Tight Enough to Fail - Short #309

Brian opens by asking whether electrical connections are always better when they are tighter, then answers that they are not. He describes a familiar maintenance routine: opening a panel, putting a screwdriver on every terminal, wiggling spade connectors, and giving each Phillips-head screw an extra snug turn. His point is that a screw turning does not reveal how much force has actually been applied or whether the conductor is making good contact. He defines torque as a turning effect—the force applied at a distance from the center of the screw. A quarter-turn is therefore not a measurement of the force applied. If a terminal or screw shows discoloration even though the wire is still present and the screw feels tight, Brian says it deserves closer investigation rather than automatically receiving another turn. A connection can be mechanically tight and still electrically poor. The important result is low resistance to current flow; poor contact can increase resistance at the connection and create unwanted heat.

Brian connects the heating problem to Watt's law: current squared times resistance. With resistance held constant, doubling the current produces four times the heating power at that connection. This explains why a connection may appear uneventful under a light load but reveal a much larger problem when the equipment draws more current. He cautions that real connections do not always follow a perfectly neat pattern as they heat. Resistance and other operating conditions can change, just as the resistance of a tungsten light-bulb filament increases as it heats. For that reason, a thermal image of a hot terminal is useful evidence but does not, by itself, identify the cause. The technician also needs to know what current is flowing, compare similar connections under similar loads, and allow the equipment enough time to warm up. Temperature should prompt an investigation, not be treated as a diagnosis on its own. Brian also notes that an overloaded circuit can damage an otherwise good connection over time, so overheating does not prove that the connection was loose.

Brian asks why a technician should not simply “twist the sucker” tighter. His answer is that terminals and their parts have limits, and some technicians are strong enough to damage threads, heads, or other hardware by applying excessive force. He recalls his father calling this “McGilligoring” something and imitates the much less technical “uga buga” approach to over-tightening. The extra force can make the original problem worse, and a torque tool cannot undo damage that has already been done. He recommends using a torque screwdriver, while acknowledging that not everyone will use one on every routine residential maintenance visit. Using one at least sometimes helps technicians develop a sense of what the correct amount of tightening feels like. He emphasizes that correct torque is often less than people expect. The tool must be set using the manufacturer’s actual specification and the correct bit. Brian also warns about units: residential work commonly specifies inch-pounds, while larger commercial or industrial work may use foot-pounds. Since 12 inch-pounds equal one foot-pound, setting a tool to 40 foot-pounds when the instruction calls for 40 inch-pounds applies 12 times the intended torque and could break the connection.

For a new connection, Brian says the technician must consider more than how tightly the screw is turned. The terminal must be intended for the conductor’s size and material. An incorrectly oversized or undersized wire, unauthorized multiple wires or double-lugging, incorrect strip length, excess exposed conductor, or insulation left in the wrong place can all create problems. He specifically points out that some terminals have a plate beneath the screw, and the wire belongs under that plate rather than directly under the screw head. The conductor must be fully seated, and technicians should be suspicious of unapproved substances or “weird goo” placed in the terminal. Ferrules, spade terminals, and ring connectors must be correctly selected for the expected current and properly crimped; changing the wire’s shape with a barrel or ferrule does not remove the need to follow the terminal’s instructions. Spring terminals have no screw to torque, but they still require the correct wire size, strip length, and insertion. Brian’s overall advice is to use “Spidey Senses” before turning anything: inspect the whole termination rather than assuming that a wire fitting, a spade being attached, or a conductor being under a screw means the connection is correct.

Brian says the best starting point for a new connection is the actual torque specification on the equipment label or in the installation instructions. If the specification is not immediately available, technicians should look up the manufacturer’s information, especially when working on unfamiliar equipment. He also notes that commercial and industrial environments may have explicit inspection or retorquing procedures, with much higher stakes than an ordinary residential service call. All termination work should be done with the power off and without voltage present. Brian does not claim that every residential technician must retorque every terminal on every visit, nor does he present an older HVAC School torque-check practice as a universal instruction. Instead, he says rules of thumb are intended to encourage better practices, while high-stakes industrial work requires exact compliance. A torque screwdriver is relatively inexpensive and helps establish what “good” looks like. He closes by repeating that tightening a connection does not necessarily improve it, and that both the physical installation and the electrical operating conditions must be investigated.