75 hp full running

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mike90040

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Hello everyone,
I hope your day is going well. I have a question. I am working on a project and its T & M and no plans. We are about to install a 75 hp 480 V 102amp full running load, compressor. We have the ampicity in panel to run it but my Question is 2.5 times 102 is 255amps. Now what kind or type of breaker do I use? Since the start up is momentary do I still need a big size breaker OR would something like a 150 amp hold up for the start up?:) I appricate your thoughts of wisdom for me.
 
In my experience compressors are hard starters, I would not count on the 150 to hang in while the compressor comes up to speed.
 
mike90040 said:
Hello everyone,
I hope your day is going well. I have a question. I am working on a project and its T & M and no plans. We are about to install a 75 hp 480 V 102amp full running load, compressor. We have the ampicity in panel to run it but my Question is 2.5 times 102 is 255amps. Now what kind or type of breaker do I use? Since the start up is momentary do I still need a big size breaker OR would something like a 150 amp hold up for the start up?:) I appricate your thoughts of wisdom for me.
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I like combination motor starters with a mag-only CBs.

cf
 
With that large of one, it probaly has an automatic unloader valve, the manufacture should have specs on the required breaker or fuse size. Is it an air screw?
 
I would see what size the breaker manufacturer for the type of breaker you intend to use recommends. NEC just gives you max values.

I have a Square D motor data slide calculator in front of me and it says to use a 125 amp breaker (type KAL) for a 75hp 460v. Other breaker type may have different suggestion.
 
kwired said:
I would see what size the breaker manufacturer for the type of breaker you intend to use recommends. NEC just gives you max values.

I have a Square D motor data slide calculator in front of me and it says to use a 125 amp breaker (type KAL) for a 75hp 460v. Other breaker type may have different suggestion.
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The KAL is a motor circuit protector and can only be used as part of a listed combination starter.
 
don_resqcapt19 said:
The KAL is a motor circuit protector and can only be used as part of a listed combination starter.
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KAL is a 250 amp frame sized molded case thermal-magnetic circuit breaker good for 600VAC made in two or 3 pole from 70 amp to 250 amp with a standard interrupt rating of 25kA @480 and 22kA @600 volts.

It has lugs on both line and load terminals this is what the "L" stands for in the catalog number. There are other termination options to the "KA" breaker.

Looking at catalog page as I write this.
 
Compressor circuit protection

Compressor circuit protection

hillbilly1 said:
With that large of one, it probaly has an automatic unloader valve, the manufacture should have specs on the required breaker or fuse size. Is it an air screw?
Click to expand...

Hillbilly is correct on the unloader. It certainly makes a difference as to the initial inrush current seen on a compressor package. I am a previous construction electrician and a retired Navy Engineering Officer. I currently work for a compressor company that has allowed me to keep up with my NEC and other training. I would like to state that we do not try to do the job of the EC. When customers buy our compressors, their electrical distribution system should have already been checked out to ensure it can handle the load and meets all installation requirements. The compressor manufacturer does not, generally, know the customer's system since the compressor packages are usually sold through a distributor or others. I believe the equipment installer (electrical) should be the one to recommend the size and type of protection based on the plant specifics, including actual supply readings, ratings and ambient conditions. I am always ready to respond to questions from personnel that are qualified to install our equipment, but this is not always the case. As a manufacturer, we do not have the on-site information required to recommend safe installation. If we check it out, it will be correct.

I enjoy this forum very much and have learned a tremendous amount of valuable information and opinions. I do respect opinions that differ from mine.

Best Regards,
Mark Beatty, CWO3, USN (Ret.)
 
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