# Power measurement

• posted
I am going to a customer site to measure machine power, while it is in an
idle state. It has a 3 phase & neutral supply(50Hz).
My plan is to use a clamp meter to measure current,
is it simply a case of P=IV for power or is there a need to multiply by
sqrt(2). Also, do I need to measure the 3 phases and add the reults together
to get the total power consumption.
Thanks.
• posted
From the question- you really don't know what you are doing so I suggest that you get someone who does know even if it costs a bit. Your customer might be far happier if someone competent did the measurements. If you want real power measurements a clamp on ammeter won't do. You need to a) have a wattmeter or some form of phase measurement b) know what you are doing.
• posted
If you don't know, just don't reply. That way I won't have to read throught he drivel you type.
• posted
Don answer was exactly right. And you still don't have a clue what you are doing. A starter might be looking up "power factor" in Wikipedia.
-- bud--
• posted
Firstly,
I can't remember saying I did have a clue what I was doing.
Secondly,
I may not be a competent electrician, but I am a qualified one so, at least in the UK, people will just have to put up with cowboys like me doing electrical work and giving superstars like yourselves a bad name.
Regards.
• posted
Well in the US, to be a 'qualified electrician' you would have to know that for a *balanced* three phase supply the total real power flow is = sqrt(3) * V* I * pf. Where pf is the power factor. Power factor can range from zero to unity based on two general things, the phase relationship between voltage and current, and the harmonic content of the current. Phase displacement happens with inductive loads (motors most common) or capacitive loads (rare). Harmonic content can be high if supplying non-linear loads (electronic power supplies most common).
So using a clamp on ammeter will give you one of these terms and you can easily get the voltage term with a simple voltmeter. Finding the power factor means you need a different type of instrument altogether. The most common instrument for this is a watt-meter. It combines all three terms (voltage, current, power factor) in one unit, eliminating a lot of the work in measuring power.
Now, if the load is *
not* evenly balanced (quite common in office environments), then you have more trouble. You can measure the current in each phase individually along with its harmonic content and phase displacement. Sum each of the three measurements (without the sqrt(3) multiplier). But you also have to consider that if you are measuring voltage line-to-line, there is a 30 degree displacement from line-to-neutral that can skew your phase displacement measurements (instrument transformers used in permanent metering can complicate this even more).
Now, if you think the others are giving you a rough time about 'not knowing what you're doing', it's probably because nothing in your original post suggested you had any idea about any of these factors. If you did know this stuff, then you wouldn't have suggested just using P=VI and you would at *
least* have known that its the sqrt(3) that gets tossed around in three-phase calculations, not sqrt(2).
daestrom
• posted
Wow, just 4 days ago Sue/Pal?The system in the UK is, admittedly, wierd.? ?The actual person doing the wiring needs no qualifications at all, specific or unspecific. He could have been at school the previous week.?
You dismissed Don?s answer as ?drivel?.
You apparently didn?t take my suggestion and look up ?power factor? in Wikipedia. If you did, you would have found a significant portion of what daestrom posted, and perhaps could have asked an intelligent question.
Somehow "superstars" like me have been given a bad name. "Superstars" like me include most licensed electricians in the US and about everyone that follows this newsgroup.
Your behavior is not conducive to getting responses.
-- bud--
• posted
--------------- I do know. You apparently don't. That is the reason for my comments. If you are qualified- then there are problems with standards in the UK. Qualified doesn't mean competent and, in your case the lack of competence is apparent. However, your "knowledge" and "competence" is, fortunately, not typical of UK trained electricians that I have met. It appears the exception makes the rule. You are out of your depth. May I suggest that you try thinking instead of sinking?
Don Kelly snipped-for-privacy@shawcross.ca remove the X to answer ----------------------------
• posted
Unfortunately, I am not familiar with the legal position surrounding the UK system. All I know is I got a job as an apprentice electrician, had a combination of 4 years mixed work/study, sat an achievement measurement test (AM2), followed by a further 6 months work then was given a card by the JIB stating I was an electrician. Not sure if there is any other route and to be honest I don't particularly care.
It was! I was looking for a few pointers. The fact of the matter is, after a couple of years electrical work, I done a BSc in software development then a masters in networking. I work in machine integration, getting hardware and software together. It has been nearly fifteen years since I had to do any basic electrical theory and when my boss asked me to do this, I thought I would ask for suggestions before commiting. I wasn't looking to be told how clueless I was.
Stick to electrcal work, claivoyance clearly isn't your thing. I did in fact look at Wiki as suggested. Then I looked out my old college notes and found the information I was looking for. I am still unsure where you got the idea I hadn't looked up the reference you gave me, albeit after you told me.
After asking a fairly basic question, I didn't get a conducive response so what difference does my behaviour make?
I don't doubt the knowledge each person in this newsgroup has in this area, but please remember that out of your particular area of expertise, you may also ask questions that seem ridiculous.
• posted
Obviously, or I wouldn't have asked
You may well be correct, but how can we compete with a nation that gave us McDonalds, George Bush and Friendly fire
Again, I stated this in a previous post
I think I have met more UK trained electricians than you and most of them can't tie their shoe laces
On the contrary, after reading through my old course notes etc, I am well within my ability with regard to the original question asked.
• posted
Do you know what 3ph is? and i don't mean 415volts. Do you know how it is produced? Does your coustomer know that you are unqualified? Where will you place the clamp? Does it have star delta starter? Capacitor start motor? Is it VSD controlled?
If you don't know don't mess. Would you measure your gas supply?
Trained industrial electricians are hard to come by, people change a plug and think they know it all
Unqualified and incompetant what a combination
Obviously you have met house bashers and not industrial trained sparks
Yes you are within your ability to ask questions but not within your ability to understand the most basic fundamentals of electricity ie Ohms law ( yes it is spelt correctly) Might i suggest you get you copy of the Yellow Pages and look up a good industrial sparky and sub contract the job out at least this way you wont end up killing yourself or anyone else.
Gavin
• posted
I was going to help until i saw the comment about UK sparks Just clamp the cables and your wife will become a very rich widow as you don't know what you are doing and have no understanding of the basics of elctricity
• posted
No.
No.
No, I am keeping it a secret, please don't tell them.
Around this green/yellow wire I have seen lying around.
No, initially it is wired star and when it is up to speed, I quickly put on a pair of rubber gloves and rewire it.
No.
No.
No, but I would measure somebody elses
Perhaps they ought to change their job title to something more fitting, a word of caution though GOD is already taken.
I am very qualified, but I don't dispute the incompetant part
I have never worked on a house, only industrial projects and most of the people I worked with were struggling alcoholics who could hardly string a sentence together. This in no way reflects on you personally, or the people you work with. I am not in a position to comment on that. I am, however in a position to comment on my personal experience and stand by what I have said.
Speed = Distance x Time. I understand perfectly
I don't need the yellow pages, all I need to do is go to the local boozer and I will find dozens there.
• posted
Oh Dear! I will regret the day I commented on UK sparks
Possibly, however I bet your wife will also miss me.
• posted
----------------------------
------------ Good- then show it.
By the way, I am not from the US and "friendly fire" was invented far earlier -and not by the US- one example was when the RAF bombed Canadian troops near Caen in WW2 because they misunderstood signals. Bush and Macdonald's - I grant you those but I've had pretty bad fish and chips in the UK.
As for the good UK electricians- how can you judge -given your admitted inexpertise?
The "drivel" was intended to show you the way- either get someone competent- or learn more. If you have done that -good for you. A BSc in software is not going to give you much information regarding polyphase measurements. Yes- I could tell you what measurements should be made, why and how, but since your background was not known when I replied- but your ignorance was- it would not serve anyone, including you, and would be irresponsible of me-like giving a loaded pistol to a baby. I thought of mentioning factors such as root (3) and power factor but then considered that that was over your head- given what knowledge that you had shown.
Case closed.
. --
Don Kelly snipped-for-privacy@shawcross.ca remove the X to answer
• posted
Did I mention that as well as being an incompetant electrician, I was no good at history.
I am sure there are some very good, knowledgeable UK electricians, my point is, the sparks I have worked with have spent the last 2/3 of their lives bending conduit and making off the ends of wire armour. Like me, they were probably taught the theory at some point, but when you don't keep using knowledge it is easily forgotten.
I wasn't trying to show how clever I was, merely point out that I had moved into a different area of work/study and offer this as a possible defence of my apparent ignorance of basic electrical engineering.
So you had two choices, not post anything or reply with an insulting post. You chose the latter.
I accept some responsibility for this, I could have given a little more of my background or at least done a quick google for power factor and found my own course notes before posting. However, I didn't expect to come under the wrath of a spark, eager to show how clever he was with his ability to insult.
• posted
I spend most of my days dealing with IT engineers some of whom claim to have engineering degrees but could not descern the difference between basket tray and cable tray. Theory is easily remembered if you try
I to do not deal day to day with installs anymore i have moved into several different areas including consulting. I do not have a degree but City and Guilds 2361; 2362; 2377; 2380; 2391 and 2400. I now run projects mainly energy saving initives and specialist computer room projects
The attitude you show is outstanding arragrant and ignorant you would make a fine traffic warden / solicitor / politician
• posted
Which course is that? and when did you take it?
Thats Newtons law Doh
• posted
Power factor improvement & three phase theory (Module No 2160070) June 1994. Much of it was covered again in the HN unit Electrical principles(Module No 2400040) which I passed with merit in June 1995 as part of an HNC electrical/electronic engineering.
• posted
So you have an HNC (electrical or electronic or other ?) and ask a basic question that you shoould already know the answer to. So much for HNC

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