Electrical Load Study?

[NY347Jersey]

I am considering performing an industrial load study on an MCC section to determine how much power is available for future loads. Is there a recommended template that anyone has used successfully in the past? Thanks

 

[Strathead]

I am considering performing an industrial load study on an MCC section to determine how much power is available for future loads. Is there a recommended template that anyone has used successfully in the past? Thanks

Not sure what you mean. Your template question implies manually taking readings. Not feasible. I just had one done. It requires certain equipment. If you aren't doing it regularly, contact a NETA qualified electrical testing firm. They will stick the proper metering on it. download the results and give you a report.

 

[Lady Engineer]

I am considering performing an industrial load study on an MCC section to determine how much power is available for future loads. Is there a recommended template that anyone has used successfully in the past? Thanks

I do them all the time. You can do a more thorough method with SKM, which is great. However, of an easy and cheap way I would gather all the motors powered from the MCC, and then non-motor loads like Panels. I would take the total motor KVA and take about 65% to 70%. For panels, I would say about 40%. After that, I would go to the utility for the peak demand load for the last 2 years and compare the two , meaning the demand and calculated demand to make sure it's reasonable. To my calculated demand, if it's close to the utility peak demand, I'd then add 20%. This not a code method, but since I do this all the time, I'm pretty sure you would get what you need.

I would not take an amp meter reading, because the pumps will cycle on and off, but you have that one occasion where there's a flood and every pump is running full blast.

 

[petersonra]

I am considering performing an industrial load study on an MCC section to determine how much power is available for future loads. Is there a recommended template that anyone has used successfully in the past? Thanks

The code provides two means by which such a load study can be undertaken. One is by calculation. There is a detailed procedure in the code for this. The other is to monitor the actual load over a period of time and use the highest load seen as the load. This is also described in the code.

 

[petersonra]

I do them all the time. You can do a more thorough method with SKM, which is great. However, of an easy and cheap way I would gather all the motors powered from the MCC, and then non-motor loads like Panels. I would take the total motor KVA and take about 65% to 70%. For panels, I would say about 40%. After that, I would go to the utility for the peak demand load for the last 2 years and compare the two , meaning the demand and calculated demand to make sure it's reasonable. To my calculated demand, if it's close to the utility peak demand, I'd then add 20%. This not a code method, but since I do this all the time, I'm pretty sure you would get what you need.

I would not take an amp meter reading, because the pumps will cycle on and off, but you have that one occasion where there's a flood and every pump is running full blast.

I know this kind of thing is a fairly common practice but where does the code allow it?

 

[Lady Engineer]

I know this kind of thing is a fairly common practice but where does the code allow it?

The code really doesn't address pump motors in their service calcs or allow diversity factors per se, but this is just 15 years of my design experience. That's a good question, maybe they should.

They mainly deal with dwellings for service sizing. It's not really covered at all, truthfully.

 

[don_resqcapt19]

I have never seen an industrial MCC that would meet the code as far as feeder size. The engineers just make a good guess as to the actual load and do not do the calculation required by Article 430.

 

[petersonra]

I have never seen an industrial MCC that would meet the code as far as feeder size. The engineers just make a good guess as to the actual load and do not do the calculation required by Article 430.

Maybe I live in a different world but most times that I see an MCC calculation it appears to have been done correctly.

 

[don_resqcapt19]

Maybe I live in a different world but most times that I see an MCC calculation it appears to have been done correctly.

Most of the ones I see, the connected load is 30 to 50% greater than the rating of the feeder and/or the MCC busing.

 

[Lady Engineer]

Maybe I live in a different world but most times that I see an MCC calculation it appears to have been done correctly.

If I had to make a "good" guess, I'd be out of business. That's ALL I do is industrial stuff.

That's not true at all. Actually, we do load studies, but the code doesn't require you to size it based on a specific method like for dwellings.

 

[petersonra]

Most of the ones I see, the connected load is 30 to 50% greater than the rating of the feeder and/or the MCC busing.

seen a fair amount of that too, but it is not the result of someone making a non-code approved calculation. it just sort of happens over time.

 

[iceworm]

Maybe I live in a different world but most times that I see an MCC calculation it appears to have been done correctly.

I'm in a similar world. The customers think keeping their stuff running, reliable, flatout, 24/7, is absolutely top of the list. They generally are not too interested in saving a few bucks on copper.

Code compliant? No, they would never stand for that poor of a job.

ice

 

[Lady Engineer]

Most of the ones I see, the connected load is 30 to 50% greater than the rating of the feeder and/or the MCC busing.

We can't determine the behavior of the pumping stations, that's why. There are times it will be 75% then sometimes 25%. Like any building, usually the demand is about 35-40% of the calculated load, this goes for offices, schools, etc.

 

[iceworm]

Most of the ones I see, the connected load is 30 to 50% greater than the rating of the feeder and/or the MCC busing.

if you had said "calculated connected load', I'd agree - because:

seen a fair amount of that too, but it is not the result of someone making a non-code approved calculation. it just sort of happens over time.

If I had to make a "good" guess, I'd be out of business. That's ALL I do is industrial stuff. ....

And yes, that too.

ice

 

[don_resqcapt19]

seen a fair amount of that too, but it is not the result of someone making a non-code approved calculation. it just sort of happens over time.

It is based on the designers understanding of the processes...the make a "guess" as to the loads that will be operating at the same time. Even newly installed MCCs often have loads that far exceed the capacity of the feeder.

 

[don_resqcapt19]

We can't determine the behavior of the pumping stations, that's why. There are times it will be 75% then sometimes 25%. Like any building, usually the demand is about 35-40% of the calculated load, this goes for offices, schools, etc.

But there is no demand factor in the code for industrial MCCs.

 

[iceworm]

It is based on the designers understanding of the processes...the make a "guess" as to the loads that will be operating at the same time. Even newly installed MCCs often have loads that far exceed the capacity of the feeder.

hummmm .... I really can't comment on the quality of designers/design your customers tolerate.

ice

 

[don_resqcapt19]

hummmm .... I really can't comment on the quality of designers/design your customers tolerate.

ice

I have never seen a main trip on one of these because of the load. The electrical designers work with the process designers so they have an idea of what the real loads are. They know that the loads will not be all on or all at full load at the same time, but the loads are not interlocked to prevent them from all being on at the same time, and without interlocks this type of design is not code compliant but works just fine in the real world.

Over the years, there have been a number of code changes for industrial occupancies, where the substantiation was, "we have been doing it that way for years without any problems".

 

[wsbeih]

Typically load list estimating for industrial is a bit involved. There are guidelines per IEEE red book.
in summary coordinating with process engineer is essential to identify loads expected to run at the same time. see the following link for industrial load list estimate:
http://www.openelectrical.org/wiki/index.php?title=Load_Schedule

Sizing Equipment on connected load basis would be so much costly and in fact unrealistic.

 

[Tony S]

As the OP is hoping to add more loads having a load analysis done would be the sensible way to go.

I just hope he doesn’t find himself in the position I did after being away from work for three months. In that time another 300HP had been added to a MCC. The feeder cables were PILC as was the custom in the 60’s and due to various plant upgrades over the years were over the design limit before the new load was added. I took the back off the MCC incomer to check the feeders for temperature.
The bitumen used to seal PILC was liquid, it melts at 155°C.

PILC (paper insulated lead covered)