The capacitor's 400 volt rating means it can be put across lines with a 400 volt difference without burning out (actually less since you should have a safety factor built in). No problem connecting across two legs of a 3 phase household circuit, 208 volts. At 2650 ohms impedance for 60 Hz, it will draw about 80 milliamps or 16 watts.
Note that some capacitors, notably "electrolytic" capacitors, are meant for DC circuits. See the capacitor specs for the suitable kinds of power that the capacitor may be connected across.
You can design a "circuit" using coils and capacitors to bridge the phase legs that would have an even greater impedance at 60 Hz and still have a negligible impedance at the frequency used by your security equipment. The only disadvantage of the plain capacitor (let alone the incandescent lamp) is consumption of billable power.
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