Domestic AC power safety notes

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Main article: Domestic AC power plugs and sockets

There are a number of important considerations when dealing with domestic AC power. Electricity can kill if it is not respected. The following are tips to consider in dealing with AC power.

Contents 1 Grounding 2 Circuit testers 3 Possible wiring errors 4 Use of travel adaptors 5 Safety note for mainland European plug types C, E, F, J, K, and L 6 Safety note for developing countries 7 Safety note for users in places using British wiring 8 Safety note for modifications 9 Placement of outlets

[edit] Grounding

An adaptor, sometimes called a "cheater plug" or "ground lift", may be used to insert a grounded plug into a two-pin socket. In order for the ground connection to remain effective, the ground tab should be attached to ground; if the outlet box is grounded (see below) this can be done by screwing the metal tab to the fixing screw on the socket. However, most people don't bother with this extra step and it is pointless to do it with two-pin sockets on non-earthed circuits. It is also common for people to just cut off the earth pin instead. Doing this, however, is dangerous and, in most jurisdictions, illegal.

Outlet boxes in older installations are often grounded via the cable armor but there is no guarantee of the quality of that ground, making the use of these adapters potentially hazardous. The most-proper way to convert an obsolete type A outlet to a safer type B is to install new cable and a NEMA 5-15 receptacle. Another accepted alternative is to replace the outlet with a ground fault circuit interrupter (GFCI) outlet, which doesn't really need a ground because it will trip on any circuit leakage.

[edit] Circuit testers

Inexpensive testers are available to verify proper outlet wiring. However, these cannot detect if neutral and earth connections have been swapped with each other and they cannot detect if the earth is adequate for the installation design (most don't measure it at all, some give a crude measurement of EFLI, but still require knowledge of the installation type to determine whether the indication given is acceptable or not). Testers can also give misleading results (such as detecting a lost neutral as a live/earth swap). For these reasons, while they are useful as a quick test for common faults they should not be regarded as a substitute for testing the wiring with proper equipment and knowledge.

[edit] Possible wiring errors

Despite the fact that it seems easy to connect a plug or socket, some mistakes may result in a working but highly dangerous installation. Also, an incorrectly wired socket or plug may cause safety problems in the whole house. The possible errors are:

• Connecting live wire to the ground contact -- this is lethally dangerous. This is especially bad because even though it can kill a human being who touches the box, the device will still work and so it may go unnoticed.
• Not connecting the ground contact at all. As mentioned above in the article, some countries and older installations have unearthed outlets. It is common to connect earthed appliances to these outlets either using an adaptor, using a European plug type with an earth contact that is not a pin or simply cutting the earth pin off. Since appliances with earth connections will generally only be single insulated this can mean that a single fault will make the case live. Nonetheless it remains common practice in many parts of the world.
• Swapping live and neutral wires. In some cases, this has no effect. In other cases, this may place the line switch in the neutral wire, leaving portions of the device energized at all times (which does not pose immediate danger but increases the risk of shock if there is another fault or if someone tries to work on the appliance). For screw-in line voltage lamps, this can also result in the shell of the lamp base being connected to the line, greatly increasing the risk of shock when changing light bulbs.
• Swapping ground and neutral wires. This can cause a number of issues. In a TT earthing system it will mean that significant current will go down the earth rod and may lead to significant voltages between the case of the appliance with the wires swapped and other appliances. However TT systems are supposed to be RCD protected anyway so the most likely outcome is an immediate trip of the RCD. In a TN-S or TN-C-S system immediate danger is unlikely but there is still the potential for danger if a neutral or earth wire also breaks. Finally combined with a live-neutral swap further back it could result in live being supplied to the earth pin.
• Not providing adequate overcurrent/short circuit protection resulting in a far greater possibility of fire in the event of a fault.

[edit] Use of travel adaptors

Travel adaptors are commonly available to connect different plug and socket types. Use of these on a permanent basis is not advisable as they often have thinner than normal pins to fit a variety of socket types (and thus are more vulnerable to falling out, overheating etc). Also such adaptors will often not provide an earth connection so sticking to class 2 (double insulated) equipment is advisable unless there is no other option. They will also often cause live-neutral reversal which may be an issue with some equipment (see above).

[edit] Safety note for mainland European plug types C, E, F, J, K, and L

Many European countries use the same basic two-pin plug designs but extended them to be earthed in different ways. Thus it is fairly common to find plug and socket combinations where the live and neutral pins will mate, but the earth pin will not. This also applies if a European plug is forced into a UK socket. Earth connections on European sockets are also sometimes absent or unreliable in old installations, especially where earthed sockets have been installed on older electrical installations that did not have earth connections.

[edit] Safety note for developing countries

Formal standards may be completely absent, or at least not enforced. Voltages and frequencies may vary greatly, by location or over time. Power supply and transmission is often very unreliable. Villages may have no power supply at all. In towns and cities, different voltages and frequencies may be supplied to the same building. Earth contacts, where they exist, may not really be connected to the ground. Safety features should not be trusted unless verified. Caution is advised. The best solution for reliable constant voltage, constant frequency power, is to use a power conditioning Uninterruptible power supply with a built in circuit breaker or fuse.

[edit] Safety note for users in places using British wiring

Opening the shutters with a screwdriver or similar object to insert a plug from another country is not advisable - it is unsafe to connect equipment to British wiring without the protection of a BS 1362 plug fuse. Also, Schuko and French plugs will not establish an earth connection. When selecting an adaptor to connect an appliance from another country to the UK electrical system care should be taken to ensure that the adaptor is BS-1362-fused and (if the appliance is earthed) that the earthing arrangements of the adaptor are suitable for the plug. The adaptor must also comply with relevant British Standards (BS 1363 or BS 5733).

[edit] Safety note for modifications

If a plug does not mate with the sockets available, neither the plug nor the sockets should be modified and the plug or socket should only be replaced if the person doing the replacement understands the applicable issues (such as different color codes,overcurrent arrangements, voltage and treatment of live-neutral reversal). Even if the modifications "work" (that is, the appliance operates initially) there is no guarantee that the setup is safe. Safety features are easily missed until a fault occurs, and then it is too late.

[edit] Placement of outlets

Electrical outlets have become ubiquitous in modern buildings. They can be found in almost any building, and occasionally in some vehicles or outdoors. Building codes often place restrictions on the number or placement of electrical outlets.

Rooms designed for certain purposes, such as computer labs or experimental labs, may require a lot of powered devices, and thus have unusually large numbers of wall outlets. It is also possible that "sensitive" electrical equipments, such as computers, are to be plugged on a separate electrical circuit from other equipment (say, vacuum cleaners). In some European countries this translates as "sensitive" circuits having red plugs, often requiring a special small adaptor meant to prevent the use of the "sensitive" circuit for unapproved equipment. In the United States, these circuits are called "Isolated Ground" circuits and use a dedicated, insulated extra wire (usually red in colour) in the building wiring to connect directly to the utility power ground in the circuit breaker panel. There is usually only one outlet on each Isolated Ground circuit, and they are also usually red in colour and labeled "Isolated Ground" along with various symbols illustrating that. These circuits are usually only found in new or newly renovated commercial buildings, schools, and libraries.

Outlets in unusual locations which may be exposed to the elements are often covered for protection. This includes floor outlets and outdoor outlets. These are often used in schools for added safety as well as convenience.