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what's a KSU & do I need one?

what's a KSU & do I need one?
A multi-line telephone system usually includes phones, wire, jacks and other hardware, and a central control unit, which is a specialized computer often called  a "KSU" (Key Service Unit). A KSU is usually about the size of a medicine cabinet, and mounts on a wall, and needs a nearby electrical outlet. We offer a variety of control units, with different capacities, features and prices.

The control unit distributes power to the phones, sends dial tone to them from the phone company's incoming lines, makes the phones ring, generates touch-tones, connects phones together for intercom and paging, provides connections for accessories such as music-on-hold players, paging amplifiers, PCs and door intercoms, and contains circuitry for basic phone functions, plus memory for functions and features.

Phone systems using KSUs generally require "home-run" wiring, with a direct path from the KSU to each phone jack. There is a simpler kind of wiring often found in homes, called "loop-through" or "daisy chain" wiring where the circuit starts at the source of dial tone, and then goes to the first jack, and then the next and the next.

 
A growing number of KSU-less phone systems use "cordless" or "wireless" phones. The phones are not completely cordless: they need a power cord for their chargers, but no phone cord, so they can go almost anywhere. The Panasonic KX-TG4500 can have up to eight cordless 4-line phones, with individual voicemail boxes. You can even have a door intercom speaker, and talk to visitors from a cordless phone in your back yard.
 
Home-run wiring is the first choice for new construction, because it allows you much more freedom in your choice of phone equipment, and it makes it easy to isolate and repair damaged wire. However, if you want to use loop-through wiring that is already in your walls, you can choose a "KSU-less" system, that provides many of the features of traditional KSU-based systems. 

Most KSU-less phones have one or two cords that plug into standard phone jacks. You'll find an additional cord that has to be plugged into an electrical outlet. This can be inconvenient or unsightly in some locations, particularly for wall-mounted phones.

Living with extra cords is the price you'll pay to avoid the KSU and costly/complicated installation. But if one phone fails, you unplug it, and the others keep going. If there was a malfunction in a KSU, all your phones might act funny or stop working.


Panasonic's KSU-less KX-T3282 2-line/intercom phone can be used in a system with up to eight phones. Features include Caller ID on Call Waiting, speakerphone, headset jack, paging, and more. It's compatible with the discontinued KX-T3280 and KX-T3281.

There are excellent KSU-less phones from Panasonic, TMC and other companies.

KSU-less phones are easy to install, but be aware of their limitations:
(1) Fewer choices of phone type
(2) Phones may be more expensive than phones used with KSUs
(3) Fewer features
(4) Can't use a separate voicemail system (except from phone company).
(5) Additional cord or cords for each phone -- a particular problem for wall phones, but if you are creative, you can put the transformer in the basement and extend the power cord.
(6) Less capacity for lines and phones in one system
(7) Usually poor integration of non-standard phones, and devices like modems and faxes
(8) Very little trade-in value
(9) Very difficult or impossible to find discontinued models
(10) Can usually be repaired only by the manufacturer, not by independent repair facilities
(11) Programming for features common to all phones (such as time-setting) may have to be done separately for each phone