroom example. You have 2A for the pump, typical macerator will be 12-15A at 24v so say anther amp for light and fan. So say 15A overall. The volt drop on 2.5mm over 20 metres round trip (you said 30 foot so about 10 metres each way) at 15A is about 10%, 2.3v, 3-4% is usually the acceptable volt drop. You would need 6mm2 cable in this case to get just under 4%

 

I used the vd calculator at 12v planet. Others are available.  The current rating of 6mm will typically  be quoted as something like 48A by the way. 

 

Hope that helps. 

[system 4-50]

I had a 12v DC bus the full length of my 60ft narrowboat.  I think it was 25mmsq (incomer sort of size) not 2.5 .

[Gybe Ho]

56 minutes ago, jonathanA said:

Going for a 24v system means volt drop isn't such a big issue, but I think 2.5mm cables to your secondary distribution board is a bit optimistic and really the point is to run some fairly beefy cables to that and reduce the overall amount of cables running back to the back of the boat. (It is usually the back)

 

 

Ok I will do some detailed calcs. Worst case would be the water pump, gulper, toilet and ceiling air extractor running concurrently. The spot lights are around 1.8w LED I read. Then there is voltage drop, what is the target, less than 5%? The next cable size is 4mm I think. A marine grade tinned multi strand 2.5mm cable is good for 696W@24V and the next size up is rated for nearly a kW but oh I just looked at the power spec for a 24v macerator toilet, it needs a 15amp fuse.

 

My motivation is to reduce cable bulk. I was watching a fitout channel and was surprised by the bulk of DC cable in the ceiling conduit. There is a lot up forward including nav lights, horn, tunnel light, his & hers USB sockets, bed head reading lights, bow thruster control, watertank level. Maybe an external GSM aerial cable and more YouTubers are fitting CCTV, plus the items I mentioned at the start of the thread. Not forgetting solar panel wires.

 

 

1 hour ago, jonathanA said:

So say 15A overall. The volt drop on 2.5mm over 20 metres round trip (you said 30 foot so about 10 metres each way) at 15A is about 10%, 2.3v, 3-4% is usually the acceptable volt drop. You would need 6mm2 cable in this case to get just under 4%

 

 

"Each way". Oh!

[nicknorman]

Ceiling conduit? Personally I think it is better to run the wiring under the gunnels. After all, most of the services are not in the ceiling, lighting excepted obvs.

[Gybe Ho]

2 hours ago, nicknorman said:

Ceiling conduit? Personally I think it is better to run the wiring under the gunnels. After all, most of the services are not in the ceiling, lighting excepted obvs.

 

I have seen allsorts in the fitout video blogs. Some form a conduit at the wall/ceiling junction with a small drop in the ceiling lining, others have a central ceiling conduit and others run under the gunnels in plastic conduit tubes because of the proximity of the 240v ring. Some feel that DC and 240AC needs to be physically separated by a few feet, I don't understand that.

 

My current plan is 240v and the 24v forward spur will run together under the gunnel with the single insulated DC wire in a conduit with a fishing line as a mouse line to resolve future problems. A less populated ceiling conduit would be kept for nav lights, horn, solar feeds and GSM aerial cable. Not forgetting the bow thruster signal cable, one for the gunnel I guess.

[Tony Brooks]

6 hours ago, Gybe Ho said:

Some feel that DC and 240AC needs to be physically separated by a few feet, I don't understand that.

 

I agree the "few feet" thing is very odd, but the RCR and best practice requires single insulated cables to be`separated by 50mm (not 100% sure on the figure), or to be physically separated like in a conduit or by using double insulated flex, usually for the mains stuff, but I would not bundle both together.

[nicknorman]

1 hour ago, Tony Brooks said:

 

I agree the "few feet" thing is very odd, but the RCR and best practice requires single insulated cables to be`separated by 50mm (not 100% sure on the figure), or to be physically separated like in a conduit or by using double insulated flex, usually for the mains stuff, but I would not bundle both together.

It’s 100mm. Most people use 3 core flex for the mains. The overall flex sheath meets the requirements to keep ac and dc wiring separate and certainly in our boat ac and dc wiring shares the same trunking. Ac and dc wiring must not share the same colours so you can’t use ac mains flex for dc wiring.

[jim mitchell]

On 20/08/2024 at 16:40, Gybe Ho said:

As I plan my future boat and design the main 24v DC circuits

? On a new boat do you NEED 24 volts forward ?  all the components you mention are readily available in 240Vac

If you are installing an inverter - with its attendant energy loss when idle (standby) in order to have a 240v circuit going forward  for ????    why also take 24 vDC  cables of any size there?

 

Yes  accept that 'traditionally'  it has been done (usually on boats that had no inverter or only a tiny one - often added after construction)  but going forward does it really match the energy requirements / comfort etc.

[IanD]

13 minutes ago, jim mitchell said:

? On a new boat do you NEED 24 volts forward ?  all the components you mention are readily available in 240Vac

If you are installing an inverter - with its attendant energy loss when idle (standby) in order to have a 240v circuit going forward  for ????    why also take 24 vDC  cables of any size there?

 

Yes  accept that 'traditionally'  it has been done (usually on boats that had no inverter or only a tiny one - often added after construction)  but going forward does it really match the energy requirements / comfort etc.

24V (or 12v) is still useful for stuff that's easier/cheaper to get than 230Vac, or stuff that has to keep on working even if the inverter or mains supply fails (or is accidentally turned off or disconnected).

 

My boat has both; all the high-power stuff*** and appliances are 230Vac, but things like LED lights and tunnel/nav lights and horn and pumps and fans (and the router and Cerbo) run off DC, mainly 24V for smaller cables and lower losses than 12V (24V DC gear is widely available because trucks use it).

 

*** except propulsion and BT and MPPTs which use the main 48V battery bank directly.

Edited August 22, 2024 by IanD

[Gybe Ho]

11 minutes ago, jim mitchell said:

? On a new boat do you NEED 24 volts forward ?  all the components you mention are readily available in 240Vac

If you are installing an inverter - with its attendant energy loss when idle (standby) in order to have a 240v circuit going forward  for ????    why also take 24 vDC  cables of any size there?

 

Yes  accept that 'traditionally'  it has been done (usually on boats that had no inverter or only a tiny one - often added after construction)  but going forward does it really match the energy requirements / comfort etc.

 

The trigger for 24v was the realization that a pair of 100amp 24v main engine alternators was the best cheap option for tow path winter charging at 1.5 to 2 kW without the expense of a travel pack £4-5k or fixed genset £8k to £10k. This dictated a 24v battery bank.

 

Then I discovered 24v slimfit down lighters with thinner wires than 12v and no 50% rectification losses with 240v ac downlights. The only downside of this formula is the cost and conversion losses for a 24/12 transformer not that I have many outlets on 12v.

 

I will be uploading some electric circuit layouts this evening for review, critique and condemnation. I know the forum excels at the the second two 😀 

[IanD]

30 minutes ago, Gybe Ho said:

 

The trigger for 24v was the realization that a pair of 100amp 24v main engine alternators was the best cheap option for tow path winter charging at 1.5 to 2 kW without the expense of a travel pack £4-5k or fixed genset £8k to £10k. This dictated a 24v battery bank.

 

Then I discovered 24v slimfit down lighters with thinner wires than 12v and no 50% rectification losses with 240v ac downlights. The only downside of this formula is the cost and conversion losses for a 24/12 transformer not that I have many outlets on 12v.

 

I will be uploading some electric circuit layouts this evening for review, critique and condemnation. I know the forum excels at the the second two 😀 

 

Most DC-powered things you might need are available in 24V. If there are a few low-power things that are 12V only (like the router, in my case) 24V-12V DC-DC converters are small and cheap.

 

I think the only bigger 12V item I have is the generator starter battery, which is trickle-charged by a DC-DC converter since it needs very little power.

[jim mitchell]

 

50 minutes ago, IanD said:

24V (or 12v) is still useful for stuff that's easier/cheaper to get than 230Vac, or stuff that has to keep on working even if the inverter or mains supply fails (or is accidentally turned off or disconnected).

 

My boat has both; all the high-power stuff*** and appliances are 230Vac, but things like LED lights and tunnel/nav lights and horn and pumps and fans (and the router and Cerbo) run off DC, mainly 24V for smaller cables and lower losses than 12V (24V DC gear is widely available because trucks use it).

 Fully agree Ian,  and all carefully considered as to why/ cost / options i am sure - i just wanted the OP and any other to consider all the options then decide the best solution for them.

 

7 minutes ago, IanD said:

I think the only bigger 12V item I have is the generator starter battery, which is trickle-charged by a DC-DC converter since it needs very little power.

  Since gybe Ho is considering a diesel engine for instance, and a 24v 'system'  why not a 24v starter battery and avoid the DC to DC  requirement for it.

 

 

 

[IanD]

Just now, jim mitchell said:

 

 Fully agree Ian,  and all carefully considered as to why/ cost / options i am sure - i just wanted the OP and any other to consider all the options then decide the best solution for them.

 

  Since gybe Ho is considering a diesel engine for instance, and a 24v 'system'  why not a 24v starter battery and avoid the DC to DC  requirement for it.

 

 

Because in my case the generator has a 12V starter motor and alternator, and all the control systems for it are 12V -- there isn't a 24V version... 😞 

 

If the Beta engine can be supplied with all 24V accessories then that would be fine, but AFAIK it's 12V only... 😉 

[jim mitchell]

2 hours ago, IanD said:

 

Because in my case the generator has a 12V starter motor and alternator, and all the control systems for it are 12V -- there isn't a 24V version... 😞 

 

If the Beta engine can be supplied with all 24V accessories then that would be fine, but AFAIK it's 12V only... 😉 

 

For info Ian a quick Email to Beta invoked this response:

 

24 volt electric start is an option an all our 4 pole 1500rev/min diesel generator sets, and our inland range of propulsion engines above 40hp.

Best Regards.

Andrew Growcoot

Email:   andrewg@betamarine.co.uk

Davy Way,   Waterwells,   Quedgeley,   Gloucestershire  GL2 2AD,   England

Tel: +44 (0)1452 723 492  Fax: +44 (0)1452 883 742 

[IanD]

4 minutes ago, jim mitchell said:

 

For info Ian a quick Email to Beta invoked this response:

 

24 volt electric start is an option an all our 4 pole 1500rev/min diesel generator sets, and our inland range of propulsion engines above 40hp.

 

Best Regards.

 

Andrew Growcoot

 

Email:   andrewg@betamarine.co.uk

 

Davy Way,   Waterwells,   Quedgeley,   Gloucestershire  GL2 2AD,   England

 

Tel: +44 (0)1452 723 492  Fax: +44 (0)1452 883 742 

 

 

I wasn't aware of that, it's not mentioned anywhere on their website or literature that I can find. Does that mean all the control panel (and alternator, and any other electrical accessories) are also 24V?

 

I also wouldn't be surprised if it's quite an expensive option. Plus it might not be desirable to use the main 24V LFP domestic bank for starting, depending on current capacity -- also if you flatten it and it disconnects, you can't then start the engine to recharge it... 😞

 

In which case you might as well keep the standard (cheap!) off-the-shelf 12V engine electrics and starter battery and small 12V alternator, there's no advantage going to 24V for all this... 😉 

 

(with a 24V-12V DC-DC trickle charger if desired, since MPPTs are likely to connect to the 24V house bank)