Sheet E-200 · Grounding & bonding
Grounding and bonding the rooftop tray
The tray sits on PVC and rubber sleepers, so it is electrically floating until someone bonds it. ANDREW publishes no grounding detail for this line, so the grounding design comes from the NEC, the site's lightning protection and the owner's or carrier's grounding standard. This page covers the full scope: what to bond, with what, in what order, how to test it, and what to ask before you buy.
The solution in eight lines
- Make the tray continuous: a bonding jumper across every splice joint and every hinge.
- Bond the tray to ground at both ends, at the roof ring ground, the lightning-protection conductor or the entry ground bar, using the owner standard's conductor (commonly #2 AWG tinned solid copper).
- Bond the step-over (RT-ST) and the hood entry (MT-365G), plus any metal within the bonding distance of a lightning-protection conductor (7 ft in AT&T's practice).
- Ground every coax shield with an ANDREW SureGround kit at the antenna end and at the entry ground bar, plus at the top and bottom of vertical drops if the standard requires it.
- Bond the entry ground bar to the building's grounding electrode system. The electrical contractor makes this connection.
- Use rooftop-safe connections: two-hole compression lugs, tinned copper, stainless hardware and antioxidant compound. No exothermic welds on a roof.
- Never drill or cut the tray to land a lug without ANDREW's written OK. Use listed tray clamps or the approved bolt location.
- Test, photograph and record every bond before the covers go on, then hand over an as-built grounding drawing.
Which rules govern
| Source | What it controls here |
|---|---|
| NEC (NFPA 70), 2023 edition in San Antonio | 392.60(A): metal tray that carries only non-power cable must be electrically continuous, through approved connections or a bonding jumper no smaller than 10 AWG. That language dates from the 2017 edition. Check the adopted text. Article 250 covers bonding methods, and Articles 800/810/820 cover coax shields, antenna masts and the bond at the building entrance. |
| NFPA 780 / UL 96A | Lightning protection. Metal within the calculated bonding distance of a lightning-protection conductor gets bonded to it, using listed fittings. If the building has a certified system, have the lightning-protection contractor make those bonds so the certification holds. |
| Owner / carrier standard | Usually the strictest, and it sets conductor sizes, connector types, kit locations and acceptance tests. Examples: AT&T ATT-TP-76416, Motorola R56, ANSI/TIA-607. Get the one for this site in writing before you buy. |
| ANDREW SureGround bulletin 7598195 | How to install the coax ground kits: stripping tool per size, 8 in (203 mm) minimum lead bend radius, and no installation in the presence of thunderstorms. |
| ANDREW Limited Warranty §8(g) | Drilling or cutting the tray for a lug is a modification. Get written authorization first (exclusions). |
A site under the exclusive control of a communications utility can fall outside the NEC's scope (NEC 90.2). The building owner, the carrier's standard and the AHJ still apply. Never treat "not NEC" as "not grounded."
1. Make the tray electrically continuous
- Default (recommended): jumper every joint. Run a bonding jumper across each splice, terminated with a two-hole lug on each side. Size it to the owner standard. It can't be smaller than 10 AWG, and #6 AWG is the common carrier minimum for unit bonds.
- Alternative: rely on the bolted splice. Only with written acceptance from the AHJ and the owner that the splice is an "approved connection", plus a measured continuity reading across each joint. ANDREW doesn't list its splices as bonding connections, so ask (RFI 12).
- Always jumper across a hinge. The hinged extension kits pivot, and a pivot isn't a reliable bond path. Use a flexible stranded jumper with slack for the full 0–45° travel.
- Covers: if a cover is clamped rather than bolted metal-to-metal, bond it as the owner standard requires.
- Parallel trays are each bonded on their own, and to each other at both ends.
2. Bond the tray to the site ground
- Both ends of every tray go to the site ground. AT&T's cell-site practice puts it plainly: tray sections "shall be connected to each other and then to the buried ground ring". On a roof, that means the roof ring ground, the lightning-protection conductor or continuous building steel, whichever the grounding drawing names.
- Lightning-protection proximity: anything metal within the bonding distance of a lightning-protection or antenna ground conductor gets bonded to it. AT&T uses a flat 7 ft with a minimum #6 AWG conductor, and NFPA 780 calculates the distance. A tray that crosses near an air-terminal conductor needs a bond at that point.
- Bond the step-over (it's steel people touch) and the hood entry (the entry ground bar mounts at it).
- Never use plumbing vents, HVAC curbs, gas piping or conduit as the ground path.
3. Ground the coax shields
| Cable | Kit part numbers | Strip tool |
|---|---|---|
| 1/2 in | SG12-06B2A · SG12-12B2U | GKT-L4SG |
| 7/8 in | SG78-06B2A · SG78-12B2U | GKT-78SG |
| 1-1/4 in | SG114-06B2A · SG114-12B2U | GKT-114SG |
| 1-5/8 in | SG158-06B2A · SG158-12B2U | GKT-158SG |
- Where: at least at the antenna end, where the cable leaves the antenna mount, and at the entry ground bar just before the cable enters the building. Add kits at the top and bottom of any vertical drop, and at any interval the owner standard requires on long horizontal runs.
- Distributor listings give a #6 AWG copper lead with a factory two-hole lug and butyl-plus-tape weatherproofing. Seal every kit per the bulletin.
- Route each lead downward toward its ground bar, short and straight, never looping up. Keep at least the 8 in (203 mm) minimum bend radius.
- Use one kit per cable per location. Each lead lands on its own hole on the ground bar, with no doubling under one lug.
- Surge arrestors and protectors, if specified, bond to the entry ground bar too.
4. Entry ground bar to building ground
- Mount a tinned-copper ground bar at the hood entry. Bond it at its lowest point with a two-hole connector to the roof ring or down conductor, with antioxidant compound on the joint. That's AT&T's practice, using #2 AWG.
- The bar ultimately bonds to the building's grounding electrode system, through the intersystem bonding termination at the service (NEC 250.94). That connection is electrical work. Have the licensed electrical contractor make it unless the Texas communications exemption clearly covers your crew (Texas licensing).
5. Materials and connections
| Item | Use | Why |
|---|---|---|
| Conductor | Tinned solid copper. #2 AWG is common for bonds to the ring, with #6 AWG the minimum for unit bonds (AT&T). Use stranded only for flexible jumpers. | Tin keeps copper from attacking the zinc on the galvanized tray |
| Connectors | Two-hole compression lugs with a hydraulic crimp, or listed (UL 467) tray grounding clamps | Two holes won't rotate loose. Clamps avoid drilling the tray. |
| Hardware | Stainless bolts, flat washers and external-tooth lock washers | Corrosion, and a bite through the coating |
| Compound | Antioxidant on every mechanical joint | Keeps moisture out of the contact |
| Touch-up | Zinc-rich coating (ASTM A780) wherever the galvanizing is disturbed | Protects the coating, and the tray warranty |
| Not on a roof | Exothermic (Cadweld-type) welds | AT&T calls them a fire hazard on rooftops, and they burn off the galvanizing. Use compression instead. |
- Attaching to the tray: use a listed clamp, or a lug under a bolt location ANDREW approves. A new hole is a modification under §8(g), so ask first (RFI 12). Prep the contact the way the connector instructions say, then touch up.
- Dissimilar metals: don't let water run off copper onto the galvanized tray, because copper-laden runoff eats zinc. Route copper below or beside the tray, not above it.
6. Routing on a non-penetrating roof
- No fasteners through the membrane. Carry ground conductors on non-penetrating supports the roofing manufacturer approves (the same approval as the tray, see roof coordination).
- Few, gentle bends. AT&T prefers a 12 in radius with 6 in minimum, and two 45° bends rather than one 90°. Never make a sharp bend or a bend back on itself.
- Keep everything exposed and accessible for inspection. Don't bury a mechanical joint under the tray or in a sleeper.
- Protect conductors at roof edges and parapets. Where they go down the building, sleeve them in PVC, not metal conduit, unless the conduit is bonded at both ends.
7. Grounding bill of materials
The estimator counts these items automatically for a straight run, using the conservative default:
| Item | Count |
|---|---|
| Bonding jumpers across joints | 1 per splice joint (sections − 1, per tray) |
| Hinge jumpers | 1 per extension kit |
| Tray-to-ground bonds | 2 per tray, plus 1 per lightning-protection crossing within the bonding distance |
| Step-over / hood entry bonds | 1 each |
| Two-hole lugs | 2 per conductor |
| Coax ground kits | At least 2 per installed cable, sized to the cable (more if the standard asks) |
| Entry ground bar | 1 per entry, with enough holes for every kit plus spares |
| Conductor | Measure from the grounding drawing and add 10% for routing |
| Consumables | Antioxidant, stainless hardware, zinc-rich touch-up, kit tape |
Example: six coax cables on an 8-run tray, 60 ft straight. That's 8 sections and 7 splices, so 7 jumpers, 2 end bonds, 18 lugs and 12 ground kits, plus the entry bar and the conductor.
8. Testing, inspection and closeout
9. Texas and San Antonio
- San Antonio enforces the 2023 NEC (with the 2024 ICC codes, effective May 1, 2025), so 392.60's continuity rule applies to any tray the code covers (details).
- South-central Texas gets frequent spring and fall thunderstorms. Schedule grounding work for dry, calm weather. ANDREW's bulletin forbids kit installation with thunderstorms present. Stop roof work when the site's lightning policy says so.
- Hot roofs (a dark membrane in a San Antonio summer can pass 150 °F) soften adhesive conductor supports and kit tape. Use products rated for the temperature.
- If the work needs an electrical permit, the bond to the building's electrode system is usually what gets inspected. Ask the inspector before you cover anything.
10. Questions to settle before ordering
- To ANDREW (RFI 12): Is the splice an approved bonding connection? Where may a bonding lug be attached without voiding the warranty? Is a jumper required across the extension-kit hinge?
- To the owner or carrier: Which grounding standard governs, and which revision? What are the conductor sizes and connector types, and where do the ground kits go? What's the acceptance test and its value? Who connects to the building ground?
- To the lightning-protection contractor: Does the tray route fall within the bonding distance? Who makes those bonds, and does that affect the certification?
Sources
- AT&T ATT-TP-76416, Grounding and Bonding Requirements for Network Facilities, Issue 3 (Oct 2010): §2.8.9 (rooftop facilities, the 7 ft / #6 AWG rule), §7.3.1.3 (cable tray to ground ring), §7.4.2.4–7.4.2.5 (#2 AWG tinned solid, two-hole connectors, no exothermic welds on rooftops, antioxidant), §7.5.3.6 (roof hatch-plates), §7.6.2.2 (bend radius), §7.6.7.2 (entry ground bar), §7.16.4 (ANDREW ribbon kits preferred), §7.17 (rooftop sites).
- ANDREW / CommScope, SureGround Grounding Kits for Coaxial Cables, Bulletin 7598195 rev E.
- NFPA 70 (NEC) 392.60(A), 250.94, Articles 800/810/820. NFPA 780 and UL 96A. Check the edition the AHJ has adopted. The 392.60(A) wording is quoted from secondary sources (2017 edition onward) and needs checking against the code book.
- ANDREW Limited Warranty (May 2025) §8(e) and §8(g). See Warranty.