Ingersoll Rand Compressor 15 HP

[the blur]

I recently installed a 15HP Ingersoll Rand Air Compressor. Fully packaged unit. came with motor starter, and everything complete. nice compressor. I ran #4's, and it runs nice. The problem is the startup in-rush current. it's about 400-500 amps in-rush. The breaker in the sub panel handles it, the #4's handle it fine. The sub panel is fine. The main 600amp service entrance panel vibrates the buss-bars. You can hear the virbration during the in-rush. It lasts a few seconds, and it's definately from the buss bars rattling. There is nothing wrong with the installation, and it all passed inspection, it's just the rattling of the main panel bothers me. Is there a soft start kit made for this ? and will it void the compressor warrenty ?

Does a soft start kit go in place of the magnetic starter ?

 

[Jraef]

#1, 600A panelboard busbars should not be rattling on startup of a 15HP motor. Something is wrong there. Are you sure it's the busbars themselves or could it be the conductors unsecured in the panelboard enclosure? If it's the bars, you have other bigger problems and the symptom you see is just the tip of the iceburg.

#2, there are soft starters for 15HP motors and they are used on compressors all the time. IR probably has a soft starter option for that if you had wanted to pay extra for it at the time. But there is no reason why one can't be retrofitted after the fact. 15HP is usually a little low to need one, and I'm a big proponent of soft starters, but they almost never hurt and can realize benefits on the machine itself. But that may end up masking that bigger problem brewing in your panelboard as mentioned above. Find the REAL problem before you fix a symptom.

 

[the blur]

There is only one way to find out, and that is to open the big panel board, and watch it under load. I did measure the inrush at the disconnect of the compressor, and it's well over 400amps per phase. 400amps is pretty serious in rush, and that's why #4's were choosen, and you can see them jumping around during the compressor startup.

 

[GeorgeB]

+1 on Jraef; I'm going to assume 208-3-60 with about 45 FLA ... 400-500 is a LITTLE higher than I'd expect, but your low impedance wiring helps it be high.

I suggest that you check the compressor's MECHANICAL settings; usually a compressor this size will start unloaded so the inrush and magnetization current won't last long at all, not long enough to vibrate the buss. If there is something wrong with the unloader, the inrush will last substantially longer and would contribute (symptom, but not cause) what you see, IMO.

 

[the blur]

did some measurments with a fancy fluke. It has a MAX setting and a PEAK setting. Inrush MAX is 300amps. Inrush peak current is 400amps which is the peak of the waveform, not RMS. I think that figure is not what we should be looking at. MAX is what we need we need to read. I don't know why they do that when one reading is .707 of the other.

regardless, the inrush is still causing a slight buzz in the panel. it was worse, but we twisted the 3 wires tightly in the panel so they can't jump around on the motor start up. maybe it's still banging deeper in the EMT and resonating in.

we have a soft starter on order, but I don't want to install it until we find the problem.

 

[weressl]

did some measurments with a fancy fluke. It has a MAX setting and a PEAK setting. Inrush MAX is 300amps. Inrush peak current is 400amps which is the peak of the waveform, not RMS. I think that figure is not what we should be looking at. MAX is what we need we need to read. I don't know why they do that when one reading is .707 of the other.

regardless, the inrush is still causing a slight buzz in the panel. it was worse, but we twisted the 3 wires tightly in the panel so they can't jump around on the motor start up. maybe it's still banging deeper in the EMT and resonating in.

we have a soft starter on order, but I don't want to install it until we find the problem.

Follow the suggestions and get your fine-teethed comb out and go through all current carying components of the 'rattler'.