The question recently arose regarding a certain synagogue that remodeled the interior of the building, and ordered special decorative Menorahs that adorned the wall both in the main sanctuary and in the study hall. These Menorahs are made from metal, use electric lights, and have seven branches, resembling the Menorah in the Bet Ha’mikdash. Some Rabbis questioned the propriety of having these Menorahs, as it is forbidden to make replicas of the furnishings of the Bet Ha’mikdash. Although this Menorah does not precisely resemble the Menorah in the Mikdash, as the branches do not have a receptacle for oil and wicks, and it runs on electricity, nevertheless, some argued that its resemblance to the Menorah in the Bet Ha’mikdash suffices to render it forbidden.
This question was addressed already by Hacham Ovadia Yosef, in a responsum that appears in the posthumously published seventh volume of Yehaveh Da’at (142; listen to audio recording for citations of select passages from this responsum), and he cites numerous Poskim who explicitly allowed such Menorahs. One such Posek is Rav Reuven David Ha’kohen Borstein (the "Radach"), who writes that it is entirely permissible even "Le’chatehila" (from the outset) to make such a Menorah, because the branches are closed at the top without a receptacle for oil and wicks. As such, such Menorahs do not at all resemble the Menorah in the Bet Ha’mikdash, and it is therefore permissible to produce them and have them in the synagogue. Hacham Ovadia cites also Rav Moshe Stern of Debrecen (Hungary, 1914-1997), who adds that electric lights are not at all similar to oil lamps, and so it is certainly permissible to make an electric Menorah with seven branches. This was also the view of Rav Yitzhak Eizik Herzog (first Ashkenazic Chief Rabbi of the State of Israel, 1888-1959), and of Rav Bension Meir Hai Uziel (first Sephardic Chief Rabbi of the State of Israel, 1880-1953). Hacham Ovadia relates in this responsum that he was first asked this question in 5722 (1972) by a rabbi in Tel-Aviv, and he ruled that this was permissible. He refers in this context to his earlier responsum on the subject, which appears in the first volume of Yabia Omer (Y.D. 12).
He acknowledges, however, that there were some Poskim over the ages who felt it appropriate to be stringent in this regard. One especially interesting anecdote is a story told by the son-in-law of Rabbi Akiva Eiger (1761-1837) about the time when a Menorah was made for Rabbi Akiva Eiger’s synagogue with seven branches. Even though the Menorah was round, and thus did not at all resemble the Menorah in the Bet Ha’mikdash, Rabbi Akiva Eiger insisted that an eighth branch must be added. The Menorah was returned to the smith, who had a very difficult time finding a way to add an eighth branch, and ended up ruining the entire Menorah. Rabbi Akiva Eiger’s son-in-law did not understand why Rabbi Akiva Eiger was so insistent that an eight branch be added, but he nevertheless expresses respect for his father-in-law’s strict fealty to Halacha.
It is told that the decorative Menorot in Congregation Shaare Zion have eight branches following the instructions of Rav Yaakov Kassin (1900-1994), who felt that a seven-branched Menorah should not be used.
Nevertheless, in light of Hacham Ovadia’s clear ruling, there is certainly room to be lenient and allow a seven-branched Menorah if it was already made.
Summary: Some Rabbis ruled that it is forbidden to make or have a decorative electric Menorah with seven branches, because it resembles the Menorah that stood in the Bet Ha’mikdash. The majority opinion, however, permits such Menorahs, and this was the position of Hacham Ovadia Yosef.