OVERHEAD DOORS - DEMAND LOAD

[PE (always learning)]

Hey all,

Quick question pertaining to overhead door motors for a giant million square foot factory. We have a panel with about 20 overhead door motors circuited to it and I was wondering if anyone else has had similar projects like this where they applied a demand factor or made a logical assumption that assumes not all of these doors will be running at the same time. I think realistically it would be safe to assume that half of these doors would be running at once. Please let me know your thoughts.

Best Regards

 

[Gary11734]

Hey all,

Quick question pertaining to overhead door motors for a giant million square foot factory. We have a panel with about 20 overhead door motors circuited to it and I was wondering if anyone else has had similar projects like this where they applied a demand factor or made a logical assumption that assumes not all of these doors will be running at the same time. I think realistically it would be safe to assume that half of these doors would be running at once. Please let me know your thoughts.

Best Regards

Where in the code do you find you can take a demand factor to this installation?

 

[tkb]

OMG, using common sense is a code violation. :lol:

 

[Gary11734]

OMG, using common sense is a code violation. :lol:

You should win the comment for the day with this quote!

 

[charlie b]

I believe 220.60 has your answer. It does not call for any control mechanism that would prevent too many doors from moving at the same time. It only says "where it is unlikely." I think that common sense can be put into play here. :jawdrop:

 

[Gary11734]

I believe 220.60 has your answer. It does not call for any control mechanism that would prevent too many doors from moving at the same time. It only says "where it is unlikely." I think that common sense can be put into play here. :jawdrop:

So, if what your stating is true, who is going to come up with the demand load and seal the drawing as the engineer of record?

 

[charlie b]

So, if what your stating is true, who is going to come up with the demand load and seal the drawing as the engineer of record?

I would do it, except that I never had a license in the OP's home state. :happyno: I would base my design choice on information I can learn from the owner / operator. I would ask such questions as,

• Are the doors opened once in the morning and closed in the evening, or do they get opened and closed as trucks arrive to deliver or remove goods?
• How long does it take for a door to go fully open or fully closed?
• What is the motor size for the doors (i.e., are they all the same or are some larger than others)?
• Are the doors operated automatically (e.g., the "open" signal is generated by a truck parking in the outer bay), or is each door opened or closed by a person pushing a button?
• Are the doors always operated by one person walking from door to door (which would limit operations to one door at a time), as opposed to by anyone working at one central operating station (which could allow simultaneous operation of all doors)?
• In the winter or summer, does the comfort level of the persons working inside the building depend on keeping the doors closed at all times other than when they need to be open in order to transfer goods?

That's a start. I would ask more questions, but this gives you a potential basis for my design choices.

 

[charlie b]

I should admit that I have, on occasion, including on this forum and in my real job, taken the opposite viewpoint on the treatment of non-coincident loading. For example, I see a difference between the present discussion and a hypothetical building that has two large motors that drive mechanical equipment. If the owner wants me to treat the two motors as non-coincident, thereby allowing for a smaller service rating, and assures me that they would never need to operate the two at the same time, I am likely to call for some type of interlock. The difference is related to two large motors as opposed to 20 smaller motors.

By the way, this whole discussion may prove to be academic. If the motors are as small as I imagine them to be, the total load on the panel will not be significantly changed by using a demand factor. Assume, for example, you have 20 motors, each rated 1/2 HP, each served at 208 volts single phase. The total current is 108 amps. The minimum panel rating you can get with 42 positions is higher than that (I am guessing 125 amps). Using whatever demand factor your fancy leads you to will not allow you to select a panel that has a lower rating.

Using this same example, the total load on 20 motors is about 23 KVA. Assigning a demand factor is not likely to drop your service size from one value to the next lower standard rating.

 

[Gary11734]

I should admit that I have, on occasion, including on this forum and in my real job, taken the opposite viewpoint on the treatment of non-coincident loading. For example, I see a difference between the present discussion and a hypothetical building that has two large motors that drive mechanical equipment. If the owner wants me to treat the two motors as non-coincident, thereby allowing for a smaller service rating, and assures me that they would never need to operate the two at the same time, I am likely to call for some type of interlock. The difference is related to two large motors as opposed to 20 smaller motors.

By the way, this whole discussion may prove to be academic. If the motors are as small as I imagine them to be, the total load on the panel will not be significantly changed by using a demand factor. Assume, for example, you have 20 motors, each rated 1/2 HP, each served at 208 volts single phase. The total current is 108 amps. The minimum panel rating you can get with 42 positions is higher than that (I am guessing 125 amps). Using whatever demand factor your fancy leads you to will not allow you to select a panel that has a lower rating.

Using this same example, the total load on 20 motors is about 23 KVA. Assigning a demand factor is not likely to drop your service size from one value to the next lower standard rating.

Hi Charlie,

I give you credit in this day of litigation mentality.

You are acting as a real engineer doing his job as a professional. That is how it should be...

Here in Florida, it got so bad from lawyers suing Engineers for so-called design errors, they no longer will stamp submittals with an "approved" sticker. Now it says, "reviewed"

Too bad we live in this but it is what it is...

 

[charlie b]

Here in Florida, it got so bad from lawyers suing Engineers for so-called design errors, they no longer will stamp submittals with an "approved" sticker. Now it says, "reviewed."

It's been that way for a long time in every engineering company I have worked for. And I think it is appropriate. The contractor is responsible for providing materials and performing labor in accordance with the contract. The engineer is not a party to the contract, and therefore cannot change it. If the contractor submits something that is not what the specs called for, and if the engineer stamped the submittal as "approved," the contractor could make the claim that he no longer is required to comply with the specs.

 

[Gary11734]

It's been that way for a long time in every engineering company I have worked for. And I think it is appropriate. The contractor is responsible for providing materials and performing labor in accordance with the contract. The engineer is not a party to the contract, and therefore cannot change it. If the contractor submits something that is not what the specs called for, and if the engineer stamped the submittal as "approved," the contractor could make the claim that he no longer is required to comply with the specs.

I know. We have this tug of war between the Engineer and Contractor. I used the phrase as I am " the installer". It's not my job to make a code compliant project when the Engineer fails to.

That being said;

These days, it's who has more lawyers and can last the longest in litigation. And I thought it was about building the project and doing a good job when I first went into business.

I always worked well with the Engineers. It's better to be on the same side and try to put the project together. It always worked well for me.

We could always find common ground to make the project work and everyone would make a profit...

 

[steve66]

I agree with Charlie that you can use a demand load.

But are the doors really that much of a load? Is it really going to save that much in cost?

At any rate, I would leave some spare capacity at the panel. If the owner comes back later and says they want to add some fans, (or heaters, or dock levelers, or anything else), you probably don't want to tell him it was engineered down to the decimal point, and there isn't any spare capacity.

Its usually a good idea to try to stick with 100 and 200 amp feeds, with maybe an occasional 60A or 150A where it seems appropriate.

Of course, there are exceptions for clients that don't want to spend a dime more than they have to. Then it's on them if there isn't any spare capacity.

 

[topgone]

I agree with Charlie that you can use a demand load.

But are the doors really that much of a load? Is it really going to save that much in cost?

At any rate, I would leave some spare capacity at the panel. If the owner comes back later and says they want to add some fans, (or heaters, or dock levelers, or anything else), you probably don't want to tell him it was engineered down to the decimal point, and there isn't any spare capacity.

Its usually a good idea to try to stick with 100 and 200 amp feeds, with maybe an occasional 60A or 150A where it seems appropriate.

Of course, there are exceptions for clients that don't want to spend a dime more than they have to. Then it's on them if there isn't any spare capacity.

I agree. This happens most of the time! Explain that to the client and go home with the money.