Data center cable and busbar
The only line items priced substantially by weight of metal. Short lead times, commodity-linked pricing, and two sizing constraints that compete with each other.
The part of the estimate that moves with commodity prices
Cable and busbar are the only line items in a data centre electrical package priced substantially by weight of metal. That makes them behave differently from everything else: lead times are comparatively short, but pricing tracks copper and aluminium markets rather than manufacturing capacity, and a quote can go stale in weeks for reasons that have nothing to do with the supplier.
Two constraints govern the sizing, and they compete. Ampacity asks whether the conductor will overheat. Voltage drop asks whether the load still sees usable voltage at the far end. On short runs ampacity decides; past a few hundred feet voltage drop usually takes over and forces a larger conductor than heating alone would require.
| Family | Typical configuration | Indicative lead time | Standards |
|---|---|---|---|
| MV Power CableMedium-voltage feeders between the utility interface, transformers and switchgear. | 5 / 15 / 35 kV #2 – 750 kcmil EPR or XLPE insulation |
~18 weeks | ICEA, AEIC UL MV-105 |
| LV Power CableEverything downstream of the main switchgear. The highest-volume item on the site. | #12 – 500 kcmil THHN or XHHW-2 Copper or aluminium |
~6 weeks | UL 83, UL 44 |
| Copper BusbarRigid conductor inside switchgear, PDUs and ground systems. | 1/2in – 4in wide 1/8in – 3/8in thick Bare or tinned |
~10 weeks | ASTM B187 |
| Fibre Trunks & Patch PanelsStructured cabling between rows, halls and the meet-me room. | OM3 / OM4 / OS2 12–144 fibre LC / SC / MPO |
~8 weeks | TIA-568 UL 444 |
Specifications that decide the selection
Ampacity, after derating
Table ampacity assumes no more than three current-carrying conductors at 30 °C. Bundle more, or run hotter, and the usable figure drops — often sharply.
Voltage drop over the run
The 3 % branch and 5 % total guidance is a recommendation, not a hard limit — but it is what decides the conductor on any long run.
Insulation type and rating
XHHW-2 is rated 90 °C wet or dry; THHN is 90 °C dry, 75 °C wet. Underground and outdoors, that distinction is the whole decision.
Conduit fill
Capped at 53 % for one conductor, 31 % for two, 40 % for three or more. Fill is what usually forces a larger raceway, not the conductor itself.
Selection criteria in practice
- Check both limits, every time. Size for ampacity, then verify voltage drop. Whichever demands the larger conductor wins; assuming it is always ampacity is how long runs end up undersized.
- Count the current-carrying conductors before trusting a table figure. Bundling derates ampacity, and shared neutrals on harmonic-heavy loads may themselves count.
- Confirm terminations are rated for the conductor material and temperature. A 90 °C cable landed on a 75 °C-rated lug is limited by the lug.
- Lock pricing where the metal content is significant. On large orders the commodity exposure is worth managing explicitly rather than absorbing.
- Specify fibre for the refresh after next. Pulling additional strands during construction is a fraction of the cost of adding a route to a live facility.
Typical applications
MV cable runs from the utility interface to pad-mount transformers and MV switchgear. LV cable carries everything downstream — feeders to panelboards, branch circuits, mechanical loads. Copper busbar forms the rigid conductor inside switchgear and PDUs, and the ground bars that bond the room. Fibre trunks link rows to distribution frames and out to the meet-me room, sized well beyond current need because retrofitting is disproportionately expensive.
Work the numbers before you specify
Related reading
Common questions
Should I use copper or aluminium?
On long feeders, aluminium is routinely chosen and the saving is real. It needs a larger conductor for the same ampacity, terminations rated for it, and anti-oxidant treatment at joints. On branch circuits and inside equipment the handling penalty usually outweighs the material saving.
Which decides the conductor size, ampacity or voltage drop?
Both, and you have to check both. Ampacity generally governs short runs; past roughly a few hundred feet voltage drop tends to take over and force a larger conductor than heating alone would require.
Is the 3 % voltage drop figure a code requirement?
No. It appears as an informational note rather than a mandatory rule, so it is design guidance rather than something an inspector enforces. It remains the number most specifications are written against.
Why is conduit fill capped at 40 % for three or more conductors?
The limits exist for heat dissipation and for the mechanical practicality of pulling without damaging insulation. The single-conductor limit is higher because there is nothing else in the raceway to bind against or heat.
Family reference pages
Each family below has its own page: how it is specified, the standards it is built to, its indicative lead time and market price band.
Specifying cable or busbar?
Every family is in the Spec Library with its configuration axes, the standards it is built to, its indicative lead time and its market price band. Take the specification to whoever supplies it — Voltfield sells nothing and is not a route to any of it.