Here is a list of 13 onboard conditions that could be fatal. This may sound rather dramatic. However some of the danger is easily overlooked and others are not even thought about until they are starting to go wrong.
Operating power tools in potentially explosive atmospheres 1
Using portable hand tools in explosive atmospheres has the potential to be fatal. Unfortunately there is also a real possibility the resulting explosion and fire could also cause serious damage to the neighboring vessels.
Most portable power tools either battery or mains powered have brush-type motors. The brushes contacting the spinning commutator generate sparks in operation. The internal workings of the tools are cooled by having a fan forcing air through the motor space. In electric drills, routers and saws the air inlet is right where the sparks are created. Vacuum cleaners and cooling fans move a lot of air and in the case of vacuum cleaners most of it is passed through the motor housing.
So what are the dangers: its things like stirring solvent based paint* with an electric drill, cutting or sanding when solvents or thinners are being used in the same space. Using house hold cooling fans to ventilate an area where volatile solvents are in use.** Volatile chemicals used as a cleaner when using sealants, with the solvent evaporating from the work cloths, picking up a drill or sander to do more work may cause a fire or explosion.
Explosions have taken place when a wet/dry vacuum was used to pick up a spill in the bilge. The dust filter offers no protection to volatile chemicals that are free to pass directly into the motor. It doesn’t have to be a fuel spill, things like dewatering fluids give of flammable vapors when evaporating. A wet/dry vacuum is a wonderful way to pick up spills, but it’s also excellent at mixing and igniting explosive vapors.
My personal experience is that a work assistant working alone forgot where he was and picked up a battery operated drill to tighten some screws in a ships back up power battery compartment. Luckily he walked away with only some minor burns. However it was a costly exercise replacing the batteries and carrying out the repairs to the compartment.
** Volatile solvents in the wood preserver painted on can been ignited by the use of cooling fans used for ventilation, it could be fatal if there’s enough oxygen for an explosion. I have even seen a magazine cover photo showing a can of paint being stirred with an electric drill, just shows how easy it is to not recognize the danger. Even in the open air the volatile solvents in the paint can waft up to be drawn into the electric drill and be ignited.
Not having a carbon monoxide detector fitted 2
Carbon monoxide is a poisonous, colourless, odourless and tasteless gas, and is formed when there is not enough oxygen present when carbon-based fuels such as, gas, petrol and fuel oil are burnt. Exposure to carbon monoxide can cause symptoms that include headaches, nausea and even death. While it’s a myth that Carbon monoxide is heavier than air it can still mean that it can fill most of the accommodation area with the poisonous gas displacing the oxygen.
 |
| Carbon Monoxide detector makes it easier to sleep in the cabin, don't want to wake up dead from the fumes |
Fit a good quality carbon monoxide detector along with a good quality smoke detector.
Failure to install a good quality smoke detector 3
Like in a house you could die in your sleep if you fail to wake up in a fire on your vessel. With fire, early detection is the best way to get on top of and perhaps control a fire on board. It could be the difference of getting the additional items required for survival off the vessel into the life raft. Or could give you enough time to actually launch the life raft so you don’t only have enough time to run on deck and jump into the water before the vessel explodes. During a fire on a vessel you literally have precious seconds and you don’t want to waste any of them.
 |
| Smoke detector, far enough away from the galley not to cause false alarms |
Not having a fire extinguisher in every space 4
As previously mentioned, during a fire on a vessel you literally have precious seconds. Have a fire extinguisher in every space including the cockpit lockers. The cockpit locker extinguisher can give you a fallback position or you may need to use it to gain access. Make sure there are at least two fire extinguishers and two fire blankets in close reach of the galley. Get the biggest fire extinguishers you can fit on board, the small extinguishers only work for seconds (honestly only seconds). One of the best things you can do for your self is to go to a fire safety day to learn how to use an extinguisher and fire blanket. While most of us think it’s easy to use an extinguisher, when faced with the real deal even in a training situation you need to know how to use them or they won’t put the fire out.
 |
| Fire extinguisher and fire blanket, the blanket is in a place adjacent to the galley so I don't have to fight flames to get the blanket. Be careful if you mount a blanket in the galley is it accessible if there is flames coming from the stove top. |
Using non-ignition protected devices in an explosive atmosphere 5
Five litres of unleaded petrol carried on board to refuel the dinghy motor turns a diesel boat into a petrol boat. It is dangerous to store outboard unleaded petrol or portable gas stove bottles on board vessels that have not been designed for ignition protection. Petrol for the dinghy motor when carried on board should be in a locker that can vent overboard just like the gas bottle locker.
The portable stove gas bottles should be able to find a home in a small space set aside in the gas bottle locker that is vented overboard.
Petrol vapours being heavier than air will flow down the companionway or open hatches as well as from lockers that are not sealed from the internal space of the boat. These fumes will flow right into the bilge and engine spaces. The starter, alternator, switches, fuses and circuit breakers will more than likely have been selected according to the various rules for a diesel engine vessel in the country of manufacture. Some vessels having undergone refits and or repairs may not have any thought put into the use of ignition protection devices.
So have look around your vessel and see if you can find any sources of ignition. Start in the battery compartment, a place certainly in need of ignition protected circuits. Check the compartment is well ventilated to limit the build up of explosive gases. Then move on to how your solvents and volatile chemicals are stored. Check the gas bottle locker regularly to ensure insects haven’t decided to nest in the vent.
 |
| If on your vessel you see that the electrical cabinet looks like it has vomited a technicolour of wires most likely safe work practices have not been followed. A good clean up of the cabinet would be a good place to start, then move on to the other systems in the vessel electrics. while its hard to see here there is an AC switch in the middle of the DC circuits. AC mixed into the DC isn't going to do any one any good. |
Using poor quality fuses and fuses holders 6
If the fuse and or fuse holder have melted (even though the fuse has not blown) it doesn’t necessarily mean the equipment is faulty and drawing too much current.
If the fuse itself has not blown but rather the fuse holder has melted, it indicates that the equipment is not drawing excessive current. It indicates that more than likely the fuse holder was making poor contact with the fuse.
 |
| The failing fuse holder, this holder was part of a dual battery charging unit sold by a large marine alternator maker. As can be seen, the holder would have been running at higher current for longer than it was designed for. |
Heating in an electrical circuit is always caused by current flowing through a resistance. If there is significant resistance in the contact between fuse and fuse holder, electrical current less than the rating of the fuse can cause enough heating to melt the fuse holder. The high resistance (and heating) may not happen straight away. When new the initial resistance may be minimal and the heating due to poor contact may not be sufficient enough to melt the fuse holder. However the ongoing heating can cause oxidation of the metal connections which in turn leads to increased contact resistance. Poor contact might also be caused by reduced spring tension on the fuses due to the heat generated in the fuse holder. This accelerates the heating effect until there is an in-rush of quickly increasing heat leading to increasing resistance, in essence a heat / resistance spiral (avalanche). This can lead to what may appear to be a sudden failure of the connected equipment even some time after installation. This sort of thing can happen to any style of fuse and or fuse holder, glass fuses with exposed solder on the end caps or the fuse holder contact is solder can give trouble due to oxidization of the solder.
 |
| Fuse on the left has soldered connection. |
The solution is relativity simple; use a good quality fuse and fuse holder. The popular automotive blade type fuses and holders may be OK at lower currents, for example 5-20 Amps. For higher currents over 20 Amps it is necessary to use good quality fuses and fuse holders, and for these higher currents use fuses that screw or bolt in place when you can.
 |
| Bolt in fuses can supply better contact and maintain load better |
Running circuits continuously at 100% load 7
While some may think there is a correlation with the previous condition this is a separate situation.
Two things that can make it a complex job trying to match circuit protection fuses and circuit breakers to the wire it protects. The first is the current (in Amps) that fuses really blow or circuit breakers trip, because this is usually considerably higher than the ratings marked on the units. Secondly the wire (along with circuit breakers or fuses) can heat up considerably when they carry 100% of their marked ratings for several minutes or more.
As mentioned earlier heating in an electrical circuit is always caused by current flowing through a resistance. Normally a fuse, circuit breaker and wire will add some resistance to the circuit, the more current flowing in the circuit will increase the heat generated. In combination with being bundled together or in a hot cabinet or cable trunk the heat produced in the wires carrying high current can melt the insulation when wires carry 100% of their rated current value.
Heat creation may become a problem when systems run for a considerable time. Large diameter wires take a longer time to heat up, intermittent operations like bow thrusters, anchor winches, and toilet pumps seldom run long enough for this kind of heating to occur.
As an example a 00 gauge wire running fully loaded may take 30 minutes to approach its maximum allowable temperature. In contrast, small diameter wires can reach peak temperature in a few minutes. When systems run continuously for 10 to 30 minutes or more, make sure to choose wire and circuit protection so the current does not exceed 80% of their rating.
As a reference ATO, SEA, Maxi and AGC fuses, and most circuit breakers will blow or trip at about 130% of their rating. High current circuit breakers and ANL fuses blow from 140% to as high as 266% of their rating. Most high current circuit breakers will usually list this fact in the instruction sheet and will list the time it will take to trip while being over loaded. If this is not satisfactory choose high current fuses.
Over loading the AC shore power cord 8
The shore power cable and connection is the most easily overloaded wiring on the boat because it feeds all of the AC systems including receptacle outlet circuits.
 |
| Overloaded plug on a shore power cable, should have been a 15 Amp plug at a minimum |
Out on the water electrical equipment on most sailing vessels will run quite well on battery power. But possibly the first thing to be connected once tied up at the dock is the shore power. At the end of a weekend away, having just sailed across the bay and motored the last couple of minutes to dock, the batteries will more than likely be in need of a good charge. The hot water system will want to heat up. Then if you want to have a cupper before heading home or settling down for the evening you will probably turn on an electric jug.
So if the above scenario is played out, more than likely the vessel AC circuit capacity has just been exceeded. If you’re not careful it doesn’t take much to overload the shore power connection.
So how does all this work out? Here are the numbers to explain the overload. The usual shore power cord/receptacle is (should be at a minimum) 15 Amps @ 240 Volts AC this equates to 3600 Watts. The power draw of a hot water system element varies but 1800 watts isn’t out of the question. The current a battery charger can draw varies with the amount of current needed to charge the batteries, however if the batteries are run down its possible the charger may require up to 900 watts. So already the usage is up to 2700 Watts, turn on the electric jug and quite quickly the current draw through the shore power lead can be up to near 19 Amps so that’s 4500 Watts, an over load of 900 Watts (25% overload).
On cold or hot days at the dock a lot of cruisers turn on a small electric space heater or air-conditioner while also running the rest of the vessel. Some of these small heaters can draw up to 2400 watts not leaving much overhead, so it’s a necessity to know the load each item can put on the electrical system.
Get to know the current draw in watts of your appliances usually written on the back, and with some quick math’s you can keep your usage to a safe limit. The result of an overload can be a short circuit and quite possibly a fire.
Inappropriate shore power cord usage and care 9
The shore power cord can easily be mistreated, take a walk down the dock and you are most likely to see the humble shore power cord undergoing all sorts of cruel treatment. The torture may include things like dunking, keelhauling, sun bleaching, and being stretched to name a few.
Something that needs mention is the habit of coiling the excess power cord and leaving it in a pile. Have you ever looked at the writing stamped on the outside of the power cord and wondered why it is necessary, and have you often thought it’s never that hot and the cord will be fine. Well if the coiled cord is used to maximum or near maximum current draw it will heat up due to the resistance in the wire. Due to the shape of the stack the heat cannot escape from the center of the stacked coil. The flow on effect is the possibility of a short circuit and fire when the insulation begins to exceed safe working temperature, melt and fail. Rather than leaving a coil, lay the excess along the finger to let the cord breathe and dissipate the heat. The same can be said for cord stored on a reel, unreel the cord before use, again the reason is to let the cord breathe and stay within safe working temperatures.
Use the shore power cord locking ring and perhaps a short lanyard on the vessel end to take the strain off the power plug to maintain a solid connection between the power cord plug and hull receptacle. The locking ring stops the plug from backing out and keeps the two components together so that the connection is not moved by normal motions. The constant movement of the connection between shore power cord plug and socket due to the boat's motion can loosen the connection.
I have also noticed there is an aversion to the use of the strain relief when connecting to the utility post or at the vessel side. Once plugged into the power use the four finger spike or cord clip on the utilities pillar to take the strain off the plug. If strain relief isn’t used and the cord is then left to hang from the power socket. Gravity and any small motion can cause the plug to wiggle back and forth in the receptacle compromising the electrical connection resulting in dangerous heating. This can damage both the plug and socket, if the socket is over heated the socket spring contact tension is compromised and it will forever be a problem.
Keep the shore power cord out of the water, over a period of time in water the insulation can harden and water can wick into the cord through microscopic holes in the insulation. Once water finds its way into the cord there is no repair, it is a throw away. The same can be said for cords that are stretched, again there is no repair.
Make sure the power cord is not subjected to abrasive wear on the dock, this is not always easy with concrete docks and the movement of the vessel. Place the cord out of the way of foot traffic and if it needs to cross a walkway look at getting a cable mat to protect the cable and minimize the trip hazard for passing pedestrian traffic. Really if you need to get to the other side of the arm to plug into the utilities pillar you should bring up the safety issue with the marina operator. You’re paying for the power so there should be a safe way to access the outlet from your side of the arm/finger. This is a real safety concern, what are some of the risks? It could be anything from grazed knees, sprains, broken bones right up to loss of life if someone trips over the cord and bangs their head as they slip into the water.
Safely handle the cord and ensure the power is turned off and the cord is disconnected from the utilities pillar before handling in case there is damage, no sense in finding out the hard way a conductor has pierced the insulation jacket and the RCD (ground fault detector) doesn’t work. Always inspect the plug pins and the sockets on the cord before use, look for burning and corrosion. Look at the sockets on the utility pillar before use, again look for heat damage and any moisture damage and corrosion.
Cheap 10 Amp house extension cords have no place out on the dock for connecting shore power to vessels. They are not up to the job and are a hazard for everyone in the marina.
Failed AC shore power ground 10
A good way to check for ground wire integrity is to connect the shore power cord to the boat and bring the shore plug into a position near the electrical panel. With all on-board AC sources isolated (eg inverter & generator off), use an Ohm meter to check that the ground (Earth) pin is solidly connected to the vessels ground. You can also check the ground at each receptacle by taking the shore power cord end and meter to test at each receptacle. The reading will vary with the length of the shore power cord and whether the system has a galvanic isolator installed. If your Australian registered vessel has a galvanic isolator installed you may want to confirm the legal requirements and Australian Standards with a qualified marine electrician about having one of these fitted.
While we don’t see them in use very often in a domestic dwelling, I know some people use these cheap (starting at $10) plug in AC receptacle testers aboard recreational vessels. How do they work, well it will all depend on the brand. These units will test for things like reversed polarity (active and neutral) or totally mis-wired plugs (think ground and active reversed). In the old days they relied on small neon’s to indicate an assortment of wiring errors. Now days its LEDs, but the tests are the same, the displayed results are slightly different due to the relatively low cost of LEDs. The problem for boat owners as I see it stems from the plug-in AC receptacle testers being so sensitive that they will indicate a good ground (Earth) even if the only connection is through a prop shaft or thru-hull fitting to water. So the moral of this story is to make sure you test or get someone like a marine electrician who knows what they are doing to test your vessels AC ground (Earth), and with tools not likely to give false positive results.
 |
| Not the best sort of tester to give you a real answer to fault conditions. Australian plug. |
 |
| Fault tester for US style recepticals. |
Note: I do know of one receptacle tester on the market in Australia that cannot test if the neutral and ground are transposed.
Incorrectly sized wire 11
There are several problems that occur when sizing wire for a boat’s electrical system.
It has taken me a while to understand why chandleries and some wire supply businesses in Australia advertise wire size by the overall outside diameter of the insulation. As it turns out it’s a system used in the automotive electrical trade, and specifies cables by the outside diameter of the insulation. Not sure who thought this one up but it doesn’t make a great deal of sense.
 |
| Good quality marine cable, wire size and temperature rating stamped on the jacket |
Peculiarly, there doesn’t seem to be specifications of what the dimensions of the insulation and conductor sizes should be. So as you can see this can result in wide variations in the cross sectional conductor area and in effect the current carrying capacity of cables from different suppliers that are specified to be of the same diameter. Since copper is worth more money than plastic most of the time the copper wire cross sectional conductor area and with it the current carrying capacity is reduced. A bit like what happens with chocolate bars, the price remains the same but the bar size shrinks over time.
The reality is you may end up with a lot of insulation and less conductor. So here is the problem, since the cross sectional conductor area of the cable is not usually listed it really requires more investigation to ensure the wire to be purchased is of adequate cross sectional conductor area for the job. Determine what the cross sectional conductor size of the cable is before using it. The metric way of listing the copper conductor size will be in mm², as an example 6 mm² is equivalent to 10 AWG.
How long is a piece of string? Using this principal (chandleries) businesses selling wire do not help when they start specifying current carrying capacity of certain wire sizes. This is all done with scant regard for the length of the wire in the circuit. The longer the wire in the circuit the more resistance there will be in the circuit. So a wire sized to be capable of carrying 10 Amps to a piece of equipment in a one metre circuit, will not deliver enough voltage to the connected equipment if the wire run was ten metres. If the cable run is increased by just a couple of metres the side effect of a cable running over loaded is that if the circuit was put into service for some time damage to the insulation will start to occur. Equipment running on undersized wire will also be in danger of not being supplied the correct voltage. Some equipment will not work to specification and some will suffer unrepairable damage. Be wary of this one size fits all approach to selling/buying wires and cable.
A simple rule for wires is that the thicker they are, the easier the current can pass through them, in other words, the less resistance they will offer, and thus the less voltage drop will result.
In Australia boat cable sold as 4mm cable has a cross sectional area of 1.84 mm² and 6mm has a cross sectional area 4.59 mm² (mm² = mm squared) makes it easy for a mistake doesn’t it?
Missing or faulty RCD circuit breaker 12
A residual current device (RCD), electrical safety switch or even known as ground fault switch, protects us from the most frequent cause of electrocution - a shock from electricity passing through the body to the earth. Yes the residual current device or RCD for short can be a life saver. Most of us have probably had an occurrence where with out one we may not be here. I know myself I had just finished filling the sink with salt water so I could rinse off the dishes. Then some how I knocked the still connected electric hand mixer into the sink and in the effort of trying to save the mixer my hand and the mixer ended up in the sink full of salt water together. The good thing was I didn’t feel a thing because the RCD did its job and tripped off the power.
 |
| RCD switch, a vessel should have (depending on wiring) two, one to protect input from the shore power then the second to protect from the output of the inverter. |
The average cruising vessel can more than likely be totally protected with just two units. One on the incoming shore power supply and a second one fitted on the outboard side of the inverter and or generator before the main electrical cabinet circuit breaker. The only thing to be aware of here is how the out put of your inverter is configured to run, RCD’s will not work on all inverters. Now may be the time to get professional advice.
RCD’s should be tested frequently, especially in areas subject to lightning or if there has been any electrical malfunction onboard. Because of the harsh atmosphere in the marine environment, these devices may have a shorter life span on a boat than they have ashore. Another hazard to be aware of on a vessel is that these units are not likely to be ignition protected and this will need to be taken into consideration when having these units fitted.
Absent inverter DC grounding 13
Inverters are connections between a boat's AC and DC power systems. I am sure most of us know the high voltage of the AC system presents a shock hazard and can certainly be lethal. The DC system is not normally an electrocution hazard but can provide a lot of current, and so is potentially a source of fire. A suitable ground must be installed between the AC and DC system. I recently had a new inverter fitted and noticed in the operating instructions the requirement for grounding connections on both the AC side and DC side of the unit’s case. This grounding can prevent shocks from AC, and fire hazard from DC.
My previous unit only had the AC grounding connection made. A fault in the DC side of the system could provide enough current to overheat the AC grounding conductor (think enough heat to melt insulation and start a fire) without blowing the large DC fuse. Keep in mind the fact that the AC ground is not fused and current will flow through the conductor until it burns out. A high amperage capacity DC grounding path back to the DC system should be made. The conductor size for the ground needs to be of sufficient cross sectional area (bigger is better) to be able to sustain enough current to blow the supply fuse.
 |
| Cross section of cables bigger is better 70 and 35mm2 shown the 70mm2 is used for inverter DC ground |
No comments:
Post a Comment