Taking current readings for new loads

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iwire

Moderator
Staff member
Location
Massachusetts
I have seen a number of posts on the forums about using an amp clamp to take a quick load reading to determine if new loads could be added.

Of course that may be a start but it does not comply with the NEC and really has a potential for failure if you take the readings at the wrong time.

Here are some screen shots of power logging a switchboard at an office building. The company I work for had me place a recording meter there for a few days to get a rough idea of the loading so they could get started with design. Now I have another meter there doing at least a 30 day recording for NEC compliance.

I have included the current and voltage graphs for just phase C but A & B where very similar. I also included the min / max report.

I just thought some would find it interesting and I think it shows the problems with doing just quick amp clamp measurements.

Volts_zpsdelqdgds.jpg




Amps_zpst8qd97cw.jpg



Min%20Max_zpsebzz06op.jpg
 

buzzbar

Senior Member
Location
Olympia, WA
Occupation
Electrical Contractor
Can you tell me what make and model of the monitoring equipment that you used? How do you like it?
 

tkb

Senior Member
Location
MA
I believe that is from a Dranetz PX5.
I have used these several times myself.

It is interesting that the graphs show how the voltage sags a little when the current rises.
 

robbietan

Senior Member
Location
Antipolo City
we usually ask if the place is "running under normal operations" before doing spot amps measurements. negative replies means certain adjustments or additional questions like "what loads are shut down now shut are usually running otherwise?"
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Just how accurate do these meters need to be for this data gathering?

I have small PLCs with 4-20 ma and 0-10v analog inputs when used in conjunction with a decent HMI can do something very similar. Things I have on the shelf for the most part.

I drool over the real meters, but justifying the cost is tough.
 

mivey

Senior Member
Let me try that again.:ashamed1: My English sucks.:(

It is good to show the problem of assuming a quick amperage read is viable for a proper load calc. It is not.
You said what was read but reading isn't going to always result in not reading what was wrote, even if the intended phrase was different from what you meant or didn't mean to convey. There are always exceptions of course.
 

iwire

Moderator
Staff member
Location
Massachusetts
What is the data interval? Amp-seconds, amp-minutes, ...? Any histogram reports?

This report was created without histograms, I do have all the meter settings but it is pages long. We would have been on 10 or 15 minute intervals.

When I have time I will try to dig up another report with histograms. I have them somewhere.

It is a Dranetz Power Explorer PX5 http://www.dranetz.com/product-services/powerxplorer-px5/ and I know I restored it to factory defaults before I recorded this file so if you happen to know the defaults you know the interval.
 

iwire

Moderator
Staff member
Location
Massachusetts
So hooking up recording meters is what happens before you get put out to pasture, huh? :p

Before? :D

I have been doing IR, recording meters and now robotic total station operator.



I actually enjoy doing the layout work, I have done the lighting lay out for two stores 400 or 500 points a piece and one roof top PV array with maybe a 80 points but it was a huge roof.
 

peter d

Senior Member
Location
New England
Before? :D

I have been doing IR, recording meters and now robotic total station operator.

I actually enjoy doing the layout work, I have done the lighting lay out for two stores 400 or 500 points a piece and one roof top PV array with maybe a 80 points but it was a huge roof.

Nice, that sure beats doing prefab at the shop or organizing stock all day. :thumbsup: But wait, that's coming next. :p
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
160403-1538 EDT

When I collect voltage and power data with a TED 1000 I use resolution of 1 sec. This means the instantaneous values are averaged over a 1 second period, and that average data is output each second.

I post process the data to reduce the file size, but still retain 1 second resolution for short time changes of more than a small amount. This works quite well and does not really loose any useful information.

iwire:

Your voltage data was interesting in that it had a daily periodic variation that looks to have some time shift relative to your currrent loading. This could mean that there are other system loads that operate on a slightly different time schedule than your building. At the start of 3/19/2016 a voltage droop uncorrelated with any current load from your monitored circuit shows up.

.
 

kwired

Electron manager
Location
NE Nebraska
One easy way that the code does allow is to look at the last years utility bills and see what the usage is.
Which only works if the utility tracks demand. If you have a usage of 1000 kW-hrs how do you know if it was all used in a few minutes, used at different peak intervals, or was fairly steadily averaged over the entire billing period with out demand tracking?
 

__dan

Senior Member
I have a very fast method for load calcs that requires good familiarity with the building.

I will separate the loads into two types, those that run always on at 100%, (for example) IT, lighting, fans, pumps, chillers, ... and those that run on and off or modulate based on demand ... electric DHW and duct heaters, humidifiers, electric heat, A/C, any large low duty cycle automatically starting electric equipment ...

Scheduled or planned, I will walk around and turn off all the modulating, on/off, or low duty cycle loads, then meter the feeder or supply with the remaining (always on full) loads at 100%. The loads that are turned off are added to the load calc at 100% of nameplate. The method complies, with the added factors for carrying 125% of the metered load and 125% of continuous type loads.

There are tradeoffs and benefits. I do not have to know every load, just the typical loads that cycle and may be off. I am also getting a better peak reading as there are times, when the building swaps to generator for example, that normally modulating loads at less than 100% will all run simultaneously at 100% when the building is out during transfer and the loads come back on at 100% to pull the building back to setpoint, chillers, ups, ...

I would probably not use this on the big mains but I can get fast and accurate load calcs at DP's and MCC's, in places people don't think I can actually calculate the load. Basically in places it is obvious they have no clue and are adding large loads to large supply illegally, without load calcs and loading over what my load calcs are showing is allowable, or prudent. In 20 minutes my calcs can show they are committing fraud.

Your graph shows a very intermittent 200 amp load that is cycling on and off. Probably heat or cooling as it is peaking after lunch. I would immediately want to know what that load is (the graph says it is misbehaving or short cycling). Either it is a brute force load that you need as is, or it is a target for an upgrade or improvement of some kind. The elegant replacement would run steady state at part load more efficiently. It is an obvious target for me.

The short cycling by itself is an indicator of probable trouble in a load of that size. In that size it should stage or have better part load modulation without short cycling 200 or so kVA.

Extended time metering is better for the business, a saleable service. But that's only a tiny portion of the market, the customers that want to spend money on monitored metering. The bulk of the market is probably adding loads and not finding out for a year or so until the feeder breaker trips, that they committed fraud when they added the new loads.
 

iwire

Moderator
Staff member
Location
Massachusetts
I have a very fast method for load calcs that requires good familiarity with the building.

I will separate the loads into two types, those that run always on at 100%, (for example) IT, lighting, fans, pumps, chillers, ... and those that run on and off or modulate based on demand ... electric DHW and duct heaters, humidifiers, electric heat, A/C, any large low duty cycle automatically starting electric equipment ...

Scheduled or planned, I will walk around and turn off all the modulating, on/off, or low duty cycle loads, then meter the feeder or supply with the remaining (always on full) loads at 100%. The loads that are turned off are added to the load calc at 100% of nameplate. The method complies, with the added factors for carrying 125% of the metered load and 125% of continuous type loads.

There are tradeoffs and benefits. I do not have to know every load, just the typical loads that cycle and may be off. I am also getting a better peak reading as there are times, when the building swaps to generator for example, that normally modulating loads at less than 100% will all run simultaneously at 100% when the building is out during transfer and the loads come back on at 100% to pull the building back to setpoint, chillers, ups, ...

I would probably not use this on the big mains but I can get fast and accurate load calcs at DP's and MCC's, in places people don't think I can actually calculate the load. Basically in places it is obvious they have no clue and are adding large loads to large supply illegally, without load calcs and loading over what my load calcs are showing is allowable, or prudent. In 20 minutes my calcs can show they are committing fraud.

Your graph shows a very intermittent 200 amp load that is cycling on and off. Probably heat or cooling as it is peaking after lunch. I would immediately want to know what that load is (the graph says it is misbehaving or short cycling). Either it is a brute force load that you need as is, or it is a target for an upgrade or improvement of some kind. The elegant replacement would run steady state at part load more efficiently. It is an obvious target for me.

The short cycling by itself is an indicator of probable trouble in a load of that size. In that size it should stage or have better part load modulation without short cycling 200 or so kVA.

Extended time metering is better for the business, a saleable service. But that's only a tiny portion of the market, the customers that want to spend money on monitored metering. The bulk of the market is probably adding loads and not finding out for a year or so until the feeder breaker trips, that they committed fraud when they added the new loads.

That method does not comply with the NEC.

It either a full article 220 calculation or the methods allowed in 220.87.

As far as the loading, it feeds a data center. The building is heated and cooled from a separate central plant.
 
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