HT vs LT Panel: Where High Tension Ends and Low Tension Begins
An HT (high-tension) panel receives the utility's high-voltage supply — commonly 11kV — and protects and switches it before the transformer. An LT (low-tension) panel takes the transformer's low-voltage output, typically 415V, and distributes it across the building to sub-distribution boards.
By Dhruv Agarwal · · 1 min read
Why it matters
Whether a building is supplied at HT or LT changes the electrical room, the capital budget, the approval route and the tariff. It is decided by the load, and it needs to be known before the building layout fixes the space for a substation.
How it works in practice
| HT panel | LT panel | |
|---|---|---|
| Voltage | Utility high voltage, e.g. 11kV | Low voltage, typically 415V |
| Position | Before the transformer | After the transformer |
| Serves | Transformer | Building distribution |
| Needed when | Load above the DISCOM's LT limit | Every building |
Common mistakes
- Planning no substation space. HT supply needs room for the HT panel and transformer, with access and ventilation.
- Underestimating load growth. A building that crosses the HT threshold later faces an expensive conversion.
- Treating the LT panel as the end of design. Discrimination and sub-distribution matter as much as the main panel.
Standards referenced
Installation safety under the CEA (Measures relating to Safety and Electric Supply) Regulations, 2023. Wiring practice under IS 732.
Standards referenced
- CEA (Measures relating to Safety and Electric Supply) Regulations, 2023 — Safety of electrical installations (Central Electricity Authority)
- IS 732 — Electrical wiring installations (Bureau of Indian Standards)
Frequently asked
When its sanctioned load crosses the threshold set by the state electricity distribution company for LT supply. Above that, the building takes supply at high voltage and needs its own transformer and HT panel. The threshold varies by state and DISCOM, so it should be confirmed early.
The capital cost is higher because of the transformer, HT panel and substation space. But HT tariffs are usually lower per unit, so for large loads it often pays back through lower running costs.
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