This paper presents measurement results on electrical crosstalk between interconnect lines and electro-optical phaseshifters in photonic integrated circuits. The results indicate that overall crosstalk originates from radiative and substrate coupling between lines and from shared ground connections. The latter is the main noise source in the structures measured in this paper and keeps crosstalk above -25 dB for interconnects and above -20 dB for phase-shifters independent of coupling distance. Measurements on the effect of electrical crosstalk on optical modulation show that -20 dB of coupling degrades modulation performance significantly, leading to at least 2 dB power penalty. A simulation approach is presented that reproduces the experimental results and gives insight into crosstalk mechanisms.