Why run 3 wires to 208V-1PH FCU

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designer82

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I've noticed engineers at my company running 3 wires + ground to mechanical equipment rated 208V-1PH (such as Fan Coil Units, VAV Boxes)

Why are they doing this when all you really need is L1, L2 + ground. Are they running a neutral for no reason, maybe as a spare? Are they doing it just in case something inside the equipment may need 120V?


Thanks
 
I suppose it can be any of the reasons you mention but my guess is he didn't know it was single phase or he wanted 3 phases in case they changed the unit in the future to 3 phase
 
Does one of the wires meet the grounded (neutral) requiremetns of Art 200 (color, ect.) If so, I'd say your guess as to possible 120v loads would be accurate.
 
Afraid someone will swap a component someday with a 120 volt component?

If new install and everything is 208 makes less sense than if an existing site and you have a mix of 208 and 120 volt components on the premises I guess.
 
Its probably because equipment instructions are really bad at specifying if a neutral for 120V loads or controls is needed or not.

If you have a sharp contractor, they will usually catch this before the wire is installed. But if you have a contractor that likes change orders, they may not notice until the wire is pulled in. Then they want paid to pull the wire back out, and add another wire, and pull it all back in. With some bad luck, the conduit may even have to be re-run in a larger size.

Only takes a couple of these before one realizes its just easier to plan for the worst case.
 
My guess is most US made fan coils and VAV's are typically going to be 120 volt. If European or Asian made probably designed for 240, but also usable on 208.
 
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