Wire harness sealing grommet

01

Fit the grommet to the panel hole

Sumitomo Wiring Systems' European application EP 1 468 877 A1 (2004) explains that a grommet mounted on the harness running from engine compartment to passenger compartment is inserted into a through-hole in the body panel to protect the harness and keep water, dust and noise out, and that grommets should install with reduced pushing force yet be held firmly afterwards. Its prior-art example has a funnel-shaped portion with a tubular portion at the narrow end and a circular groove near the wide end that engages the rim of the panel hole, the panel being held between two groove walls. [1]

US patent 5,739,475 (Sumitomo Wiring Systems and Inoac, 1998) describes grommets pulled through dash or cowl panel openings and notes that when panels are inclined, the burring around the opening can lean by 0–20° instead of standing perpendicular, leaving a clearance in the grommet's mounting groove through which water leaks; bending the harness sharply at the grommet exit widens that clearance. Its grommet, moulded from ethylene propylene rubber (EPDM), is designed to seat flush on such burrings. [2]

Editorial note: send the supplier the hole drawing — diameter or shape, panel thickness, whether there is a burring and its angle — and the direction of insertion, and ask for push-in and pull-out force figures and how full seating is checked on the line.

Give the supplier the panel hole shape and size, panel thickness and edge (flat, flanged, burred and angle), insertion direction, harness diameter or wire list (count and outside diameters), number of passages, sealing requirement (water, dust, noise; test method), temperature range, fluids exposure, elastomer preference, colour, push-in and retention force limits, tape or clamp interface on the tube, and quantities.

02

Seal the harness and choose the material

US patent 6,402,155 (Sumitomo Wiring Systems, 2002) describes grommets with a small-diameter tube that tightly holds the wire group and a conical enlarged portion with a panel-engagement recess, used on engine-compartment harnesses through the firewall and on floor harnesses. Water can still pass through the gaps between the individual wires and between the tape and the harness, so a sealant is provided between the wires; its method fills the grommet with a low-viscosity, free-flowing sealant that cures on absorbing atmospheric moisture, naming cyanoacrylates and silicones as candidates. [3]

US 5,739,475 adds that EPDM has poor adhesive strength, so its design shapes the medium-diameter portion as an inverted taper to stop a poured filler from falling out. [2]

Editorial calculation: 19 wires of an assumed 2.0 mm outside diameter packed hexagonally lie about 5 wire diameters across, so the bundle is about 10 mm in diameter; size the grommet's small tube for that bundle and ask the supplier how the gaps between the wires will be sealed. [3]

03

Read panel-thickness bands, material and temperature from a grommet catalogue

Heyco, a US maker of wire protection parts, sorts its rubber grommets by panel thickness: grommets for panels up to .063 in (1.6 mm), from .063 in (1.6 mm) to .125 in (3.2 mm) in steps of 1.6, 2.0, 2.4, 2.8 and 3.2 mm, from .125 in (3.2 mm) to .188 in (4.8 mm), and thick-panel versions. It states that these rubber grommets are SBR unless noted, with an operating temperature range of −40 °C to 105 °C, and that SBR grommets “have good water resistant characteristics and are suitable for most moderate chemicals and wet or dry organic acids”. [4] Its UL-listed thermoplastic rubber grommets come in six diameters for panels from 0.8 to 2.0 mm thick and mounting holes from 12.7 to 31.8 mm, are listed under UL file E103541, and are rated 0 °C to 50 °C. [5]

These catalogue grommets fit a single hole and wire bundle; the automotive designs in the Sumitomo patents above add a conical body, panel groove and sealed wire tube for engine-bay pass-throughs, so take sealing and insertion-force data from the harness supplier. [1] [2] [3]

Editorial calculation: the 1.6–3.2 mm band is covered in five sizes at 0.4 mm steps; a grommet rated −40 to 105 °C covers a span of 145 °C, against 50 °C for the UL-listed TPR line.

Give the supplier the panel thickness, hole diameter, wire bundle diameter and temperature range, and ask for the material, its temperature rating and any UL or automotive approvals.

04

A moulded-rubber supplier listing wiring-system grommets

Nangong Letu lists wiring-system rubber grommets among its moulded rubber parts; ask it for the panel-groove drawing, push-in and retention forces and the sealing test that the Sumitomo designs above call for. [1]

05

Panel groove, funnel, small tube, sealant fill, lips and elastomer

Three of these features answer the leak paths the patents name: the groove for the hole rim, the lips for inclined burrings and the sealant fill for gaps between wires. [1] [2] [3]

06

Hole and panel, burring angle, push-in force, bundle grip, sealant and elastomer for a grommet order

The burring angle and inter-wire sealing rows are the ones a hole diameter alone does not cover: US 5,739,475 traces leaks to burrings leaning 0–20°, and US 6,402,155 to gaps between the wires. [2] [3]

07

Send the panel, harness and sealing data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Panel: [hole; thickness; burring angle]
Harness: [wire count; diameters; tape]
Sealing: [water; dust; noise; test]
Material: [elastomer; hardness; temperature]
Assembly: [push-in force; retention; direction]
Supply: [drawings; samples; quantity]

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