x1 and x2 capacitors

[alireza7]

hi
i'm working on a switching power supply and i was searching about capacitors and i faced to x1 and x2 type capacitors.
can you tell me anything about these types and their characteristics?

[Toasty]

AC Safety capacitors.

"There are two major types of interference suppression/AC line filter safety capacitors, type X and type Y. The function of these capacitors is to protect against surges and transients, as well as providing EMI filtering . Safety capacitors are circuit-specific, and serve to protect the circuit and the user from high voltage surges by shunting the impulse energy to ground. One common cause of such surges is lightning strikes." (1)

X caps are used ACROSS the mains. X capacitors may NOT be used from mains to ground or casing because if an X cap FAILS, the metal frame/housing may become energized and pose an electrocution hazard.  If installed as designed and it fails, it will (should) blow the equipment fuse.

Y caps are used FROM mains to frame/ground. Y capacitors can also be used as an X-style cap across the mains. They are engineered to fail OPEN.  However, if they fail shorted, they can pose an electrocution hazard if the equipment ground is lost.

Rated impulse voltages:

X1 - 4kV - X2 - 2.5kV

Y1 - 8kV - Y2 - 4Kv

T

(1) - Tecate Group - AC Safety Capacitors

[joseph nicholas]

Glad Toasty cleared up the confusion.