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#201104 05/11/11 12:36 PM
Joined: Mar 2011
Posts: 5
will_87 Offline OP
New Member
My question is this:

After finally pinning down the boss Ive eventually convinced him we can have our equipment replaced!

We had a data logger record our equipment for one week (voltage, currents, KW, KVAr, KVA ect) and decided to use the data to compile a report to indicate the size required for install.

The question is about the current waveform results:
Do we use the maximum average RMS value (the true effective value of the waveform) or the maximum max recorded value (the amplitude) to size are equipment.

I am as you can appreciate concerned about under sizing equipment due to fault or effectively over sizing and costing the company unnecessarily

Many, many thanks in advance for your thoughts and suggestion on this!

Joined: Jun 2004
Posts: 1,273
All industry calcs are performed on RMS power.

True peak voltages are of concern only when designing circuits such as a low pass filter.

Joined: Mar 2011
Posts: 5
will_87 Offline OP
New Member
Many thanks for the reply Tesla,

What if the equipment in question were an at L.V 415V system?

Would this still be the peak current and not the peak to peak current?

Joined: Dec 2002
Posts: 318
One weeks worth of data does not help much, but that depends on the type of equipment you are looking at. Our replies would be better if we knew what type of equipment you are looking ate. If you are looking at feeders and load centers your data would be better collected over a 6 month to one year period unless you have some way of ensuring worst case loading.

But yes still RMS current not peak to peak.


Joined: Nov 2002
Posts: 134
I would be concerned if the peak current is waaaaay above the RMS. I'd want to know the duration of the 'peaks'.

You need to be able to supply RMS as well as the peak or you are going to starting popping fuses.

I do feel your pain. In work in a large mfg facility and it's always difficult to determine how much room is left on a bussbar without doing some data logging, field observations, and then some estimation (I hate to use the words 'best guess'). In the end that's what fuses are for.

But like sabrown sez...and unless I missed it in the'd need to tell us more about the load.

Joined: Jun 2004
Posts: 1,273
Harmonic AC waveforms dictate that Peak Voltage = 1.414 x RMS.

Unless you've introduced non-harmonic back-EMF that's your answer.


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