Underground Standards Documents
Underground Standards Documents
This document contains information pertaining to Maritime Electric Company, Limited's standard construction practices for underground supply facilities. This document is provided to assist personnel involved in the construction of such facilities for Maritime Electric’s use or to connect to Maritime Electric’s system. This document will help bring some uniformity with respect to construction practices, and is designed to be used in conjunction with Maritime Electric underground standard drawings.
1.2 Division of Ownership of Facilities
All facilities constructed for Maritime Electric use shall be built to the standards contained in this document and the associated drawings. Facilities constructed for use in conjunction with Maritime Electric’s facilities, such as customer owned service ducts, shall meet the appropriate provincial and national standards. The customer is responsible for installing ducts and service conductors ensuring to leave adequate length of conductor at the end to which Maritime Electric will connect to Maritime Electric facilities. This includes, but not limited to sealing of the ducts to prevent any potential water problem, which is to be completed at the time the service conductor is installed to a temporary seal in the event constructed is delayed.
1.3 Expectation of Customer/Contractor
Maritime Electric’s most significant expectation of the contractor is to maintain a safe and secure workplace for their employees, Maritime Electric employees and the public. Maritime Electric expects all facilities installed for Maritime Electric use will be constructed to Maritime Electric standards and/or the project plan. All facilities shall be constructed with the correct type and number of ducts, and with a focus on a water tight and obstruction free finished product, minimizing sharp bends. No trenching or backfilling shall be completed during the period of December 15 to April 15 of each year without explicit approval from Maritime Electric. This is to avoid any complications due to frost and winter conditions. If installation is approved during this time it is crucial to follow cold temperature instructions for duct installation, as well as good working practices.
It is expected that the customer/contractor contact Maritime Electric at a minimum of 48 hours prior to the commencement of construction to provide a construction timeline. This is to coordinate an appropriate time to complete an inspection.
1.4 Route and Grade Design
No excavation or installation shall commence until the route and final grade has been established and proper approval obtained from appropriate governing body, other utilities, owner and Maritime Electric. An agreement must be in place between all necessary parties, typically consisting of approved drawings and/or plan. Any work carried out without this approval may result in removal and replacement at the customer’s expense. A general construction timeline should be provided during the approval process.
The customer/contractor shall ensure that the site is at final grade at locations where Maritime Electric facilities are to be installed. These facilities shall be installed a minimum of 150 mm (6 inches) above the center of the roadway in all subdivision applications. An indication of the final grade shall be provided by the customer/contractor by means of a grade stake or other applicable method. Maritime Electric will not be obligated to approve a proposed underground supply route that in Maritime Electric’s judgment it would be inadvisable. Examples of this include, but not limited to:
- Wet areas where excessive frost heaving may be expected
- Areas with limited access for installation, maintenance or future replacement
- Areas without proper drainage where subsurface facilities may be continuously subject to water
- Duct banks without proper clearance to existing water and sewer facilities
1.5 Design and Construction Details
Maritime Electric will work in conjunction with the customer or anyone hired to work on the customer’s behalf to develop a design for underground supply facilities. The customer is responsible to provide Maritime Electric with as-built drawings at the completion of the project, which is to be professionally completed. These drawings should be supplied electronically to Maritime Electric as a .pdf or .dwg file. This drawing shall contain information such project specifics as transformer size and location, number and size of conduit, size and length of conductor, trench detail and location of other equipment such as high voltage junction enclosures, secondary pedestals, area lighting and pull pits.
Facilities owned by other utilities may cause re-routing of the underground system to maintain any and all clearances. This may cause depths of duct banks to change to accommodate other systems, or the requirement of encasement in concrete for the duct banks. Maritime Electricshall be informed if other utilities are present, or have any future plans to install underground facilities.
1.6 Warranty Period
The contractor shall warrant all material and work supplied in the approved plan and drawings for a period of 12 months following Maritime Electric final approval and acceptance. All work shall be completed in accordance to Maritime Electric standard underground practices. The contractor shall correct any defects which may arise during construction, installation and under normal used at their own expense. This includes, but is not limited to, maintaining proper back-fill material, asphalt reinstatement and equipment heaving or movement.
Duct Banks, Fittings and Installation
2.1 Conduit Types
Two types of conduits are used, rigid PVC conduit and type DB2. The average dimensions of rigid conduit and DB2 duct are shown below in Table 1. Please note that rigid conduit is approximately twice as thick as DB2 duct.
DB2 duct shall conform to CSA C22.2 No.211.1
Rigid PVC shall conform to CSA C22.2 No.211.0 & C22.2 No.211.2
For horizontal to vertical transition to a riser pole, a rigid PVC 1,525 mm (60 inches) utility bend shall be installed. This applies to conduit transitions that will contain both primary and secondary cables. Only rigid PVC conduit is to be installed above ground – DB2 duct is not to be used above ground. For horizontal to vertical transition to pad-mounted equipment, such as transformers and sectionalizing enclosures, a smaller 915 mm (36 inches) bend can be used.
For horizontal transitions rigid PVC 1,525 mm (60 inches) radius bends are to be used for all bends. (i.e. 22.5⁰, 45⁰, 90⁰) All bends are to be of rigid PVC.
Maritime Electric may request the use of rigid PVC conduit throughout the underground system if such environmental factors deem it necessary.
¹Source – IPEX Electrical Inc.
2.2 Conduit Joints, Bends and Terminations
A run of conduit between outlets or termination points shall not have more than the equivalent of four 90º bends, including the bends located at the outlet or termination point.
All rigid PVC and DB2 duct fittings, bends, couplers, joints and elbows shall be jointed with solvent cement designed for that purpose. It is important to follow the manufacturer’s instructions when applying this solvent. "Push-fit only" fittings are not approved for use.
Bends in duct runs may be accomplished by the use of 22.5º, 45º or 90º bends and may be supplemented by the use of a 5º coupling. All bends shall be cleaned appropriately and joined using solvent designed for that purpose.
Minor changes in elevation or direction can be accommodated without the use of fittings by field bending of DB2 duct. Please note that axial deflection should not be attempted at joints. Also, as the temperature approaches the freezing point, less offset distances are recommended. It is important to follow the duct manufacturer’s instructions for the allowable offset. Below is a sample of allowable offsets permitted by a manufacturer.
All transitions from PVC rigid to DB2 duct are to be made with a conduit to duct adapter designed for that purpose.
All spare conduits shall be sealed or capped with an approved cap or plug designed for that purpose. The conduit must be sealed properly against water and debris ingress. Conduit that require to be capped underground, shall have permanently cemented caps installed. Prior to sealing – a hole of sufficient size shall be drilled below the capping area to allow for pulling rope to be terminated. A pulling rope of 6 mm poly or nylon rope shall be used as a pulling rope with 3 m of excess rope on either end of the conduit.
All conduits that terminate in a high voltage device (transformer, sectionalzing cabinet, riser pole, etc.) must be fitted with bell ends at the point of termination. The purpose of the bell end is to protect the cable jacket from abrasion during pulling. The bell end is to be separate fitting – the flared section at the end of a length of conduit or duct is not considered to be a bell end for this purpose. These are to be permanently installed at the entry of equipment, with the exception of a riser pole where the bell end should be fitted only to allow for conduit height adjustment. This emphasizes the importance of appropriate lengths of conduit remaining in pad-mounted equipment-please see the appropriate drawing. If the conduit enters through a concrete wall, the curved section of the bell end shall be flush with the concrete.
2.3 Number of Conduits
The requirement of the number and size of conduits depends on the specific system design including the size and number of cables, spare duct requirements, contingency planning and pulling distances. Maritime Electric shall be consulted to determine the exact number and size of conduits. General or typical requirements are listed below.
Three phase primary application – will require two conduits if triplexed cable will be installed or four conduits if single conductor cable will be installed. This will accommodate a spare conduit. The size of the conduit is dependent on the percent fill and the length of the run. Typically 5" conduit is required for three phase applications.
Single phase primary application – will require two 4" conduits. This will accommodate for a spare.
Secondary application – will require two 4" conduits.
Maritime Electric may request that a test mandrel be pulled through the conduit in the presence of Maritime Electric upon completion of the work, or at another reasonable time. The presence of water and/or debris shall render suspect the construction process and may result in additional work required prior to approval. This additional work will be completed at the customer/contractors expense. Maritime Electric will supply the test mandrel, if necessary.
All duct and fittings to be joined should be exposed to the same temperature prior to assembly. It is recommended to use a primer prior to solvent cementing.
2.5.1 Cold Temperature
Conduit installation at a temperature below freezing shall be approved by Maritime Electric. This restriction is due to the risk of damage to conduit and fittings. If installation is permitted at temperature lower than 5ºC, a PVC primer must be applied prior to solvent cementing.
2.5.2 Solvent Cementing
The proper procedure must be used when cementing conduit to ensure a permanent watertight fit and an obstruction free interior. This is a general guideline and it is not met to replace manufacture's installation instructions.
- Conduit to be cut shall be cut square with its longitudinal axis and all ridges, burrs and uneven surfaces removed.
- Dry fit test to ensure proper fit.
- Thoroughly clean the end of the conduit and inside of the fitting.
- For cold temperature installation-apply primer to the inside socket surface of the fitting. Use a scrubbing motion to ensure penetration. Apply primer to conduit to depth of fitting socket. Again apply primer to the inside socket surface.
- Apply cement lightly, but uniformly to the side socket surface. Keep excess cement out of the socket transition area. Apply cement to the outer surface of the conduit.
- Immediately forcefully bottom the conduit end in the socket and give a quarter turn to ensure the solvent is spread evenly on the material.
- Hold together until the joint is made.
- Wipe excess cement from conduit at the end of the fitting. A properly made joint will normally show a bead around the entire circumference.
PVC solvent cement is fast drying and must be applied as quickly as possible, usually within 20 seconds after application. The joint must be held in place for approximately one minute to prevent the duct from backing out of the fitting. Force should not be exerted to joints following cementing. Set times are dependent on temperature. Below are recommended set times:
3 Riser Pole
A riser pole is the location of transition from aerial supply conductor to underground supply cable. All conduits are to be attached to the pole using metal pole straps in a quadrant of the pole as to prevent obstruction for guying requirements, damage due to vehicles and snow removal equipment and any other project specific considerations. It is important to contact Maritime Electric to determine the proper quadrant of the pole to install the ducts.
3.1 Primary Riser
Riser poles containing high voltage cable shall contain a bell end fitting to be temporarily placed until the final duct height is determined. The minimum height is 2.5 m above grade, however if on a joint use pole the height is be 1.0 m above the communication facilities. It is important to contact Maritime Electric to determine the proper duct height. Typically, primary riser poles have metal guards to act as mechanical protection at the base of the pole. However this will be determined by Maritime Electric, as particular circumstances may require the use of concrete. All primary riser poles are to have utility 90º bends installed on the horizontal to vertical transition. Please see Section 2.1.
3.2 Secondary Riser
Riser pole containing low voltage cable, such as a customer’s service, shall contain an expansion joint at the base of the vertical section of conduit. There is a maximum of two secondary risers to be installed on a pole.
General considerations for trenching for any part of an underground system is the safety during excavation, selection of backfill material, the method of compaction, and any future maintenance.
Backfilling procedures shall not cause distortion or damage to ducts. Suitable backfill material shall be used, considering the prevention mechanical damage to the ducts, compaction ability, drainage ability, and adequate heat dissipation. Sand is required to be the backfill material for under, between and above all conduits installed in the trench.
Frozen backfill material is not to be used. All frozen excavated material is to be removed and disposed of by the customer or contractor. If backfilling during temperatures near or below freezing, all backfill material shall be as dry as possible. If conditions warrant, Maritime Electric may deem it necessary for all conduits to be encased in concrete. Please consult Maritime Electric if concrete is required. This will normally be determined in the design or approval stage of the project.
Compaction of sand is required under and around the conduits laid in the trenches. This is to be completed in layers as the conduits are installed. That is, if the trench requires conduits to be vertically stacked, a compacted layer of sand is required for each level of conduits. To minimize the possibility of duct damage, the trench shall be hand tamped from the bottom of the trench to 150 mm above the top level of conduits. An additional 450 mm of backfill material shall be used, to total 600 mm cover, prior to power tapping equipment being used.
The customer/contractor shall be responsible to maintain the backfilled trench area for the warranty period of 12 months as outlined in Section 1.5 This includes, but not limited to, maintenance due to settlement of the trench, concrete or asphalt repairs or drainage issues that arise.
4.4 Conduit Bank Layout
The location of the conduits in the bank shall be as shown in Drawing E-88-296 of Maritime Electric Underground Standard Drawings. If design complexities require more conduits in a bank, Maritime Electric shall be consulted. In all cases, warning tape is to be installed 300 mm below finished grade.
4.5 Trench Bottom
The trench bottom shall be firm, uniform, and free of debris with no large rock protruding into the trench. Prior to laying out conduits, 150 mm of well taped sand is to be installed at the trench bottom. In order to provide continuous support for the conduits, the grade of the sand shall be uniform. This is shown in Drawing E-88-296 in Maritime Electric Underground Standard Drawings. No blocking or supports are to be used underneath the conduit that would create a stress point. Base spacers shall not be used for direct buried installation.
In unstable soil areas, Maritime Electric may require existing base material to be excavated and replaced with crushed stone or gravel with a particle size of 15 mm to create a stable base prior to installing sand. As mentioned in Section 2.1 please consult Maritime Electric if conduits are required to be installed in concrete.
Maritime Electric requires a legal easement for all underground infrastructure located on privately owned property prior to the commencement of construction. This includes, but not limited to, private right of ways and areas owned by others. These documents shall be obtained and registered at the owner’s expense. Prior to registering with the appropriate government body, Maritime Electric will proof read the easement documents to confirm accuracy.
5.1 Underground Conduit and Cables
Easement requirements for underground conduits and occasionally direct buried conductor will normally be 4 m wide with an additional 4 m at the start and end of the trench. Maritime Electric should be contacted to obtain the area where conduit and/or cables are installed.
5.2 High Voltage Padmounted Equipment
Easement requirements of padmounted equipment, such as transformers and sectionalizing cabinets will normally be a 4 m² area. Maritime Electric should be contacted in all instances to confirm the proper area required for high voltage padmounted equipment.
5.3 Low Voltage Secondary Equipment
Easement requirements of secondary junction boxes or URD’s will normally be a 3 m² area. Maritime Electric should be contacted in all instances to confirm the proper area required for all secondary subsurface equipment.
6 Transformer Foundations
The customer/contractor is responsible for installing an appropriate foundation on which a padmount transformer will be installed. Both concrete and fiberglass are acceptable by Maritime Electric provided the following requirements are adhered to.
There are three standard sizes of concrete transformer foundations, all three have construction details and dimensions included on the corresponding drawings. The concrete used shall be 25MPa.
6.1.1 Poured in place
Once the appropriate grade is established the form can be constructed and the concrete pad can be poured in place provided environmental conditions allow or provisions to cover the pad for a period of time following the pour are in place.
6.1.2 Prefabricated concrete
A prefabricated concrete foundation manufactured by a credible provider. It is important that all required site work is completed prior to transporting the concrete pad to the work site.
A fiberglass pad manufactured to Maritime Electric standard and design for this purpose may be used. Drawings E-12-01 and E-12-02 show the dimensions required for the fiberglass pad. If dimensions differ from this drawing, Maritime Electric shall be consulted prior to installing or ordering equipment.
The location of a transformer foundation shall be approved by Maritime Electric prior to construction. The major consideration should be given to accessibility with respect to transformer installation, maintenance and replacement. Other important considerations are listed below:
- There should be no obstructions 3 m directly in front and 1.5 m on the other three sides of the transformer. This includes property lines.
- A minimum 1,200 mm flat area directly in front of the transformer shall be maintained in locations where slope exists
6.2.1 Blast Wall
A blast wall is a wall or barrier with non-combustible surfaces or material (concrete blocks) constructed on edges of the transformer foundations. A blast wall is required if the transformer will be within 3 m from any combustible surface or material on a building and 6 m from any window, door or ventilation inlet or outlet on a building³. Typical construction of a blast wall will consist of 200 x 200 x 300 mm concrete blocks and extended 150 mm above the height of the transformer. 10 m vertical reinforcing bar shall be installed with no more than 600 m spacing.If a blast wall is to be used please consult Maritime Electric for transformer foundation size requirements and transformer height. However extending each side and back of the foundation by 300 mm is generally sufficient. Maintenance of the blast wall is at the owner’s expense. Please note that a fiberglass transformer pad shall not be used if a blast wall is necessary.
Bollards are required when mechanical protection of the transformer is deemed necessary by Maritime Electric. All three phase transformers will require mechanical protection. However, single phase transformers may also require bollard installation, Maritime Electric will make the decision if bollards are required and should be contacted to determine this requirement. This will not be debated, as this is important to ensure public safety as well as unnecessary service interruptions. Typical locations that require bollard installation are, but limited to, parking lots, driveways or areas where the transformer may be exposed to damage.
Concrete bollards shall have a 200 mm diameter and a height of at least 2,400 mm, with 1,065 mm above grade. Sono tube is to be used for forms. Rebar to be installed shall be set at least 135 mm in the ground. Construction of a concrete bollard shall be in conjunction with Drawing E-85-144 in Maritime Electric Underground Standard Drawings.
The installation of bollards is to conform with the Canadian Electrical Code and CSA C22.3 No.7-10. Failure to install bollards where deemed necessary by Maritime Electric will result in non-approval, thus delay service connection.
³ Canadian Electrical Code Rule 26-242
The customer/contractor shall supply all labor and material associated with the installation of the transformer foundation, including primary and secondary conduit, grounding provisions and base materials. The minimum number and layout of secondary conduits shall be adequate to meet Maritime Electric and the customer’s requirements. This is generally determined in the design or approval stage of the project. The following are minimal requirements for the customer/contractor. Communication with Maritime Electric is important to ensure a timely and efficient project.
- Contact Maritime Electric at a minimum 48 hours prior to the commencement of work to establish an inspection schedule.
- Excavate an area to the transformer pad plus 1 m on all sides to a depth of 1,300 mm or 1,600 mm, depending on the installation specifics. Refer to drawing E-88-296.
- Install all ducts to standards in this document and associated drawings. Ensure proper configuration – high voltage on the left hand side and low voltage on the right.
- Install the grounding system as per drawing E-85-143.
- Install sand surrounding the conduits. This is required as there will be gravel installed at the base of the pad.
- Install concrete bollards – if required.
- Backfill with well compacted, course gravel. Backfill material shall be no larger than 25 mm (1 inch) and no smaller than 12.5 mm (½ inch).
- Install transformer pad. Ensure the pad is level and square in relation to the surroundings.
- Backfill to final grade with crushed stone.
- Cut conduits such that they protrude above the concrete surface by 25 mm (1 inch). If fiberglass pad is used the conduits shall be half the distance between the gravel base and the top surface of the pad.
- Tag all conduits with weatherproof tag indicating civic number, lot number or secondary pedestal in which it terminates.
- Warranty all work for a period of 12 months immediately following the final inspection by Maritime Electric. This includes, but not limited to, workmanship, equipment and ground settling issues.
The customer/contractor will be responsible for the removal of any transformer foundation that is no longer in use. This includes, but not limited to, foundation removal and site restoration. The retirement of a transformer pad is typically initiated by a service no longer in use or upgrade of existing customer equipment.