2013
Bonding
Bonding NEC 2011 article 392, section 392.18 Cable Tray Installation ‐ Clearly indicates that cable tray systems must be electrically continuous. The required electrical continuity is maintained, in most connections, within the Snap Track system based on the high cross sectional area (surface contact) of the aluminum components. This is distinctly seen when the cross sectional area of Snap Track channel is compared to the minimum requirements set forth under NEC 392.6 (A). (Partial) NEC Table 392.60 (A) Metal Area Requirements for Cable Trays Used as Equipment Ground Conductors Maximum Aluminum Tray Ampere NEC Requirement Snap Track Setting 2” Channel 4”‐6” Channel mm 2 In. 2 mm 2 In. 2 mm 2 In. 2 60 100 200 400 600 129 129 129 258 258 0.20 0.20 0.20 0.40 0.40 258 258 258 258 258 0.40 0.40 0.40 0.40 0.40 387 387 387 387 387 0.60 0.60 0.60 0.60 0.60 The entire Snap Track system, including the assembly of fittings, has been tested and is classified by Underwriters Laboratories, both UL and CUL, file number E249472 and was found to be suitable for use as an equipment ground conductor (EGC) up to 500 ampere. Techline Mfg. has placed a 5:1 safety factor on this rating and has rated the Snap Track system including assemblies of splices, tee’s, crosses, elbows etc. for use as an EGC up to 100 ampere. Based on these ratings, bonding requirements for the Snap Track system is separated into two categories. P 1 A.) Bonding requirements for Snap Track with non‐power conductors or in power circuits equal to or less than 100 ampere. Informational Note: Examples of non‐power conductors include nonconductive optical fiber cables and class 2 and class 3 remote control signaling and power limiting circuits. Per NEC section 392.60 Grounding and Bounding – The Snap Track system is permitted to be used as an EGC where continuous maintenance and supervision ensure that qualified persons service and install the cable tray system. By design and based on the afore mentioned approvals and permissions the Snap Track system, when assembled properly, is allowed to function as an equipment ground conductor, when supporting circuits are equal to or less than 100 ampere. In these instances’ bonding is required only in the following circumstances: 1.) Transitions NEC Section 392.60 Grounding and Bonding (C) Transitions. Where metallic cable tray systems are mechanically discontinuous, as permitted in 392.18 (A), a bonding jumper sized in accordance with 250.122 shall connect the two sections of the cable tray, or the cable tray and the raceway(s) or equipment. Bonding shall be in accordance with 250.96. NEMA VE‐2 2006 Section 4.7.1 states that if the cable tray is to be used as an EGC bonding jumpers must be installed on both side rails of dis‐connected segments. P 2 For the purpose of maximum cable protection Techline Mfg. recommends that mechanically discontinuous sections, requiring bonding jumpers, be limited to awkward transitions only. Engineers and Designers are encouraged to refer to the current Snap Track catalog, and fully utilize available fittings. As defined in NEC 2011, section 392.60 Grounding and Bonding – Transitions include not only mechanically discontinuous sections but also transitions from one cable tray system to another and transitions to equipment. Consequently, bonding jumpers should be installed when transitioning the Snap Track system from ladder tray and when transitioning to equipment (point of use). 2.) Adjustable Fittings The Snap Track system includes both horizontal and vertical adjustable fittings. These fittings are provided to address offsets and miter cuts. When these fittings are used bonding jumpers should be installed in a manner to span the potential electrical discontinuity (across the total length of the fitting), which may result from the mechanical (bolted) adjustable connection. P 3 3.) Thermal Expansion splices All Snap Track fittings are designed for use as a thermal expansion plate (See Thermal Expansion). When Snap Track splices or fittings are utilized as a thermal expansion fitting, they are by design allowed to move. Therefore, the bonding potential is reduced and bonding jumpers are required. Techline Mfg. recommends that All bonding jumpers be installed per NEMA VE‐2 NEMA VE‐2 2006 Section 4.7.1 states that if the cable tray is to be used as an EGC bonding jumpers must be installed on both side rails. Note: Techline Mfg. offers a wide selection of bonding jumpers in various lengths and colors. Snap Track bonding jumpers are designed to meet the ratings of the Snap Track system and provide a 5:1 safety factor, to ensure proper bonding in a fault condition. Should original Snap Track bonding jumpers not be used it is the responsibility of the installer to use the appropriate gage bonding jumper. In all cases bonding jumpers should be 8 gage or larger and constructed with copper wire. P 4 B.) Bonding requirements for Snap Track in circuits over 100 ampere. The Snap Track system is not limited to applications or circuits below 100 ampere. However, when used to support circuits with a combined current over 100 ampere, a different design criterion applies. In these applications the entire Snap Track system should be bonded, as indicated in section (A) with appropriately sized bonding jumpers and a separate equipment ground conductor is required. The appropriate size or gage of the bonding jumper and separate EGC are outlined by NEC and listed in NEC article 250. NEC Table 250.122 Minimum Size Equipment Grounding Conductors for Grounding Raceway and Equipment Rating or Setting of Wire Size Automatic Overcurrent AWG or kcmil Device in Circuit Ahead of Copper wire Size Aluminum or Copper – Clad Equipment, Conduit Etc. Aluminum* Not Exceeding (Amperes) 15 14 AWG 12 AWG 20 12 10 30 10 8 40 10 8 60 10 8 100 8 6 200 6 4 300 4 2 400 3 1 500 2 1/0 600 1 2/0 800 1/0 3/0 1000 2/0 4/0 1200 3/0 250 kcmil 1600 4/0 350 2000 250 kcmil 400 2500 350 600 3000 400 600 4000 500 800 5000 700 1200 6000 800 1200 * See Installation restrictions in 250.120 P 5 In most applications when installing multi‐conductor cable circuits over 100 ampere there will be an individual ground conductor. Under NEC 250.119 these conductor(s) may be used as an EGC in facilities where conditions of maintenance and supervision ensure that only qualified persons service the installation. EGC conductors in multi‐conductor cables may be bare, covered, or insulated. If covered or insulated, the outer finish must be green or green with one or more yellow strips. At time of installation the conductor or conductor(s) utilized as the EGC must be permanently identified as an Equipment Ground Conductor at each end and at every point where the conductor is accessible by one of the three methods indicated in NEC 2011 250.119 (B). When installing circuits over 100 ampere and where an EGC (ground conductor) is not contained within the cable(s) installed, a Separate EGC must be installed. When required a separate EGC, rated for the maximum ampere of the circuit breaker, in accordance with NEC table 250.122 should be installed either in the tray or on the side rail of the Snap Track system. When a separate EGC cable is mounted in or on a tray system it should be bonded to the Snap Track tray with a grounding clamp or other suitable device allowed under NEC section 250. This is NOT a requirement of NEC but considered best practice and recommended by Techline. Connections may be made within the tray or along the side rail. Informational Notes: (1) A Parallel EGC IS NOT REQUIRED UNDER NEC for installation 100 ampere and below. However, electrically paralleling a single conductor EGC with the cable tray may provide some degree of improved safety for the facility and personnel and consequently, is considered by some engineers a desirable practice. (2) In all cases, when installed as a cable tray, the Snap Track system should be electrically continuous and installed in a manner that ensures the system operates as an equipment ground conductor. P 6 (3) NEC articles 250.119 (B) Muticonductor Cable clearly allows an existing (contained) conductor can be used as the EGC when installed and maintained properly. There is no differentiation under the NEC for ventilated channel tray. This practice has been utilized with conduit for many years. (4) A bare copper EGC should not be used with Snap Track aluminum tray. In all cases the Snap Track system should also be bonded back to the source, transitions to other cable tray systems, and transitions to conduit or other wiring drops. P 7