The PRIMARY reason why dedicated neutrals make so much sense is because of what happens during maintenance of the system.
To safely work on a circuit, every hot that's mated to its neutral has to be shut off, too.
In a 480Y277 system (ultra-common) that's a very big foot-print of dark territory. This is especially true for high-bays in a warehouse.
In contrast, it's as common as dust for grocery stores to use 3-hots (A,B,C) on ONE (oversized?) neutral for strip fluorescents. It's not so bad if a single row of lamps goes dark. BTW, these circuits are never loaded more than 10-11 amps on a 20 amp breaker at 277VAC to ground.
Hence, they're half-way to an oversized neutral via design restraint.
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For those who've never wired large structures:
Voltage drop is a serious issue. CWA driven lamps will fail to fire up should you be so foolish as to wire up a circuit up towards NEC minimums. Such 'site lighting' runs must use 208VAC or better... only loading the conductors rather lightly. Any attempt to break this iron law will have you out -- time and again -- coming back on warranty calls as the fixtures misbehave.
Like motor loads, CWA's pull heavy to start. Their constant wattages mean extra heavy amps when the voltage drops. This can make them 'self-snuffing.' (The only solution is more wire.) This was alluded to in a prior post INRE EM fixtures.
Last edited by Tesla; 03/06/14 10:29 PM.
