Broadcast remote power — quiet electrons, clean ground.

The isolation transformer, before the rack

Every broadcast tie-in we do passes through an isolation transformer. The standard rig is a 5-kVA Powerstax 1:1 toroidal — 120 V in, 120 V out, with the input neutral floating from the output neutral. The output XO is bonded to a single-point ground at the case lug; that bond is the only place the secondary system touches earth. The result is a separately-derived system per NEC 250.30, with no path for the venue’s service neutral to inject 60 Hz hum into the truck’s audio bus.

For multi-rack OB vans we use a 10-kVA dual-bus Hammond C1F005CES with two isolated outputs — one for audio, one for video. The two outputs are independently grounded at independent star points, and the two ground references are tied together only at the input side of the iso transformer (the safety-ground bond). The video and audio systems thus see independent reference grounds at the truck end, which is what their internal star grounding expects.

Single-point grounding — the star and only the star

The ground audit is what eats most of the labor on a broadcast call. We walk the truck’s ground system from the iso XO bond back to the venue service ground; we measure resistance with a Fluke 1623-2 ground tester, looking for less than 5 ohms from the truck case to the venue ground rod array. We measure ground-loop current with a Fluke 376 FC clamp meter; a clean install reads less than 50 milliamps at 60 Hz, and a dirty one reads multiple amps. We have seen 7 A of ground-loop current at Bridgestone on a 2019 NHL Awards remote — turned out the truck’s satellite uplink dish had bonded to the parking-lot rebar through the dish mast, completing a second ground path that was sourcing several amps of stray current.

NEC 250.97 governs the bonding of metal raceways and equipment grounding conductors that supply sensitive electronic equipment, and it requires a low-impedance return path. We use #6 stranded green-yellow EGC from every truck case to the iso transformer’s XO; we do not rely on the metal case of the shore-power feeder receptacle for safety grounding (the threads can corrode). We tape the EGC into the same cable bundle as the phase conductors so it stays close to the source.

TVSS at the tie-in

Surge protection is non-optional. We install an Eaton SPD3 series-mode TVSS at the tie-in side of every OB van shore-power feed. The series-mode design (versus shunt-mode MOV) means the device sits inline and dissipates surges through a low-pass filter; it does not depend on a low-impedance ground return for diversion, which matters in a parking-lot tie-in where the local ground is unknown.

The SPD3 is rated 100 kA short-circuit current at 480 V, and it carries a Class I lightning rating per UL 1449 4th edition.¹ We replace the SPD3 after any documented lightning strike within a mile of the venue (we get the call from Vaisala’s NLDN alerting service) or after seven calendar years from install, whichever comes first.

UPS on critical buses

Two APC Symmetra LX 8-kVA UPSes ride between the iso transformer and the truck’s critical bus on every broadcast remote we power. The Symmetra runs double-conversion online, which means the truck sees regenerated 60.0 Hz at all times — no transfer event when the shore power drops out, just a seamless handoff to battery. Battery capacity sustains 50% load for 90 minutes; we have run on battery once, on a 2022 country-music special at the Ryman when the venue’s service tripped on a transient, and the broadcast did not lose a frame.

For audio-only remotes (Tiny Desk Field Recording, the NPR cycle), the UPS is a single 1.5-kVA model sized for the cap-mic preamp rack and the audio interface. The video isn’t in the chain on those calls, so the iso transformer plus UPS is the entire deck.

Audio isolation — the Jensen and the Lundahl

For input audio that comes from a venue’s mixing console or from a stage-mounted mic-pre — sources at the deck that we don’t control — we recommend an audio isolation transformer at the truck end. Jensen JT-MB-D for line-level inputs; Lundahl LL1521 for mic-level. Both transformers are wired with internal Faraday shields tied to the truck’s clean ground; the result is a galvanic break between the venue’s audio reference and the truck’s, with no degradation of frequency response in the 20 Hz – 20 kHz band.

We do not use cheap audio isolators (the rebranded eBay kind); we have replaced two of those on emergency calls because they introduced 0.6 dB of insertion loss at 10 kHz and were summing the signal back into the secondary through capacitive coupling. The Jensen and Lundahl pieces have insertion loss flat to 0.1 dB across the band and a frequency response specified to the audio engineer’s satisfaction.

Lead time, price, and the way to book

Lead time is four working days for any broadcast remote inside metro Nashville, including ground-audit and TVSS install; six working days for any remote that requires us to roll the truck to a regional venue. Price band is $1,800 (single Tiny Desk field recording, one iso transformer, one UPS) to $7,400 (a three-truck NHL or NFL remote with full ground audit, dual-bus iso, redundant TVSS, and 24-hour on-call).

For booking, send the truck builder’s shore-power requirement sheet via /advance/. We need the cable gauge, the connector type (powerCON, twist-lock, or hard-wired), the expected current draw, and the audio iso requirement (none, single-ended, or differential).