Starter

Not true. They sometimes are much larger than that, but on a small grid, or distant wiring, there may be restrictions to such small sizes.

As Tornado says, the limit is not always 5hp. The figure depends on regulations and maybe local specs. But the basic reason is due to high starting current, 6 - 8 x FLC, which could be too high for the supply network.

The question is installation-specific, rather than a global phenomenon, as DOL is used routinely at much higher powers, particularly on MV motors. So the answer can be best addressed by looking at standards and practices within the installation in question. It may be:

• a matter of local policy, or
• a matter of local utility supply resilience, or
• some other reason or combination of reasons.

As no other reader here can see either the local installation or its constraints, the full answer is unlikely to come from a global anonymous Engineering forum on the internet.

Thank you all of you for guidance.

I've worked on 800HP DOL and there are some bigger than that.

900HP @ 460V was the largest motor I started DOL. The starter however was rated for 1200HP, so I suppose those must exist.

Largest motor I've started DOL was 15,000HP, but that was 12.47 kV.

Is there any starting current limiting device in DOL

Yes. One would ordinarily expect two <...current limiting device[s]...> to be in circuit:

• (a) circuit protection device(s), such as (a) fuse(s),
• A motor overload protection device.

The topic that embraces this is called "co-ordination", and full protocols can be found within the applicable national electrical code; in the UK, BS7671 applies.

Assuming you mean 380-480V 3 phase. There are standards for starting vs running current choices for induction motors to ease supply limits on starting current, but compromise on starting torque at zero speed.

Reactors or transformers can be used for reduced voltage/current starting but with sacrifice of starting torque.

It depends on the load torque/speed relation versus motor torque/speed - there can be a "hang" where the motor does not reach full speed - the motor overload operates or motor overheats and fails.

Modern electronic "soft Starters" or inverter drives could be a solution.

Fans are low torque at zero speed and more suitable for transfo or star/delta starters.