Choosing the wrong starter is one of the quiet reasons submersible motors burn. A big motor started the wrong way takes a heavy jolt of current every time it starts, which heats and weakens its winding and cable. This guide explains, in plain words, whether your motor needs a DOL or a star delta starter, and what to choose if your village gets juice line or 2 phase power.
The short answer
| Your motor and supply | BTCO starter |
|---|---|
| Single cable 3 phase motor, 3 to 10 HP, normal 3 phase supply | DOL-03 (3–7.5 HP or 7.5–10 HP) |
| Double cable 3 phase motor, 7.5 to 30 HP, normal 3 phase supply | Star Delta FASD-03 (7.5–12.5, 15, 20 or 25–30 HP) |
| Single cable motor up to 10 HP, juice line or 2 phase supply | Combined DOL-2/3 (3–8 HP or 7.5–10 HP) |
| Double cable motor 7.5 to 25 HP, 2 phase supply (juice line only up to 10 HP) | Combined Star Delta FASD-2/3 |
| Single phase motor, 2, 3 or 5 HP | Single Phase FASP-01 (Domestic or Agro) |
What is a DOL starter?
DOL means direct on line: the starter connects the motor straight to the full supply. That is fine for smaller, single cable motors up to 10 HP. The BTCO DOL-03 adds full digital protection through its MPAU unit: dry run, overload, single phasing, earth fault and imbalance, and cable faults, with the reason for every trip on the display.
What is a star delta starter, and why do bigger motors need it?
Bigger motors draw a very high current if they are switched straight on. A star delta starter first runs the motor in star, which takes much less current, and after a few seconds switches it to delta for full power. This is much easier on the motor winding, the cable and the supply. Double cable motors from 7.5 HP upwards are made for star delta starting, so a DOL starter is the wrong choice for them.
On the BTCO Star Delta starter, you set the SD delay (how long the motor stays in star) to suit your motor. Watch how:
Juice line or 2 phase supply? Choose a Combined starter
In many villages the 3 phase supply is reduced for some hours of the day: one line comes in at around 300 V and the other two are very low. This is called juice line or series line. Normal DOL and star delta starters need full 3 phase supply. The Combined DOL runs single cable motors up to 10 HP on juice line, 2 phase and 3 phase supply. The Combined Star Delta runs double cable motors from 7.5 to 25 HP on 2 phase and 3 phase supply, and on juice line only up to 10 HP, because running a bigger motor on juice line is not safe. Combined starters need capacitors, which our dealer or technician chooses for your motor and supply.
Either way, protection is what stops burning
Whichever starter fits your motor, what saves it from burning is the protection inside. Every BTCO 3 phase starter has the MPAU: it learns your motor’s normal current by itself, trips on overload, dry run and supply faults, shows the reason on the display, and starts the motor again by itself when power comes back. Read how dry run protection saves your motor and why submersible motors keep burning.
Every BTCO starter also works with the GSM Module, so you can control it from your phone. What is a mobile starter?
Frequently asked questions
DOL or star delta: which starter does my motor need?
Single cable 3 phase motors up to 10 HP use a DOL starter. Double cable motors from 7.5 to 30 HP use a star delta starter, which starts the motor gently to reduce the starting current.
Can I use a DOL starter on a 15 HP motor?
No. Motors above 10 HP are double cable motors made for star delta starting. Use the BTCO Star Delta starter, which comes in 7.5–12.5, 15, 20 and 25–30 HP variants.
Which starter works on juice line?
The BTCO Combined DOL starter runs motors up to 10 HP on juice line, 2 phase and 3 phase supply. The Combined Star Delta starter runs on juice line only in its 7.5–10 HP variant; bigger variants run on 2 phase and 3 phase.
What is the SD delay?
The time the motor runs in star before the starter switches it to delta. You can set it on the BTCO Star Delta starter to suit your motor.
Do both starters protect the motor from burning?
Yes. Every BTCO 3 phase starter has the MPAU unit, which trips the motor on dry run, overload, single phasing, earth fault and cable faults and shows the reason on the display.
Protect your motor with BTCO
Call or WhatsApp us with your motor’s HP and your power supply, or visit your nearest BTCO Starters dealer. Tell us your motor’s HP, whether it is single or double cable, and your supply, and we will confirm the right starter. More answers in our motor starter FAQ.
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