Connected Load and Demand Load - Try searching already

[malachi constant]

I am not missing that fact at all. 220.14(C) tells us to calculate the outlet load for motors in accordance with 430.22 and 430.24. That means that the 25% factor is already part of the "connected" load. The same number is carried through to the "demand" load in Part III.

For instance, lets take a look at a panel with nothing but motors. Say a panel that had four branch circuits feeding four 5HP, 208V, 3ph motors. Per 220.14(C), each motor branch circuit has a load of 7,521VA (as calculated per 430.22.) The total connected load on the panel (the sum of all the branch circuit loads) is 4*7,521VA=30,084VA.

Now lets apply the demand factors for the panel feeder, from Article 220 Part III. 220.50 directs us to 430.24, which tells us that the load would be (16.7A*1.25 + 3*16.7A) * 208V * 1.732 = 25,570VA. The load after the demand factors of Article 220 Part III are applied is smaller than the load calculated for the individual branch circuits per Part II of Article 220.

Good example, in that it points to where we disagree.

You are correct that an individual branch circuit would have a load of 7521VA. But you are calling the loads this:
CONNECTED: 4*(16.7A*1.25*208*1.732)=30,084VA.
DEMAND: (16.7A*1.25 + 3*16.7A) * 208V * 1.732 = 25,570VA.

Whereas I would call them this:
CONNECTED: 4*(16.7A*208*1.732)=24,065VA.
DEMAND: (16.7A*1.25 + 3*16.7A) * 208V * 1.732 = 25,570VA.

Or again, maybe it is semantics, because we get the same "demand" load at the end of the day. I would never show a connected load of 30kVA in this scenario.

In the above example, the way my panel spreadsheet is set up, for one of those motors you would enter a load of 6016VA (2005VA per each of three phases), the spreadsheet figures out the amperage and multiplies it by 1.25 to get a breaker size. (For simplicity's sake it does this regardless of whether it is a motor load, lighting load, receptacle load, non-continuous load, etc. I don't think this conservative approach affects anything in practice.) Then I would enter the load into three other breakers. The "connected load" in my spreadsheet would be 6,016*4=24,065VA (as shown above). Then my spreadsheet figures out what the largest motor load on the panel is (whether it is actually on the panel or subfed from a different panel), multiplies that number by 0.25, and adds it in. So I would end up with a "demand load" on that panel of 25,570VA.

 

[JoeStillman]

Or it means that the calculated demand load really is higher than the actual connected load. Please see my post #5 above. In each case for which the demand was the higher value, that particular schedule had nothing but motors.

So let me ask you to do the following math: Put five motors on a panel. Count four of them at 100% and one of them at 125%. Which value will be higher: demand :happyyes: or connected?:happyno:

Your question answers itself. 125% is always greater than 100% (At least, outside of Washington DC.)

It seems you and I don't use the same definition of "demand load." It's interesting that the Code defines "Demand Factor" in terms of the "demand of a system", but doesn't define what the "demand of a system" is :?. You would be hard put to find a tighter tautology. It also does not give a name to the 125% factor found in 210, 215 and 430.

I think of demand as the running load - same as you see on a commercial electric bill. It is the load you have left after you've applied a "demand factor" as in 220.42, 53, and 55; and all those factors are less than 1. What you're referring to is what I call "wire sizing amps." The code refers to continuous and non-continuous loads, but not "demand load", just "demand factors" for various types of loads. To me, demand load is always less than connected load. And connected load is always less than wire sizing amps.

 

[malachi constant]

Joe, I'll buy that.

I think we have three terms here:
Step 1, "connected load", I think we mostly are all in agreement on what that is.
Step 2, "demand load", from here on out I will defer to your definition, as it makes logical and linguistic sense, and reflects the terminology used in code. (In the past I have not seen this as a separate step, and have integrated it directly into the next one - therefore called them one and the same.)
Step 3, Instead of "wire sizing amps" as you suggest, I propose referring to that one as "calculated load". I believe some in this thread are using "demand" and "calculated" interchangeably as step 2.

Note I'm not at all proposing a code change here. Just trying to reconcile what terms mean in my own head with what they mean in those of others so that I can communicate better.

 

[JoeStillman]

Joe, I'll buy that.

I think we have three terms here:
Step 1, "connected load", I think we mostly are all in agreement on what that is.
Step 2, "demand load", from here on out I will defer to your definition, as it makes logical and linguistic sense, and reflects the terminology used in code. (In the past I have not seen this as a separate step, and have integrated it directly into the next one - therefore called them one and the same.)
Step 3, Instead of "wire sizing amps" as you suggest, I propose referring to that one as "calculated load". I believe some in this thread are using "demand" and "calculated" interchangeably as step 2.

Note I'm not at all proposing a code change here. Just trying to reconcile what terms mean in my own head with what they mean in those of others so that I can communicate better.

I often see the term "Wire Sizing Amps" on HVAC equipment cuts. They always give me WSA and MOCP (maximum overcurrent protection), but look at me like I have two heads when I ask for RLA (compressors) and FLA (fans). It's frustrating to try to determine a multi-motor "calculated load" when all you have is WSA for a building full of condensing units.

 

[kingpb]

Not looking for a debate, but demand will always be less than or equal to the connected. Load is load, i.e. KVA is KVA.

I believe there is some confusion going on here that the load value used for SIZING the equipment and conductors has nothing to do with connected load, i.e. sum total of all the loads physically connected, or the demand load, i.e. the maximum possible running load under any circumstance.

They are three separate values.

 

[david luchini]

Good example, in that it points to where we disagree.

You are correct that an individual branch circuit would have a load of 7521VA. But you are calling the loads this:
CONNECTED: 4*(16.7A*1.25*208*1.732)=30,084VA.
DEMAND: (16.7A*1.25 + 3*16.7A) * 208V * 1.732 = 25,570VA.

Whereas I would call them this:
CONNECTED: 4*(16.7A*208*1.732)=24,065VA.
DEMAND: (16.7A*1.25 + 3*16.7A) * 208V * 1.732 = 25,570VA.

Or again, maybe it is semantics, because we get the same "demand" load at the end of the day. I would never show a connected load of 30kVA in this scenario.

Well, we seem to agree that when filling out a branch circuit panelboard load schedule, you would sum the branch circuit loads in the panel to get the "connected load." In other words, the connected load on a panel or feeder is the sum of the branch circuit loads on that panel or feeder.

My question to you would be, when you are filling out the branch circuit loads why wouldn't you use the method proscribed in Part II of Article 220 of the code? The feeder load calculation procedure in 220.40 says that the calculated load on a feeder shall not be less than the sum of the branch circuit loads supplied, as determined by Part II of Article 220, after any applicable demand factors have been applied. In the example above, you do not calculate the branch circuit load for each motor in accordance with 220.14(C).

In the above example, the way my panel spreadsheet is set up, for one of those motors you would enter a load of 6016VA (2005VA per each of three phases), the spreadsheet figures out the amperage and multiplies it by 1.25 to get a breaker size. (For simplicity's sake it does this regardless of whether it is a motor load, lighting load, receptacle load, non-continuous load, etc. I don't think this conservative approach affects anything in practice.) Then I would enter the load into three other breakers. The "connected load" in my spreadsheet would be 6,016*4=24,065VA (as shown above). Then my spreadsheet figures out what the largest motor load on the panel is (whether it is actually on the panel or subfed from a different panel), multiplies that number by 0.25, and adds it in. So I would end up with a "demand load" on that panel of 25,570VA.

This illustrates my point in Post #14, your spread sheet is multiplying the sum of your loads by 125% to figure for continuous load, and you are calling this "demand load." In your spread sheet, you are entering motor branch circuit loads that are smaller than the Code tells you to include (so that the spread sheet can automatically calculate 125% of the largest motor for the feeder demand) but this is giving you a "connected load" for the panel which is smaller than the Code says it should be.

If you look at the demand factors in Parts III, IV and V of Article 220, you will see that ALL of the demand factors are 100% or smaller. If you apply these demand factors to the sum of all the branch circuits loads on a feeder, as determined by Part II of Article 220, then the "demand" load will always be equal to or smaller then the "connected" load.

 

[malachi constant]

Let's start over with the more simple example of lighting. Say you have a 208V/3P main service to a commercial building that for the sake of this example contains only lighting. Thirty 120V lighting circuits, spread equally over each phase, each breaker with 1000VA of load.

Tell me where we disagree:
1. Start with 220.40. Move on.
2. 220.42. Lighting demand factor of 100% applied.
3. So each branch circuit has 1000VA of connected load on it.
4. 1000VA / 120V = 8.3A. To get the branch circuit feeder and OCPD we look to 215, which says a continuous load must be multiplied by 125%. So 8.3A x 1.25 = 10.4A. If there was an 11A breaker we could use it here, but as we live in a world where this is not readily available we'll put it on a 15A or 20A breaker.
5. Total "connected load" on the panel is 30 x 1000VA = 30,000VA. No demand factor applied here.
6. 30,000VA / 208V / 1.732 = 83A.

Holy smokes. I think I found where I've been led astray. I thought the next step is you go to 215 (or some other article?) and size the panel feeder by multiplying all your non-continuous loads by 100% and your continuous by 125%. But 215.1 says this article is only for sizing BRANCH CIRCUIT loads, not FEEDERS to PANELS or MAIN SERVICES. How I would have done the next step is this:

7. <For some reason...> Multiply all your non-continuous loads by 100% and your continuous loads by 125%. 30,000VA x 125% = 37500VA -> 104A, and voila you need a minimum 125A panel.

Have I been doing this wrong? Can you size this panel off the 83A connected load without applying the 125% continuous factor? Could this panel be a 100A panel? If so I have been taught incorrectly, and my spreadsheets have some issues, and apologies will be forthcoming for my haughtiness.

 

[david luchini]

Let's start over with the more simple example of lighting. Say you have a 208V/3P main service to a commercial building that for the sake of this example contains only lighting. Thirty 120V lighting circuits, spread equally over each phase, each breaker with 1000VA of load.

Tell me where we disagree:
1. Start with 220.40. Move on.
2. 220.42. Lighting demand factor of 100% applied.
3. So each branch circuit has 1000VA of connected load on it.

I think you've already gone astray here. You seem to be applying the feeder demand factors to branch circuits.

4. 1000VA / 120V = 8.3A. To get the branch circuit feeder and OCPD we look to 215, which says a continuous load must be multiplied by 125%. So 8.3A x 1.25 = 10.4A. If there was an 11A breaker we could use it here, but as we live in a world where this is not readily available we'll put it on a 15A or 20A breaker.

You would go to Article 210 to size the branch circuit conductors, not to Article 215. Article 215 is for Feeders, not Branch Circuits.

5. Total "connected load" on the panel is 30 x 1000VA = 30,000VA. No demand factor applied here.
6. 30,000VA / 208V / 1.732 = 83A.

This is where you would apply the demand factors. The FEEDER to the panel has a load of 30kVA. The FEEDER gets the demand factors. The demand factor for lighting is 100%, so the load stays at 30kVA.

Holy smokes. I think I found where I've been led astray. I thought the next step is you go to 215 (or some other article?) and size the panel feeder by multiplying all your non-continuous loads by 100% and your continuous by 125%. But 215.1 says this article is only for sizing BRANCH CIRCUIT loads, not FEEDERS to PANELS or MAIN SERVICES. How I would have done the next step is this:

You had it right in the first place. Article 215 is for the sizing of FEEDERS, not BRANCH CIRCUITS.

7. <For some reason...> Multiply all your non-continuous loads by 100% and your continuous loads by 125%. 30,000VA x 125% = 37500VA -> 104A, and voila you need a minimum 125A panel.

Have I been doing this wrong? Can you size this panel off the 83A connected load without applying the 125% continuous factor? Could this panel be a 100A panel? If so I have been taught incorrectly, and my spreadsheets have some issues, and apologies will be forthcoming for my haughtiness.

You haven't been doing this wrong (except that you would need a feeder OCPD that is minimum 110A, not 125A.) Your feeder load after applying your demand factors is 30kVA. It is all continuous load. Therefore the minimum feeder ampacity would 104A and the minimum feeder OCPD would be 110A.

Lets say that after applying demand factors, the load is 30kVA, but 15kVA is continuous and 15kVA is non-continuous. Then the minimum feeder ampacity would be 93.7A, and the minimum feeder OCPD size would be 100A.

Or if after applying demand factors, the load is 30kVA, but it is all non-continuous. Then the minimum feeder ampacity would be 83A, and the minimum feeder OCPD size would be 90A.

But in all 3 cases, the load is 30kVA.

 

[kwired]

I still don't see how demand can be more than connected. I also have not seen a demand factor of more than 100%, someone please point out where some of these are if they exist.

220.14(C) points us to 430.22 and 430.24, yet both of those sections are about minimum conductor size and not about demand issues.:? How does one call that a demand factor?

 

[charlie b]

220.14(C) tells us to calculate the outlet load for motors in accordance with 430.22 and 430.24. That means that the 25% factor is already part of the "connected" load. The same number is carried through to the "demand" load in Part III.

This is where we disagree. But it is a matter of terminology. We are in the middle of the classical debate that I like to characterize as follows:

• The first person says, ?The sky is blue.?
• The second person says, ?No you are wrong, the grass is green.?
  

Using your 5HP motor example, I believe you and I would both come up with the same design choices for branch circuit wiring and for panel sizing. But I would use the phrase ?connected load? to refer to the 16.7 amp (6,012 VA) load on each branch circuit, not the 16.7 amps times 125% (7,515 VA) that is used to determine the branch circuit wiring. I have ?connected? a 5 HP motor to the circuit. I have not ?connected? a 5 x 125% HP motor.

That is why my panel schedule would show a ?connected load? of 4 times 6012, or 24.0 KVA, while at the same time showing a ?demand load? of 7515 plus 3 times 6012, or 25.5 KVA. So if the OP comes across a panel schedule from a design of mine and sees a demand load that is higher then connected load, this will be the reason. If anyone sees the situation differently, it is not because one of us is right and the other is wrong, it is because we are using the words differently.

Please note that the NEC does not define either ?connected load? or ?demand load.? So neither one of can say that ?only I am right in my use of the phrases.?

 

[charlie b]

I still don't see how demand can be more than connected.

It is all in the manner in which you are using those two phrases. Please see my post immediately above this one.

 

[kwired]

It is all in the manner in which you are using those two phrases. Please see my post immediately above this one.

I see what you are getting at. That said your demand load and connected load on your panel schedules are meaningless if they are not defined, JMO.