Demand Factors

[Danielt]

All the plans I see from electrical engineers have the load calculations on the panel schedules, with "Demand Factor" percentages that don't appear, as far as I see, in the NEC.

They are very unlike the calculations in the Code, that we used on our tests since I started.
I found one source for information about this:

Demand Factor, Diversity Factor, Utilization Factor, Load Factor

Energy management: Demand Factor, Diversity Factor, Utilization Factor, Load Factor, Utilization Factor, and Coincidence Factor.

electrical-engineering-portal.com

Do we, as plan reviewers and Master electricians, just assume these calculations are correct? An EE stamp, and we accept the load calculations?
I certainly don't want to take the time to calculate a whole building just to check behind them.
Am I making a big deal out of nothing?

 

[RWC/NC.]

Well, my answer would be, I'd probably just check behind him (EE 's math) on the numbers that he's provide. Reasoning in saying this, most every set of Job Specifications that I've encounter (Division #15 Mechanical & Division #16 Electrical) most all have denoted common term (or equal) embedded after preferred manufacturers apparatus decription, listed in Job Specifications, per the applicable Division. If there's an excepted change per the Engineer of (or equal) would you have this accepted change (submital approval) on equipment, via the Mechanical or Electrical, in folder on your desk (?) Probably not.. I'd run numbers (checking his math provided) and correlating behind him w/ copy NFPA 70.

 

[electrofelon]

I never understood a lot of this nonsense of putting all this loading info on panel schedules, especially if its not an NEC compliant method. Just Provide NEC calcs if required on plans/for plan review and stop putting this clutter and meaningless nonsense on a panel schedule.

 

[Danielt]

Well, my answer would be, I'd probably just check behind him (EE 's math) on the numbers that he's provide. Reasoning in saying this, most every set of Job Specifications that I've encounter (Division #15 Mechanical & Division #16 Electrical) most all have denoted common term (or equal) embedded after preferred manufacturers apparatus decription, listed in Job Specifications, per the applicable Division. If there's an excepted change per the Engineer of (or equal) would you have this accepted change (submital approval) on equipment, via the Mechanical or Electrical, in folder on your desk (?) Probably not.. I'd run numbers (checking his math provided) and correlating behind him w/ copy NFPA 70.

I don't understand most of your response, perhaps because I am not an electrical engineer. I could check the calculations myself, but that would take an incredible amount of time.

 

[RWC/NC.]

Brother like you, I`m not a (EE) either.. You not find my name in stamp, right-handed side, of any contract documents. I'm electrician, just like you. And I would attempt in doing "his job". Are these drawings (contract documents) first draft, that you are viewing @ the office(?)

 

[RWC/NC.]

Typo..wouldn't attempt doing his job.

 

[topgone]

All the plans I see from electrical engineers have the load calculations on the panel schedules, with "Demand Factor" percentages that don't appear, as far as I see, in the NEC.
View attachment 2560751View attachment 2560751
They are very unlike the calculations in the Code, that we used on our tests since I started.
I found one source for information about this:

Demand Factor, Diversity Factor, Utilization Factor, Load Factor

Energy management: Demand Factor, Diversity Factor, Utilization Factor, Load Factor, Utilization Factor, and Coincidence Factor.

electrical-engineering-portal.com

Do we, as plan reviewers and Master electricians, just assume these calculations are correct? An EE stamp, and we accept the load calculations?
I certainly don't want to take the time to calculate a whole building just to check behind them.
Am I making a big deal out of nothing?

The sample worksheet posted looks fine. For example, receptacle loads for non-welling installs is computed as 10,000 VA+(receptacle load - 10,000VA) x 50% which is correct: 10,000 + (66,100-10,000)(0.5) = 38,500VA.
The questionable computation there is the HVAC and motor. We use 125% on those types of loads. Also, for other loads, use 70 to 80% demand factor, depending on what type of load they are (ex. Physics/ Chem lab = 70 to 80% but any lab = 32 to 37%)

 

[electrofelon]

I don't understand most of your response, perhaps because I am not an electrical engineer. I could check the calculations myself, but that would take an incredible amount of time.

Most of that schedule you posted in the OP looks like hogwash to me - at least as far as NEC compliance. Note there is no "under engineering supervision" provision in article 220. As far as whether to run with it or make waves.......Tough call. On one hand, I find calcs pretty much worthless in most situations anyway and equipment very lightly loaded so I wouldnt be too concerned. Om the other hand, it seems you are responsible and liable for the electrical installation......

 

[RWC/NC.]

I don't mean to attempt in suggesting, in how to do your job, you have my respect. But as a "Plan Examiner" does the actual intent, go beyond basics of viewing the document in assurances, of code compliance(?)

 

[mtnelect]

I am in wonder ... All of you putting everything on the line for this "Bidding Process". I started out doing this too, until a GC took me to the "cleaners". It took me five years and five attorneys to win in court. Never again .... I now only deal with owners.
There got to be a better way in the Constuction Industry.

 

[RWC/NC.]

I am in wonder ... All of you putting everything on the line for this "Bidding Process". I started out doing this too, until a GC took me to the "cleaners". It took me five years and five attorneys to win in court. Never again .... I now only deal with owners.
There got to be a better way in the Constuction Industry.

And not my intent to high-jack another individuals thread, but betting that's darn interesting story, in it's self. I surely enjoy reading it..

 

[Danielt]

The sample worksheet posted looks fine. For example, receptacle loads for non-welling installs is computed as 10,000 VA+(receptacle load - 10,000VA) x 50% which is correct: 10,000 + (66,100-10,000)(0.5) = 38,500VA.
The questionable computation there is the HVAC and motor. We use 125% on those types of loads. Also, for other loads, use 70 to 80% demand factor, depending on what type of load they are (ex. Physics/ Chem lab = 70 to 80% but any lab = 32 to 37%)

I would be much happier if this way of calculating were in the Code. When I review a set of plans and send them out, I'm saying they are Code compliant. I just don't like approving calculations I'm not 100% sure of.
Realistically, in the example above, I know the 600 amp main will never be overloaded. I'm probably being too overcautious about this.

 

[retirede]

I would be much happier if this way of calculating were in the Code. When I review a set of plans and send them out, I'm saying they are Code compliant. I just don't like approving calculations I'm not 100% sure of.
Realistically, in the example above, I know the 600 amp main will never be overloaded. I'm probably being too overcautious about this.

In that case, you can send them back and request an NEC load calc. May or may not relate to what’s on the panel schedule.

 

[jobuTupaki]

Not engineering related, but I keep seeing people refer to people as "him/his". There are many women in this field and growing - just some professional advice and something to keep in mind for future responses.

 

[Charged]

For what it’s worth the revit drafting program is doing most of the work in the example above. I doubt much thought went into it. They must of did something for some of them but for the most part it calculates per code. The receptacle demand factor looked odd to me when I first started using the software because I never see it presented that way.

 

[Mike01]

My thoughts, the panel will likely never be overloaded I have seen installations metered after install with a year or more of trended data to support the actual diversified load based on space utilization is 50% or less then the NEC calculated method for installs in healthcare, office, lab spaces, etc. of course different then a data center or some manufacturing facilities that run higher or push the limits of their service capacities. However I do not get it either how one can stamp drawings as code compliant however ignore the NEC code compliant methods for calculations and define your own diversity factors. The only way I see this is for example if the HVAC and non-concurrent loads [heating vs cooling] where you only need to use the worst case however either way that worst case is still at 100% not 75% because someone assumes the mechanical engineer always overdesigns their systems. Its interesting I see some firms around town that use NEC methods only some that have these "demand factors" not defined anywhere yet I have never seen a plan reviewer challenge the calculations and although these may be out of the box "software defaults" I hope someone somewhere is still checking them last time I checked software companies have big disclaimers about this stuff.

 

[JoeStillman]

For what it’s worth the revit drafting program is doing most of the work in the example above. I doubt much thought went into it. They must of did something for some of them but for the most part it calculates per code. The receptacle demand factor looked odd to me when I first started using the software because I never see it presented that way.

I'm told the only diversity factor Revit knows how to do on its own is the receptacles - 1st 10 kVA + 50% of the rest. Anything else is a factor applied by the designer. It's a good way to block out the non-coincident load such as heat vs air conditioning or pump and a spare.

 

[Leo Li]

The sample worksheet posted looks fine. For example, receptacle loads for non-welling installs is computed as 10,000 VA+(receptacle load - 10,000VA) x 50% which is correct: 10,000 + (66,100-10,000)(0.5) = 38,500VA.
The questionable computation there is the HVAC and motor. We use 125% on those types of loads. Also, for other loads, use 70 to 80% demand factor, depending on what type of load they are (ex. Physics/ Chem lab = 70 to 80% but any lab = 32 to 37%)

I just want know why use 125% on loads of HVAC and motor? Is thsi NFPA requires ?Thanks !

 

[Knightryder12]

Correct me if I am wrong, but there is no diversity allowed in a calculation except for kitchen and receptacle loads for a commercial building, which this looks like it is since I see labs in the calculation. All other loads have to be taken at 100% and 125% of the largest motor load.

 

[topgone]

Correct me if I am wrong, but there is no diversity allowed in a calculation except for kitchen and receptacle loads for a commercial building, which this looks like it is since I see labs in the calculation. All other loads have to be taken at 100% and 125% of the largest motor load.

When you have a feeder supplying both continuous and non-continuous loads, you have to take 125% of the continuous load plus 100% of the non-continuous loads for consideration for sizing. HVAC is considered a continuous load hence the factor of 125%.
See Article 440.32 "Single Motor-Compressor. Branch-circuit conductors supplying a single motor-compressor shall have an ampacity not less than 125 percent of either the motor-compressor rated load current or the branch-circuit selection current, whichever is greater.
Please see also Article 460.8 which specifies even a 135% sizing of conductors supplying capacitor motors.