Cable Tray Grounding Chart (Tray as the EGC)
A metal cable tray can serve as the equipment grounding conductor for the circuits it carries — if it has enough metal in its cross-section to clear a fault. Find the largest overcurrent device protecting any circuit in the tray and read off the minimum tray metal area, in square inches, for steel and aluminum trays. Values per NEC Table 392.60(A); the qualifying conditions of 392.60(B) apply.
Minimum tray metal area to serve as the EGC
| Max OCPD (A) | Steel tray (in²) | Aluminum tray (in²) |
|---|---|---|
| 60 | 0.20 | 0.20 |
| 100 | 0.40 | 0.20 |
| 200 | 0.70 | 0.20 |
| 400 | 1.00 | 0.40 |
| 600 | 1.50 | 0.40 |
| 1,000 | — | 0.60 |
| 1,200 | — | 1.00 |
| 1,600 | — | 1.50 |
| 2,000 | — | 2.00 |
The qualifying conditions — 392.60(B)
The table is only half the rule. To use the tray as the EGC, the installation must be one that qualified persons service and supervise — the classic industrial and commercial maintenance condition — the tray sections and fittings must be legibly marked with their metal cross-sectional area so this table can actually be applied, and the run must be electrically continuous: splice plates, expansion fittings, horizontal and vertical adjustable connectors, and any discontinuous segments bonded so fault current has an unbroken path. Where those conditions don't hold, the tray is just cable support — each circuit carries its own EGC, sized from the breaker on the ground wire (EGC) size chart.
Reading the table like an inspector
The ampere column is the actual fuse rating, breaker trip setting, or ground-fault relay setting — not the breaker frame size, which is often a size or two larger. The governing device is the largest one protecting any circuit in the tray system, so one big feeder sets the requirement for the whole run. And the metal area is the tray's side rails (both of them, totaled) for ladder and trough tray — rungs don't count — or the minimum metal cross-section for channel and one-piece trays, which is why manufacturers mark the value on the product. A wire-type EGC run in the tray instead must be 4 AWG or larger, and bare copper in an aluminum tray is asking for electrolytic corrosion — use insulated conductors there.
Common questions
Can a cable tray be used as the equipment grounding conductor?
Yes — NEC 392.60(B) permits a steel or aluminum cable tray system to serve as the EGC for the circuits it contains, but only where qualified persons service the installation, the tray sections and fittings are legibly marked with their metal cross-sectional area, that area meets Table 392.60(A) for the largest overcurrent device involved, and the tray run is electrically continuous — bonded across splices, expansion fittings, and discontinuities.
Why can’t a steel tray be the EGC above 600 amps?
Table 392.60(A) simply stops: steel cable trays are not permitted as the EGC for circuits with ground-fault protection above 600 A, and aluminum above 2000 A — no amount of extra tray metal buys more. Above the cutoff you run a wire-type EGC in or on the tray, sized from the breaker per Table 250.122.
Which ampere rating do I take into the table?
The actual fuse rating, breaker trip setting, or ground-fault relay setting of the largest device protecting any circuit in the tray — not the breaker frame size, which is often larger. One 800 A-protected feeder in an otherwise small-circuit steel tray disqualifies the whole tray as the EGC.
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