Was involved in a discussion in another forum about how to determine panel loads in an existing building... most of the discussion centered around "load calculations".... it was my contention that load calculations were great for sizing services before construction but that to determine actual load after occupancy, you would have to use a recording ammeter for a period of days or weeks to determine a pattern of usage by the occupant and to check for unbalanced load on each of the ungrounded conductors... was wondering if anyone here has also had experience with utilizing a recording ammeter for this purpose.... thanks
Recording Ammeter
- Thread starter jackmcg
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- Lockport, IL
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- Semi-Retired Electrical Engineer
Re: Recording Ammeter
The Washington State Department of Labor and Industries has published a method by which they will review electrical plans, prior to issuance of a permit. The document includes a worksheet that the submitter can use to demonstrate adequate capacity of an existing facility. What you do is to take a continuous reading of amps (samples taken every 15 minutes would suffice) over a 30 day period, determine the maximum current during that period, and run it through their worksheet. The math works like this:
Multiply the max KVA (i.e., max amps times nominal voltage times 1.732) times 125%. Next, multiply by three factors, the values of which are to be determined by the engineer: (1) Seasonal Adjustment Factor, (2) Occupancy Factor, and (3) Other Adjustment Factor. Add this value to the new load being installed in the present project. Convert back to amps. The answer is compared with two things: (1) The rating of the panel, and (2) The ampacity of the feeder.
The Washington State Department of Labor and Industries has published a method by which they will review electrical plans, prior to issuance of a permit. The document includes a worksheet that the submitter can use to demonstrate adequate capacity of an existing facility. What you do is to take a continuous reading of amps (samples taken every 15 minutes would suffice) over a 30 day period, determine the maximum current during that period, and run it through their worksheet. The math works like this:
Multiply the max KVA (i.e., max amps times nominal voltage times 1.732) times 125%. Next, multiply by three factors, the values of which are to be determined by the engineer: (1) Seasonal Adjustment Factor, (2) Occupancy Factor, and (3) Other Adjustment Factor. Add this value to the new load being installed in the present project. Convert back to amps. The answer is compared with two things: (1) The rating of the panel, and (2) The ampacity of the feeder.
charlie
Senior Member
- Location
- Indianapolis
Re: Recording Ammeter
Why not use the NEC?
220.35 Optional Calculations for 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 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.
The views and opinions expressed herein are solely those of the author and do not necessarily represent the views of any organization.
[ August 15, 2003, 02:22 PM: Message edited by: charlie ]
Why not use the NEC?
220.35 Optional Calculations for 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 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.
The views and opinions expressed herein are solely those of the author and do not necessarily represent the views of any organization.
[ August 15, 2003, 02:22 PM: Message edited by: charlie ]
flightline
Senior Member
Re: Recording Ammeter
Depending on how the panels are metered, you might be able to get historical kw and demand data from the serving utility. Many times, when adding a generator or some such task, we have used this historical data to acurately provide maximum loads and trends.
This obviously wont work on a system that has multiple panels off of a common meter, but would work for,,,lets say,,,a tennant with one panel.
Juat a thought.
Depending on how the panels are metered, you might be able to get historical kw and demand data from the serving utility. Many times, when adding a generator or some such task, we have used this historical data to acurately provide maximum loads and trends.
This obviously wont work on a system that has multiple panels off of a common meter, but would work for,,,lets say,,,a tennant with one panel.
Juat a thought.
Re: Recording Ammeter
Jack
A recording meter is one way to determine the panel demand. E-Mon is one brand that I am familiar with. The unit will provide KWH's and KW Demand.
Their webb site is www.emon.com. As the other posters have said you need to record over a long period of time. A months reading would be adequate. However, this time period may not be practical.
[ August 22, 2003, 02:31 PM: Message edited by: bob ]
Jack
A recording meter is one way to determine the panel demand. E-Mon is one brand that I am familiar with. The unit will provide KWH's and KW Demand.
Their webb site is www.emon.com. As the other posters have said you need to record over a long period of time. A months reading would be adequate. However, this time period may not be practical.
[ August 22, 2003, 02:31 PM: Message edited by: bob ]
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