Technical Information

What does a fuse do?

A fuse wire glows red hot then ruptures when excessive current flows through it. The heavier the wire, the greater the current that is needed to rupture it.

If a fuse wire had combustible plastic around it, it would catch fire before rupturing.

If a length of wire in your boat is not protected by a fuse, the wire will act as the fuse and will heat and rupture if excess current flows through it. If the wire's insulation isn't high grade incombustible insulation, it will catch fire.

If the wire is protected by a fuse or circuit breaker that is rated too high, the wire will be the lowest rated component and will act as the fuse. It will heat, and catch fire. If the wire has high grade insulation, it won't catch fire itself, but any combustible material near it, such as plastic conduit, ties, or other wire with low grade combustible insulation, will catch fire. Some automotive wire has combustible insulation.

All wire has a current rating based on it's cross sectional area and length. Calculation of the rating of over-current protection (fuse, circuit breaker, etc.) is based on this.

Every length of wire in your boat should be protected by a correctly rated fuse or circuit breaker. Two common problems are wires with no protection (often some wires are protected, but others are not), and wires that are fed via an incorrectly rated fuse or circuit breaker, allowing them to overheat as though they had no protection at all.

Although fuses and circuit breakers are interchangeable in many applications, there are some that require a particular type of fuse or circuit breaker, in order to provide the correct level of protection. The choice of over-current protection for sensitive equipment should be made by an expert. For example; there is a difference between thermal and magnetic circuit breakers. Each type of device is designed to work best in a particular application. The wrong device could either, give trouble with nuisance tripping, or not trip quickly enough to give the required protection. This applies to fuses as well as circuit breakers. A point worth noting is that manufacturers warranties usually cover faulty parts and workmanship. If a device fails because it has not been given the correct level of overload protection, the manufacturer is under no obligation to repair or replace it.

We see many electrical distribution boards installed and wired by inexperienced people. These boards have circuit breakers or fuses that are rated too high for the wire they are feeding, effectively providing no over-current protection at all. All that money spent on an expensive distribution board that will allow a situation to develop in which the vessel could burn to the waterline if an electrical fault occurred. When this is done by an amateur, it is usually done in an attempt to save money. The attitude is "It must OK because it works". These boat owners will find that, if such a disaster occurs, the money they saved will be lost many times over because most insurers would refuse their claim.

Where should a fuse not be used?

If a fuse or circuit breaker, even a correctly rated one, is not an 'ignition protected' type, it must not be used in a location where potentially combustable gases might be present. Examples of such locations are: Near batteries, near LPG fumes, in an engine compartment or other area where petrol fumes might be present, etc.

Why you need a warrant of fitness

Any vessel that is to be connected to a low voltage (230 or 400 volt) AC supply from a shore mounted power source, must have a current warrant of electrical fitness BEFORE being connected to the electricity supply. The NZ electricity act allows for penalties of tens of thousands of dollars for anyone connecting a vessel to an electricity supply when that vessel does not have a current WOEF. If you plug your boat into a shore power supply when it doesn't have a current WOEF, you risk being prosecuted for doing so.

Those who claim that their vessel is safe and doesn't need to be inspected fail to understand the purpose of the regulations. First, only a qualified registered electrician or electrical inspector is competent to determine whether an installation is safe. Second, if the installation is safe, there should be no problem getting it certified so that electricity suppliers can see that it is safe for them to supply electricity to the vessel. How are they to know which installation is safe and which isn't without inspection and certification? It is irresponsible, and illegal for anyone to supply electricity to an electrical installation that might be unsafe. The only way that an electricity supplier can know that an installation is safe to be supplied with electricity is to see a WOEF.

Every arrangement of wiring is harmless before electricity is connected to it. It is connecting an electricity supply to it that can make it unsafe. Therefore, any person who supplies electricity to an unsafe installation is the person who makes it unsafe, and is the person liable to be prosecuted for doing so. Understandably, the marina operators and other suppliers of electricity to boats need to be sure that they are supplying electricity to a safe installation. They face fines of up to fifty thousand dollars for allowing electricity to be supplied to an installation that does not have a current WOEF.

Who can carry out installation of low voltage electrical systems?

Only a registered electrician may carry out any part of a low voltage electrical installation. This is 'prescribed' electrical work. If you are not a registerd electrician with a current practicing license you may not carry out such work on any boat or in any building (including your own home). Home owner permitted work is extremely limited and applies only to your own home in which you yourself reside. It does not extend to any other building you own, or to any boat. An unregistered person may not carry out prescribed electrical work with the expectation that they can get someone else to certify it. If you are not a registered electrician with a current practicing license, you are not allowed to do much more than replace a fuse or change a plug on an appliance or extension lead. Some people object to the these regulations, but that comes from ignorance. Many a dangerous situation has arisen out of a lack of knowledge or understanding.

In summary, if you have any electrical work to be done on a system that operates above 60 volts, it must be done in it's entirety by a registered electrician with a current practicing licence. Many marine electricians are NOT registered and not permitted to carry out this work. Before allowing anyone to work on an electrical sytem that operates at a voltage above 60 volts, you should ask to see their CURRENT electricians practicing license (check the name and expiry date). They must be a registered electrician or hold an employer, or provisional, license under the Electricity Act and be working under the supervision of a registered electrician. They cannot work alone if they are an electrical service technician, unsupervised apprentice, or anything other than a fully registered electrician.

If an electrical installation is carried out illegally, you can expect your insurer to refuse any claim you make as a result of any failure of that system. Fire and electric shock are very real possibilities.

One word that we hear repeatedly misused is 'Electrolysis'. Electrolysis is a chemical and/or electromechanical change in a solution, occurring when an electric current is passed through it. This word 'electrolysis' is often used incorrectly as a general description of the corrosion of submersed metals in seawater. There are two types of electric current related metal corrosion that occur in seawater, and to some extent in fresh water. One is 'Galvanic corrosion'. The other is 'Stray current corrosion'.

Galvanic corrosion

Galvanic corrosion is the reaction that occurs between dissimilar metals in an electrolyte, or in impure water. This is similar to the way a flooded cell lead acid battery works. In the battery, plates made of different metals are immersed in an electrolyte (sulfuric acid). The result is that a voltage is generated between the plates. In a given electrolyte, the actual voltage depends on the type of metals used for the plates. If one metal is only slightly more noble than the other, the voltage will be lower than it would be if one metal was a lot more noble than the other. For example, zinc and mild steel are not very far apart on the noble scale, but gold and magnesium are at opposite ends of the scale. Therefore, if zinc and mild steel were used for the plates in our battery the voltage would be very much lower than it would be if gold and magnesium were used. So what we now know is that different metals will have a different voltage between them. The next thing we need to understand is that as the voltage increases, so does the rate of corrosion. Also, it is the less noble metal that will corrode. Boats have a variety of different metals below the water line, that are in contact with seawater and might also come into contact with bilge water. Voltage differences will occur between these different metals which will result in corrosion of the less noble metals. There are a couple of simple steps we can take to prevent this corrosion. The first is to connect all the metals together using a copper wire so that the difference in voltage between them is minimized. The second is to introduce another less noble metal into that circuit so that the less noble metal will be sacrificed instead of the metals we want to protect. Typically, zinc is used for this purpose. The piece of zinc used is referred to as a 'sacrificial anode'. There are formulas for the preliminary calculation of the amount of zinc required. The amount of zinc used determines the voltage difference between the protected metals and other metals (or our test probe). This voltage must be within the correct range for the anode to be effective. It is not only possible to have too little zinc, but also possible to have too much zinc. Too much zinc will also cause corrosion. More detailed information is beyond the scope of this article but the information we have provided should help you to understand the principals involved and perhaps recognize a problem or potential problem.

Stray current corrosion

We have looked at the voltage differences between dissimilar metals causing a destructive current flow between those metals. Sometimes a destructive current flow can occur even though we have bonded the metals together and fitted a 'sacrificial anode'. This current flow can be caused by a problem with the boats electrical system. If the electrical system is not arranged correctly or has developed a fault, it is possible for current to flow through the water from one submerged metal component to another submerged component. This current flow can cause the corrosion of metals in a similar way to galvanic corrosion. This is 'stray current corrosion'.

Testing for corrosion or potential corrosion

Testing for corrosion is a specialized job that requires special equipment. This work should be carried out by an experienced person. Every new boat should be tested in this way to verify that the correct level of corrosion protection is provided. If you change the submerged metals or rearrange the 'sacrificial anodes' on your boat, you should have these tests carried out to ensure that the level of protection is still correct.

Impressed current

Impressed current is a means of controlling the voltages between metals by introducing an electrical circuit with a controllable voltage that can be adjusted to maintain the protection voltage within the 'safe' range. It requires specialist installation and will fail if the battery runs flat. It will not be discussed any further in this article.

Galvanic isolator

We have heard people offer the opinion that having shore power connected to a boat can cause corrosion problems "because 110 or 230 volts AC will do that". While it is true that a shore power connection can introduce a corrosion problem, it is not for the reason that most people seem to think. A big contributor to corrosion problems is the shore power's earth wire. For safety reasons the earth wire is connected to various metal parts of your boat. Some of those could be in contact with the water. The same applies to all the other boats that are also connected to shore power. The earth wire is a common connection that connects all these boats together, even when the main switch is off. This common connection between boats allows the metals on those boats to react with each other, causing galvanic corrosion. One solution to this problem, and the least costly for an existing installation, is to install a device called a galvanic isolator. A galvanic isolator is installed in the shore power earth wire to protect the boat from galvanic corrosion without inhibiting the function of the earth wire. A galvanic isolator must only be installed by a registered marine electrician. Never try to install this device yourself.

Waste water holding tank installation - Self emptying design

Engine mount life can be extended considerably by limiting horizontal loads. Thrust is the biggest load. Twist of the engine under load creates upward load on the mounts on one side and downward load on the mounts on the other side (vertical loads). Correctly sized mounts easily absorb vibration and handle these verticle loads that are nowhere near as great as thrust loads that are trying to drive the mounts horizontally (fore and aft horizontal load). Fore and aft movement can also cause some shaft seals to leak.

Fore and aft horizontal thrust movement of engines can be limited by ties rods, transmission mounted horizontal thrust mount/s, or a shaft mounted thrust bearing. In an existing installation, tie rods are usually the easiest solution.

Fault finding is like detective work. We need clues. Some people seem to think that if they employ an expert. "They will know what to do to fix it". This is not necessarily true. You would not expect a police detective to solve a crime without asking a lot of questions and receiving a lot of information. Your electrical or mechanical detective is no different.

The more information you can provide, the easier it will be to identify the fault. With enough information, an expert in their field will often be able to correctly identify the fault without carrying out any tests at all. Confirming the fault requires tests, but often the initial diagnosis can be made quite accurately from information alone.

The information we need to consider is 'History' and 'Symptoms'.

When we ask these questions we often find that no attention was paid to the points listed above and therefore, the information is not available. If you ask yourself these questions and record your answers, you might just find that you are able to discover the cause of the problem for yourself. If you can't locate the cause at least you will have the necessary information to help an expert find the problem more easily.

Some faults are intermittent and won't occur at the time that we are looking for the cause. In this case the information that you provide becomes extremely important. With enough information we might still be able to solve the problem with reasonable certainty. Without that information, it would be almost impossible to identify the cause of the fault. You need to understand that if we don't have enough information, and the fault doesn't occur at the time that we are looking for it, then all we can do is to report that "there was no apparent fault at that time".

When you are being charged by the hour for the services of an expert, you can help yourself greatly by supplying all the information you can. Even if you don't think it is relevant. At this point I can't resist offering some very good advice. Provide the information when it is requested, but do not start offering helpful suggestions as to what you think the fault might be or what tests should be made while the technician is working on finding the fault. This is not only very annoying but is also distracting and will usually result in the job taking longer than it needs to. Every trades person hates this.