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Interesting. Surprised there is such a gulf between opinions.

I am a trainee, we're covering motors at the moment. I happen to have Trevor Linsley's book open at this page:

3 phase supply size uploadfromtaptalk1397480029966 - EletriciansForums.net

This suggests there's a "root three" in there somewhere!

I'm not proffering an opinion, just interested to learn. This could well be one of those cases where the text book means diddly squat. Be useful to know, though, if that's the case! :)
 
Yes the book is 100% correct never argued the calcs ...what the OP asked was is the KW of a 3ph load per phase or not ...

If you use the calcs shown above to work it out you indeed do apply root3 to establish the running current per phase.

If you have a Motor the Kw rating is the power output energy through the motor shaft (also in HP) its not an electrical measurement par se' and using either calcs as above or the plated amps this will show Amps per phase.

I think i see why your arguing my point but think you have approached it a different way... im been careful to word it correctly as telling the OP 7.8Kw is not per phase may give the impression to divide by 3 and hey presto but when reading a power plate its the Kw per phase and yes you use the root3 in the calcs to convert this to amps per phase.
 
Have to say I have never heard anyone quote KW or KVA per phase in relation to 3 phase. KW is power and usually means total power required by the machine. It would be like quoting total amps for a 3 phase machine when amps per phase is the norm.
 
It maybe my teaching is old hat but was taught as you rightly say that the Kw or Kva is the power required but because some machines especially with heating banks can have a KVA or Kw value given as a single Phase value where the machine can sometimes be converted to 3ph you divide the value by 3 first to get your 3Ph Kw rating.

It may not be correct to ask the question if the Kw is across the phases or per phase but instead ask how to calculate the load per phase of a 3phase - 7.8kw machine.

I work on chinese old solder machines and the Kw needs dividing by 3 as they stated the total of each phase and not like we mark them over here common on machinery that can be converted to 1ph by linking together element banks.

Hindsight I should have shown the formula early on... but for the OP -

Hindsight I think showing the equation early on would have cleared the confusion up...

I = P/(voltage * PF * 1.732)

I = 7800 (400 * 0.8 * 1.732)

I = 7800 / 554.24

I = 14.07 amps per phase.

If its indeed a motor then efficiency should be in the calcs as well. Note PF is estimated at 0.8 for a pump motor? - info lacking
 
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Kärcher Centers & Stores | Kärcher UK

Give 'em a call?

"Whether for Industry / Professional or Home & Garden, Kärcher Centers are committed to providing professional advice on selecting the correct cleaning solution for your requirements. The staff at Kärcher Centers are experienced in all products groups and applications, having undergone thorough training at the Kärcher Academy."
 
Thanks for the Link .... Would have been useful earlier ;)...

http://www.karcher.co.uk/document/BTA-5339762-000-02.pdf

Page 41 .... took 30-seconds to find

It requests a fuse size as slow... I would confirm with their tech' support if a type C mcb will be suitable as its vague but does give you a fuse rating for each model and voltage.
 
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If you get a motor and it says 4kw 400v then its per phase.
If you buy a 4 kW motor it will be 5.5HP regardless of whether it's single phase or 3-phase. I'd respectfully suggest that 4kW indicates the total energy consumption regardless whether it's a single phase or 3-phase motor.

I would expect the 7.8kW stated in the OP to be the total energy consumption so it would be 7.8kW across 3 phases.

As Nick says above, don't take my word for it, give them a call and confirm.
 
If you buy a 4 kW motor it will be 5.5HP regardless of whether it's single phase or 3-phase. I'd respectfully suggest that 4kW indicates the total energy consumption regardless whether it's a single phase or 3-phase motor.

I would expect the 7.8kW stated in the OP to be the total energy consumption so it would be 7.8kW across 3 phases.

As Nick says above, don't take my word for it, give them a call and confirm.

Sorry Darkwood, you are wrong on this one

Total load, split across the phases
 
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Yes Marvo im getting the impression my old school terminology differs but just to confirm a 4KW motor means it output 4KW of energy down the shaft it is not what it consumes, my thinking really here as i mentioned is its wrong to ask if the KW is across the phases or per phase as the KW has no electrical meaning its a modern convertion of horse power ratings.

You wouldn't ask if the horse power is per phase or across them you would ask if the plated ampage is if anything... this is why I have approached it the opposite way and yes confused matters but the OP's back and getting relevant info'

Ill hold my hands up ad say my advice was incorrect in the way it was given and i should have explained it better by giving the KW to I equation expressing the KW is a energy available at shaft and requires the calculation to turn it into something more meaningful.
 
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Allan, my course tutor, has just told me that (in his opinion) if the plate on a 3 phase motor says (eg) 10kW, that's the total consumption.
 
That he does. :)

Apologies to the OP for diverting this thread. Mods please feel free to delete my posts.
 
Yes Marvo im getting the impression my old school terminology differs but just to confirm a 4KW motor means it output 4KW of energy down the shaft it is not what it consumes, my thinking really here as i mentioned is its wrong to ask if the KW is across the phases or per phase as the KW has no electrical meaning its a modern convertion of horse power ratings.

You wouldn't ask if the horse power is per phase or across them you would ask if the plated ampage is if anything... this is why I have approached it the opposite way and yes confused matters but the OP's back and getting relevant info'

Ill hold my hands up ad say my advice was incorrect in the way it was given and i should have explained it better by giving the KW to I equation expressing the KW is a energy available at shaft and requires the calculation to turn it into something more meaningful.

Good onya Darkwood!!!!
 
Your tutor knows his stuff.

As we had the general banter here Ill offer an apology expressing you were wrong but hope through my latter posts you see the angle I approached from and a consequence of the overlapping Engineering terminology and general Electrical Terminology I was taught.

The opportunity was missed by all to simplify what the OP wanted at the end of the day and it was ampage per phase so he could design the supply.

He has now been given this and a Link to a PDF for the fuse info'
 
I sourced this off a different website - the OP didn't have this info - Karcher could be more informative on their original spec ...we can only guess the motor might have some form off soft start hence I would still ring Tech' on this matter.
I think clicking on the link "product manuals" under more information from the OP link may have given a clue!
 

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