Demand Calculations for storage area and office

[mull982]

I have been asked to oversee a project for putting together the electrical design for a new small office/warehouse that will be located in a structure located in our existing industrial facility. The final design will be produced and stamped by and enginner that will review this but in the mean time I want to try to put togther some numbers myself as an exercise in creating a preliminary design.

Does this design need to be stamped by a PE, or can a licenesed electrical contractor put together the design? Not that I would, but could a plant EE as myself finalize this design and submit it for permitting?

I have attached the general layout of the small area I am looking at if anyone cares to comment. I was curious the best approach to take for coming up with the demand and making assumptions for certain things that are shown without great detail yet.

What approach would you take for coming up with these demand calcs and final circuit designs. Here are a couple of my thoughts:

1) There is a bathroom shown which I believe based in the NEC the bathroom needs seperate designated circuits with gfi protection. Does each of the two bathrooms located next to each other need seperate designated circuits?

2) For the lighting should we first determine a number of fixtures, or should a square footage calculation be performed with 3VA per sq ft as I've seen before? How to divide up the circuits. Same with receptacles?

3) There will be some outlets shown for welding receptacles etc.. What is a good rule or procedure for coming up with ratings for these receptacles without knowing the type of equipment that will be plugged in?

4) There is an A/C unit shown as a 3-ton unit. Without knowing the specifics of this unit can a load assumption be made from this size?

 

[LarryFine]

Whether you can do the drawings yourself will be up to your local building department. Assumptions are bad. By the way, there is no attahment.

1. Nope. The two baths need not even have a circuit for both. Put the receptacles (which are optional) on a receptacle circuit, and the lights on a lighting circuit.

2. It depends on whether the actual lighting installation will be greater than the NEC minimum. Use whichever is more.

3. You need either actual equipment data or your best guesses from Art. 220.

4. You can get kinda-sorta close if you know the voltage, but I wouldn't waste the time. Wait until you get real data.

 

[mull982]

By the way, there is no attahment..

Sorry forgot the attachment.

1. Nope. The two baths need not even have a circuit for both. Put the receptacles (which are optional) on a receptacle circuit, and the lights on a lighting circuit.

O.k. but they do need a seperate circuit from the rest of the areas correct? I forget what section requires seperate circuit for bathroom.

2. It depends on whether the actual lighting installation will be greater than the NEC minimum. Use whichever is more.

What section is this in? Is this the 3 VA/sq ft rule? Does the same apply for receptacles?

4. You can get kinda-sorta close if you know the voltage, but I wouldn't waste the time. Wait until you get real data.

I guess I'll have to find out voltage and make a best guess for now. Any references of where to find A/C unit loads at a given voltage for a given tonnage?

 

[LarryFine]

By the way, there is no attahment.

Sorry forgot the attachment.

That's okay; I forgot the 'c'.

O.k. but they do need a seperate circuit from the rest of the areas correct? I forget what section requires seperate circuit for bathroom.

No, and none.

What section is this in? Is this the 3 VA/sq ft rule? Does the same apply for receptacles?

All this stuff is in Art 220.

I guess I'll have to find out voltage and make a best guess for now. Any references of where to find A/C unit loads at a given voltage for a given tonnage?

Well, a pile (pun intended) of rules-of-thumb have been posted here, but the "how can we put #14 on a 30a breaker?" discussions should tell you that you're only guessing without the real data.

When someone wants a price for something like this, I tell them I can either make expensive (to them) guesses, or wait for the information - in writing - about each piece of equipment.

 

[construct]

Does this design need to be stamped by a PE, or can a licenesed electrical contractor put together the design? Not that I would, but could a plant EE as myself finalize this design and submit it for permitting?

In Missouri, if you were licensed by the state as a Professional Engineer, then you could sign and seal the drawings. Also in Missouri by State Statutes, if the structure contains more than 20,000 cubic feet or more than 9 occupants, the drawings are required to be done by a Professional Engineer with his seal and signature.

 

[mull982]

O.K. I started creating the line items for adding up the loads using the optimal demand method (assuming that is o.k.) and came up with the following line items for adding up the total load

1) Lighting and Receptacles - using 3 VA / sq ft
2) Appliances and / or tools - Circuits for power tools in shop
3) Motors - Circuits for fan and blower motor shown
4) Heating / AC - Largest of the Heating and A/C loads.

Does this look like the total number of line items I need for this performing this calculation, or am I leaving something out?

Now I would just have to go about finding the information/loads for lines 2-4.

 

[mull982]

3. You need either actual equipment data or your best guesses from Art. 220.

What sectioni of Art. 220 would you suggest for circuits for such things as welders, grinders, lathes, etc... that may be plugged in to an outlet?

 

[mull982]

I have sent out a request for the HVAC load, and the motor loads and am waiting on this information.

Once I have all of this then I assume I apply the percentages to the first XX kVA etc.. as outlined in Art 220.

The one thing that I'm held up on is a good design choice for determining the loads for the tool outlets I want to install? I guess there could be a variety of tools plugged into these outlets so I'm looking for a good safe number.