How to calculate kVA of stabilizer?

To calculate stabilizer kVA, add the kW of all loads that run at the same time and divide by the 0.8 power factor. Multiply by 1.25 for starting margin, then choose the next standard rating. For example, a 90 kW running load needs about 140.6 kVA, so a 150 kVA servo stabilizer fits.

How much kVA servo stabilizer is required?

Your required kVA equals the running load in kW divided by 0.8, times 1.25, rounded up to the next standard size. Most homes need 10 or 15 kVA, workshops 25 to 50 kVA, and factories 75 kVA and above. For example, a 60 kW running load needs about 94 kVA, so choose 100 kVA.

What is 1 kVA equal to?

One kVA equals about 0.8 kW at a 0.8 power factor, which is typical for motors, ACs and pumps. At a power factor of 1, as with heaters, 1 kVA equals 1 kW. So a 10 kVA stabilizer carries about 8 kW at full rating, or about 6.4 kW with a 25% margin.

Which kVA servo stabilizer is needed for a home?

Most homes need a 10 kVA or 15 kVA servo stabilizer. Add the ACs, refrigerator, pump, TV, lights and fans that run together, divide by 0.8 and add 25%. A 3BHK with three 1.5 ton ACs runs about 7.25 kW, which needs about 11.3 kVA, so 15 kVA fits.

How many kVA stabilizers are required for 1.5 ton AC?

A 1.5 ton split AC needs about 2.8 kVA of stabilizer capacity, because it runs at about 1.5 to 1.8 kW. By the formula, 1.8 kW ÷ 0.8 × 1.25 gives 2.8 kVA, so a 3 to 4 kVA appliance stabilizer suits one AC. For several ACs and the rest of the home, size a whole-home servo stabilizer instead.

How much kVA stabilizer is required for a 180 amp per phase load?

A 180 A per phase load needs a 200 kVA three-phase servo stabilizer. At 415 V, the load is 1.732 × 415 × 180 ÷ 1,000, or 129.4 kVA. Adding the 25% margin gives about 161.7 kVA. If 180 A is only on one phase, size on that phase.

What kVA stabilizer is required for a 5 HP 3-phase motor?

A 5 HP motor needs about 5.8 kVA of stabilizer capacity: 3.73 kW, divided by the 0.8 power factor, plus a 25% margin. A 10 kVA three-phase unit, SG Power’s smallest, gives extra room for direct-on-line starting. A 10 HP motor works out to about 11.7 kVA, so choose 15 kVA.

How much kVA stabilizer does a 20 HP motor need?

A 20 HP motor needs about 25 kVA of stabilizer capacity. Size it from the nameplate full-load current, which already includes efficiency: about 27–28 A at 415 V, or about 20 kVA running. Adding the 25% margin gives about 24.7 kVA, so a 25 kVA unit fits one motor. For DOL starting or extra loads, ask for a check.

Should I oversize a servo stabilizer?

Size a servo stabilizer with a 25% margin, and add capacity only for machines you will install within about two years. A unit far larger than needed costs more, needs more floor space and oil, and can hunt on very light loads. Moving heaters off the stabilizer often avoids oversizing.

Can I use my sanctioned load to size a stabilizer?

A sanctioned or contract load is a ceiling set by your electricity board, not a stabilizer sizing figure. Most sites run well below it. Size from your running load, clamp meter readings or the maximum demand on your bill, then check the result does not exceed the sanctioned load.

Is the kWh on my electricity bill the same as my load?

Units of kWh on the bill show energy used over the billing period, not the load a stabilizer must carry. A home using 600 kWh a month may still run 6 kW at its peak. Size the stabilizer from kW or the maximum demand in kVA, never from kWh.

Is stabilizer kVA the same as UPS or inverter kVA?

Stabilizer kVA and UPS kVA are sized the same way for the running load, but a UPS also needs battery capacity in watt-hours for backup time. A servo stabilizer stores no energy and only corrects voltage. For power cuts, size a UPS, inverter or generator separately, and keep the stabilizer before it.

Is a 10 kVA stabilizer enough for a house with three ACs?

A 10 kVA stabilizer runs about 6.4 kW with a 25% margin. Three 1.5 ton ACs with a fridge, TV, lights and fans come to about 6 kW, so 10 kVA fits. Add a 1 HP pump and a washing machine, and the load passes 7 kW, so choose 15 kVA.

What happens if a servo stabilizer is undersized?

An undersized servo stabilizer runs hot and trips on overload, especially when motors and compressors start. Its transformers and carbon brushes wear faster, and output correction can lag under heavy load. Sizing with the 0.8 power factor and a 25% margin avoids these problems.

How to Calculate Servo Stabilizer kVA: Formula and Chart

Servo Stabilizer kVA Calculation in Brief

In short, the servo stabilizer kVA calculation needs only your running load and two fixed numbers. Divide the running load in kW by 0.8 to get kVA, multiply by 1.25 for a safety margin, then round up to the next standard size. The table shows the four steps with one worked example.

Formula: Required kVA = running load (kW) ÷ 0.8 × 1.25

Step	What to Do	Example (90 kW factory)
1. Running load	Add the kW of all loads that run together	90 kW
2. Convert to kVA	Divide by the 0.8 power factor	90 ÷ 0.8 = 112.5 kVA
3. Add the margin	Multiply by 1.25 for starting current and growth	112.5 × 1.25 = 140.6 kVA
4. Choose the size	Pick the next standard rating	150 kVA

Method used by Indian stabilizer makers, including SG Power. Reviewed November 2026.

Servo Stabilizer kVA Calculation in Brief
Want Your kVA Calculation Checked?
What Is kVA, and Why Are Stabilizers Rated in kVA?
How to Calculate Servo Stabilizer kVA in Four Steps
What Is the Servo Stabilizer kVA Formula?
How Do You Find the Running Load for Stabilizer Sizing?
How to Calculate Stabilizer kVA for a Home
How to Calculate Stabilizer kVA for a Factory
How to Calculate kVA From Amps or Your Electricity Bill
How Do Motor Starting and Phase Imbalance Affect Stabilizer kVA?
Servo Stabilizer Size Chart: 10 kVA to 500 kVA
One Mainline Stabilizer or One Per Machine?
Does the Input Voltage Range Change the Stabilizer kVA?
Which Loads Should Not Go on the Stabilizer?
What Are the Common Servo Stabilizer Sizing Mistakes?
What Do Indian Forum Users Ask About Stabilizer Sizing?
After Calculating kVA: Air or Oil Cooled, Balanced or Unbalanced Stabilizer?
Servo Stabilizer kVA Calculation Checklist
Servo Stabilizer kVA Calculation: Key Facts
Frequently Asked Questions About Servo Stabilizer kVA Calculation
Sources and References
Learn More

Want Your kVA Calculation Checked?

If you would rather not size the stabilizer alone, SG Power's engineers can check your stabilizer sizing for free. SG Power makes servo stabilizers from 10 kVA to 500 kVA at its Ghaziabad factory and sizes them from its Noida office, so its team does this every day. Share your figures, and you get a recommended size with the reasons behind it.

What You Share	What the Team Checks
Load list or machine nameplates	Running load and the kVA it needs
Clamp meter readings or electricity bill	Measured load and peak demand
Phase-wise voltage readings	Phase balance and the input range you need
Plans for new machines	Room for growth

Get a Free Sizing Check Talk to an Engineer

What Is kVA, and Why Are Stabilizers Rated in kVA?

kVA (kilovolt-ampere) is the apparent power a stabilizer must carry, while kW is the real power your loads use. A servo stabilizer is rated in kVA because its transformers and variac heat up with current, whatever the load's power factor. That is why the kW to kVA step comes first in every calculation.

kW (real power): the power that does useful work, shown on most nameplates

kVA (apparent power): volts × amps ÷ 1,000, which sets the current through the stabilizer

kVAR (reactive power): the part of kVA that magnetises motors and transformers; it does no useful work but still loads the stabilizer

Power factor: kW ÷ kVA; motors, compressors and pumps usually run at about 0.8

1 kVA ≈ 0.8 kW at a 0.8 power factor, so a 10 kVA stabilizer carries about 8 kW at full rating

When your loads' real power factor is known and is lower than 0.8, use the real figure. For example, a 40 kW load at 0.7 power factor is about 57 kVA, not 50 kVA.

Load Type	Typical Power Factor
Induction motors, pumps and compressors	0.70–0.85 (lower on light load)
Refrigeration and AC compressors	about 0.8
CNC machines and drives	0.8–0.95, depending on the drive
Computers, LED lighting and electronics	0.85–0.95
Heaters, geysers and ovens	1.0
Mixed home or factory load	about 0.8 (the standard sizing value)

Typical values; a power analyser or your electricity bill gives the real figure for your site.

How to Calculate Servo Stabilizer kVA in Four Steps

You can calculate servo stabilizer kVA in four steps, using a load list or nameplate readings. Each step removes a common error: counting standby machines, forgetting the power factor, leaving no starting margin, or buying a non-standard size. Work through them in order, and keep your figures for the quote.

List the running load: add the rated kW of every machine, AC, light and appliance that runs at the same time. When calculating, leave out standby machines and loads you will keep off the stabilizer.

Convert kW to kVA: divide the total by 0.8, or by your measured power factor.

Add a 25% margin: multiply by 1.25 to cover motor starting current and modest growth.

Choose the next standard size: for example 10, 15, 20, 25, 30, 40, 50, 60, 75, 100, 125, 150, 200, 250, 400 or 500 kVA.

What Is the Servo Stabilizer kVA Formula?

The servo stabilizer kVA formula is simple: required kVA = running kW ÷ 0.8 × 1.25. This works out to about 1.56 times the running load in kW. Turned around, a stabilizer's safe running load is about 0.64 times its kVA rating. Use these related formulas when your figures are in amps or horsepower.

To Find	Formula	Example
Required stabilizer kVA	kW ÷ 0.8 × 1.25	40 kW ÷ 0.8 × 1.25 = 62.5 kVA
kW from HP	HP × 0.746	10 HP × 0.746 = 7.46 kW
Single-phase kVA from amps	volts × amps ÷ 1,000	230 V × 40 A = 9.2 kVA
Three-phase kVA from amps	1.732 × 415 V × amps ÷ 1,000	1.732 × 415 × 100 A = 71.9 kVA
kVA on one phase	phase voltage × phase amps ÷ 1,000	240 V × 100 A = 24 kVA
Safe running load of a stabilizer	kVA × 0.64	100 kVA × 0.64 = 64 kW

Horsepower on a motor nameplate is output power. The motor draws more from the supply, because its efficiency is usually 85–95%; efficiency classes IE1 to IE3 are set out in IS 12615, published by the Bureau of Indian Standards. The nameplate full-load current already includes efficiency and power factor, so use it whenever it is shown.

The 1.732 in the three-phase formula is the square root of 3. At 415 V, three-phase kVA is about 0.72 times the current per phase. Each phase of a 415 V supply is about 240 V (415 ÷ 1.732), while a single-phase home supply is nominally 230 V.

Some sizing guides use a 15–20% margin instead of 25%. A 25% margin is safer for motor-heavy loads, and it is the margin used throughout this guide and on SG Power's product pages.

How Do You Find the Running Load for Stabilizer Sizing?

For stabilizer sizing, the running load is the total kW of loads that actually run together, not everything connected. Many sites connect far more than they use at once. Take the figures from nameplates or the typical values below, then remove standby machines and loads that never run at the same time.

Connected load: every machine and appliance wired to the supply, used or not

Running load: what runs together at your busiest time; this is what you size for

Demand or diversity factor: running load ÷ connected load; measure it with a clamp meter if you can

Standby loads: spare pumps and backup machines do not add to the running load

Typical Running Watts for a Stabilizer Load List

These typical running watts help you build a stabilizer load list when nameplates are hard to read. They are approximate values for Indian homes, offices and workshops. Always use the rating label when you can, because models differ, and remember that motor loads draw several times their running current at start.

Load	Typical Running Power
LED bulb or tube light	10–20 W each
Ceiling fan	50–75 W each
LED TV with set-top box	120–200 W
Refrigerator (single or double door)	150–350 W
Washing machine	400–700 W (up to about 2,000 W on a hot wash with its heater)
Microwave oven	1,000–1,400 W
1 ton split AC	1,000–1,200 W
1.5 ton split AC	1,500–1,800 W
2 ton split AC	2,000–2,400 W
Water pump, 1 HP	about 750 W
Desktop computer with monitor	150–300 W
Geyser or water heater	2,000–3,000 W (keep off the stabilizer)

How to Calculate Stabilizer kVA for a Home

To calculate stabilizer kVA for a home, list the ACs, refrigerator, pump, TV, lights and fans that can run together on a hot evening. Leave out geysers, irons and induction cooktops, which work on almost any voltage. Then apply the same formula and pick the next size.

Worked example: a 3BHK home with three 1.5 ton ACs

Load	Running Power
Three 1.5 ton split ACs (about 1.6 kW each)	4.8 kW
Refrigerator	0.3 kW
LED TV with set-top box	0.2 kW
Washing machine	0.5 kW
Lights, fans and router	0.7 kW
Water pump, 1 HP	0.75 kW
Total running load	7.25 kW

Required kVA = 7.25 ÷ 0.8 × 1.25 = 11.3 kVA, so a 15 kVA servo stabilizer fits. Adding a 2 kW geyser would push the need to about 14.5 kVA, leaving almost no margin. That is why heaters belong on a separate, unstabilized circuit.

Single-phase homes: for a mainline stabilizer for home use, SG Power's 10 kVA and 15 kVA air cooled units suit most flats and villas.

Three-phase homes: size on the most heavily loaded phase, as explained below.

Check your supply first: a 15 kVA single-phase unit draws about 65 A. Many homes with three or more ACs have a three-phase connection, so check your connection type and sanctioned load before choosing a single-phase or three-phase stabilizer.

One appliance only: a single 1.5 ton air conditioner (AC) needs about 2.8 kVA by the formula, so a 3–4 kVA appliance stabilizer is enough; a servo stabilizer is for the whole home.

How to Calculate Stabilizer kVA for a Factory

To calculate stabilizer kVA for a factory or other industrial site, add the kW of machines that run together on your busiest shift. Include CNC machines, compressors, pumps, chillers and lighting. Leave out standby machines and furnaces that do not need stabilized voltage. These worked examples show the formula on typical Indian sites.

Site	Running Load	Calculation	Required kVA	Choose
Small workshop	15 kW	15 ÷ 0.8 × 1.25	23.4 kVA	25 kVA
Machine shop	40 kW	40 ÷ 0.8 × 1.25	62.5 kVA	75 kVA
Plastics unit	75 kW	75 ÷ 0.8 × 1.25	117.2 kVA	125 kVA
CNC shop, 12–15 machines	90 kW	90 ÷ 0.8 × 1.25	140.6 kVA	150 kVA
Cold storage plant	37 kW	37 ÷ 0.8 × 1.25	57.8 kVA	75 kVA
Larger plant or mall	110 kW	110 ÷ 0.8 × 1.25	171.9 kVA	200 kVA
Textile mill	260 kW	260 ÷ 0.8 × 1.25	406.3 kVA	500 kVA

A stabilizer for a 100 kW load works out to 156.3 kVA, just above 150 kVA. Choose 200 kVA, or bring the stabilized load down to about 96 kW by moving heaters and ovens to a separate feeder.

Not sure which machines run together? Send the machine list, and SG Power's team will work out the running load with you.

Get a Free Sizing Check Talk to an Engineer

How to Calculate kVA From Amps or Your Electricity Bill

When you do not have a full load list, calculate stabilizer kVA from amps or from your electricity bill. A clamp meter reading at your busiest time is the most reliable. A bill gives a quick estimate. Add the same 25% margin to either figure, and confirm it before ordering.

Method	How to Calculate	Example
Clamp meter, single phase	230 V × peak amps ÷ 1,000, then × 1.25	40 A → 9.2 kVA → 11.5 kVA → 15 kVA
Clamp meter, three phase	0.72 × highest phase amps, then × 1.25	160 A → 115 kVA → 144 kVA → 150 kVA
Maximum demand (MD) on the bill	Recorded MD in kVA × 1.25	90 kVA MD → 112.5 kVA → 125 kVA
Sanctioned load or contract demand	A ceiling, not a sizing figure	Check it against the running load

Measure at peak: take readings when ACs, compressors and the largest machines are all running.

Use the highest phase: in three-phase supplies, size on the most heavily loaded phase.

Remove unstabilized loads: subtract heaters, furnaces and other loads that will not go through the stabilizer.

Check the MD period: use the highest MD from the last 12 months, as summer loads are often higher.

Know what MD means: the Electricity (Rights of Consumers) Rules, 2020 define maximum demand as the highest average load in kVA or kW over any 30-minute period in the billing cycle, unless your state commission sets another period.

How Do Motor Starting and Phase Imbalance Affect Stabilizer kVA?

Motor starting current and phase imbalance are the two things that most often trip a correctly calculated servo stabilizer. The 25% margin covers normal starting of small and medium motors. Large direct-on-line motors and heavily unbalanced phases need a closer check before you choose the size.

Starting Method	Typical Starting Current	Effect on Stabilizer Size
Direct-on-line (DOL)	About 5–7 times running current (inrush or locked-rotor current)	Check large DOL motors before ordering
Star-delta starter	About one-third of DOL current	Usually covered by the 25% margin
Soft starter	Set on the starter, often 2–4 times	Usually covered by the 25% margin
Variable frequency drive (VFD)	Close to running current	No extra allowance needed

When one DOL motor makes up a large share of the load, share its kW and starter type. The size can then be checked against its starting current.

A stabilizer has two ratings: a continuous kVA rating and a short-time overload rating. A DOL start usually lasts only a few seconds, so ask the maker how much overload the unit carries, and for how long, before choosing a larger kVA.

How Do You Size a Stabilizer for Unbalanced Phases?

For unbalanced phases, size the three-phase stabilizer on the most heavily loaded phase, not on the total. Each phase of a three-phase unit carries one-third of its rating. If one phase carries far more than the others, a unit sized on the total can overload that phase while the others run light.

Example: after converting to kVA, phase R carries 30 kVA, Y carries 22 kVA and B carries 18 kVA, a total of 70 kVA.

Sized on the total: 70 × 1.25 = 87.5 kVA, so 100 kVA, but phase R needs 37.5 kVA against a capacity of 33.3 kVA per phase.

Sized on the highest phase: 3 × 30 × 1.25 = 112.5 kVA, so 125 kVA, which covers phase R safely.

For any 3 phase servo stabilizer kVA calculation with mixed loads, work out the kVA requirement of each phase first.

Rebalance first: move single-phase loads so each phase carries about 23.3 kVA. The same 70 kVA load then needs only 70 × 1.25 = 87.5 kVA, so a 100 kVA unit fits instead of 125 kVA. Ask your electrician whether loads can be shifted between phases before you buy.

Homes, hospitals and hotels with ACs and lights on different phases often suit an unbalanced servo stabilizer, which corrects each phase on its own.

Servo Stabilizer Size Chart: 10 kVA to 500 kVA

This servo stabilizer size chart lists each standard rating with its safe running load and its full-load current. Find the first row whose safe running load is above your running load. That row is your size. The safe running load already includes the 0.8 power factor and the 25% margin.

Servo stabilizer kVA sizes from 10 kVA to 500 kVA, air cooled and oil cooled — SG Power servo stabilizer range from 10 kVA to 500 kVA

Rating	Safe Running Load	Full-Load Current	Cooling in SG Power's Range
10 kVA single phase	about 6.4 kW	about 43 A at 230 V	Air
15 kVA single phase	about 9.6 kW	about 65 A at 230 V	Air
10 kVA three phase	about 6.4 kW	about 14 A per phase	Air
15 kVA three phase	about 9.6 kW	about 21 A per phase	Air
20 kVA	about 12.8 kW	about 27.8 A per phase	Air
25 kVA	about 16 kW	about 35 A per phase	Air or oil
30 kVA	about 19.2 kW	about 41.7 A per phase	Air or oil
40 kVA	about 25.6 kW	about 55.6 A per phase	Air or oil
50 kVA	about 32 kW	about 70 A per phase	Air or oil
60 kVA	about 38.4 kW	about 83.5 A per phase	Oil
75 kVA	about 48 kW	about 104 A per phase	Oil
100 kVA	about 64 kW	about 139 A per phase	Oil
125 kVA	about 80 kW	about 174 A per phase	Oil
150 kVA	about 96 kW	about 209 A per phase	Oil
200 kVA	about 128 kW	about 278 A per phase	Oil
250 kVA	about 160 kW	about 348 A per phase	Oil
400 kVA	about 256 kW	about 556 A per phase	Oil
500 kVA	about 320 kW	about 696 A per phase	Oil

Safe running load = kVA × 0.8 × 0.8 (power factor, then the 25% margin). Three-phase current = kVA × 1,000 ÷ (1.732 × 415). Other capacities are built to order.

For example, 150 kVA to kW is about 120 kW at full rating, while its safe running load is about 96 kW.

The full-load current in the chart is also the figure your electrician uses to choose the input and output cables and the breaker. Cable size then depends on the cable run and voltage drop, as covered in the installation guide. The stabilizer body also needs a sound connection to the site's earth electrode.

Which kVA Range Suits Which Site?

Most sites fall into one of four stabilizer kVA bands, from single-phase homes to large process plants. Use this table as a starting point, then confirm the size with your own load list. Your exact machine list, phase loading, voltage swing and duty cycle decide the final rating.

kVA Range	Supply	Typical Sites
10–15 kVA	Single or three phase	Flats, villas, clinics, shops and small offices
25–50 kVA	Three phase	Workshops, showrooms, schools, small offices and small factories
75–150 kVA	Three phase	Engineering units, CNC shops, cold storage, hospitals, hotels and commercial buildings
200–500 kVA	Three phase	Textile mills, plastic moulding, food processing and large plants

Above about 500 kVA, large plants with their own HT supply often correct the voltage on the high-tension side instead, with an HT AVR transformer.

What Load Can a 10 kVA or 15 kVA Stabilizer Run?

A 10 kVA stabilizer runs about 8 kW at full rating, or about 6.4 kW with a 25% margin. A 15 kVA stabilizer runs about 12 kW at full rating, or about 9.6 kW with the margin. These two sizes cover most single-phase homes, clinics, shops and small offices.

10 kVA: two or three 1.5 ton ACs with a fridge, TV, lights and fans

15 kVA: three or four ACs with a pump, fridge, washing machine, lights and fans

One Mainline Stabilizer or One Per Machine?

You can size one mainline stabilizer for the whole site, or smaller dedicated units for critical machines. A single unit at the main incomer is simplest and protects everything downstream. Dedicated units cost more but give tighter protection where a fault would be expensive. Many plants use both.

Approach	How to Size It	Best For
One mainline stabilizer	Total running load of the site ÷ 0.8 × 1.25	Most homes, offices and factories
Dedicated stabilizer per machine	That machine’s kW or full-load current, plus 25%	CNC lines, medical imaging, lifts and other critical machines
Mainline plus dedicated units	Size each on the loads it feeds, without counting any load twice	Plants with one or two very sensitive or very large machines

Size a mainline stabilizer on the load it protects, not on the rating of your distribution transformer. Most transformers are rated well above the running load, and heaters or furnaces fed from them may stay off the stabilizer.

Does the Input Voltage Range Change the Stabilizer kVA?

A servo stabilizer's input voltage range does not change your running load, but it affects how hard the unit works. At the lowest input voltage, the stabilizer draws more current from the mains to hold the output steady. Choose an input range that covers the lowest and highest voltages you actually record on site.

Record your voltage: note the lowest and highest readings on each phase over a few days, including summer evenings.

Match the range: SG Power’s standard ranges are 295–465 V or 340–460 V for three phase, and 170–270 V or 190–270 V for single phase.

Wider is bigger: a wider input range needs a larger variac and transformer for the same kVA.

Ask about derating: check whether the kVA rating holds at the lowest input voltage, or is derated there.

Output and regulation: across its input range, a servo stabilizer holds the output at about 230 V single phase or 415 V three phase; SG Power’s units regulate within ±1%.

Low voltage areas: where dips below the standard range are common, ask for a custom range rather than simply a bigger kVA.

Which Loads Should Not Go on the Stabilizer?

Resistive loads rarely need a servo stabilizer, because geysers, heaters, ovens and furnaces work on almost any voltage. Keeping them on a separate feeder can cut the required kVA sharply. Some electronic loads also need a different device, so check these before you add them to your load list.

Leave off: geysers, room heaters, irons, induction cooktops, electric ovens and heating furnaces

Use a UPS instead: computers and servers that must not lose power during a cut; a stabilizer does not store energy

Add surge protection: lightning and switching spikes need a surge protection device, not a bigger stabilizer

Check inverters: place the stabilizer before a home inverter or UPS, never on its output, and include the battery charging load

What Are the Common Servo Stabilizer Sizing Mistakes?

The most common servo stabilizer sizing mistakes are sizing on connected load, forgetting motor starting current and ignoring one overloaded phase. Mixing up kW and kVA and leaving no room for growth are also common. Each mistake gives a unit that trips under load, or one far larger than the site needs.

Using connected load: machines that never run together inflate the size.

No starting margin: compressors and large DOL motors trip an exactly sized unit.

Ignoring phase imbalance: one heavily loaded phase can overload a unit sized on the total.

Mixing up kW and kVA: buying a 10 kVA unit for a 10 kW load leaves it overloaded.

Oversizing far beyond the margin: a much larger unit costs more, takes more space and can hunt on very light loads.

Forgetting growth: if you will add machines within two years, include them now.

Using kWh from the bill: kWh is energy used over the billing period, not load. Size from kW or kVA, and divide kW by the power factor, never multiply.

What Do Indian Forum Users Ask About Stabilizer Sizing?

Indian forum users most often ask what kVA they need for a whole house, how many ACs a stabilizer can carry, and where it should go. Threads on Quora, Reddit, TechEnclave, HiFiVision, NoBroker and Physics Forums repeat the same questions, and the same lessons.

Forum Question	What It Teaches
Is a 30 kVA three-phase stabilizer right for a house after an 11 kV line fault? (TechEnclave)	Size to the real running load per phase; a stabilizer cannot stop high-voltage faults, so fit surge protection
What kVA does a home with a 3 HP treadmill need? (Physics Forums, Indian user)	Count motor peaks, and choose an input range that covers the lowest voltage seen, here 180–190 V in summer
Which mainline stabilizer for two 2 ton ACs, PCs, TVs and three water heaters? (TechEnclave)	Without the 3 kW of water heaters, the running load is about 7.25 kW and needs about 11.3 kVA; with them, about 16 kVA
What size servo for a home with five ACs? (TechEnclave)	Count only the ACs that run together; one home runs five ACs, usually three at once, on a 15 kVA servo
Can a stabilizer go on the inverter’s output? (TechEnclave)	Place the stabilizer before the inverter, ask for rated amps as well as kVA, and use wiring rated for the stabilizer’s current
Single-phase or three-phase servo for a whole house? (HiFiVision)	Ask how a three-phase unit behaves if one phase fails, and confirm local service before buying

Across these threads, Indian homeowners give the same practical advice:

Measure first: record your site voltage for a few days, and read the real wattage of the largest loads from their labels.

Watch the pump: a 1–2 HP submersible pump causes a visible voltage dip when it starts, so include it in the margin.

Check the wiring: if appliances restart even in bypass mode, the fault is in the house wiring, not the stabilizer.

Forum threads checked November 2026. Prices and brand names from the threads are not used here.

After Calculating kVA: Air or Oil Cooled, Balanced or Unbalanced Stabilizer?

Once you have calculated the servo stabilizer kVA, choose the cooling and the design. In SG Power's range, air cooled units cover 10 to 50 kVA and suit clean indoor rooms. Oil cooled units cover 25 to 500 kVA for continuous duty and hot or dusty sites. Phase loading decides between balanced and unbalanced.

Choice	Choose This When
Air cooled	Load up to 50 kVA in a clean, ventilated indoor room
Oil cooled	Above 50 kVA, 24×7 duty, or hot and dusty sites
Balanced	Three-phase motors and production lines that load each phase equally
Unbalanced	Homes, hospitals, hotels and offices with single-phase loads on different phases

To see how the variac and buck-boost transformer correct the voltage, read how a servo stabilizer works. For cable, breaker and earthing after sizing, see the servo stabilizer installation guide. At 50 kVA the choice is open, so compare the 50 kVA air and oil cooled models before you order.

Want a second opinion on your size? SG Power's team can check your calculation against your load list and voltage readings.

Get a Free Sizing Check Talk to an Engineer

Servo Stabilizer kVA Calculation Checklist

Use this servo stabilizer kVA calculation checklist before you ask for quotes. It makes sure every supplier sizes the same load, so the offers can be compared fairly. Keep a copy with your load list and voltage readings, and share both when you request a quotation.

Running load listed, with standby machines removed
Heaters, geysers and furnaces moved off the stabilized load
kW converted to kVA at 0.8 or the measured power factor
25% margin added
Load per phase checked, and the highest phase used for three-phase supplies
Large DOL motors and their starters noted
Lowest and highest site voltages recorded on each phase
Machines planned for the next two years included
Next standard kVA size chosen
Cooling type and balanced or unbalanced design chosen

Servo Stabilizer kVA Calculation: Key Facts

These are the main facts about servo stabilizer kVA calculation, written as short statements for quick reference:

Formula: servo voltage stabilizer kVA = running kW ÷ 0.8 × 1.25.

Safe running load: about 0.64 times the stabilizer’s kVA rating.

From current: three-phase kVA at 415 V is about 0.72 times the amps per phase.

Unbalanced loads: size on the most heavily loaded phase, times three.

Examples: 15 kW needs 25 kVA; 60 kW needs 100 kVA; 90 kW needs 150 kVA.

Never use kWh: bill units show energy, not load.

Frequently Asked Questions About Servo Stabilizer kVA Calculation

Still unsure about your size? Send your load list and voltage readings, and SG Power's engineers will recommend a size, input range and design for free.

Get a Free Sizing Check Talk to an Engineer

Sources and References

This guide uses the standard kW, kVA and power factor relationships and SG Power's sizing method and capacity range. Appliance wattages are typical values, and forum findings were checked in November 2026. Always confirm the final size with your load list, site voltage readings and the stabilizer maker.

SG Power Products Pvt. Ltd., product catalogue (February 2026) and KNEUTRON servo stabilizer catalogue: capacity range, cooling and input ranges
IS 9815 (Part 1), Indian Standard for voltage stabilizers, published by the Bureau of Indian Standards
Power factor, Wikipedia: background on kW, kVA and power factor
Volt-ampere, Wikipedia: background on apparent power
IS 12615, Energy Efficient Induction Motors: Three Phase Squirrel Cage (efficiency classes IE1 to IE3)
Electricity (Rights of Consumers) Rules, 2020, Ministry of Power: definition of maximum demand
Forum threads on Quora, Reddit, TechEnclave, HiFiVision, NoBroker and Physics Forums on stabilizer sizing (checked November 2026)

Learn More

To go further, these pages cover the stabilizer types, sizes and steps that follow a kVA calculation. They help when you are choosing between air and oil cooling, comparing balanced and unbalanced designs, planning the installation or protecting the site from surges.

Servo voltage stabilizer: range from 10 kVA to 500 kVA
How does a servo stabilizer work?: the variac, buck-boost transformer and controller explained
Balanced vs unbalanced servo stabilizer: which design suits your phase loading (guide coming soon)
Servo stabilizer installation guide: cables, breakers and earthing after sizing
How to compare servo stabilizer quotes: what to check on every offer (guide coming soon)
Surge protection devices: for lightning and switching spikes
3 phase stabilizer: three-phase models from 10 kVA to 500 kVA
HT AVR transformer for large plants: voltage correction on the HT side

Ready to size your stabilizer? Send your load list, and SG Power will confirm the kVA, input range and design.

Get a Free Sizing Check Talk to an Engineer

How to Calculate Servo Stabilizer kVA: Formula, Worked Examples and Size Chart

Servo Stabilizer kVA Calculation in Brief

Table of Contents

Want Your kVA Calculation Checked?

What Is kVA, and Why Are Stabilizers Rated in kVA?

How to Calculate Servo Stabilizer kVA in Four Steps

What Is the Servo Stabilizer kVA Formula?

How Do You Find the Running Load for Stabilizer Sizing?

Typical Running Watts for a Stabilizer Load List

How to Calculate Stabilizer kVA for a Home

Worked example: a 3BHK home with three 1.5 ton ACs

How to Calculate Stabilizer kVA for a Factory

How to Calculate kVA From Amps or Your Electricity Bill

How Do Motor Starting and Phase Imbalance Affect Stabilizer kVA?

How Do You Size a Stabilizer for Unbalanced Phases?

Servo Stabilizer Size Chart: 10 kVA to 500 kVA

Which kVA Range Suits Which Site?

What Load Can a 10 kVA or 15 kVA Stabilizer Run?

One Mainline Stabilizer or One Per Machine?

Does the Input Voltage Range Change the Stabilizer kVA?

Which Loads Should Not Go on the Stabilizer?

What Are the Common Servo Stabilizer Sizing Mistakes?

What Do Indian Forum Users Ask About Stabilizer Sizing?

After Calculating kVA: Air or Oil Cooled, Balanced or Unbalanced Stabilizer?

Servo Stabilizer kVA Calculation Checklist

Servo Stabilizer kVA Calculation: Key Facts

Frequently Asked Questions About Servo Stabilizer kVA Calculation

Sources and References

Learn More