[TZ] Curious about 3 phase power

[Milton Holladay]

If there is 240 supplied, then the power feed is a delta, and both 120 and 
240 are supplied from the secondary of one transformer. Thus, if there is 3 
phase being supplied, there is/was something that required 3phase. Judging 
by what you say, not likely a delta in this case.

On the other hand, if 3 phase is supplied and there is/was no 3phase 
equipment to use it, the service is likely a Y*, supplying 3 legs of 120 
volts-to-neutral and 208 volts between any two of the three 120 volt "hots". 
[No 240 here.]
Thus, if one primary phase is tripped/blown, one leg of 120 is out and two 
legs of 208 are out,.
Your idea is perfectly plausible, or the xfmr may be bad...(No, that never 
happens,,,,noooooo.)
M
*There will be 3 xfmrs on the pole, or one large all-in-one cabinet unit on 
the ground.

----- Original Message ----- 
From: "Steve Lewis" <steve at theengineeringbureau.com>

> No, this isn't inspired by anything stronger than Pepsi J
>
> I've been living out of town in a motel for a few weeks, and last week a
> horrific thunderstorm passed right over the top of the establishment just
> about dusk.  I stood in the doorway enjoying the show, and several times 
> the
> lights flickered.  I happened to notice that half the exterior lights on 
> the
> building facing me didn't come back on while my room lights came back on
> just fine.
>
> It wasn't long before the heat and humidity caused me to notice that the 
> air
> conditioner wasn't running.  Upon inspection, the control panel was on and
> displaying "br" and a light on what appears to be a GFI at the plug was 
> on.
> It hadn't tripped.  Weird.
>
> The motel is fed 3 phase to one or more large transformers on the 
> property.
> Each building is apparently fed 240 (120/120) and by luck, rooms are on
> allocated somewhat randomly about the two halves of the 240, and long
> strings of outside lights fed off one side or the other.
>
> Sure that the motel was fed 3 phase, and nothing on the property required 
> 3
> phase, I hypothesized that one of the three legs of the primary was out. 
> I
> couldn't really wire the big distribution transformer in my head to supply
> power to the several buildings in such a way as to have lost a leg of the 
> 3
> phase going in, and coming out as 240 (120/120) dropping one side of the 
> of
> the 240 which allowed lights to be on in some rooms and outdoor lights in
> some areas to work but the (I assume) 240 volt AC units not to function.
>
> The next day, when nothing had been repaired, I took a look at the three
> fused cutouts feeding my motel and a couple of others, and sure as heck 
> the
> fuse had been expelled and the cutout was hanging open.  Since I saw no
> damage to the primary on the poles that feed these various motels, I came 
> to
> the conclusion that when the lights blinked the several times then turned
> back on, there was severe inrush current trying to restart air 
> conditioners
> which blew the fuse on the pole.
>
> I post this because I'm wondering how a 3 phase transformer would have to 
> be
> wired to essentially feed the two halves of the 240 from more than a 
> single
> phase.  Any thoughts on this?
>