Power strip
From Wikipedia, the free encyclopedia
A power strip (also known as a plug board, power board, power bar, distribution board, gangplug, plugbar, multibox, or relocatable power tap) is a strip of sockets that attaches to the end of a flexible cable and allows multiple devices to be plugged in. As such it can be considered a type of trailing socket though that term is more often used for single and double cable mounted sockets. The term is also used to refer to the complete assembly with the power strip on one end and a plug on the other. Power strips are often used when many electrical devices are in proximity, especially with audio/video and computer systems.
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[edit] Control
Power strips can include a switch to turn all devices on and off. Some have outlets individually switched. Some strips can detect one device being turned on or off (say the PC itself in a computer setup) and turn everything else on or off. Remote control strips also exist to allow a group of devices to be switched remotely
[edit] Surge protection and filtering
Many power strips have built in surge protectors and/or EMI/RFI filters: these are sometimes described as electrical line conditioners. Some also provide surge suppression for phone lines, TV cable coax, or network cable. Power strips are often colloquially called "surge suppressors" even when they have no ability to suppress surges.
Surge suppression is usually provided by one or more metal-oxide varistors (MOVs), which are inexpensive two-terminal semiconductors. They act as very high speed switches, closing at any of several designed voltages. The most commonly used are built to close at a voltage somewhat above the local mains supply. In the US, this is (nominally) 115 VAC. It should be borne in mind that this voltage is RMS, not peak, and also that it is only a nominal value.
In most of the developed world, mains electrical circuits are (supposed to be) grounded (earthed), so there will be a live wire, a neutral wire, and a ground wire. Power strips often come with only one MOV mounted between the live and neutral wires. More complete (and desirable) power strips will have three MOVs, mounted between each possible pair of wires. Since MOVs degrade somewhat each time they are triggered, power strips using them have a limited, and unpredictable, protective life.
More elaborate power strips may use inductor-capacitor networks to achieve a similar effect of protecting equipment from high voltage spikes on the mains circuit. Such arrangements are more expensive, but less prone to silent degradation than MOVs.
Overload protection is different from surge protection. Some boards only have overload protection but this does not mean that you will be protected from electricity spikes (surges), it only means that the device will trip itself when too many devices are plugged into it. The standard rating for overload protected powerboards is 2400W in Australia and means that you cannot exceed that power, if you do then the board will trip. An overload protected board cannot cause damage or trip distribution boards when plugged into them, that damage can only be done by surge protected board by the way the MVO's inside them are manufactured. Both boards have a reset switch. Overload protection boards generally do not have a power light on them.
[edit] Indication
Many power strips have a neon light for power indication. Surge protected strips are likely to have more lights to indicate the status of the surge protection system.
[edit] Socket arrangement
Socket arrangement varies considerably, but for access reasons there are rarely more than two rows. In the UK units featuring four sockets in a square arrangement are fairly common although these are not strip-shaped and hence not normally referred to as power strips.
The bulkiness of European plugs and sockets tends to result in European power strips having somewhat fewer outlets than their American counterparts and usually only one row.
In some countries where multiple socket types are in use, a single power strip can have two or more kinds of socket.
If sockets on a power strip are grouped closely together, a cable with a large "wall wart" transformer at its end may cover up multiple sockets. Various designs address this problem, some by simply increasing the spacing between outlets. Other designs include receptacles which rotate in their housing, or multiple short receptacle cords feeding from a central hub.
[edit] Safety
Overloading can be a problem with any sort of power distribution adaptor. This is especially likely if multiple appliances with heating elements, such as electric room heaters or benchtop cooking appliances like electric frying pans are plugged into a power strip or similar device.
In the U.S. and some other countries, power strips generally have a circuit breaker integrated to prevent overload. In the UK power strips are usually protected by the fuse in the BS 1363 plug. Some brands especially the more expensive ones also have a 13A BS1362 fuse in the socket end. Whilst this is not much use if they are being fed with a 13A plug it can be very helpful for providing safe protection to adaptor leads from a higher current plug type.
Power strips are generally considered a safer alternative to "double adaptors", "two-way plugs", "three-way plugs" or "cube taps" which plug directly into the socket with no lead for multiple appliances. Two-way and three-way plugs are generally not fused (although later three-way adaptors in the UK and Ireland are). Therefore in many cases the only protection against overload is the circuit fuse which may well have a rating higher than the adaptor. The weight of the plugs pulling on the adapter (and often pulling it part way out of the socket) can also be an issue if adaptors are stacked or if they are used with brick-style power supplies. Such adaptors, while still available, have largely fallen out of use in some countries (two-way and fused three-way adaptors are common in the UK and Ireland).
[edit] US requirements
- Underwriters Laboratories standard 1363 contains requirements for relocatable power taps. Included in the scope section of the standard is the statement:
- “1.1 These requirements cover cord-connected, relocatable power taps rated 250 V AC or less and 20 A AC or less. A relocatable power tap is intended only for indoor use as a temporary extension of a grounding alternating-current branch circuit for general use.”
- National Electrical Code recognizes power strip as Multioutlet Assembly in Article 220.
[edit] See also
