Changeover switch for generator: which rating for DG sets in hotels and sites in Gangtok, Namchi and Pelling
Changeover switch for generator: use a 4 pole on-load changeover rated above the DG set full-load current and main breaker, e.g. 100A for a 62.5 kVA set.
A changeover switch for a generator should be a 4 pole on-load changeover for a three-phase building, rated at or above both the DG set’s full-load current and the main incoming breaker. As a rough guide a 3-phase set draws about 1.4 A per kVA at 415 V, so a 62.5 kVA DG set needs a 100A changeover and a 125 kVA set needs about 200A. For hotels, hospitals and sites that cannot wait for someone to walk to the panel, use an automatic changeover (ATS / AMF panel) instead of a manual one.
Power cuts in the hills are part of life. A landslide or a fallen tree in the monsoon can take a feeder out for hours, and hotels, homestays, hospitals and construction sites in Gangtok, Namchi, Pelling and Rangpo depend on their DG sets. The changeover is the switch between the two. This guide is for contractors, panel builders and building owners in Sikkim, and the same advice applies across North Bengal and Bihar.
What does a changeover switch do with a generator?
A changeover switch connects your building to one source at a time: mains (the utility supply) or the generator. It has three positions on most manual units: Mains – Off – DG (often marked I – 0 – II).
It does two jobs:
- Protects your generator and your wiring. Mains and generator are never connected together, so the set is not damaged when power comes back.
- Protects line workers. Without a changeover, generator power can travel back up the service line while the lineman thinks the line is dead. This is why a proper changeover (or interlock) is a must, not an option. Never connect a generator to a socket or bypass the changeover, whatever anyone at site says.
Which changeover switch rating for which kVA DG set?
The rule contractors use: changeover rating ≥ the larger of (a) the DG set full-load current and (b) the main incomer MCB/MCCB rating. Full-load current for a 3-phase, 415 V set is roughly kVA × 1.39. The table below is a working guide based on that calculation and common switch sizes; your electrical designer’s load calculation and the SLD always win.
| DG set (kVA, 3-phase) | Approx. full-load current (A) | Typical changeover rating |
|---|---|---|
| 15 kVA | 21 A | 32A, 4 pole |
| 20 kVA | 28 A | 32A or 40A, 4 pole |
| 30 kVA | 42 A | 63A, 4 pole |
| 45 kVA | 63 A | 100A, 4 pole (63A is too tight) |
| 62.5 kVA | 87 A | 100A, 4 pole |
| 82.5 kVA | 115 A | 125A, 4 pole |
| 125 kVA | 174 A | 200A, 4 pole |
| 160 kVA | 223 A | 250A, 4 pole |
| 250 kVA | 348 A | 400A, 4 pole |
| 320 kVA | 445 A | 630A, 4 pole |
| 500 kVA | 696 A | 800A, 4 pole |
Two common site mistakes:
- Matching the changeover to the DG set but not to the mains. If the building has a 125A main MCCB and a 62.5 kVA set, a 100A changeover will be the weak link when mains is on. Size it for the bigger of the two.
- Picking a size that sits right on the current. Leave headroom; a closed panel in a warm DG room runs hot.
On-load or off-load changeover: which one do I need?
| Type | When it can be operated | Where it fits |
|---|---|---|
| On-load changeover | Can be switched with the load connected (within its rating) | Hotels, shops, offices, hospitals, flats — anywhere someone may switch without first shutting all loads |
| Off-load changeover | Only after the load is switched off upstream/downstream | Large incomers where the operator follows a fixed procedure and switches off the breaker first |
For most buildings in the 32A to 100A range, pick on-load. As an example from a brand page we read today, Havells lists its four pole load changeover switch in a 32A–100A rating range, at 415 V for three and four pole versions, with standard conformity to IS/IEC 60947-1 and 3. Their general purpose switchgear range also shows off-load changeovers from 200A to 2000A. Lauritz Knudsen (L&T), Siemens, Schneider and Legrand make changeovers too — ask us which brand matches the rest of your panel.
3 pole or 4 pole changeover for a DG set?
For a three-phase building with a DG set, the usual choice is 4 pole — three phases plus neutral are all switched. Switching the neutral keeps the mains neutral and the generator neutral separate. This matters if you have RCCBs or earth-leakage relays downstream, because a shared neutral is a common cause of nuisance tripping. (If an RCCB already trips without reason, see our guide on MCB, RCCB, RCBO and MCCB.)
For single-phase homes with a small portable generator or an inverter, a 2 pole (DP) changeover is used. Final pole count follows your designer’s earthing and neutral scheme for the DG set.
Manual changeover vs automatic changeover (ATS): which is better?
| Point | Manual changeover | Automatic (ATS / AMF panel) |
|---|---|---|
| Who switches | A person at the panel | The panel, when mains fails and returns |
| Start of DG | Manual or remote start | AMF panel can start and stop the set |
| Downtime | Minutes, depending on staff | Seconds |
| Cost | Lower | Higher (contactors or motorised switch, controller) |
| Best for | Homes, small shops, sites with a watchman | Hotels, hospitals, labs, server rooms, lifts, water pumps |
In Gangtok and Pelling, many hotels and homestays sit on slopes with the DG set below the building and the reception on top. Nobody wants to run down to the DG room in the rain late at night. That is where automatic changeover pays back. For a construction site or a small home, a good manual on-load changeover is enough.
What to write in the BOQ for a changeover switch
Big buyers, consultants and tender contractors should spell it out so every quote is like-for-like:
- Type: on-load / off-load; manual / automatic (with controller details).
- Rating: current (A), poles (2P / 4P), voltage (240 V / 415 V).
- Standard: IS/IEC 60947-3 for switch-disconnectors and changeovers (check the brand’s catalogue for the exact standard of your model).
- Execution: open (for mounting inside a panel) or in an enclosure; door-coupled or extended handle if the panel is closed.
- Cable: size and type of incoming mains, DG and outgoing cables, and glands — see our cable gland and lug guide.
- Brand list and whether the panel must be a single brand.
Changeover tips for sites in Sikkim’s hills
- Damp and condensation. In the monsoon, panels in DG rooms and basements sweat. Use a closed enclosure, seal gland plates, and keep cable entries from the bottom.
- Earthing for the DG set. The generator neutral and body need their own earthing as per IS 3043 and your designer. Common practice is separate pits for neutral and body; test them before handover.
- Transport. For big changeovers or AMF panels going up to Mangan, Pelling or Namchi, plan for boxes that can be carried by hand on the last stretch. WhatsApp us your site location and we’ll tell you how we can supply.
- Labelling. Mark MAINS, OFF and DG clearly, in a language the staff read. Clear labels stop staff from switching to DG before the set is running.
Always get the changeover installed and tested by a licensed electrician. Never work on the incoming side without isolating it at the meter or the utility end.
Why buy changeover switches from a local authorised dealer?
A changeover is a safety item, so it pays to buy the right one once. Shree Shyam Suppliers is an authorised dealer for Havells, Lauritz Knudsen (L&T) and Mescab, and we also deal in Siemens, Schneider and Legrand. That means genuine stock, the right rating checked against your DG set and main breaker, and the cable, lugs, glands and enclosure for the job in one itemised quote. You can browse our distribution panels and changeovers, or simply send the list.
Ordering tip
WhatsApp Shree Shyam Suppliers with: the DG set size (kVA) and phase, the main incomer breaker rating, manual or automatic, on-load or off-load, number of poles, open or enclosed, brand preference, the cable sizes for mains, DG and load side, quantity, and the site location (Gangtok, Namchi, Pelling, Rangpo or anywhere else). We’ll send an itemised quote with today’s rate.
Quick answers
Which changeover switch for a 62.5 kVA DG set?
A 62.5 kVA three-phase set draws about 87 A at 415 V, so a 100A 4 pole on-load changeover is the usual choice, provided the main incomer breaker is not bigger than 100A.
Which changeover is used for a 125 kVA generator?
A 125 kVA set draws about 174 A, so a 200A 4 pole changeover is typical. Check it against the main MCCB rating and the designer's SLD.
Is a 4 pole changeover needed for a DG set?
For a three-phase building with a DG set, a 4 pole changeover is the usual choice because it switches the neutral too and keeps mains and generator neutrals separate.
What is the difference between a changeover switch and an ATS?
A changeover switch is operated by hand. An ATS or AMF panel switches to the generator automatically when mains fails and back when it returns, often starting and stopping the set too.
Can I connect a generator without a changeover switch?
No. Without a changeover or interlock, generator power can feed back into the supply line and endanger line workers, and the set can be damaged when mains returns. Get a licensed electrician to install one.
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