The following eight paragraphs outline a suggested specification for Formex® Duct Terminator Modules to be used for underground distribution systems. For each suggested specification, the reasoning behind it is stated. On many projects, underground duct bank configurations are complex. May we suggest that when designing a duct system utilizing several sizes or types of duct, Formex could possible help keep costs down if consulted in advance. Any questions concerning the following should be directed to your Formex® representative or to the factory.
- Duct terminator modules shall be provided in manhole and/or vault walls where shown on the drawings. They shall be the product of Formex Manufacturing, Inc. or approved equal. Terminator modules shall be made of high impact, high strength ABS plastic.
REASON: Formex® uses high strength ABS plastic because it offers a superior combination of properties, all of which are important to the structural integrity of the terminator module. These properties include high strength, an optimum combination of rigidity and impact strength, and excellent high and low temperature resistance to thermal deformation and embrittlement. The maximum curing temperature of concrete will not distort the ABS used in the Formex duct terminator under loads normally encountered in the casting of manholes and/or vaults.
- Terminator modules shall interlock and where indicated on the project drawings shall be sealed together using a recommended plastic solvent cement, to provide a panel of openings which shall match the specified duct bank configurations terminating at each manhole and/or vault wall. Horizontal and vertical separations between all terminator openings shall conform to the dimensions shown on the project drawings.
REASON: By sealing the terminator modules together before attaching them to the form jackets of the manhole and/or vault, correct horizontal and vertical separations are assured and so doing will enhance the watertightness of the structure.
- The outside wall to outside wall dimensions of the terminator module shall be ___ inches.
REASON: Presently Formex® makes the duct terminator modules in two basic depths. The dimensions from outside wall to outside wall are a standard 2 7/8″, or a special 6″. If other depth dimensions are required, please consult your Formex® representative or the factory.
- In the coupling area of the terminator, openings shall be slightly tapered to facilitate entry of duct. The I.D. of the terminator opening shall accommodate the O.D. of the duct to be terminated.
REASON: To assure a mechanically strong, watertight termination, it is important to hold the I.D. of the terminator opening as close as possible to the O.D. of the ducts to be used. Plastic solvent cement is used to bond the ducts to the terminator.
- Terminators will include interior buffer or shoulder. The height of the shoulder shall equal or slightly exceed the wall thickness of the specified ducts. The shoulder shall be slightly radiused towards the belled wall (facing inside the manhole and/or vault) of the terminator.
REASON: A radiused shoulder which is equal to or slightly higher than the inside wall of the duct will prevent the conductor or cable from coming in contact with sharp edges of irregularly cut duct.
- The openings of the terminator facing the inside of the manhole or vault shall be belled.
REASON: A belled contour is desirable because it is less abrasive to coverings of conductors and cables.
- Where the project drawings require duct terminators for duct lines to be installed at some future date, the duct terminators shall include the watertight membrane.
REASON: A duct terminator with a watertight membrane will eliminate the necessity to use caps or plugs until such time as the duct is brought to the opening. It is simpler and time saving to cut the membrane out rather than drill an opening through a solid concrete wall.
- After duct lines are mandrelled, Formex® locking caps will be fastened to each opening on the inside of the manhole and/or vault.
REASON: By closing off each duct line with the Formex® locking cap, duct lines may be kept clear until such time as cable or conductors are ready to be pulled.