INTELLIGENT WORK FORUMS FOR ENGINEERING PROFESSIONALS
Come Join Us!
Are you an Engineering professional? Join EngTips now!
 Talk With Other Members
 Be Notified Of Responses
To Your Posts
 Keyword Search
 OneClick Access To Your
Favorite Forums
 Automated Signatures
On Your Posts
 Best Of All, It's Free!
*EngTips's functionality depends on members receiving email. By joining you are opting in to receive email.
Posting Guidelines
Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Phase To Neutral Calculations

ansible (Industrial) (OP) 
8 Oct 08 18:22 
I am planning to run a series of eballasts on phase to neutral power, with an equal number of ballasts on each phase for a balanced load. The phase to phase difference is 400v do I use that or the 400/SQRT(3)v when calculating watts. It doesn't seem right that when you calculate watts using
Watts =V*I*pf*SQRT(3)
The answer is greater than the sum of all the ballasts watts. Am I missing something here?
Also am I right in assuming that line and phase voltage can be considered the same if your running the same number of identical ballasts on each phase. 

dpc (Electrical) 
8 Oct 08 18:37 
If the ballasts are connected line to neutral, you need to use the linetoneutral voltage to compute watts used by each ballast. Then add up how many ballast you have on each phase.


NAZ55 (Electrical) 
8 Oct 08 18:43 
Your equation is for a Three Phase Power
3 Phase Watts: SQRT(3)* V(LL)* I * pf
1 Phase Watt: V x I x pf 

ansible
dpc and zazmat are correct, in addition, base on zazmat formula.
Basic Ohms Law;
P(Watts) = V x I x pf (eq. 1)
Where; V = Voltage, per your post, it is 400Volts I = Current pf = power factor, assumed as 1
Since you will buy lighting fixtures, the fixtures is complete with lamp and ballasts.
Let us assume 1 Lamp (40 Watts) per fixture. Sometimes, fixture has more than 1 lamp.
To find the line current (I);
From eq. 1;
I (Current) = P(Watts) / V (Voltage) x pf (Power Factor)
Substitute the given data;
I = 40/ 400 x 1
I = 0.1 Ampere
Your last question is confusing. Let me know the following.
1. Does your panelboard a 3Phase, 4 wire?
2. What is the rated voltage of your input power supply.
If we follow your phasephase voltage above, it should be 692.8 Volts. Regards Bilegan 

waross (Electrical) 
9 Oct 08 21:23 
If your phase to phase voltage is 400V then your phase to neutral voltage will be 231V. 1> Select your ballasts for either 400 volts or 230 volts. 2> Use the nameplate watts to determine the energy consumption. 3> Use the nameplate amps to determine the circuit loading and KVA. 4> If you use 400V fixtures you must connect them phase to phase and use a 2 pole breaker. 5> If you use 230V fixtures you must connect them phase to neutral and use a 1 pole breaker. 6> If you connect from phase to neutral you can not use a floating neutral. The neutral must be connected back to the supply transformer neutral. 7> There will be harmonic currents on the neutral and the neutral size must not be reduced. Bill  "Why not the best?" Jimmy Carter 

lefty51 (Electrical) 
10 Oct 08 9:52 
If these are fluorescent ballasts, and you are in canada, they have to comply with he following rule: (4) Each fluorescent luminaire installed on branch circuits with voltages exceeding 150 voltstoground shall be:
(a) Provided with a disconnecting means integral with the luminaire that simultaneously opens all circuit conductors between the branch circuit conductors and the conductors supplying the ballast(s); and
(b) Marked in a conspicuous, legible, and permanent manner adjacent to the disconnecting means, identifying the specific purpose 

Lefty, What do they mean by "disconnecting means intergral with the luminaire"? This sounds to me that a switch has to be integrated, that is, a part of, the luminaire. This doesn't sound practical, so I must be interpreting it incorrectly. K2ofKeyLargo 

waross (Electrical) 
12 Oct 08 10:18 
A plug connection will serve. Bill  "Why not the best?" Jimmy Carter 



