Commercial receptacle loads

[shermjw]

Gentlemen:

I am entering the electrician field and am in training. We have been reviewing the commercial load calculation process and I was wondering about receptacle load calculation, in particular. I am having a problem figuring out how the receptacle count is derived. In residential, square footage/VA, receptacles per linear feet etc. are pretty well spelled out, but the commercial side is a different animal. It seems that a raw receptacle count is supplied and the 180VA @ strap is used. However, I am wondering how the count per area, room, etc. is established. It seems vague, other than looking at the bldg. prints and doing a manual count
For example, a hospital patient bed requires 6 receptacles for each bed, but I cannot find an NEC derived formula such as :
# of beds * # of rooms * 180VA = total receptacle VA load
OR
For a 70'X65' bldg., the receptacle count formula is :
70' X 65' X 180VA X 1.25 = continuous load receptacle count. It produces a very high count!

The code for office and bank receptacles references the 1VA @ sq. ft., so that covers some of the issue, but it leaves me a little puzzled. I personally am enjoying the "math behind the method" aspect of this field, so getting answers like this are important to me. From what I have seen so far, much hard work and care have been applied to the code, so I am taking this very serious and with great respect. Please shed some light on this newbie and I will be grateful.

Thanks
shermjw

 

[LarryFine]

Sherm, welcome to the forum!

The simple answer is that there aren't general receptacle placement requirements in non-residential installations.

Plans and specs are all there are. Receptacles are placed where they're needed per the customer and the designer.




Oh, one more thing: Don't call us gentlemen; it's confusing. :grin:

 

[iwire]

We have been reviewing the commercial load calculation process and I was wondering about receptacle load calculation, in particular. I am having a problem figuring out how the receptacle count is derived.

By counting.

Really, the NEC requires very few receptacles in a non-dwelling unit.

You might have a 300,000 sq ft warehouse with 6 receptacles so the count is 6, on the other hand you might have a 150 sq ft kiosk in the mall that sells small lamps and has 100 receptacles so the count would be 100.

Once you get into commercial the NEC relies much more the designer to make sure the electrical system is adequate for the use.

 

[erickench]

It's done by rule of thumb. Sometimes there are standard design requirements that are used as a basis to place receptacles. You're not a designer so don't worry about that. As for hospitals there is no such formula just the requirement spelled out in NEC 517.9(B)(2). Again it is up to the client and his designer to determine the number of hospital beds.

 

[kwired]

It's done by rule of thumb. Sometimes there are standard design requirements that are used as a basis to place receptacles. You're not a designer so don't worry about that. As for hospitals there is no such formula just the requirement spelled out in NEC 517.9(B)(2). Again it is up to the client and his designer to determine the number of hospital beds.

Receptacle placement may be done by rule of thumb, load calculations are not. The question was about calculating the load.

I am not a designer either but do many smaller projects and usually am forced to be the designer on these. They are often design as you install or at least after you show up to install and before you actually do install. If I don't do it one of my competitors will and then he gets to do the job.

 

[shermjw]

Much better

Much better

Thanks for clearing up the confusion on my part. I had a feeling that I was overthinking the problem. I will relay this to my fellow students as well.
Take care and be safe.

 

[kearycrew@yahoo.com]

I am taking a license prep course and can`t fiind where in the code book it shows how to determine the total connected load for 32 receptacle service loads used for eight hours each day in a commercial building is ??? volt amps