Separation From a New Power Run
During rough-in of a 200-outlet floor, you discover that the electrical contractor has installed a 480 V, 3-phase feeder in the same ceiling space, running parallel to your Cat 6A bundle for 25 m (82 ft). The feeder is in rigid conduit, but the conduit is not grounded yet and the run is only 75 mm (3 in) from your bundle at the closest point. Your cable is unshielded Cat 6A. The electrician says 'it's in conduit, you're fine.' The ceiling closes in 3 days. The customer's network will run 10GBASE-T to the desktops.
1. Evaluate the separation and the electrician's claim.
Read the worked answer
'It's in conduit' is not sufficient by itself. TIA/BICSI guidance calls for separation between telecommunications cable and power wiring based on voltage, current, and whether the power run is in grounded metal conduit. For a 480 V feeder, the required separation is substantially greater than 75 mm - guidance tables typically call for several hundred millimeters of separation for high-voltage/high-current runs even in conduit, and more when the conduit is not yet grounded or the run is long and parallel.
The ungrounded conduit is a particular problem: a grounded metallic raceway provides shielding; an ungrounded one does not, and it can also be a shock hazard. A 25 m parallel run at 75 mm with 480 V is a real EMI/crosstalk risk for unshielded Cat 6A at 10GBASE-T.
Action: do not accept the current condition. Require either increased separation, a grounded metallic barrier between the runs, or relocation of one of the runs.
2. What are your options to resolve it before the ceiling closes?
Read the worked answer
In order of preference:
- Relocate your bundle to achieve the required separation from the feeder - route along the opposite side of the corridor or drop below the feeder. This is usually the cheapest and fastest if the ceiling is still open.
- Relocate the feeder - unlikely at this stage and expensive; the electrical contractor will resist.
- Install a grounded metallic barrier (e.g., a grounded steel partition or a grounded metal raceway for your cable) between the runs - acceptable if it achieves the equivalent separation and is properly bonded.
- Switch to shielded Cat 6A (F/UTP or S/FTP) with proper grounding - a design change that requires customer/architect approval and adds cost; do not do it unilaterally.
- Require the electrician to ground the conduit immediately - necessary regardless, but grounding alone does not eliminate the separation requirement.
Issue an RFI and get the resolution in writing before the ceiling closes. Document the as-built separation.
3. The customer asks whether shielded cable would let them ignore separation. What do you tell them?
Read the worked answer
No. Shielding reduces susceptibility but does not eliminate the separation requirement, and it introduces its own requirements:
- Shielded cable must be properly grounded/bonded at the TR (and per the manufacturer's scheme) or the shield becomes an antenna and performance gets worse.
- The shield must be continuous through patch panels, outlets, and cords; a break in the shield path defeats it.
- TIA/BICSI guidance still recommends separation even for shielded cable; shielding is a mitigation, not a waiver.
- It is a design change requiring the customer's and architect's approval, a cost/time impact, and updated submittals.
Recommendation: fix the separation first (relocate or barrier). Consider shielded cable only if separation cannot be achieved and the customer accepts the grounding and cost implications.