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Category Archives: Shore Power

AC Grounding

AC current must alternate between two points making a circuit.

Coming from the power source is the “hot” wire, which normally has black insulation, and returning is the neutral or “grounded” conductor, which is white. “Neutral” carries the same current as the hot wire. As long as the current remains in this closed circuit there is no danger, but if it should escape (a “fault” or “short circuit”), it will attempt to go directly to ground.

Most modern AC circuits have a green third wire, which is a “grounding” wire. It is connected to the third prong of the common three-prong plugs; it parallels the white wire and it connects to neutral at the power source. It’s supposed to ground the circuit when a short occurs.

In a household system the third wire works well as long as three-prong plugs are used and the grounding wire is intact. (Note: it won’t protect you if you touch the hot and neutral wires at the same time.) Household electrical systems are grounded through a metal rod driven into the earth under or next to the building. Between that rod and the people in the house are many layers of wood, concrete and other electrically insulating materials.

In a boatyard, where workers may be standing or crawling on wet ground, there is a potential for electrocution. When a boat is floating, the water is the ground and any metal that has an electrical path to it, including the hull of a metal boat or the engine of a glass or wood boat via the shaft, becomes a path to the ground. Touching any of these items and a hot wire at the same time can send current through the body.

Anderson Connectors

Anderson Connectors or Anderson Plugs as they are more commonly known, are designed for connecting large cables used in high current applications.

Each plug is a mirror of the other and are simple to assemble, There is no Male & Female. One simply connects into another of the same amperage. The plugs push together to form a very solid and reliable connection.

A common application in marine would be in the wiring that distributes AC power.

From the Anderson Power Products website:

Anderson Power Products is an industry leader in the manufacture of high current, quick-disconnect power connectors and provides a variety of interconnect solutions for the material handling, telecommunications, medical, power electronics and other industries. Our connectors are available from 10 to 700 amp maximum ratings for use through 600 Volts continuous, AC or DC operation. We are well known for our ability to develop creative solutions for our customers’ power interconnect requirements. We are flexible and will make modifications to standard products or develop complete custom solutions to satisfy particular customers’ needs. APP provides a complete engineered interconnect solution for all types of power distribution needs.

Boat Yard and Marina Safety

Working inside a boat up on blocks is essentially the same as one in the water, if it is grounded through its three-wire power cord. If the vessel is not grounded and a fault develops in the hot lead, workers outside the boat on wet ground or contacting metal ladders or stands are in danger.

Extension cords, especially the household two-prong type, increase the risk; wearing rubber boots and rubber gloves can reduce the risk somewhat. Using an AC on the exterior of a floating boat is courting disaster. If a power drill or sander gets splashed or falls overboard, seawater will conduct current from the hot wire to the case, making the tool hot. If the grounding wire is not effective, any path to the sea via wet decks or a metal conductor makes the worker part of the circuit. Divers and swimmers in the water are susceptible to electrical shock, especially if there is a direct short such as would occur if a live power cord drops into the water.

Even a relatively low-voltage fault can establish an electrical field around the boat, which could cause a current flow through a swimmer’s body causing fibrillation. Current leakage into the water can also paralyze muscles and cause drowning with no visible evidence of electrocution.

GFCI

GFCI A GFCI, or ground fault circuit interrupter, is an inexpensive (~$20 each), switch-like device that continuously monitors current in the hot and neutral conductors. When the GFCI detects an imbalance between the two, as would occur if there were a short to ground, it instantly trips the circuit.

A single GFCI can protect persons throughout the boat if it is located on the main AC feed, but because boats usually have various small current leaks, the unit may trip frequently with no indication of the source of the fault. It may be more practical to install one GFCI on each of the circuits to wet locations, such as head, galley, engine room, and weather deck.

GFCIs are extremely sensitive and can be tripped by “steam” or dense moisture in the air such as from cooking or showering, so they should be mounted in dry locations. On gas-powered boats, GFCIs must be ignition protected, or located in areas where fumes cannot collect. GFCIs should be checked at least monthly.

Marine AC Circuits

When the boat is afloat, inverters and gensets are grounded to the water via the engine and shaft, which act like the metal rod driven into the ground under your house.

The risk aboard a boat comes from a short that bypasses the grounding system and finds an alternative route to the sea. Standing in bilge water or touching a metal object like rudder stock or engine block, while contacting a hot wire, could make you the conductor if there is no functional grounding wire.

Marine electrical shore power presents a different set of potential problems. The shore power circuit is grounded at the dock junction box through the shore power cord and receptacle. Faulty installation, reversed polarity, defective or damaged cord or boat receptacle can create a situation that could be hazardous to persons or contribute to stray current corrosion damage to the boat.

Marine AC Safety

By Terry Johnson , University of Alaska Sea Grant, Marine Advisory Program

We all live safely with alternating current (AC) electricity in the home. But with the same voltage, the marine AC system is potentially more dangerous because the boat and the people who work on it are surrounded by water.

A person who becomes part of the pathway between a hot wire and the sea can experience severe shock. Forget the blinding flash and the smoking flesh. It doesn’t take a lot of juice to kill a person. Remember, what makes the heart tick is a faint electrical impulse generated within the muscle itself. It takes only a very small amount of current through the chest to disrupt the heart rhythm, causing fatal fluttering of the heart muscle called fibrillation.

A critical factor is where the current passes through the body. Touching hot and neutral leads with one hand can give you a jolt and maybe even a burn, but won’t kill you. But grabbing a hot lead with one hand and a neutral with the other, or the lead with one hand while standing in water, can send the current through the chest.

One effect that electrical current has on the body is to make muscles contract, so a person getting a shock may be unable to release the item that’s carrying the current. The body isn’t a perfect conductor of electricity, but passing through the chest it takes only 0.05 amp to kill. That’s barely enough to light a small bulb, and an amount which easily can pass through a human body that becomes a conduit between a hot AC wire and ground.

No one intentionally grabs a hot wire, but things happen. Two-prong plugs get put into sockets backwards (a condition known as reverse polarity). Circuitry chafes or cracks, exposing bare wire. Wiring inside a power tool breaks and contacts the metal case. Pick up with one hand an electric drill that has a loose wire inside, while bracing against the engine block with the other hand, and you could be the next industrial fatality.

Marine Wire

by Allied Wire & Cable, Inc.

The marine environment is a hostile one for electrical wire. Wire used on board a marine vessel will potentially be exposed to numerous obstacles, such as salt water, sunlight, heat and other outside hindrances. All electrical wires are not constructed to endure the problems associated with marine conditions and therefore will not be suitable wiring on boats or ships. In these situations, marine wire or boat cable may be necessary.

Marine wire, boat cable, and marine primary wire are terms you may have heard used in reference to electrical wiring for boats or marine vessels. Wiring specified as "marine" or "boat" is different in several ways from other types of electrical wire, such as power wire used in the home, or automotive wire, etc. A main difference is that the conditions surrounding marine installations require marine wire and boat cable to perform better than other wires designed chiefly for land use.

A marine wire is specifically designed and engineered for the electrical wiring of boats and is intended for all possible uses abroad a ship. Marine wire may be distributed to the pleasure boat and commercial marine industries and is often used by boat builders. The term "boat cable" may often be used interchangeably with marine wire or marine cable. Boat cable usually refers to general electrical wiring used on a boat. Marine wire that may fall into the sweeping category of "boat cable" often starts as a single conductor cable. Extra wires are added from there into one cable, consequently creating multi conductor boat cable.

Because of the demanding marine environment, approved marine wire usually possesses a copper conductor. In addition, the jacket of the cable will most likely have been tested for flammability safety. The jacket and the insulation should be rated water resistant.

The most frequently requested single conductor boat cable styles are marine primary wire and marine battery cable. The cables are extremely similar. The main factor that differentiates the two is the AWG size of the cable. According to General Isles Marine, single conductor boat cable in sizes 16 AWG up to 8 AWG are widely known as primary wire sizes. The larger single conductor marine cables ranging from size 6 AWG up to 4/0 AWG are known as battery cable sizes.

Often times, marine wire and boat cable provided by a manufacturer or distributor will meet the requirements of UL, SAE, Coast Guard, ABYC, and NMMA. The American Boat and Yacht Council (ABYC), the United States Coast Guard (USCG), the National Marine Manufacturers Association (NMMA) and the Society of Automotive Engineers (SAE) have developed safety standards and guidelines for marine electrical installations specifically serving manufacturers, technicians, and even boat owners.

Corrosion is a primary cause of electrical failures on a boat. In order to avoid the common problem, marine wire and boat cable are built to resist quick decay. In both wet and dry conditions, marine wire needs to behave consistently in order to perform properly. Marine wire, boat cable and marine primary wire may possess PVC insulation for added defense against the elements. After all, they need all of the help they can get.

The remaining links will examine the various types of marine wire and boat cable on the market today.

Common Types of Marine Wire

Marine Primary Wire (Tinned Copper)

Marine Primary Wire may also be listed as Tinned Primary Wire. The copper conductor will usually possess a tin coating which causes the strand to be called "tinned copper." Tinned copper marine primary wire is built to reduce corrosion and prevent electrical failure.

Marine Primary Wire (Tinned Copper) can be used in 105"C marine applications, in the internal wiring of electrical equipment and for general circuit wiring. It is employed for electrical connections in the marine and automotive environments where a tinned conductor is preferred. The marine primary wire may additionally be utilized for motorcycles and other applications requiring a high temperature primary wire. Tinned copper marine wire performs well in all marine environments, even in saltwater.

You may see marine primary wire listed as UL 1426 marine grade wire. Most brands of tinned primary wire will meet the requirements of the US Coast Guard and ABYC, as well as others.

Marine Primary Wire (Bare Copper)

Marine Primary Wire (Bare Copper) can be used in 105"C marine applications, in internal wiring of electrical equipment and for general circuit wiring. The marine primary wire shares many of the same applications and properties as tinned primary wire. However, the conductor is bare copper instead of tinned copper.

SAE Primary Wire

SAE Primary Wire is General Purpose Thermoplastic (GPT) insulated primary wire that corresponds to SAE specifications, generally specifications J1128 and J378. SAE Primary Wire may be used for general purpose marine and automotive applications. It usually has a temperature range of -20"C to 105"C and voltage rating of 50 volts.

Flat Boat Cable

Flat Boat Cable is a multi-conductor marine cable that can be used for marine or brake cable. The boat cable usually meets UL Standard 1426 and UL Style BC-5W2. Flat boat cable also may meet DOT Coast Guard specs. The boat cable has a PVC insulated multi-conductor.

Round Boat Cable

Round Boat Cable is much like flat boat cable. However, round boat cable makes for easy installation where tight, jagged spaces are present. Many installers of boat cable favor round cables because they are easier to arrange. Additionally, round boat cable may be used for harsh environments.

Marine Battery Cable

Marine Battery Cable generally has a temperature range of -20"C to 105"C and a voltage rating of 50 volts. The battery cable also resists oil, fuel and acid. Marine battery cable is designed to survive the harsh marine environments. The cable normally has a high strand count cable with tin plated copper stranding. Marine battery cable may be used in battery installations.

Minimize Electrical Risk

Minimize electrocution risk from an onboard AC electrical system by ensuring that the vessel is properly wired by a professional marine electrician, and inspecting it periodically for damage or deterioration.

If your electrician isn’t familiar with ABYC (American Boat and Yacht Council) standards, find one who is. Use only copper multi-strand wire (preferably tinned “boat cable”), of correct size for the load, with marine color coding.

Ensure that all connections are inside a panel box so that it’s impossible to touch them accidentally. Better yet, make them accessible only with the use of tools. There should be no bare wires anywhere on the boat. All connectors must be properly sized “captive” (ring-type) terminals match the size of the screws, with insulated shanks, and should be made of corrosion resistant materials.

Tension relief and drip loops should be incorporated. All AC outlets on board must be three prong type. Appliances should plug directly into three-prong wall sockets, not extension cords, and multiple socket plugs shouldn’t be used on board. Maintain correct polarity by using only approved plugs and if anything in the system has been modified or repaired, check it with a polarity tester. When making up plugs, ensure that the black wire goes to the brass or black screw, the white wire to the silver screw, and the green wire to the green screw.

Service outlets on the exterior of the boat are a potential problem and to be avoided. Never interconnect the AC and DC systems. The green wire must connect to the boat’s bonding system or metal underwater hardware, but the AC white wire must not. Don’t confuse the black insulation on an AC power lead with the negative on a DC system.

When you switch between a generator, inverter or shore power, the grounding connection must switch too. (If the boat is on shore power the green wire connects to the underwater metal hardware of other boats on the same shore power system. This creates a galvanic cell that promotes stray current and galvanic corrosion. A galvanic isolator on the green wire allows passage of AC but not DC, thereby isolating the boat from the others. A more sophisticated device for the same purpose is called an isolation transformer.)

Here are a few more tips for minimizing risk when working around an AC system:

Turn off the breaker at the shore power box before disconnecting the cord, and disconnect from the dock end first. Connect at the boat end first and switch on the dock breaker last.
Use only tools and appliances with three-prong plugs, and if you must use extension cords temporarily with power tools, use only cords with three-prong sockets.
Shut off generator, inverter, and main AC panel switch before working on the AC system
If you must work on live AC, do like professional electricians and work with one hand behind your back to avoid touching hot and neutral or ground at once.
Remove jewelry, wrist bands, or other conductive items.
Protective clothing, including rubber boots, rubber kneepads, and rubber gloves offer some protection from shock. Rubber or plastic insulated handles on tools like pliers and screwdrivers also help.
When working on the end of a cord with multiple wires, tape off all but the one wire you’re working on. • Unless you’re trained in marine AC systems, leave it to a professional.

Multimeter Safety

Using an electrical meter safely and efficiently is perhaps the most valuable skill an electronics technician can master, both for the sake of their own personal safety and for proficiency at their trade. It can be daunting at first to use a meter, knowing that you are connecting it to live circuits which may harbor life-threatening levels of voltage and current. This concern is not unfounded, and it is always best to proceed cautiously when using meters. Carelessness more than any other factor is what causes experienced technicians to have electrical accidents. Multimeter

The most common piece of electrical test equipment is a meter called the multimeter. Multimeters are so named because they have the ability to measure a multiple of variables: voltage, current, resistance, and often many others, some of which cannot be explained here due to their complexity. In the hands of a trained technician, the multimeter is both an efficient work tool and a safety device. In the hands of someone ignorant and/or careless, however, the multimeter may become a source of danger when connected to a "live" circuit.

There are many different brands of multimeters, with multiple models made by each manufacturer sporting different sets of features. The multimeter shown here in the following illustrations is a "generic" design, not specific to any manufacturer, but general enough to teach the basic principles of use:

You will notice that the display of this meter is of the "digital" type: showing numerical values using four digits in a manner similar to a digital clock. The rotary selector switch (now set in the Off position) has five different measurement positions it can be set in: two "V" settings, two "A" settings, and one setting in the middle with a funny-looking "horseshoe" symbol on it representing "resistance." The "horseshoe" symbol is the Greek letter "Omega" (Ω), which is the common symbol for the electrical unit of ohms.

Of the two "V" settings and two "A" settings, you will notice that each pair is divided into unique markers with either a pair of horizontal lines (one solid, one dashed), or a dashed line with a squiggly curve over it. The parallel lines represent "DC" while the squiggly curve represents "AC." The "V" of course stands for "voltage" while the "A" stands for "amperage" (current). The meter uses different techniques, internally, to measure DC than it uses to measure AC, and so it requires the user to select which type of voltage (V) or current (A) is to be measured. Although we haven't discussed alternating current (AC) in any technical detail, this distinction in meter settings is an important one to bear in mind.

There are three different sockets on the multimeter face into which we can plug our test leads. Test leads are nothing more than specially-prepared wires used to connect the meter to the circuit under test. The wires are coated in a color-coded (either black or red) flexible insulation to prevent the user's hands from contacting the bare conductors, and the tips of the probes are sharp, stiff pieces of wire:

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The black test lead always plugs into the black socket on the multimeter: the one marked "COM" for "common." The red test lead plugs into either the red socket marked for voltage and resistance, or the red socket marked for current, depending on which quantity you intend to measure with the multimeter.

To see how this works, let's look at a couple of examples showing the meter in use. First, we'll set up the meter to measure DC voltage from a battery:

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Note that the two test leads are plugged into the appropriate sockets on the meter for voltage, and the selector switch has been set for DC "V". Now, we'll take a look at an example of using the multimeter to measure AC voltage from a household electrical power receptacle (wall socket):

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The only difference in the setup of the meter is the placement of the selector switch: it is now turned to AC "V". Since we're still measuring voltage, the test leads will remain plugged in the same sockets. In both of these examples, it is imperative that you not let the probe tips come in contact with one another while they are both in contact with their respective points on the circuit. If this happens, a short-circuit will be formed, creating a spark and perhaps even a ball of flame if the voltage source is capable of supplying enough current! The following image illustrates the potential for hazard:

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This is just one of the ways that a meter can become a source of hazard if used improperly.

Voltage measurement is perhaps the most common function a multimeter is used for. It is certainly the primary measurement taken for safety purposes (part of the lock-out/tag-out procedure), and it should be well understood by the operator of the meter. Being that voltage is always relative between two points, the meter must be firmly connected to two points in a circuit before it will provide a reliable measurement. That usually means both probes must be grasped by the user's hands and held against the proper contact points of a voltage source or circuit while measuring.

Because a hand-to-hand shock current path is the most dangerous, holding the meter probes on two points in a high-voltage circuit in this manner is always a potential hazard. If the protective insulation on the probes is worn or cracked, it is possible for the user's fingers to come into contact with the probe conductors during the time of test, causing a bad shock to occur. If it is possible to use only one hand to grasp the probes, that is a safer option. Sometimes it is possible to "latch" one probe tip onto the circuit test point so that it can be let go of and the other probe set in place, using only one hand. Special probe tip accessories such as spring clips can be attached to help facilitate this.

Remember that meter test leads are part of the whole equipment package, and that they should be treated with the same care and respect that the meter itself is. If you need a special accessory for your test leads, such as a spring clip or other special probe tip, consult the product catalog of the meter manufacturer or other test equipment manufacturer. Do not try to be creative and make your own test probes, as you may end up placing yourself in danger the next time you use them on a live circuit.

Also, it must be remembered that digital multimeters usually do a good job of discriminating between AC and DC measurements, as they are set for one or the other when checking for voltage or current. As we have seen earlier, both AC and DC voltages and currents can be deadly, so when using a multimeter as a safety check device you should always check for the presence of both AC and DC, even if you're not expecting to find both! Also, when checking for the presence of hazardous voltage, you should be sure to check all pairs of points in question.

For example, suppose that you opened up an electrical wiring cabinet to find three large conductors supplying AC power to a load. The circuit breaker feeding these wires (supposedly) has been shut off, locked, and tagged. You double-checked the absence of power by pressing the Start button for the load. Nothing happened, so now you move on to the third phase of your safety check: the meter test for voltage.

First, you check your meter on a known source of voltage to see that it's working properly. Any nearby power receptacle should provide a convenient source of AC voltage for a test. You do so and find that the meter indicates as it should. Next, you need to check for voltage among these three wires in the cabinet. But voltage is measured between two points, so where do you check?

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The answer is to check between all combinations of those three points. As you can see, the points are labeled "A", "B", and "C" in the illustration, so you would need to take your multimeter (set in the voltmeter mode) and check between points A & B, B & C, and A & C. If you find voltage between any of those pairs, the circuit is not in a Zero Energy State. But wait! Remember that a multimeter will not register DC voltage when it's in the AC voltage mode and vice versa, so you need to check those three pairs of points in each mode for a total of six voltage checks in order to be complete!

However, even with all that checking, we still haven't covered all possibilities yet. Remember that hazardous voltage can appear between a single wire and ground (in this case, the metal frame of the cabinet would be a good ground reference point) in a power system. So, to be perfectly safe, we not only have to check between A & B, B & C, and A & C (in both AC and DC modes), but we also have to check between A & ground, B & ground, and C & ground (in both AC and DC modes)! This makes for a grand total of twelve voltage checks for this seemingly simple scenario of only three wires. Then, of course, after we've completed all these checks, we need to take our multimeter and re-test it against a known source of voltage such as a power receptacle to ensure that it's still in good working order.

Using a multimeter to check for resistance is a much simpler task. The test leads will be kept plugged in the same sockets as for the voltage checks, but the selector switch will need to be turned until it points to the "horseshoe" resistance symbol. Touching the probes across the device whose resistance is to be measured, the meter should properly display the resistance in ohms:

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One very important thing to remember about measuring resistance is that it must only be done on de-energized components! When the meter is in "resistance" mode, it uses a small internal battery to generate a tiny current through the component to be measured. By sensing how difficult it is to move this current through the component, the resistance of that component can be determined and displayed. If there is any additional source of voltage in the meter-lead-component-lead-meter loop to either aid or oppose the resistance-measuring current produced by the meter, faulty readings will result. In a worse-case situation, the meter may even be damaged by the external voltage.

The "resistance" mode of a multimeter is very useful in determining wire continuity as well as making precise measurements of resistance. When there is a good, solid connection between the probe tips (simulated by touching them together), the meter shows almost zero Ω. If the test leads had no resistance in them, it would read exactly zero:

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If the leads are not in contact with each other, or touching opposite ends of a broken wire, the meter will indicate infinite resistance (usually by displaying dashed lines or the abbreviation "O.L." which stands for "open loop"):

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By far the most hazardous and complex application of the multimeter is in the measurement of current. The reason for this is quite simple: in order for the meter to measure current, the current to be measured must be forced to go through the meter. This means that the meter must be made part of the current path of the circuit rather than just be connected off to the side somewhere as is the case when measuring voltage. In order to make the meter part of the current path of the circuit, the original circuit must be "broken" and the meter connected across the two points of the open break. To set the meter up for this, the selector switch must point to either AC or DC "A" and the red test lead must be plugged in the red socket marked "A". The following illustration shows a meter all ready to measure current and a circuit to be tested:

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Now, the circuit is broken in preparation for the meter to be connected:

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The next step is to insert the meter in-line with the circuit by connecting the two probe tips to the broken ends of the circuit, the black probe to the negative (-) terminal of the 9-volt battery and the red probe to the loose wire end leading to the lamp:

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This example shows a very safe circuit to work with. 9 volts hardly constitutes a shock hazard, and so there is little to fear in breaking this circuit open (bare handed, no less!) and connecting the meter in-line with the flow of electrons. However, with higher power circuits, this could be a hazardous endeavor indeed. Even if the circuit voltage was low, the normal current could be high enough that an injurious spark would result the moment the last meter probe connection was established.

Another potential hazard of using a multimeter in its current-measuring ("ammeter") mode is failure to properly put it back into a voltage-measuring configuration before measuring voltage with it. The reasons for this are specific to ammeter design and operation. When measuring circuit current by placing the meter directly in the path of current, it is best to have the meter offer little or no resistance against the flow of electrons. Otherwise, any additional resistance offered by the meter would impede the electron flow and alter the circuit's operation. Thus, the multimeter is designed to have practically zero ohms of resistance between the test probe tips when the red probe has been plugged into the red "A" (current-measuring) socket. In the voltage-measuring mode (red lead plugged into the red "V" socket), there are many mega-ohms of resistance between the test probe tips, because voltmeters are designed to have close to infinite resistance (so that they don't draw any appreciable current from the circuit under test).

When switching a multimeter from current- to voltage-measuring mode, it's easy to spin the selector switch from the "A" to the "V" position and forget to correspondingly switch the position of the red test lead plug from "A" to "V". The result -- if the meter is then connected across a source of substantial voltage -- will be a short-circuit through the meter!

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To help prevent this, most multimeters have a warning feature by which they beep if ever there's a lead plugged in the "A" socket and the selector switch is set to "V". As convenient as features like these are, though, they are still no substitute for clear thinking and caution when using a multimeter.

All good-quality multimeters contain fuses inside that are engineered to "blow" in the event of excessive current through them, such as in the case illustrated in the last image. Like all overcurrent protection devices, these fuses are primarily designed to protect the equipment (in this case, the meter itself) from excessive damage, and only secondarily to protect the user from harm. A multimeter can be used to check its own current fuse by setting the selector switch to the resistance position and creating a connection between the two red sockets like this:

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A good fuse will indicate very little resistance while a blown fuse will always show "O.L." (or whatever indication that model of multimeter uses to indicate no continuity). The actual number of ohms displayed for a good fuse is of little consequence, so long as it's an arbitrarily low figure.

So now that we've seen how to use a multimeter to measure voltage, resistance, and current, what more is there to know? Plenty! The value and capabilities of this versatile test instrument will become more evident as you gain skill and familiarity using it. There is no substitute for regular practice with complex instruments such as these, so feel free to experiment on safe, battery-powered circuits.

REVIEW:

A meter capable of checking for voltage, current, and resistance is called a multimeter,
As voltage is always relative between two points, a voltage-measuring meter ("voltmeter") must be connected to two points in a circuit in order to obtain a good reading. Be careful not to touch the bare probe tips together while measuring voltage, as this will create a short-circuit!
Remember to always check for both AC and DC voltage when using a multimeter to check for the presence of hazardous voltage on a circuit. Make sure you check for voltage between all pair-combinations of conductors, including between the individual conductors and ground!
When in the voltage-measuring ("voltmeter") mode, multimeters have very high resistance between their leads.
Never try to read resistance or continuity with a multimeter on a circuit that is energized. At best, the resistance readings you obtain from the meter will be inaccurate, and at worst the meter may be damaged and you may be injured.
Current measuring meters ("ammeters") are always connected in a circuit so the electrons have to flow through the meter.
When in the current-measuring ("ammeter") mode, multimeters have practically no resistance between their leads. This is intended to allow electrons to flow through the meter with the least possible difficulty. If this were not the case, the meter would add extra resistance in the circuit, thereby affecting the current.

Published under the terms and conditions of the Design Science License Disclaimer

Category Archives: Shore Power

AC Grounding

Anderson Connectors

Boat Yard and Marina Safety

GFCI

Marine AC Circuits

Marine AC Safety

Marine Wire

Minimize Electrical Risk

Multimeter Safety

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