One must take care that the wire that serves as the lintel stretches over the poles, not alongside them, as in a tzurat ha-petaĥ the lintel sits atop the doorposts. Even if the post is low and the wire runs far above its tip (as with power lines), as long as the wire runs directly over the post, and the post is at least ten tefaĥim high, it is considered a valid doorpost, and the wire is considered a valid lintel. But if the wire is not directly above the pole, the eruv is invalid. If the pole is crooked, the wire must extend directly above the tip of the pole; if the wire is above any other part of the pole, the eruv is invalid (SA 362:11; MB ad loc. 64).
Utility poles and the cables they support cannot serve as tzurot ha-petaĥ, because the cables generally do not pass directly over the poles, but alongside. In order to solve this problem, additional poles, each about a meter high, must be erected directly underneath the cables.
If a pole has a hole near the top, according to most poskim one can thread the wire through it. The wire is not considered situated on the side of the pole, since it is still situated above the section of the pole below it. Even though the pole continues above the wire, this is not a problem. This is the approach of AHS 362:32 and Ĥazon Ish 7:9. However, Pri Megadim and MB 362:64 are stringent. Since the pole continues above the wire, the wire cannot be considered situated above the pole. The same disagreement applies to a pole that has deep grooves, where the wire is wrapped around them in such a way that it is contained completely within the grooves. Those who are lenient consider the wire situated above the pole, while those who are stringent maintain that since the pole continues above the wire, the wire cannot be considered situated above the pole. In a time of necessity, one may rely on those who are lenient.
. When several utility poles are situated in a straight line, it is enough to erect eruv posts underneath the cables of the two outlying utility poles. The poles in the middle are not considered doorposts, but only extra supports for the lintel. This is the opinion of most poskim, including Divrei Malkiel 3:16. Nevertheless, some are stringent and require placing an eruv pole underneath every single utility pole, because otherwise those who see them may mistakenly think that utility poles never need to be supplemented with eruv poles.
What I have written concerning utility poles is the opinion of the vast majority of poskim. A lenient opinion maintains that only if one constructs a tzurat ha-petaĥ but attaches the wire to the side of the poles does he show that he is not interested in constructing a valid tzurat ha-petaĥ. In contrast, if poles are erected for a different purpose, such as in the case of utility poles, and wires are attached to the sides of these poles, this does not show that one is not interested in a tzurat ha-petaĥ. Therefore, this opinion allows these poles to be used for an eruv (Sho’el U-meshiv, Mahadura Kama 2:88). Some are lenient because the settings over which electrical wires pass are tightly connected to the utility pole and are considered part of it, so the wires are above the pole in accordance with the lenient opinion in the previous note. Furthermore, according to some, Rif and Rambam maintain that even if the wire is situated at the side of the pole, this does not invalidate the eruv. This opinion is quoted in Ĥelkat Yaakov 1:200. In practice, we do not use utility poles for tzurot ha-petaĥ without first making the adjustments described above. See R. Elimelech Lange, Hilkhot Eruvin ch. 4 nn. 60, 66, and 67.