Our position
Five decisions, in that order. Fault current comes first because it is the only one that invalidates everything below it, and it is the one most enquiries leave out. Load current arrives with the RFQ. Transformer kVA and impedance almost never do, and without them a breaker choice is a guess with a part number on it.
The error runs both ways. Boards reach us under-specified where it is dangerous and over-specified where it is only expensive: breaking capacity taken from whatever the catalogue lists first, then an ACB on an incomer an MCCB would hold, AC3 contactors on resistive feeders, capacitor duty treated as ordinary duty, and IP chased upward with no derating applied to anything inside. A part number copied off the last expansion drawing causes more of this than ignorance does.
Where our own advice costs you: coordination tables do not cross manufacturers, so on a board that must prove discrimination we tell you to buy the feeder set from one brand, and that removes your freedom to shop each line on price. On a small board with no discrimination requirement, that advice is wrong. Mix and keep the money.
In short
- Fault level sets the ceiling; load current only picks the rung
- If transformer kVA and impedance are not on the enquiry, the selection is not finished
- Most boards we see are under-specified on breaking capacity and over-specified on frame size
- Coordination is a brand decision, so it gets made before the price comparison, not after
- A higher IP rating you do not derate for is a slower failure, not a safer panel
Direct answer
First 40–60 words of the post. Declarative, no preamble.
Selecting LT switchgear comes down to five decisions made in order: the prospective fault current at the board, the continuous current of each feeder, the coordination scheme between devices, the duty class of every switching device, and the enclosure conditions that derate all of it. Get the fault current wrong and nothing downstream is valid.
Credibility line
One sentence, immediately after the answer.
We have specified and supplied LT switchgear since 2013, and we learned the fault-current rule the expensive way — on a [year] board where the discom revised the fault level mid-project, and every device that was correct for its feeder was wrong for the board.
Figure to pull before publishing: Skylights Energy has specified and supplied LT panel components since 2013. Replace this line with one concrete, checkable fact: the number of panels supplied, the years in the trade, or a specific specification error that taught you something.
Section outline
1. Start with the prospective fault current, not the load
- Why transformer kVA and impedance set the ceiling for every device choice
- Where to get the figure: transformer nameplate, discom fault level letter, or calculation
- The consequence of guessing: a breaker that cannot interrupt the fault it is asked to interrupt
- Rule stated plainly, with the calculation shown once
2. Size the incomer and the feeders
- Continuous current, diversity, and the factor you apply above load current
- Frame size versus trip rating: why they are not the same decision
- Where ACB stops being justifiable and MCCB is correct
- Link down to the MCCB rating and breaking capacity post
3. Choose the breaking capacity class
- Icu, Ics and Icw in one paragraph each, then link out to the full explainer
- Why Ics matters more than Icu for panels that must be back in service the same day
- Common Indian practice versus what the standard actually requires
4. Decide the coordination scheme
- Discrimination between upstream and downstream devices
- Type 1 versus Type 2 coordination for every motor feeder
- The brand-locking consequence: coordination tables do not transfer across manufacturers
- This is the section that justifies buying a feeder set from one brand
5. Switching devices and duty class
- AC1 versus AC3 versus AC4 and the over-ordering mistake it causes
- Capacitor duty is a separate class and a standard contactor will not survive it
- Contactor plus overload relay sizing, linked to the sizing post
6. Power factor correction
- When fixed compensation is enough and when APFC pays back
- Detuning: what harmonic content forces the decision
- Capacitor failure modes in Indian panel conditions
7. Metering and instrument transformers
- CT ratio, burden and class, linked to the CT selection post
- Metering class versus protection class and why the substitution is unsafe
- Resin cast versus oil filled for indoor LT panels
8. Terminal blocks and internal wiring
- Termination technology by vibration environment and rework frequency
- Current rating by conductor cross-section
- Why the cheapest terminal is rarely the cheapest installed cost
9. Enclosure, IP rating and the derating it forces
- The trade-off almost every page skips: higher IP means worse heat dissipation
- Internal panel temperature rise above ambient in Indian conditions
- Applying the derating factor before finalising device selection
10. Standards and what an inspector checks
- IS and IEC references, stated as references and not paraphrased as requirements
- Type-tested versus partially type-tested assemblies
- Documentation the buyer should demand at handover
11. Sourcing: what to check before you place the order
- Verifying the part number against the manufacturer catalogue, not the quotation
- Lead time realism by brand and category
- Genuine product verification
- Link to the marketplace collections