Parallel groove clamps for taps, jumpers and mid-span repairs
Two grooves, a pressure cap and one or two bolts: the standard way to join two conductors without cutting either. Sized on the conductor's outside diameter, which is where most specifications go wrong.
A parallel groove clamp joins two parallel conductors without cutting either of them: two grooves, a pressure cap and one or two bolts. It is the standard way to tap a service off a main run, to make a jumper around a fitting, or to repair a conductor that has been damaged mid-span. Specify it by the outside diameter in each groove and the bolt torque — not by the conductor's nominal cross-section, which tells you nothing about whether it will grip.
Why the groove diameter, not the mm²
This is the single most common specification mistake on this product. Two conductors of the same nominal cross-section can differ by several millimetres in outside diameter — a compacted AAAC 150 mm² and a conventional ACSR 150 mm² are not the same object in the hand. A clamp sized on mm² alone will either not close or will close on air.
So the enquiry needs the measured outside diameter, or the conductor designation and stranding so we can look it up. Where a clamp has to take two different conductors — a common case when tapping a smaller service off a larger main — the two grooves are different sizes, and that is a standard variant rather than a special.
Where the joint goes wrong
Parallel groove clamps fail for reasons that are almost all installation rather than manufacture.
| What you see | Why it happened | What prevents it |
|---|---|---|
| Hot joint within a year | Bolt not taken to the specified torque, or taken up once and not re-torqued after thermal cycling | Torque wrench on site, and a re-torque after the first load cycles |
| Conductor slipped in the groove | Groove oversized for the conductor, or the wrong groove used on a two-size clamp | Groove diameter matched to measured OD, not to nominal mm² |
| Corrosion at the interface | Aluminium against copper without a transition, or no inhibitor in a coastal site | Bimetallic clamp or a plated interface, plus jointing compound |
| Clamp body cracked | Cast body over-torqued, or a bolt of the wrong grade | Stated torque and the bolt grade the clamp was designed for |
Materials
Bodies are extruded 6xxx aluminium or cast in an aluminium alloy, depending on the section — extrusion gives a straighter groove and better dimensional control, casting gives the thicker sections a heavy clamp needs. Bolts are galvanised steel as standard; stainless is available where the specification asks for it, with the same galvanic caveat as any aluminium body.
For coastal and industrial atmospheres the whole assembly can be supplied with a plated interface and a jointing compound sachet packed with each clamp, which is cheaper than specifying a different alloy.
Ordering
Send the two conductor designations and, if there is one, the drawing of the existing clamp. Matching an existing fitting matters more here than on a lug: the clamp has to sit on a conductor that is already in service, and the groove that was right for the original conductor may not be right for the replacement.
Hot-stick compatible versions, with the eye or the bail the stick fits, are quoted on the same drawing route.
Buyer questions
Can I use one clamp for two different conductor sizes?
Yes — that is a standard variant, with a different groove on each side. Give the outside diameter of both conductors and the clamp is made to suit; it is not a special order.
Does it need to be re-torqued?
Yes, once after the first thermal cycles. Aluminium creeps under clamp load, so the joint that was correct at installation loosens slightly as it heats and cools. This is normal practice in every utility maintenance schedule we have seen.
Is it suitable for live-line work?
Hot-stick versions are available with the fitting the stick engages. Say so at enquiry, because the body and bolt layout differ from the standard clamp.
Aluminium or bimetallic?
Aluminium for aluminium-to-aluminium. Where the tap is copper, use a bimetallic clamp or a plated interface — a bare aluminium clamp on a copper conductor is a galvanic couple with a short life in humid air.
What about insulation piercing?
That is a different product for insulated service cable, and we do not list it here. For bare overhead conductor, the parallel groove clamp is the right part.
Related
Send both conductor designations.
Or the measured outside diameters — that is the number the groove is cut to.