Adding Loads to Existing Condo Building (200+ units)

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buddyshuffle

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A customer is looking to add electric ranges and electric dryers to existing units in a condominium building. The plan is to add a new panel at each floor of the building (each floor contains 9+ units) to allow for new feeds for ranges and dryers in each unit.

I've been working in 220.18 and 220.19 for load calcs, but with over 200 ranges and 200 dryers being added, I wondered if a better method could be used since Tables 220.19 & 220.18 stop far short of the 200 in both cases.

220.30 won't work because the exisiting dwelling units have only a 60A feeder which is less than the required 100A.

220.31 results in a larger estimate than 220.18/220.19 so this is also not acceptable

Any suggestions...Thanks!
 
I have a concern with this arrangement (presuming I have correctly understood what you are describing). I have a feeling that what you are describing is a code violation. But someone is going to have to help me with a code reference, as I can't find it. What I think you are saying is that each unit now has a 60 amp panel, with its own disconnecting means. What they want to do, for each unit, is provide a separate branch circuit from a panel in the hallway to serve the range, and another separate branch circuit to serve the dryer. That is, the panel in the hallway will have 9+ breakers serving the ranges in 9+ units, and another 9+ breakers serving the dryers in 9+ units. Is that right?

My concern is that a building is only allowed to have a single service. I recognize that the "service" in this case is the power coming into the building, and each unit is powered by a "feeder." So the restriction of 230.2 would not apply. But to me it just seems wrong to have one feeder for the unit's panel and two separate branch circuits from a panel outside of the unit. You will have to turn off three breakers to kill power to the unit.

Can anyone tell me if my concern is valid?

Back to your question. Both 220.18 and 220.19 (2002 version of the NEC) have the ability to handle 200+ items. Table 220.18 addresses "42 and over" dryers, and Table 220.19 addresses "61 and over" ranges. But those would only apply to the feeder that ultimately powers all of the new hallway panels. Each hallway panel will only feed power to 9 ranges and 9 dryers (or whatever the number is for that hallway panel). So you can only use that number when looking up demand factors in the tables.
 
Charlie B said:
I have a feeling that what you are describing is a code violation. But someone is going to have to help me with a code reference, as I can't find it.
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I think the reason is that by some stroke of oddness, this could be legal. But I'm tired, I could be missing it too. I too take issue with it.

I think this would only be illegal if the units were considered seperate structures. Then 225.37 could be applied.

Also, see 240.24(B).
 
Response

Response

Thanks for the concern with whether this is a code violation or not. I was also concerned. I (and others including code advisor board members) have been reviewing the code and have not found an article that doesn't allow this. I agree that it is a stange installation and ultimately the local Authority Having Jurisdiction is going to have to give his/her blessing. I hope to meet with him/her this week.

I believe that as long as everything is marked including the existing dwelling unit panels to indicate that the other circuits are located elsewhere, I do not believe that there is a code violation here.

Getting back to my original posting, I was hoping that since the quantities of dryers and ovens are SIGNIFICANTLY above the largest quantities on the demand tables, there was another method that could be used...any thoughts?

Thanks!
 
Re: Response

Re: Response

buddyshuffle said:
Getting back to my original posting. . . .
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Let me go back to my question about your original posting. No wait, I did not express it in the form of a question. Guess I'll never make it on Jeopardy. :lol:

Will you be adding a new "master" panel that will, in turn, feed all of new panels on all the floors? In other words, will there be one panel that feeds all 200+ ranges and all 200+ dryers (via smaller panels on each floor)? Are you concerned about sizing that "master" panel or sizing the panels on each floor?

The panels on each floor should be easy to figure out. The total number of ranges and dryers on any one floor panel will be well within the tables. But as to the one big panel that feeds 200+ ranges and dryers, the answer to your question is "no." There is no place you can turn to get a lower demand factor than tables 220.18 and 220.19.

A quick guess at the sizes gives me an estimate of 1000 amps to serve the dryers and 800 amps to serve the ranges. Yes that is a significant size of a panel. But you are asking it to do a very big job.
 
I also have concerns about the layout of this proposed job. Are the existing panels fed with feeders or service entrance conductors? What will you post at the existing panels to indicate that the panel will not disconnect all power to the condo?
 
thanks...

thanks...

Thanks for the responses...more details as requested...

The plan is to add (1) 200A 3-phase panel to a common area on each floor to serve the (6+) dwelling units. The feeders for these panels will originate in one of (2) existing distribution panels each rated for 1000A+.

I am actually making (2) calculations, (#1) for the feeder for several floors and (#2) the overall effect to an existing distribution panels that will be the source for the feeders serving multiple floors. The most recent calculations show that I can use a single 250A3P feeder for (3) floors and therefore (3) 200A panels.

A calculation is made for every (3) floors (each proposed feeder) to determine each feeder size and then again for the total number of appliances to get the overall load impact.

I am just making sure that there is not another method to reduce loads calculated for each (feeder and overall). Sounds like there is not...

As far as the most recent posting, the existing dwelling unit panels are fed from the same existing distribution boards mentioned above.

Thanks to all....
 
Re: thanks...

Re: thanks...

buddyshuffle said:
A calculation is made for every (3) floors (each proposed feeder) to determine each feeder size and then again for the total number of appliances to get the overall load impact.
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That makes sense.

buddyshuffle said:
The most recent calculations show that I can use a single 250A3P feeder for (3) floors and therefore (3) 200A panels.
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That does not make sense. Are you saying that from a 1000 amp panel, you will use a feeder rated for 250 amps, and it will provide power to a 200 amp panel on one floor, and to a second 200 amp panel on another floor, and to a third 200 amp panel on still another floor? Do you mean that the feeder will run from panel to panel to panel to panel? If that is the case, you have to be careful with the use of the demand factors.

Here's an example.

Let's say the first 3 floors have 6 condos each. That means a total of 18 ranges and 18 dryers.
  • The feeder going from the initial 1000 amp panel to the first floor 200 amp panel will supply 18 dryers. You can use a 40% demand factor to calculate that run.
  • The feeder going from the first floor 200 amp panel to the second floor 200 amp panel will supply 12 dryers. You can use a 46% demand factor to calculate that run.
  • The feeder going from the second floor 200 amp panel to the third floor 200 amp panel will supply 6 dryers. You can use a 75% demand factor to calculate that run.
  • You don't get to use the 40% demand factor for the entire run.
Does that make sense? Does that make your problem worse?
 
Follow up...

Follow up...

Using your example, why wouldn't you view the Feed to (3) panels as a single calculation for 18 dryers and 18 ranges. It's the feeder that we are performing a calculation on?

I understand that the panel on each floor would be calculated based on the # of loads it serves, why wouldn't the feeder to multiple floors be calculated the same way?

To help clarify, there are actually (3) calcualtions...
#1) Each Floor teo determine size of floor panel
#2) Each Feeder for 3 floors
#3) Overall load at each distribution board where Feeders originate.

I'm not really sure why I would have to lower the number of appliance as the 250A3P feeder traveled up to each floor...its the same feeder...

Make sense?
 
Re: Follow up...

Re: Follow up...

buddyshuffle said:
I'm not really sure why I would have to lower the number of appliance as the 250A3P feeder traveled up to each floor...its the same feeder...
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But it's not the same feeder. The wires will be cut and landed on the first 200 amp panel. Then a separate set of wires will be landed on the feed-through lugs, and will be run to the second 200 amp panel. That makes it a separate feeder. Similarly, the wires from the second 200 amp panel to the third comprise another separate feeder. You have three feeders, and you have to size them separately.
 
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