ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Top Posters(30 Days)
Potseal 11
Recent Posts
Dimmable LED 2x4 lay in fixtures
by HotLine1. 04/24/17 05:43 PM
Old decora style outlets
by Lostazhell. 04/22/17 07:59 PM
Permit Snafus...AHJs and Contractors Jump in
by gfretwell. 04/22/17 01:11 PM
How do you find a good employee?
by HotLine1. 04/22/17 10:44 AM
Electrode boilers question
by SteveFehr. 04/21/17 08:32 AM
New in the Gallery:
SE cable question
Popular Topics(Views)
234,690 Are you busy
169,424 Re: Forum
162,740 Need opinion
Who's Online Now
0 registered members (), 79 guests, and 8 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate This Thread
Page 1 of 2 1 2
#137473 - 07/09/03 02:23 PM 3 phase kVA to amps per phase query  
Steve|Uk  Offline
Member
Joined: Jul 2003
Posts: 18
Horley, Surrey, UK
Hi all. Call me noobie [Linked Image] Been reading for a few days, and like it.

Long story short, I'd like a refresher on how to ascertain the amps per phase if given a kVA / 3 phase rating.

For instance, an appliance is 75 kVA three phase. What is the current per phase ?

I've seen various (differing) answers on websites, which in turn give different results; Only one can be correct.

Would anyone be so kind as to refresh my memory - I'm due to start a job in industrial electrics; I've spent the last 15 years house bashing :-)

TIA

Steve|Uk


Test Equipment:
Large Selection of Test Equipment For Electrical, HVAC, Test & Measurement
Large Selection of Test Equipment For Electrical, HVAC, Test & Measurement

#137474 - 07/09/03 03:11 PM Re: 3 phase kVA to amps per phase query  
C-H  Offline
Member
Joined: Sep 2002
Posts: 1,497
Stockholm, Sweden
Welcome to ECN! I like your use of the | divider.

The kVA is the easy one:

current = VA/(phase-to-phase voltage x square root 3 )

or in another form

current = VA/(phase-to-neutral voltage x 3)

75kVA on a 230/400V system is

75000/(230 x 3)= 109 Amps


[This message has been edited by C-H (edited 07-09-2003).]


#137475 - 07/09/03 03:14 PM Re: 3 phase kVA to amps per phase query  
Steve|Uk  Offline
Member
Joined: Jul 2003
Posts: 18
Horley, Surrey, UK
Hi. Thanks for the welcome.

Yeah I did think it was that, but was getting all sorts of confuzzled input.

Just as you replied, I found this helpful page right here at electrical-contractor.net
https://www.electrical-contractor.net/ubb/Forum15/HTML/000043.html

I can see me liking this place [Linked Image]

Bye for now.

Steve


#137476 - 07/09/03 03:38 PM Re: 3 phase kVA to amps per phase query  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Hi Steve, and welcome to ECN.

I see you've already gotten a really quick answer to your question so there's nothing I can add there.

I reckon the industrial side will be quite different to what you've been doing. I've not been inivolved in that side of the job either; I do mostly residential with just a little very light commercial from time to time. That being the case, even where 3ph supplies are involved it's mostly single-phase loads, so it's so easy to forget those forumlas if you're not using them regularly.


#137477 - 07/09/03 05:24 PM Re: 3 phase kVA to amps per phase query  
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
For 400V 3ΓΈ, a rule of thumb is 1.4(4) amperes/kVA.

600V >> 1A/kVA
480V >> 1.2A/kVA
240V >> 2.4A/kVA
208V >> 2.8A/kVA


#137478 - 07/09/03 07:30 PM Re: 3 phase kVA to amps per phase query  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,211
SI,New Zealand
Gidday there Steve,
Welcome along to ECN, mate!. [Linked Image]
The other guys have just stolen all the thunder out of this one, no worries though.


Let's face it, these days if you're not young, you're old - Red Green grin

#137479 - 07/10/03 01:45 AM Re: 3 phase kVA to amps per phase query  
old Appy  Offline
Member
Joined: Mar 2001
Posts: 118
Auckland, New Zealand
Very easy to forget if you aint using it!! even when you have just learnt it all again.
CW


#137480 - 07/10/03 05:53 AM Re: 3 phase kVA to amps per phase query  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,211
SI,New Zealand
Appy,
You've got that right!. [Linked Image]
When I last went to do a Refresher Lines Course at the Power Board, we were ALL handed an exam paper, made up by one of the Inspectors, in things like 3P theory, Neutral Currents in Star systems, etc.
I had an OK time with it all, but some of the old Lineys, really kicked up a stink about it and they also failed miserably.
They thought that they were just there to wear some gloves and do a few Pole Top Rescues.
Was good to give the Grey matter a good work out though! [Linked Image]
[Steve, sorry about the threadjack!]

[This message has been edited by Trumpy (edited 07-10-2003).]


Let's face it, these days if you're not young, you're old - Red Green grin

#137481 - 07/10/03 06:24 AM Re: 3 phase kVA to amps per phase query  
Steve|Uk  Offline
Member
Joined: Jul 2003
Posts: 18
Horley, Surrey, UK
Jack away!!!!

I've said it once, and I'll say it again. I think I'm going to like it here [Linked Image]

Steve


#137482 - 07/10/03 09:58 AM Re: 3 phase kVA to amps per phase query  
lyledunn  Offline
Member
Joined: Jun 2002
Posts: 159
N.Ireland
Remember, it is usual to mark plant such as generators and transformers in kva and plant which "consumes" energy in kw. Thus a piece of piece of equipment requiring 30 kw at a power factor of 0.5 would need to be fed from a source that could deal with the current associated with 60kva.


regards

lyle dunn

Page 1 of 2 1 2

Member Spotlight
Admin
Admin
NY, USA
Posts: 3,439
Joined: October 2000
Show All Member Profiles 
Featured:

2017 NEC and Related
2017 NEC
Now Available!

Shout Box
Powered by UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.015s Queries: 15 (0.002s) Memory: 0.8187 MB (Peak: 0.9955 MB) Zlib enabled. Server Time: 2017-04-25 20:24:30 UTC