3 phase supply size

[James sparks]

Hi all,

I need to put in a 3 phase supply for a piece of equipment in a commercial unit. They've sent the spec sheet for the item over and all it says is

Current type (Ph/V/Hz): 3/420/50
Power rating (kW): 7.8


I just want to clarify if it's 7.8kW per phase or 7.8kW total over all 3 phases.

Thanks!!

 

[sparks1234]

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

 

[Darkwood]

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.

 

[happysteve]

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.

 

[micknew]

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.

Your tutor knows his stuff.

 

[happysteve]

That he does.

Apologies to the OP for diverting this thread. Mods please feel free to delete my posts.

 

[sparks1234]

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!!!!

 

[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'

 

[Richard Burns]

As DW says p41 does give it away somewhat!

 

[Darkwood]

As DW says p41 does give it away somewhat!
View attachment 24293

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.

 

[Richard Burns]

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!

 

[netblindpaul]

There are also still some glaring errors in posts on this thread ignoring the so called "misunderstanding" of kW per phase or across 3 phases that are sufficient to kill people.

 

[Darkwood]

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.

Do us a cheeky favour tell your tutor the KW rating on a motor is the energy output down the shaft and a replacement value for horsepower and not to be confused with what the motor consumes thus the relevant equation has to be done to get the current before you can say whether its across the phases or per phase - Im interested ho you are taught today and what his answer would be!

 

[Marvo]

There are also still some glaring errors in posts on this thread ignoring the so called "misunderstanding" of kW per phase or across 3 phases that are sufficient to kill people.

Yes there are but it's a discussion, not a tutorial and if anything should be taken from the thread by a person looking for advice it should be that they ought to confirm with the agents or supplier before making any assumptions.

 

[trev]

Deleted following a PM conversation

 

[happysteve]

Do us a cheeky favour tell your tutor the KW rating on a motor is the energy output down the shaft and a replacement value for horsepower and not to be confused with what the motor consumes thus the relevant equation has to be done to get the current before you can say whether its across the phases or per phase - Im interested ho you are taught today and what his answer would be!

To be fair to Allan, he did say rather a lot more than the sentence I typed quickly on my phone during the brew break! I realise now that in my rush, I probably misrepresented what he explained. Apologies.

Over 3-4 minuts he talked about how (as you say) it's related to the output power of the motor in terms of the work it can do. He mentioned horsepower, and when he put it in this perspective it started to make sense. He did mention efficiency too; he didn't actually say, "Your total electrical power consumption will be greater than the rated power due to the efficiency always being less than one (100%)," but we covered the equations in an earlier lesson so I guess he left this for us to work out.

I like Allan. He's alright.

 

[Silly Sausage]

@NickD

I'll apologise now for taking this off topic (as I know it's now frowned upon)

Nick do you find Asperger's is much of a hindrance to how you deal with your life on a day to day basis?
My great nephew has it and it's a daily struggle for him.

I reckon he had his Bell End pulled and he's replaced it with this lame attempt.

 

[trev]

Deleted following a PM conversation

 

[Silly Sausage]

I wonder what he'll think when he gets access to Arms!

 

[GLENNSPARK]

I wonder what he'll think when he gets access to Arms!

eh?...

 

[GLENNSPARK]

it`s what others will think....

 

[Silly Sausage]

eh?...

Av a shufty in the pub, you'll see!