Err....not exactly. A
dimmer pack with 120V outputs connected to a 208Y/120 service is
WYE connected, not DELTA connected. Your statement about multiplying the
phase current by
1.732 to get the
line current only applies to delta-connected equipment that does not use a
neutral. In a wye-connected
system, the
phase current measured on each of the three phases equals the
line current.
So where might we encounter delta-connected loads in the
theatre? The most common is a
power distribution feeding three-phase chain motors or automated lights that operate at 208V single-phase, typically arc lights with 1200W sources.
ST
This is an interesting area, and while I am not an expert in it, and my posted reply is an over simplification, here is my understanding
First is that the transformers used in buildings are infact delta
wye typically since the
power company does not supply a
neutral usually, but the inside connection is typically
wye
second is that with single
phase loads on three
phase supply, the thinking now is that you should provide an independant
neutral for each of the three
phase legs when they are being used in a single
phase setup
third is that you should spec the amp
rating of the
neutral leg at a minimum to 1.73 times the
rating of the other legs.
So again my understanding, and an over simplification is that you cannot simply take the amp ratings of the feeds and add them up since your
neutral in an unbalanced configuration could have 1.7 times the
current of a
leg in a
wye setup where you are using the legs as individual 120 volt connections, or when you are using two of them in a 208 connection.
Common wisdom was that the neutal would be zero, and again in a perfect world with all balanced
etc, it is, but typically now in wiring for feeders from a
company switch practice seems to be moving to over
rating the
ampacity of the
neutral by almost a factor of 2. This typically was not the practice, if you look at prosoundweb for instance there has been a lot of discussion re
neutral ratings and the need to change what we use on feeders for the
neutral in unbalanced situations (Which is really just about all our setups)
This is typically NOT how most electricians have done it
So as far as I understand it, in a three
phase wye connection that is NOT
balanced, you cannot simply add up the amp readings on the hots, but take into consideration the amps on the
neutral.
Again not claiming to be an expert, but my understanding is that a lot of the thinking on this has recently changed
http://www.itic.org/archives/articl...computers_and_electronic_office_equipment.php
Sharyn