Batteries

One of the most common problems I run into on surveys is dead or severely depleted batteries. The usual reason why boat batteries are dead is due to having the wrong type, size or quality to meet the vessel's demands.

Today’s boats have become increasingly dependent on electricity. A growing number of toilets cant even be flushed without it! While the explosive growth of electrical equipment and electronic equipment over the past decade or two has bought about a revolution in comfort and ease of boat handling, electrical equipment malfunctions have become the most common maintenance problem onboard boats, especially those with aging, hodgepodge, or poorly installed electrical circuits.

Generally, it is my experience that few boats surveyed today meet all of the applicable standards for marine electrical system fabrication and installation. This situation may be further aggravated by the wet and corrosive marine environment, and often by the owner's tolerance for poor installations, do-it-yourself add-ons, and a general lack of preventative maintenance. 

The marine environment is a terrible place for electricity. To be trouble free, electrical circuits must be installed with great care and to the highest standards. But no matter how carefully an electrical installation is carried out, the entire system must be carefully balanced in the first place or it will soon become a source of endless problems and a constant drain on the pocket.

Because of improperly set-up systems, many boat owners repeatedly find them selves with dead batteries, outright battery failure, and lengthy charging times. Fixing immediate problems does nothing to resolve the overall imbalance in the system, guaranteeing that the next difficulty is just around the corner. Attention to compliance with electrical standards is critical to avoiding conditions that may lead to fires, explosions, personal injury, or death.

Often older boats came straight of the production line with potential problems built in. Thus the first requirement for electrical problem solving and repair is to understand the peculiar needs of a boats 12 volt electrical system, and to make sure the overall system is in balance. Therefore, when the surveyor's limited visual inspection of an electrical system raises significant concern regarding standards compliance, the recommendation will be made to employ a qualified marine electrician for an in-depth inspection.

Consider first a car. A 12-volt battery provides the energy to crank a starter motor, normally just for a second or two, after which the engine fires up and the alternator cuts in. The alternator subsequently supplies all the cars electrical needs, plus an extra margin to replace the juice the starter motor drew from the battery. The cars electrical system runs on the energy supplied by the alternator, not that supplied by the battery.

Although starter motors use a tremendous amount of energy, they do so for a very brief time, and thus pull next to nothing from a battery, and is replenished by the alternator in just a few minutes. In normal usage a car battery is almost always fully charged, and the batteries do very little work. This holds true for all cars, regardless of size, electrical complexity, or use.

Contrast this with a sailboat. The average boat spends most of its time on its berth. Periodically the owner cranks the engine, motors down the river or out if the slip, shuts the engine down, and goes sailing. Apart fro the time spent motoring, the boats electrical system runs directly off the battery. The battery will be discharged more deeply than a car battery, the engine will be run far less than a car engine, and the charging time will be minimal.

Now consider the average power boat, (Broads Cruiser). The engine will be run for longer periods of time than to a sail boat, with usage patterns similar to that of a car. But most power boats, especially cruising boats, still will have extended periods when the engine is shut down and the boats electrical system is running off the batteries.

Compared with cars, the majority of boats need both bigger batteries to with stand the extra electrical drain, and bigger alternators to replenish the juice more quickly during the reduced engine running times.

No two boats even identical production boats experience the same usage or have the same electrical needs. It is not possible to deal in generalities, as one can do with cars. Every boat must be treated as a separate entity and its electrical systems evaluated in relation to its particular usage.

There are four steps to take in evaluating a boats DC electrical system.

This is extremely important. Assuming a 100-Ah daily consumption, a 100-Ah battery will meet our immediate needs (but will leave no reserve for engine starting) if we plan to discharge our batteries 100 per cent at each cycle. However no battery should be ever fully discharged. This applies to deep cycle batteries just as much as car batteries. Repeated 100 percent discharge of any battery will shorten its life drastically.

But if we do not fully discharge a battery, we cannot utilize its full capacity. If we need 100 Ah, and we only intend to discharge a battery by the 50 percent level, we will need a 200-Ah battery. Bigger batteries last longer, but they cost more, weigh more, and take up more space. Somewhere we must make a trade off between battery size and the degree of discharge in daily use. With deep cycle batteries this is normally done at around 50 percent discharge. We try to set up our total electrical system so that the battery is not discharged beyond 50 percent of its capacity in normal use. Occasionally discharging to 80 percent or so then can be taken in stride.

A discharged battery can be recharged rapidly to around 70 to 80 percent of the fully charged level. Thereafter, the rate of charge must be tapered off sharply or battery damage will result. Since charging time is at a premium on most boats, it makes sense to bring batteries back merely to the 80-percent level. As we are only discharging to the 50 percent level, our regular, usable storage capacity is reduced to just 30 percent of overall battery capacity.

No battery operates at 100 percent over its full life. To take this into account, wee need to make an allowance of say 20 percent.

Where does this leave us? For are hypothetical boats 100-Ah daily consumption taking a conservative approach utilizing only 30 percent of the battery capacity, we need 333 Ah. Add in the 20 percent factor, and we need 400Ah of battery capacity. If we are a little less conservative and are using top of the range deep cycle batteries, which can be discharged consistently to 30 percent of capacity before recharging, we would only need a battery capacity of 250 Ah to meet our 100Ah daily demand. However this is an absolute minimum, and leaves almost nothing in reserve, and will virtually halve anticipated battery life compared with a battery discharged only to 50 percent of capacity.

Starter motors draw very high amperages for short periods of time. During operation considerable heat is generated in the starter motor windings. When voltage falls off, the motor compensates by pulling more amps, thus generating more heat. Not only will cranking be sluggish, but there is a risk of burning up the starter motor. Thus it is essential to maintain an adequately sized, fully charged battery that is reserved solely for engine cranking.

Many people believe that deep cycle batteries are unsuited for engine cranking appliances. In fact, they can be used, but because of the thicker plates deep cycle batteries retard the rate of acid diffusion compared with thin plate cranking batteries, and therefore retard the rate at which energy can be released, a larger capacity deep cycle battery is required to produce the same cranking capacity as a thin plate battery.

How much larger? If a deep cycle battery is to be used for engine cranking it is necessary to make sure that it has sufficient cold cranking amps to start the boats engine. This should be given in the engine specifications, if not the battery should have at least as many cold cranking amps as the cranking battery it is replacing. (this information can be obtained from any good battery supplier).

We now have two options for engine cranking:

Whatever is done there should be a means of paralleling both battery banks for difficult engine starts. This is normally done via a dual purpose battery isolation switch.

Battery isolation switches should do exactly what their name implies: Isolate the batteries. Apart from the cables from the batteries to the switch, there should be no connections to the switch nor to the batteries on the battery side of the switch. In practice there are always a few exceptions to this rule: certain pieces of electronic equipment that need to be hooked up directly to the battery to operate properly; automatic bilge pumps, so that the boat can be left with the batteries isolated but the pumps operational; and battery charging devices that are to operate when the boat is unattended.

All equipment that bypasses an isolation switch must be wired to the highest standards and properly fused. This includes even small capacity solar panels (which are rarely fused in practice). Any short in wiring hooked to the battery will carry full battery current. The fuses need to be as close to the batteries as possible to reduce the length of the unprotected wiring to a minimum.

Battery isolation switches carry the full starting current of an engine and must be rated to carry this load-atleast 300Amps in most situations. The cables to the switch and back to the starter must be adequate for the task, as voltage drop can be very damaging to starter motors.

On those charging circuits that pass through the switch, turning off the switch with the engine running can blow out all the alternator diodes. To guard against this, isolation switches need to:

Have either a clearly printed label, STOP ENGINE BEFORE SWITCHING TO OFF POSITION, or better still, be of the type that disconnects the field circuit to the alternator momentarily before the battery circuit is broken. This effectively disables the alternator and prevents diode loss even if the engine is running. Be of the type that “makes before it breaks“. In other words, when switching from one battery to another the switch makes the circuit to the second so both are now “ON”) before breaking the circuit to the first. In this way there is no interruption of the alternator output to the batteries.

Diodes

How they work. Diodes are essentially switches that allow electricity to flow in one direction, while preventing its flow in the opposite direction. Diodes are produced by bonding N- and P- type material together in such a way as to encourage the flow of electrons in one direction, while preventing flow in the other. This produces a switch, or one way valve, which fortunately is all we need to know about the workings of diodes.

Example: A yacht, used extensively for cruising, that had seen minimal engine running and therefore minimal battery charging time. Its frugal electrical system worked fine for year; then it changed hands. The new owner installed a small, poorly insulated 12 Volt electric fridge. The batteries died. The owner concluded he had insufficient battery capacity and added another battery. This died also. He added two more, and these died.

Regardless of how much battery capacity a boat has, if the various charging devices are not putting back what is being taken out, the batteries eventually must go dead. The solution to this boats problem was not more batteries, but a more efficient fridge and more charging capacity, in the guise of longer engine running time, a high output alternator, or a solar panel or wind generator.

Batteries constitute an underestimated danger onboard boats. A fully charged battery contains a tremendous amount of stored energy-more than enough to melt in half a spanner placed carelessly across the terminals. A batteries electrolyte-a solution of sulphuric acid-will eat through clothing and cause severe burns. Take great care with battery acid. Any splashes should be immediately and liberally doused with water.

The battery compartment should be well ventilated. When being charged or rapidly discharged, batteries emit explosive, lighter than air gases-hydrogen and oxygen. Never generate sparks around a charging battery, or one that is being rapidly discharged, such as during long engine cranking. Batteries can explode spraying acid in all directions.

Batteries also emit corrosive fumes. Never install electronic equipment near a battery compartment. The equipment will likely suffer irreparable damage.

Batteries should be kept in well-built, acid proof (plastic, fibreglass, or epoxy saturated plywood) boxes with secure, vented lids. Ventilation is important not just to remove explosive gases, but to dissipate heat generated during rapid charging. Because of this, the degree of ventilation may well have a significant impact on charging times. It will also prolong battery life by keeping batteries cool. As long as the batteries don’t freeze, the cooler the temperature the longer the battery life.

Routine maintenance

Keep batteries topped up with distilled or clean fresh water. The batteries internal plates are irreparably damaged by exposure to air. Maintain fluid levels one-quarter to one-half inch above the plates, but no higher: Overfilling will lead to spewing of electrolyte from the filler caps during charging.

Keep the tops of batteries clean. A small amount of dirt, water, or acid will provide a path for electric leaks that will drain the battery over time.

Periodically remove the battery cables (negative first) and clean the terminal posts and clamps. When removing the clamps, do not lever them up with a screwdriver. This is likely to damage the battery plates and may tear a terminal post loose, destroying the battery. Loosen the clamp bolt and ease the clamp jaws open; work the clamp gently from side to side and then lift it off. After replacing the cable clamps, coat them liberally with petroleum jelly to inhibit corrosion.

Dead batteries maybe the result of prolonged power drain. Check for:

A battery that shows nearly full voltage with no load, but a falling voltage when load is added, needs to be charged. On the other hand a discharged battery whose voltage comes up rapidly on charging is sulphated. It will, go dead rapidly in use, since only a small fraction of its plates are still active. An isolated and unused battery who’s voltage shows an appreciable drop over two to three weeks has an internal short. A drop from full charge to 75% or less should certainly be considered appreciable.

Finally a battery may simply be old and dying. It may have an accumulation of problems: sulfation, shorts, shedding of material, etc. Like everything else, even well maintained batteries wear out.

During repeated charges and discharges a coating of lead sulphate builds up through out the battery plates. This is called sulphation, and it inhibits the batteries ability to either except a charge or to discharge. Initially the sulphate is recently soft and porous, and the battery continuous to operate, although not at peak efficiency. Over time, however, the sulphate hardens and battery performance declines steadily.

Sulphation is a particularly acute problem with deep-cycle batteries that are deeply discharged repeatedly and never brought back up to 100 charge-precisely the operating conditions of many boat batteries. What happens is the more accessible areas of the battery plates are recharged at each cycle, while the less accessible interior parts of the plates remain discharged; the sulphate slowly hardens. If, after charging, all cells test low with a hydrometer, sulphation is the likely problem. While the process of sulphation is inevitable, certain steps can be taken to contain the damage done.

Sulphation needs to be dealt with before it hardens. Never leave batteries in a discharged state: The sulphate formed will harden and ruin the battery.

Soft sulphates can be reconverted into active plate material or dislodged from plate surfaces by slowly bringing the battery back to full charge over an extended period of time. This is known as equalisation or conditioning and should be carried out on all conventional (WET) boat batteries at least once a month. (gel type batteries should not be equalised). The long slow charge allow the acid to diffuse through all the interior plate areas.

Unfortunately, there is a catch. The process of sulphation increases internal battery resistance. The battery voltage rises as accessible plate surfaces are charged, but before less accessible areas are fully charged. This fools most voltage regulators into thinking the battery is fully charged when it is not. The regulator then shuts down the charging output and, regardless of engine running time, equalisation fails to occur.

There are three ways to test a battery: by measuring its open circuit voltage; by measuring the specific gravity of its electrolyte; and by using a load tester.

The problem with any simple method of testing batteries is that it is only good for proving the negative. That is, you can prove that a battery has low power or is bad, but without a load tester you can't prove the overall condition. If you have wet cell batteries, using the hygrometer is useful under controlled conditions, like before charging when the electrolyte is well mixed. After charging the electrolyte tends to concentrate near the top and give false readings. But with sealed batteries all you can do is test the voltage which will only tell you the present state of charge, not the likely remaining useful life.

The voltage on a fully charged battery should be about 12.7-12.8 volts. If it's higher, the charger is on. Batteries will usually fail to start an engine at 12 volts or less. This is dependent on the age of the battery. A new, but depleted battery may only fail to start at a voltage as low as 11.5 volts.

Open circuit volts Percent of full charge

There is hardly a boat around that does not at some time shut down its engine and run off its batteries, deeply discharging them. Even the best car batteries cannot be deep cycled more than 30 to 40 times before failing. Unless a boat has a permanent charging capacity equal to demand, it should be fitted with deep-cycle batteries. The lone exception is a marine cranking battery reserved for engine starting.

The BSS recommend highly preparing your boat (if kept on inland waterways) to the current BSS requirements, indeed meeting all the points in the list of checks below will give you confidence that your boat meets the general requirements and is safer for you and your crew too. Reinforcing this, the new edition of the BSS Essential Guide will urge people to meet all industry excepted standards, to install equipment following suppliers guidelines, to use only equipment designed for the rigours of the marine environment and carry out routine checks and maintenance

Examination Checking Procedures 

There are four relevent BSS generall requirements:

1. All electrical systems must be designed, installed and mainatained in a way that minimises the risks of explosion or a fire starting and spreading.
2. All electrical systems must be capable of being safely and quickly disconnected from their power source in an emergency.
3. Control and emergency devices, or means of operation, must be marked when not in clear view or when their function is not clear.
4. All battery compartments containing unsealed or open vented batteries must be adequatley ventilated to prevent build up of a flammable mix of gases.

Battery securing All batteries shall be securely installed so as to prevent movement and damage. All battery compartments shall be adequately ventilated and covered with insulating and non-corrosive material. No battery may be fitted beneath or adjacent to any petrol or LPG tank, cylinder, cock, pipe or filter.

Definition

A battery compartment is an enclosure specifically designed to contain the batteries only.

Batteries and battery compartments may be secured by attaching them to the permanent structure of the vessel by means of;

The method used should ensure that the batteries remain secure under any condition up to 45 degrees to the horizontal.

Batteries should be installed with insulating material between them and the hull.

Where batteries are fitted in accommodation areas they should be enclosed in gas tight compartments.

Visually check presence of battery securing system. Manually check for movement that must not exceed 10mm in any direction.

Example images:

This battery exceeds more than 10mm of  movement in any one direction and will require securing properly.

All battery compartments are to be adequately ventilated to ensure the dispersal of hydrogen gas produced during battery charging.

Hydrogen is lighter than air and the simplest way of providing ventilation is by means of holes or louvers near the top of the compartment.

Where the compartment is fitted with a lid, this must also be provided with holes or slots to ensure that an unventilated pocket is not created beneath it where hydrogen could accumulate.

Where batteries are installed in an engine compartment it should not be necessary to provide battery ventilation providing the engine compartment is ventilated to the outside air.

Where batteries are fitted in accommodation areas they should be enclosed in gas tight compartments which are ventilated to the outside air.

Where battery compartment ventilation ducts are installed, the IEE Regulations Section 14.12 state that:

No.cells x capacity in amps.hrs (ah) x 1.935=area in sq.mm

The top of the battery is to be protected by insulating and non corrosive material.

Where the top of the battery is sealed so that only the terminals are exposed, insulated terminal covers are acceptable. This applies to batteries also contained in compartments.

For the traditional type of battery top where the inter cell connectors are also exposed, a cover needs to be provided to protect the whole top surface of the battery.

Where this type of battery(s) is contained in a compartment, a cover for the compartment is acceptable.

Protection may be achieved in two ways:

In all cases, the presence of a cover or compartment must not impede the ventilation of the surface of the batteries so that the battery gas emissions can be dispersed.

Suitable materials are wood, plastics, vulcanised rubber.

Metallic covers are not acceptable.

If batteries are installed below deck, the deck board over them is acceptable as an insulated cover providing it does not have to be lifted or removed for any purpose other than access to the batteries.

Visually check presence of a battery cover or terminal covers and identify material used.

Visually check that no part of any metal terminal or any metal connection is exposed.

For the purpose of this Standard: The term “battery” includes any part of a battery.

There should be a separation of 0.5m in any direction between the batteries and the petrol or LPG installation.

Electrical Cables Cables shall be of adequate current carrying capacity and of suitable construction and grade. They shall be insulated and/or sheathed so as to be impervious to attack by fuel or water. They shall be adequately supported or run in adequately supported suitable conduits. BSS latest: (Main battery cables fitted with effective proprietary connections are as acceptable as pressure crimped, swaged or soldered connections).

Cable definition

Its not possible within the scope of the Boat Safety Scheme inspection to carry out meter testing of the electrical circuits but a reliable assessment can be made by checking the physical size of ther cables described in the tables below.

CABLE (master switch in positive wire) MIN. SIZE

Example image.

Circuits connected to the battery not properly protected by fuses.

Battery to battery connections

All battery to battery connections are to be at least 25mm sq.

10mm sq cable has a rating of 60Amps.

25mm sq cable has a rating of 110Amps.

Cables to electrical equipment are not likely to be visible for checking but providing the circuits are properly protected by fuse or circuit breakers of the correct rating this is not likely to be a problem in a sound installation.

Any cable terminations that can be seen in the distribution box or panel must be visually examined and their ratings assessed by comparison with samples of known size and rating.

The rating of the fuse or circuit breaker in the circuit in question must then be determined by visual examination and compared with the rating of the cable. The rating of the protective device must always be less than the cable its protecting.

Verify that the following cables are of a minimum size:

• Battery to master switch 25mm sq
• Battery to starter motor 25mm sq
• Battery to battery 25mm sq

Other cables between battery and fuse/distribution box suitable current carrying capacity for the installation.

Multi strand cables

The specifications for multi strand cables construction, number of strands, diameter etc are given in the BMEA Code of Practice.

Solid conductors are acceptable for existing boats i.e. non-CE marked boats manufactured prior to June 1998.

When any cables with solid conductors are repaired or replaced multi-strand cables must be used, and any modifications or additions to the installation must be made with multi strand cables.

There are three main types of terminal:

Is good practice for all conductors to be fitted with suitable terminations for connections to battery terminals.

Except for pillar terminals, bare wires should not be used to connect to terminals and the use of ring or captive spade connectors is recommended wherever possible.

If connectors are not used, the bare wires should be soldered over a sufficient length to enable the soldered end to be formed into a loop or hook.

Soldered connections should not be used for connecting or terminating any conductor greater than 25mm sq.

This is the only type of terminal where it would be acceptable for the connection to be made with the bear ends of the conductors

Care is need to make sure the conductors are bared to the correct length for the terminal and that they are properly engaged by the shank of the screw securing them to the terminal.

The clamping pressure should be applied through an intermediate part, such as washer, clamping plate or ant-spread device and not directly by the head of the securing screw or nut.

Visually check the type of any conductors that can be seen at any termination or junction.

Visually check cables for presence of suitable terminations and connectors. All connections and terminations must be examined for signs of;

Cables-grading

Cables are graded according to the type of PVC installation used to protect them. Cables of suitable grade will be resistant to damage by:

PVC insulation is the most widely used but other types include:

The following are not permitted.

Fabric covered cables are not acceptable as the covering is not impervious to attack by fuel or water.

Unless the cable is visibly marked, the grade cannot be determined by visual examination.

Visually check all cables that can be seen for signs of:

Visually check for presence of outer insulation or sheathing to cables and for any signs of deterioration or damage caused by reaction with fuel or water.

Where the cables are fixed directly to the structure of the boat they should be supported by insulated clips or fixings at approximately 300mm centres.

If the cables are run in conduits, the conduits are to be supported at intervals of approximately 900mm.

Where cables pass through bulkheads and partitions they should be supported by grommets or sleeves so there is no direct contact between the cables and the hole through which they pass.

Example image.

Here is an example of poorly supported cables.

The British Standard for non-metallic conduits is “BS 4607 Non-metallic conduits for electrical installations. Part 1. Specification for fittings and components of insulating materials”.

The standard states that all conduits must be made of insulating material and must be resistant to:

There is also a requirement that all conduit, fittings and components complying with the standard shall be durably and legibly marked to indicate compliance but it is acceptable for the marking to be applied to any carton or package containing theses materials, therefore the conduit itself may not be marked.

Visually and manually check cables for either: support in a safe position or enclosure in supported conduit.

Visually check conduit for signs of damage by:

Main circuits Main circuits shall be installed above bilge water level and all except starter circuits shall be protected by circuit breakers or fuses of the appropriate rating and of suitable design. (BSS latest: Electrical cables installed below bilge water level are compliant if protected by a proprietary watertight enclosure).

Main circuits installation

For the purpose of this standard, main circuits are any circuits which are not allowed to be in the bilge. Circuits which are allowed to be in the bilge are those supplying equipment specially designed to operate in the bilge such as:

All other cables are to be installed above bilge water level as constant immersion in bilge water may result in damage and degradation to the insulation.

It may be possible to run cables under the cabin sole or floor providing the level of the floor is above bilge water level.

The bilge water level can be determined by:

Visually check position of main circuits in relation to normal bilge water level.

Example image.

Here this AC shore power cable runs unsupported directly through the bilge, below bilge water level.

Circuit breakers & fuses

Circuit breakers and fuses are protective devices which will:

The current rating of the device must therefore always be less than the cables it is protecting.

Any protective devices should be examined for indications that additional circuits have been installed which could jeopardise the safety of the system.

The most obvious sign of this is the use of wiring of different construction, design, and colour from that used in the original wiring.

The Standard requires that all main circuits except starter circuits shall be protected by fuse or breakers but at present no check is made that every individual circuit is protected and the absence of protection is not a failure point.

Owners are still required to comply with the requirements of the Standards.

There is no requirement at present that AC circuits should be protected by RCDs although it is stongly recommended by the BMEA Code of Practice that they should always be fitted where 240V supplies are installed. (It has been suggested that this will soon become part of the Boat Safety examination).

Visually examine any fuses or circuit breakers that can be seen and check that rating is not greater than that specified on the fuse holder or body of the circuit breaker. Check that the fuse rating is less than the current capacity of the cable protected.

Loose, open ended AC shore power cables found in locker!

Circuit breakers and fuses are to be of appropriate design which means:

AC circuits are protected in a different manner.

The system of wiring should terminate at domestic socket outlets or a fused outlet. Appliances are connected by means of square pin plugs fitted with 13 Amp fuses.

The incoming supply should be fed via a 30Amp double pole circuit breaker so that both line and neutral conductors will be isolated when the circuit breaker operates in response to an overload condition.

Where power is taken from a shore power supply, the need to break both line and neutral also guards against the possibility of reversed polarity at the shore power connection.

Residential current devices should be installed between the circuit breaker and the wires going to all the AC power outlets to protect people from electric shocks.

The use of fuses and circuit breakers of the correct rating and design provides some protection against the use of unsuitable cables as the fuses or circuit breaker will operate to disconnect the circuit in the event of failure or overloading of the cable.

Testing RCD’s

There is no (present) requirement for RCD,s to be tested.

Surveyors/examiners need to be able to see the fuses and the circuit breakers to carry out their checks and it is the owners responsibility to ensure that they are visible as part of the pre-examination preparation.

Example image

This is a good example of tidy circuits, properly covered fuses, competently installed.

Checking

Visually examine distribution box for presence of lid or cover if required.

Visually examine fuses and circuit breakers and determine:

Visually examine fuses and circuit breakers to ensure that they are:

Protection of cables against damage All cables shall be installed as high as is practicable in the vessel, and they shall be run clear of all sources of heat such as exhaust pipes. They shall not be run adjacent to fuel or gas pipes unless contained in suitable conduit. PVC insulated and/or sheathed cables shall not be run in direct contact with polystyrene thermal insulation. (Latest from the BSS is although a clearance of at least 30mm is recommended, electrical cables that are not touching LPG or fuel pipes are acceptable).

Installation height

Cables are to be installed in the boat as high as practicable to minimise the risk of damage caused by:

Visually check height of all visible cables within the vessel.

Cables are to run clear of all sources of heat such as:

Electric cables are generally rated to operate in ambient temperatures of around 20 degrees centigrade but some of the above appliances can produce local temperature rises of more than 40 degrees or more.

The recommended clearance is 125mm but 75mm should be considered the absolute minimum.

Visually check routing of cables for proximity of heat sources and examine cables for signs of heat damage e.g. deterioration of insulation.

Cables are not to be run adjacent to any fuel or gas pipe unless contained in a suitable conduit.

Where thay are not run in conduit a minimum clearance of 30mm should be maintained.

Suitable Conduit : All conduits must be made of insulating material and must be reistant to :

Checking

Visually check electrical cables are supported clear of fuel pipes. Minimum clearance is not specified.

Visually check electrical cables are supported 30mm clear of gas pipes.

Battery master switch A master switch capable of disconnecting the system (including starter circuits) shall be installed in a readily accessible position as close to the battery as possible. The master switch must be capable of carrying the maximum current of the system. Electric bilge pumps, security alarms, fire pumps and electronic navigation equipment with memories when fitted may have circuits which by-pass the master switch but only if separately protected by fuses or circuit breakers. If the master switch is not visible, its position must be clearly marked.

Installation

Where there are separate circuits e.g. for starting and boat services, each battery bank or batteries will require a master switch if the switching is done in the postive line.

If the switch is installed in the negative line, one switch to which all the negatives are connected is acceptable but not recommened.

Visually check presence of master switches.

Properly installed bow thruster battery and isolator switch.

Capacity to Disconnect the System

The master switch must be cable of disconnecting the system.

To achiecve this in all circumstances it should be fitted in the positve line.

If it is fitted in the negative, it will not disconnect the services system if it is opened while the engine is running as these circuits will continue to receive current from the alternator even though they are isolated from the battery.

In these circumstance, it is possible-even likely-that the current will be cut off by the alternator, fuses or circuit breakers. However, it does mean that the master switch is not, by itself, capable of disconnecting the system in all circumstances which is the purpose of this standard.

Where there are separate batteries or banks of batteries and the switch is installed in the positive line, visually check that a switch is provided for each bank of batteries and that the switch disconnects all none-essential equipment.

Visually check every master switch is ready accessible when boat is in normal use.

Master switches are to be installed as close to the batteries as possible.

It is recommended that it should be located not more than 1 metre from the battery it serves.

Access, however takes precedence over distance from the battery.

Where there is a long run of unprotected cable, it would be good practice to install a second master switch as close to the batteries as possible.

Visually check master switch as close as possible to the batteries. Note that accessibility takes precedence over distance.

The master switch must be capable of carrying the maximum current of the system.

The recommended minimum rating is 100 Amps.

Visually examine the master switch and the cables connceed to it for any signs of:

Circuits by-passing the Master Switch

The following equipments may have circuits which by-pass the master switch providing they are separately protected by fuses or circuit breakers:

This is permitted to allow these equipments to remain operable when the rest of the electrical installation is isolated by the master switch.

It is essential, however, that such circuits are separately protected by fuse or circuit breakers.

Visually check that circuits supplying equipment which by-pass the battery switch i.e. electric pumps, security alarms, fire pumps and electrical navigational equipment with memories are protected by suitable fuse or breaker circuits.

The marking should be placed in a prominent position as close to the switch as practicable.

It should be:

Main, starter & spark plug leads Main and starter motor leads subject to high current shall have soldered or pressure crimped connectors. Spark plug leads shall be supported clear of the engine block and cylinder head.

Main & Starter Motor Leads

Ring or captive spade connectors should be used.

Conductors must not be secured directly to terminals by:

The use of screw clamps in which the shank of a screw acts directly on the bare wires of the cable is not permitted. There is a risk of damge to the conductors and it is extremely difficult for the screw to secure all the conductors in the cable.

Clamps which include a sleeve or plate acting between the screw shank and the bare conductors are acceptable for existing boats only.

Connectors of this type ensure that:

Example image  

Properly coverd pillar terminals and properly secured battery.

Checking

Visually check that starter motor leads are fitted with soldered ends or crimped connectors.Visually check for battery terminals fitted with screw clamps on existing vessels and verify use of spreader plate in terminal.

Spark plug leads are to be supported clear of the engine block and cylider head by attachement of permanet fixtures.

Example image

These leads are touching the rocker box. It is essencial once the engine is installed that they are supported clear of the engine and cylinder head so there is no risk of the heat causing damage or deterioartion to the insulation.They  should be supportd by clips or fastenings to give clearance of approximately 125mm.

Ignition protected equipment All electrical devices fitted in any compartment containing petrol or gas shall be ignition protected in accordance with BS EN 28846 .

BS EN 28846 (ISO 8846)

This international standard describes test methods and requirements for the design of electrical devices to be used on small craft so that they may be operated in an explosive atmosphere without igniting surrounding flammable gases.

It does not cover ignition protection procedures for products or components that may operate in hydrogen and air mixtures.

Items of equipment are marked with:

Markings such as the following, on their own, are not acceptable:

A petrol compartment is any compartment in which petrol is used or staired, including petrol engine compartments.

Visually check for presence of electrical devices in any petrol compartment and determine presence of marking to indicate compliance with BS EN 28846.

Vessels manufactured prior to 16 June 1998 are not required to comply with this standard where it is not practicable to comply.

The exemption will be applied at the request of ther owner and surveyors/examiners will make a note in their records that this was done.

When any device is replaced or any modifications or additions are made, the new or replacement device must be ignition protected in accordance with BS EN 28846.

Two wire systems All electrical equipment shall be two-wire insulated except in respect of engine circuits where there must be a low resistance return conductor between the battery and the engine. Engine installations with two wire insulated electrical systems do not require fitting of the low resistance return conductor.

Two Wire Installation

Two wire installations are necessary so that no part of the hull of the boat is used as part of the return circuit.

The object of insulating the electrical system from the hull is to prevent corrosion caused by electrolytic action.

A single wire system could only be found on a boat with a steel hull because it usese the hull as the return circuit. This is not permitted.

Checking

Visually check suitable device e.g. horn, headlamp, navigation light for presence of two wire insulated cable.

A single wire installation will have only one insulated conductor connected.

Although there may be electrical connection between the hull of a boat and the bodies of electrical equipment such as alternators and starter motors, an electrical path of low resistance is to be provided between the battery and the engine.

The hull or superstucture is not to be used as one of the conductors.

It is recommended that a heavy duty cable with conductors of at least 25mm squared be used.

Identify any temperature, oil pressure sender, stop solenoid etc mounted on the engine and count the wires going to the device.

If there is only one wire, the engine is a single wire installation and a visual check should be made for the presence of a low resistance return conductor between the battery and the engine.

Electrical suppression The spark ignition and generating systems of engines and all electrical equipment on the vessel shall be effectively suppressed against causing radio and television interference. (No BSS requirement at present, however there may be requirements under law). At present, suppression of radio and TV interference will not be checked as part of the Boat Safety Examination.

Please read our other pages for the latest technical information on BSS gas and fuel installations.