1.5 Support Systems: Strut, Hangers, Fasteners & Seismic Restraint

1.5 Support Systems: Strut, Hangers, Fasteners & Seismic Restraint

Quick Answer: Task A-4 of the Red Seal Occupational Standard makes the industrial electrician responsible for fabricating support structures, installing brackets, hangers and fasteners, and installing seismic restraint systems. The three questions to answer before hanging anything are: what is the load (dead weight plus pulling forces plus anything a worker might stand on), what is the base material (solid concrete, hollow block, steel, bar joist, or a suspended ceiling that supports nothing), and what does the governing document require — the Canadian Electrical Code demands secure mounting, while the National Building Code of Canada decides whether seismic bracing is required.

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1. Strut Channel Systems

Strut channel — commonly called by trade names such as Unistrut, Superstrut or Kindorf — is the structural backbone of industrial electrical support. It is cold-formed steel or stainless, usually 41 mm wide, in depths from 21 mm (half-height) through 41 mm (standard) to 82 mm (back-to-back or "deep" channel).

Load capacity is a table lookup, never a guess

Three variables determine what a run of strut can carry:

1. Span — the distance between supports. Capacity falls off roughly with the square of the span, so doubling the span cuts the safe load to about a quarter.
2. Loading direction — a channel loaded on its back (the closed side, with the slot facing the load) uses its full section depth. The same channel loaded on its open face is far weaker, because the open slot is where the section wants to spread.
3. Deflection limit — manufacturers publish both a strength limit and a deflection limit, typically span/180 or span/240. On a long cable tray run the deflection limit almost always governs, not the strength limit.

Field rule: if the run is carrying cable tray, a 3-phase Teck90 bundle, an MCC-fed conduit bank, or anything that a worker might step on during maintenance, the span and load come out of the manufacturer's published table for the specific channel, fitting and finish. Nothing about the exam or the job rewards eyeballing it.

Cutting, deburring and protecting cut ends

Strut leaves the factory with a finish — pre-galvanized, hot-dip galvanized, painted, PVC-coated or stainless — and every field cut exposes bare steel.

• Cut with a bandsaw, portable metal chop saw or strut cutter, not an abrasive wheel that scorches the finish for 100 mm either side of the cut.
• Deburr every cut end. A burred strut end will slice cable jackets, gloves and forearms, and it prevents the strut nut from seating square.
• Field-coat the cut end with a cold galvanizing compound on galvanized channel, or the manufacturer's touch-up on coated systems. In a wet, chemical or wash-down environment, an uncoated cut end is where the rust starts and it will migrate under the finish.
• Cap open ends in areas where personnel move.

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2. Fasteners and Anchors: Match the Anchor to the Base Material

Anchor failures in electrical work are almost always selection failures, not installation failures.

Anchor engineering basics that appear on exam questions

• Tension versus shear. An anchor pulled straight out of the surface is in tension; an anchor loaded parallel to the surface is in shear. Manufacturer tables give different values for each, and a diagonal load must be resolved into both components.
• Edge distance and spacing. Expansion anchors generate bursting pressure. Installing too near a slab edge or too close to another anchor lets the concrete cone fail long before the steel does. The manufacturer's minimum edge distance and spacing are part of the rating.
• Embedment depth. The published capacity is for a specific embedment. A wedge anchor bottomed out in a shallow hole is not the anchor in the table.
• Hole preparation. Adhesive anchors fail from dust, not from adhesive quality. Blow, brush, blow — as the manufacturer instructs — or the bond develops on drilling dust.
• Powder-actuated fasteners are for light, static loads into sound concrete or structural steel, require specific operator certification in most jurisdictions, and are not used for overhead sustained loads in many site specifications. Never fire into hollow block, brittle or spalled concrete, or within the manufacturer's minimum edge distance.

Threaded rod and trapeze hangers

The workhorse of industrial raceway support is a trapeze: two threaded rods dropped from structure with a strut channel spanning between them.

• Rod is sized for the tensile load and is available in plain, galvanized and stainless. The most common industrial size range is 10 mm through 16 mm (3/8 in through 5/8 in).
• Rods must be plumb and long enough to take a nut, a lock washer and full thread engagement on both sides of the channel.
• Where vibration is present — near compressors, screens, crushers, or under a roof-mounted fan — use double nuts, lock nuts or thread-locking compound. A single plain nut on a rod carrying a vibrating conduit bank will walk off.
• Do not use the trapeze as a ladder. Supports are rated for the raceway and cable, not for a worker.

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3. Galvanic Corrosion and Material Compatibility

Industrial electrical rooms are often wet, salty, chemically loaded or subject to washdown, and support systems mix metals freely: aluminium cable tray on galvanized strut, stainless hardware into carbon steel channel, copper bonding jumpers landed on aluminium.

When two dissimilar metals are in electrical contact in the presence of an electrolyte, the less noble metal becomes the anode and corrodes. Aluminium against stainless or against copper, in a wet environment, is the classic case: the aluminium sacrifices itself, the joint loses both mechanical strength and electrical continuity, and the bonding path quietly degrades.

Practical controls:

• Match materials wherever possible — aluminium tray on aluminium supports, stainless on stainless.
• Isolate with non-conductive washers, bushings or isolation pads where materials must be mixed, but remember that isolating a bonding connection defeats its purpose — isolate the structural joint and provide a separate, properly compatible bonding jumper.
• Use compatible listed connectors for aluminium-to-copper electrical connections (dual-rated AL9CU connectors with the manufacturer's inhibiting compound); the same principle applies to structural hardware.
• Specify the finish for the environment: electro-galvanized for dry indoor, hot-dip galvanized for damp and outdoor, PVC-coated or Type 316 stainless for corrosive chemical and marine service.

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4. Seismic Restraint: Which Code Actually Requires It

This is the part of Task A-4 candidates get wrong, because they look for a rule number in the Canadian Electrical Code.

• The Canadian Electrical Code requires that electrical equipment be securely mounted and adequately supported and that raceways be supported at the intervals its Section 12 rules specify. It does not contain the seismic design provisions.
• Seismic restraint requirements come from the National Building Code of Canada (and the provincial building codes derived from it), through the building's seismic hazard values and the importance category of the structure. Post-disaster buildings — hospitals, emergency operations centres, water treatment plants, fire halls — carry the most stringent requirements, and their electrical systems are among the specifically listed components that must remain operational after a design earthquake.
• Provincial amendments and the project's structural specification determine the actual restraint design. The electrician's job is to install what the seismic design drawings and the manufacturer's certified details specify, not to invent bracing.

What seismic restraint looks like in the field

Three details that repeatedly fail inspection:

1. Rod stiffeners omitted. Sway bracing puts a hanger rod into compression; a slender rod buckles. The stiffener is not optional trim.
2. Bracing tied to the wrong thing. Bracing anchored to metal deck flutes, ductwork, or another trade's hangers transfers nothing to structure.
3. Flexible connections omitted at seismic joints. Where a raceway crosses a building seismic separation, a flexible connection must accommodate the relative movement — and, because it is usually a non-conductive or high-impedance path, an external bonding jumper must span it to keep the equipment bonding path continuous.

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5. Fabricating Support Structures

Task A-4.01 expects the industrial electrician to fabricate, not merely assemble.

• Measure and lay out from a single datum. Working from a common benchmark keeps a 40 m conduit rack straight; chaining measurements from each preceding support accumulates error.
• Square and plumb everything before final torque. Strut fittings allow slop deliberately so a run can be adjusted; once torqued, that slop is gone.
• Weld only where permitted. Welding to structural steel changes its properties and is normally subject to structural engineering approval, a hot work permit and a certified welder. In a hazardous location it is subject to a gas test and continuous fire watch.
• Provide for thermal movement. A long indoor-to-outdoor conduit rack moves. Expansion fittings, slotted holes and sliding clips absorb it; rigid clamping at both ends does not, and the resulting force will pull anchors or buckle the rack.
• Leave the installation maintainable. Supports that box in a breaker, block a valve, or make it impossible to pull a cable later are technically correct and practically worthless.