Electric Insulation

Electric Trench Constructuion

Project designers should first determine whether the trench will be constructed on site or a precast concrete trench system will be installed as prefabricated sections. Jinmeng provides a customized range of composite trench covers engineered to match standard trench dimensions and ensure reliable performance. These covers are available for H-20 traffic loading, Tier 15, and Tier 8 pedestrian applications, offering strength, safety, and corrosion resistance. Trench systems and vaults must be designed to accommodate utilities, cables, piping, and associated non-conductive infrastructure. Jinmeng design guidelines assist architects and engineers in seamlessly integrating composite trench covers into efficient and durable trench or vault installations.

Precast Concrete Manholes

Precast concrete manholes are a perfect example of value-added electrical engineering. Precast concrete is nontoxic and environmentally safe and resists buoyancy. Installed quickly and easily, precast concrete electric manholes strengthen over time, can be made watertight and provide excellent durability during backfill and use. Utility equipment and accessory items can be pre-installed or cast-in, saving time and money on most underground utility projects. Due to the multiple and versatile engineering of the electric control unit and cable connection points, the concrete manholes retain real design flexibility. The non-conductive properties of fiberglass manhole covers are the first choice for covering precast concrete electric manholes to prevent electrical hazards. Aside from protecting the vital connections and controls for utility distribution, fiberglass cover is ideal for underground protection and access applications.

Onsite Construction Manholes

In some cases, such as large-scale power facilities that do not mate well with precast manholes, uniquely designed pipeline systems, or security and confidentiality considerations, precast manholes are not allowed in most governmental, military, industrial, hospital, educational, and business areas where people gather. In this case, a Steel Reinforced Poured-in-Place Concrete Manhole is the only option. Jinmeng FRP composite covers are high-performance products produced via sheet moulding compound (SMC) to create durable, non-conductive covers that fit most electric manholes.

1. Electrical Manhole Structural Instance

1.1 General Construction

New electrical manholes shall be cast-in-place reinforced concrete construction designed for underground electrical distribution systems.

The minimum internal clear dimensions shall be:

10 ft (L) × 10 ft (W) × 8 ft (H) clear inside space.

Structure shall be designed to withstand earth loads, groundwater pressure, and surface vehicular loading.

1.2 Reinforcement

Reinforcing steel shall conform to ASTM A615 Grade 60.

Reinforcement shall form a fully tied continuous reinforcing cage for walls, base slab, and roof slab.

Minimum concrete cover:

3 in. below grade surfaces

2 in. interior surfaces

1.3 Concrete Requirements

Concrete compressive strength shall be minimum 5,000 psi at 28 days.

Concrete shall include:

Air entrainment (5–7%)

Sulfate-resistant cement where required

Waterproofing admixture

1.4 Waterproofing

Exterior surfaces below grade shall receive:

Elastomeric waterproof membrane or crystalline waterproof coating.

All pipe penetrations shall utilize mechanical compression seals.

Joints between:

Wall sections

Riser structures

Frame assemblies

shall be sealed with non-shrink waterproof sealant.

1.5 Warranty

Manufacturer or contractor shall provide a minimum seven (7) year warranty against:

Structural cracking

Groundwater infiltration

Leakage through joints or penetrations

1.6 Sump System

Manhole shall include an integrated sump:

24 in. diameter

24 in. depth

Sump shall accommodate automatic dewatering pump operation.

1.7 Ventilation

Provide two independent ventilation ducts:

One high exhaust vent

One low intake vent

Vent system shall support:

Natural convection airflow

Forced mechanical ventilation

Vents shall include corrosion-resistant grilles and rodent screens.

2. Hardware and Electrical Equipment

2.1 Manhole Frames and Covers

Frames and covers shall meet AASHTO H-20 or HS-20 load rating.

Covers shall include:

Cast or engraved 3 in. lettering “ELECTRIC”

Unique identification number

Non-slip surface finish

Stainless steel lifting handles

High Traffic Areas

Heavy-duty ductile iron frame and cover.

Minimum 36-inch clear opening diameter.

Bolted or locking cover recommended for safety.

Non-Traffic Areas

Flush aluminum or composite covers permitted.

Rated for H-20 loading.

Minimum 30-inch clear opening.

2.2 Power Distribution Inside Manhole

Service power panel shall include:

150 Amp, 120/240V AC circuit breaker

NEMA 4X thermoplastic enclosure

Corrosion-resistant construction

2.3 Switching Devices

Lighting and ventilation switches:

20A, 120V rated

Installed in weatherproof enclosure

Located near entry opening for external access

2.4 Lighting System

Lighting fixture shall be:

LED vapor-tight ceiling mounted luminaire

Wet location rated

Minimum 5,000 lumen output

2.5 Ventilation Fan

Exhaust fan shall:

Meet OSHA confined space requirements

Provide minimum 6 air changes per hour

Be corrosion-resistant aluminum or polymer construction

2.6 Electrical Receptacles

Provide:

One (1) 20A GFCI duplex receptacle

One (1) L5-20R twist-lock receptacle for sump pump (non-GFCI)

Weatherproof in-use covers

Installed near top wall for safe accessibility.

2.7 Dewatering Pump

Pump shall meet or exceed the following:

Submersible cast iron sewage pump.

120V motor with twist-lock plug.

Vortex impeller non-clog design.

Fully cast iron housing components.

Stainless steel fasteners and hardware.

Float-activated automatic switch.

Oil-filled hermetically sealed motor.

Thermal overload protection.

Rated to pass 3/4 in. solids.

2 in. NPT discharge connection.

2.8 Cable Management

Provide pulling eyes:

Minimum one per short wall

Minimum three per long wall opposite duct banks.

Medium-voltage cables shall be supported by:

Thermoplastic elastomer cable clamps

UV and chemical resistant materials.

2.9 Grounding System

Install minimum two grounding electrodes per manhole.

Ground rods:

Copper clad steel

Minimum 3/4 in. × 10 ft length.

Grounding shall comply with NEC requirements.

2.10 Conduit Interfaces

All conduits shall terminate with bell ends.

Provide watertight duct entry seals.

2.11 Access Ladder

Provide corrosion-resistant ladder system:

Fiberglass or hot-dip galvanized steel ladder.

Ladder shall include removable extension above opening.

2.12 Hardware Materials

All exposed hardware shall be:

Stainless steel, or

Hot-dip galvanized steel.

Result:

This regenerated specification provides:

Larger square manhole configuration

Higher concrete strength

Updated OSHA/NEC practices

Improved sump and ventilation design

Modern LED lighting and corrosion-resistant hardware