Service Calculations and Article 220.87

[Joe S.]

I am starting an electrical design to move people and equipment from a leased buildng to an existing, unoccupied owned building. I have completed my load summary based on connected load (using nameplate information) of the existing owned building loads and the connected load moving to the owned buildng, and the total is more than double the existing service. I have been asked to try to "make it fit" into the existing owned building service by using the peak demand for the leased building's service from the electric utility's data for the past year and substituting this number instead of using connected load for the equipment moving over. What are your thoughts on this. I am uncomfortable signing and sealing drawings that "make it fit" this way and believe that using the connected load is the proper way to go. I was thinking NEC 2005 Article 220.87 can't be used in this manner. City building inspectors and fellow P.E.'s what do you think?

 

[charlie b]

I agree with your concern, but I will say that 220.87 can be used in this situation. You can take a year's worth of the utility load data (presuming it includes peak values, and not just KW-Hr info). If that building has been unoccupied for a year, that is OK. It will just mean that the utility data will tell you there is not much load being served at present. Here's the important thing, however: You have to add 25% to the max demand as reported by the utility, and then you add the new load. That means you add all the (connected) load that will be moved into the building. If you have reason to know that not all of the new load will be operating at the same time (e.g., if the control system will only allow two of the three installed pumps to run at the same time), then you can subtract the non-coincident loads from the total. When you do all that, if your result is higher than the service capacity, you must take some action to resolve the overload condition. You cannot create an overload by trying to "fit it in," as had been suggested. See 220.87(2).

 

[Joe S.]

This is not the typical 220.87. I am being asked to use utility peak from electric bills from the location being moved out of for the new load. To re-word I am being asked to not use connected load for my added load.

 

[rcwilson]

As I understand it, you have at least a year's worth of utility data including peak demand for the equipment and processes that will be moved to the "new" building. You also have utility data for the "new" building's loads such as heat and lights.

That means you have actual, real world data for the two sets of loads which will be combined in the new building.

If that is correct, I would not be concerned unless the sum of the two peak demands was close (>80%) to the service rating. But I would also verify that the operation in the future will be the same as it was in the past. Will two lines be operating instead of one? Will the new space allow more machines to run at the same time? Was last year's power use down because business was slow and machines only ran at half speed?

Another consideration is the cost of a service upgrade now compared to the future when production has to be shut down for a few days during the change. If there is a chance of future load growth, upgrading now may be more economical.

 

[Joe S.]

Thanks for the posts guys. As Bob calls it, my "new" bldg hasn't been occupied since the company bought it 6 years ago, and when it was occupied many years ago it was a very different use. So, I was using connected load for lights, HVAC, elevator, etc. When I add the utility data peak demand for the equipment moving in, to the bldg connected load, I am still over the existing service. The only likely way I may be under the service is to use peak demand for both, but I haven't been comfortable with the idea of using utility bills from 6+ years ago. Your thoughts one more time?

 

[charlie b]

You say that the building has not been occupied for six years. Does that mean that the electricity has been turned off for all that time? In other words, you have utility records from six years ago, but do you have utility records for the past year? I believe the code requires you to use the maximum demand over a recent 12 month period, even if the words in the code do not explicitly state that as being a requirement.

But let me presume for a moment that you do have utility data for the previous year, and that the data includes the peak demand for that period. I believe you can start with that value, add 25%, and make a ?correction on the basis of engineering judgment? that would account for the fact that the building has not been occupied (i.e., that lights and ventilation were used at a minimal rate). That can be your starting point. For the amount of load to be added, I believe you can use the peak demand of the equipment that is being moved to the new location. I am not certain how you can determine that value, however. If all you have is the utility data (i.e., no meters directly measuring the equipment itself), then the peak demand will include the lights and ventilation for the ?old building.?

 

[T.M.Haja Sahib]

If the building you are moving into is provided with a generator catering to its entire load,the maximum demand of the building may be calculated from the load the generator is taking over a period.

 

[iwire]

If the building you are moving into is provided with a generator catering to its entire load,the maximum demand of the building may be calculated from the load the generator is taking over a period.

Perhaps, but it will be at least a 30 day period. See exception.

220.87 Determining Existing Loads. The calculation of a
feeder or service load for existing installations shall be
permitted to use actual maximum demand to determine the
existing load under all of the following conditions:

(1) The maximum demand data is available for a 1-year
period.

Exception: If the maximum demand data for a 1-year period
is not available, the calculated load shall be permitted
to be based on the maximum demand (measure of average
power demand over a 15-minute period) continuously recorded
over a minimum 30-day period using a recording
ammeter or power meter connected to the highest loaded
phase of the feeder or service, based on the initial loading
at the start of the recording. The recording shall reflect the
maximum demand of the feeder or service by being taken
when the building or space is occupied and shall include by
measurement or calculation the larger of the heating or
cooling equipment load, and other loads that may be periodic
in nature due to seasonal or similar conditions.

(2) The maximum demand at 125 percent plus the new
load does not exceed the ampacity of the feeder or
rating of the service.

(3) The feeder has overcurrent protection in accordance
with 240.4, and the service has overload protection in
accordance with 230.90.

 

[hmspe]

If this is a job in the Phoenix metro area I'd suggest you "just say no". Most of the plans reviewers in the municipalities here would not like a calculation based on high demand where they are moving from.

 

[bob]

When I add the utility data peak demand for the equipment moving in, to the bldg connected load, I am still over the existing service. The only likely way I may be under the service is to use peak demand for both, but I haven't been comfortable with the idea of using utility bills from 6+ years ago. Your thoughts one more time?

If you are already over the service capacity when you use the demand reading for the building
being moved from to the building you are moving to, you have no choice but to increase the service. The code provide you with the information in 220 for the vacant building. Lts 3 w/sqft,
A/C 100%, kitchen/break room facilities, computers etc. You can't be under on the service size. It tends to turn to smoke. The code requires up to date demand readings if you use this method and don't forget the added 25%.

 

[Andrzej]

I agree with your concern, but I will say that 220.87 can be used in this situation. You can take a year's worth of the utility load data (presuming it includes peak values, and not just KW-Hr info). If that building has been unoccupied for a year, that is OK. It will just mean that the utility data will tell you there is not much load being served at present. Here's the important thing, however: You have to add 25% to the max demand as reported by the utility, and then you add the new load. That means you add all the (connected) load that will be moved into the building. If you have reason to know that not all of the new load will be operating at the same time (e.g., if the control system will only allow two of the three installed pumps to run at the same time), then you can subtract the non-coincident loads from the total. When you do all that, if your result is higher than the service capacity, you must take some action to resolve the overload condition. You cannot create an overload by trying to "fit it in," as had been suggested. See 220.87(2).

I would be very carefull in making adjustments to building demand.
Demand of total load very seldom equals sum of demands.
therefore you have to use demand from the building you are moving at 125% plus all nameplate loads from the building you moving to

 

[T.M.Haja Sahib]

Let us say you ascertain the maximum demand of present occupied building from the POCO's records.You need to determine the load factor.If the load factor is less than 80%,there is always scope for substantial reduction in maximum demand by implementing energy conservation measures.Determine the reduced maximum demand thus.Add 25% to it.Ascertain the maximum of the building you are moving into either by running the entire building generator, say, for a day or from the existing records of the POCO.Determine the load factor.If it is again less than 80%,the maximum demand can be reduced correspondingly by implementing energy conservation measures.Add 25% to the reduced maximum demand.Sum up the two and see if it is less than the service capacity.

The only problem is the willingness of the authorities to incur initial expenditure for implementing energy conservation measures.

 

[bob]

TM
The max demand includes a load factor.

 

[T.M.Haja Sahib]

TM
The max demand includes a load factor.

bob
I am afraid you are mistaken.Please take a look at the definition of load factor.

 

[bob]

TM
You are correct. The information given is the max demand that had occured over a period of time.

 

[Joe S.]

Thanks everyone for the help. I decided to go with connected load after consulting with peers and reading these posts.