Wiring a new shore power / 240v ring main

[Beren]

Hi,

Probably the first of many dumb questions, for which I apologize in advance!

The current wiring on the boat I am looking at is a bit messy and does not fit our requirements for a family live aboard. If we buy the boat I am definitely going to have to add one and probably two rings to make sure we have a safe and sufficient 240v supply when we are on shore power.

I am planning on running trunking through the boat and then wiring through the trunking, that way I can ensure that there is no way of any gradual damage to the insulation and make sure my work is a lot cleaner.

However, that leads me to a whole mess of questions:
If you were running 12v DC and 240v A/C would there be any reason to trunk them separately?
Is there really a genuine difference between Marine and Normal cabling when used for internal wiring?

Over the next 6 months I will probably have to completely re-wire and add another solar panel, install a new inverter and upgrade the house batteries, Is there a guide for boat electrics that you would recommend?

I don't know the impact of high frequency charging/discharging of batteries and drawing a reasonable number of Amps from the system, so when it comes to upgrading I am going to need to understand a lot more about battery technology and whether there is a better way to go than lead acid cells. I get the demand side from wiring houses prior to the silly electrician requirements, but I need to understand a lot more about how to mix a hybrid supply and storage system when I have Wind/Solar/Shore/Alternator all supplying both the battery and the current load at the time of supply.

 

[prv]

If we buy the boat I am definitely going to have to add one and probably two rings

Rings are unusual on boats; the supposed advantages aren't really relevant and the shape is all wrong. Boats are generally wired as radials.

Since the incoming supply will only be 16 amps (unless you frequent marina berths intended for quite large motorboats with air-con) you certainly won't be needing two socket circuits for capacity reasons.

If you were running 12v DC and 240v A/C would there be any reason to trunk them separately?

For one thing, on land I believe it would be illegal not to. The same principles presumably apply on a boat, but more so given the movement and the tendency to use voids simultaneously for both wiring and stowage, and to cram lots of stuff into the stowage. You really don't want to give one last shove to that slab of beer to get the locker door to close, and suddenly have 240v bridged onto all your 12v wiring.

Is there really a genuine difference between Marine and Normal cabling when used for internal wiring?

Tinned cable is certainly better, and I always use it for 12v wiring which goes all over the boat. I pulled a lot of useless black flaking non-tinned cable out before doing so. However, tinned mains cable seems to be less readily available and hopefully will be better protected from damp, so maybe it's less of an issue there?[/QUOTE]

Pete

 

[VicS]

Rings are unusual on boats; the supposed advantages aren't really relevant and the shape is all wrong.

Pete[/QUOTE]

You might enjoy John Ward's views on ring circuits !

Many of JW's video are worth watching ........ not too many in one sitting though

 

[VicS]

Hi,

Probably the first of many dumb questions, for which I apologize in advance!

The current wiring on the boat I am looking at is a bit messy and does not fit our requirements for a family live aboard. If we buy the boat I am definitely going to have to add one and probably two rings to make sure we have a safe and sufficient 240v supply when we are on shore power.

I am planning on running trunking through the boat and then wiring through the trunking, that way I can ensure that there is no way of any gradual damage to the insulation and make sure my work is a lot cleaner.

However, that leads me to a whole mess of questions:
If you were running 12v DC and 240v A/C would there be any reason to trunk them separately?
Is there really a genuine difference between Marine and Normal cabling when used for internal wiring?

Over the next 6 months I will probably have to completely re-wire and add another solar panel, install a new inverter and upgrade the house batteries, Is there a guide for boat electrics that you would recommend?

I don't know the impact of high frequency charging/discharging of batteries and drawing a reasonable number of Amps from the system, so when it comes to upgrading I am going to need to understand a lot more about battery technology and whether there is a better way to go than lead acid cells. I get the demand side from wiring houses prior to the silly electrician requirements, but I need to understand a lot more about how to mix a hybrid supply and storage system when I have Wind/Solar/Shore/Alternator all supplying both the battery and the current load at the time of supply.

It would a good idea if you obtained, by fair means or foul, copies of the latest editions of:

ISO 13297 The standard for low voltage AC installations in small craft.

ISO 10133 The standard for extra low voltage DC systems in small craft

But as said there is no merit in ring circuits.

Your 12 volt DC circuits should be kept separate from your 240 volt circuits. ISO 10133 spells out the requirements in detail.

Your 12volt circuits can use so called "thin wall" cable.
The cable cross sectional area must be sufficiently large , compared with 240volt wiring, to keep voltage drop within acceptable limits.

 

[Beren]

Thank you all for the advice so far. I had not really considered running 4 sockets off a radial, but they are only going to be for low Ampage devices so I can put a 16amp mini RCD on and 26 Amp wire and that will be both safe and sufficient for 2 bedrooms.
I will definitely invest in double trunking, it is just too much risk not too.
The YouTube video was great, it helped clarify things for me in terms of what circuits I should use. Thanks Again.

 

[PaulRainbow]

Thank you all for the advice so far. I had not really considered running 4 sockets off a radial, but they are only going to be for low Ampage devices so I can put a 16amp mini RCD on and 26 Amp wire and that will be both safe and sufficient for 2 bedrooms.
I will definitely invest in double trunking, it is just too much risk not too.
The YouTube video was great, it helped clarify things for me in terms of what circuits I should use. Thanks Again.

Use tinned cable for the 12v circuits, arctic flex for 240v circuits, don't use single core domestic stuff.

Lead acid is fine for live aboard. Big bank for domestic use, single battery for engine. Alternator to engine battery, solar and wind to domestics (if you don't yet have wind, forget it and spend the money on more solar, IMO). Dual sensing VSR between the two banks. As much solar as you can fit, quality panels and controller, sited to minimise shading.

Mains charger with dual outputs to go to both banks. But, keep as much stuff 12v as possible. All lights LED, TV and sound system can be 14v or 19v and run from DC-DC converters, as can a laptop, much more efficient than an inverter.

 

[<152587>]

Double poled breakers are safest, isolates both poles protects from shock from the neutral if reversed polarity occurs.

 

[Poignard]

Doesn't the 16A marina supply incorporate an RCD? If so, why is it necessary to have one on the boat?

Incidentally, I visited someone's boat recently who had a 20Amp consumer unit fitted. Supplied by a 16Amp shore cable plugged into a 16A shore supply.

 

[GEB]

Because RCDs are electro-mechanical devices which may fail to operate. Various studies on their reliability have been carried out - the worst result giving a 14% failure rate.

Two RCDs in series reduce the probability of failure by a significant amount. In addition - the RCD on your boat is under your control the marina RCD is not.

 

[Poignard]

Because RCDs are electro-mechanical devices which may fail to operate. Various studies on their reliability have been carried out - the worst result giving a 14% failure rate.

Two RCDs in series reduce the probability of failure by a significant amount. In addition - the RCD on your boat is under your control the marina RCD is not.

OK thanks, good point.

 

[prv]

Doesn't the 16A marina supply incorporate an RCD? If so, why is it necessary to have one on the boat?

Have you seen some of the crappy battered leaky boxes supplying power on some pontoons and quaysides?

I'm also thinking of one place where the random assortment of sockets are just daisy-chained off each other, with three or four breakers locked in a manky box covering the whole site. I doubt those breakers are 16 amp otherwise they'd be tripping all the time.

Best not to trust what you're plugging into, and add what protection you can immediately it comes on board.

Pete

 

[Poignard]

Have you seen some of the crappy battered leaky boxes supplying power on some pontoons and quaysides?

I'm also thinking of one place where the random assortment of sockets are just daisy-chained off each other, with three or four breakers locked in a manky box covering the whole site. I doubt those breakers are 16 amp otherwise they'd be tripping all the time.

Best not to trust what you're plugging into, and add what protection you can immediately it comes on board.

Pete

Yes, I am now convinced. I will fit my own. It's like trusting your own anchor and chain instead of relying on a mooring of unknown provenance.

 

[VicS]

A couple more of John Ward's videos that might be of interest

One explaining what RCDs are, what their purpose is and how they work.

and a similar one on circuit breakers. Worth noting the the difference between B. C and D rating for mcbs.

 

[billcole]

Tinned cable is certainly better, and I always use it for 12v wiring which goes all over the boat. I pulled a lot of useless black flaking non-tinned cable out before doing so. However, tinned mains cable seems to be less readily available and hopefully will be better protected from damp, so maybe it's less of an issue there?

If you do use cable which is not ready-tinned then it is worth tinning the ends yourself with a soldering iron, as that will discourage moisture being drawn in to the cable by capillary attraction. It does make the end of the cable stiff though, so more prone to fracture problems if done anywhere where vibration is an issue

 

[RupertW]

Have you seen some of the crappy battered leaky boxes supplying power on some pontoons and quaysides?

I'm also thinking of one place where the random assortment of sockets are just daisy-chained off each other, with three or four breakers locked in a manky box covering the whole site. I doubt those breakers are 16 amp otherwise they'd be tripping all the time.

Best not to trust what you're plugging into, and add what protection you can immediately it comes on board.

Pete

Having your own also gives peace of mind if you find the only socket left if 2P 32A one so need to connect your 32A to 16A adaptor. Although in theory you will never be using more than you did when plugging into a 16A socket you can no longer rely on the pontoon protecting you even if it is wired up correctly.