A junction block including: - an insulating body delimited by two substantially parallel lateral planes (PL1, PL2), - a movable fastening leg connected to a link area of the rear face of the insulating body and intended to hold the junction block on a support rail, the fastening leg comprising at least two elastic branches (11a, 11b, 11c) connecting the link area of the rear face of the insulating body and a link area of a fastening member, the fastening member having an elongate shape extending in a general direction between a first end comprising fastening means intended to interact with an edge of the support rail and a second end comprising a retaining member intended to block a tool so as to be able to displace the fastening leg against the force exerted by the at least two elastic branches (11a, 11b, 11c), the junction block comprising at least one housing for a connection terminal, said housing extending at least partially inside a volume delimited by: - a first plane transverse to the two lateral planes (PL1, PL2) delimiting the insulating body, substantially parallel to the general direction joining the first end and the second end of the fastening member, and passing through the link area of the fastening member, and - a second plane transverse to the two lateral planes (PL1, PL2) delimiting the insulating body, substantially parallel to the first plane and passing through the link area of the rear face, - at least one third plane transverse to the two lateral planes (PL1, PL2) delimiting the insulating body, substantially transverse to the first plane and the second plane, and passing through the elastic branch farthest from the fastening means intended to interact with an edge of the support rail, and - at least one fourth plane transverse to the two lateral planes (PL1, PL2) delimiting the insulating body, substantially transverse to the first plane and the second plane, and passing through the retaining member intended to block a tool, said junction block being characterized in that all elastic branches (11a, 11b, 11c) are disposed at the same location of the same side relative to the housing of the connection terminal. - an insulating body delimited by two substantially parallel lateral planes (PL1, PL2), - a movable fastening leg connected to a link area of the rear face of the insulating body and intended to hold the junction block on a support rail, - a first plane transverse to the two lateral planes (PL1, PL2) delimiting the insulating body, substantially parallel to the general direction joining the first end and the second end of the fastening member, and passing through the link area of the fastening member, and - a second plane transverse to the two lateral planes (PL1, PL2) delimiting the insulating body, substantially parallel to the first plane and passing through the link area of the rear face, - at least one third plane transverse to the two lateral planes (PL1, PL2) delimiting the insulating body, substantially transverse to the first plane and the second plane, and passing through the elastic branch farthest from the fastening means intended to interact with an edge of the support rail, and - at least one fourth plane transverse to the two lateral planes (PL1, PL2) delimiting the insulating body, substantially transverse to the first plane and the second plane, and passing through the retaining member intended to block a tool,