What conduit clamps and straps actually do

Clamps, straps and hangers keep a raceway aligned and transfer its weight to an approvedsupporting surface or system. They also help prevent movement at boxes, fittings and bends.

A clean installation requires more than adding a strap whenever the conduit starts to sag.The raceway type determines the support rules. The trade size and environment determine thehardware. The mounting surface determines the fastener or anchor.

Before laying out the run, identify:

• The raceway type and trade size.
• The applicable securing and support intervals.
• The location of boxes, cabinets, conduit bodies and other terminations.
• The mounting surface and approved attachment method.
• Whether the location is dry, damp, wet or corrosive.
• Whether temperature changes require room for expansion and contraction.
• Any project-specific structural, seismic or wind-bracing requirements.

Quick support-reference checklist

These references are a planning aid. Check the complete section, project documents,product instructions and any applicable exceptions before installation.

Eight installation mistakes that cause problems

1. Using the wrong support for the raceway

A strap that fits around the conduit is not automatically suitable for it. Confirm thesupport's intended raceway, trade size, material and application. A support made for EMTshould not be substituted for rigid conduit, PVC or flexible raceway unless the productinformation identifies that use.

One-hole straps can work well where their listing and the mounting surface permit them.Two-hole straps provide two attachment points and may offer better control where thespecification, raceway size or installation conditions call for it.

2. Treating every raceway's spacing rule as the same

EMT, rigid PVC, FMC, LFMC and ENT do not share one universal support interval. Check theraceway-specific section before marking the supports.

Start with required securement near terminations. Then lay out the intermediate supportsso no span exceeds the applicable limit.

3. Forgetting securement near terminations

Meeting the maximum spacing between supports does not automatically satisfy the separaterequirement near boxes, cabinets, conduit bodies or termination fittings.

Do not assume that a connector attached to a box replaces every required securement point.Read the applicable code language and confirm any disputed layout with the authority havingjurisdiction before rough inspection.

4. Attaching to something that is not an approved support

Raceway supports need to transfer load to the building structure or another approvedsupport system. Do not attach to ceiling grid, existing piping, ductwork or miscellaneousbuilding components unless the system and attachment are specifically permitted for that use.

Suspended runs may require threaded rod, strut, beam attachments or a designed trapeze.Do not drill structural steel or alter a structural member without approval.

5. Choosing the wrong anchor or fastener

Wood, structural steel, light-gauge framing, concrete and concrete masonry units requiredifferent attachment methods. Match the anchor to the substrate, load and installationcondition.

Follow the anchor manufacturer's requirements for hole size, embedment, edge distance,spacing and installation torque. Drywall alone should not be treated as a structural support.

6. Overtightening the clamp or strap

A support should hold the raceway without crushing it, flattening it or damaging its finish.Overtightened hardware can deform thin-wall tubing, strip fasteners and restrict movement.

Use the manufacturer's torque value when one is provided. Otherwise, install the fastenerand support according to the product instructions without distorting the raceway or hardware.Replace damaged components rather than trying to straighten them in place.

7. Ignoring moisture and corrosion exposure

A zinc-plated indoor strap may not be suitable for a wet, corrosive or salt-exposed location.Select hardware based on the actual environment, compatible materials, product listing andmanufacturer guidance.

On exterior Long Island projects, examine direct weather exposure, salt exposure, dissimilarmetals and the condition of the supporting surface. Do not promise that one finish will workfor every coastal installation.

8. Locking PVC conduit so it cannot move

Aboveground PVC conduit expands and contracts as its temperature changes. Supports must holdthe run while permitting the movement required by the installation design.

Long exterior runs may require expansion fittings. Position fixed points, supports and theexpansion fitting according to the fitting manufacturer's instructions. Set the expansiongap for the expected installation and operating temperatures.

Jobsite examples

Example 1: A 40-foot EMT run between two boxes

For a straightforward EMT run, first mark the securement points within 3 feet of eachtermination. Then add intermediate supports so no interval exceeds 10 feet.

One possible layout is at approximately 3, 10, 20, 30 and 37 feet. Actual locations mayshift to reach suitable structural attachment points, provided the completed layout stillmeets the applicable requirements.

Example 2: A 25-foot run of 1-inch rigid PVC

Consult NEC Table 352.30 for the maximum support spacing. For rigid PVC from 1/2 inch through1 inch, the table lists a maximum support spacing of 3 feet. Lay out the supports within thatlimit and secure the raceway near terminations as required.

Do not clamp every support so tightly that the run cannot expand and contract. If thecalculated movement requires an expansion fitting, install and set it according to themanufacturer's instructions.

Example 3: Multiple conduits on a trapeze

Confirm the load from the raceways, conductors, strut and hardware. Verify the beam attachment,threaded rod, strut and clamps as a complete support assembly. Keep the conduits aligned andleave adequate working room for installation and future service.

Final inspection checklist

• Every support matches the raceway type and trade size.
• Required securement is provided near terminations.
• No support interval exceeds the limit for that raceway.
• Anchors and fasteners match the mounting surface.
• Supports connect to an approved structural or support system.
• The raceway is not crushed, flattened or visibly damaged.
• Hardware is suitable for the environment.
• PVC movement and expansion fittings are not obstructed.
• Bends, offsets and vertical runs remain aligned.
• Product instructions and required closeout records are saved.

Frequently asked questions

How far apart should EMT straps be?

NEC 358.30 generally requires EMT to be securely fastened within 3 feet of each box,cabinet or other termination and supported at intervals no greater than 10 feet.Review the complete section for conditions and exceptions.

Are one-hole or two-hole conduit straps better?

Neither style is automatically better for every installation. Use a support identifiedfor the raceway and trade size, then consider the substrate, required stability andproject specification.

Can conduit be supported from a suspended ceiling grid?

Do not use the ceiling grid or its existing support wires as the default raceway support.Provide an independent or specifically approved support method that complies with theapplicable requirements.

Can metal straps be used on PVC conduit?

Use only hardware compatible with the PVC raceway and environment. The support must notdamage the conduit or block required thermal movement. Check the support and racewaymanufacturer information before installation.

How tight should a conduit strap be?

Follow the product instructions and any published torque value. The support should securethe raceway without deforming it, damaging its finish or stripping the fastener.