T&T: Why the Wye? (2 30a to 1 50a/240)

[Peter Bennett]

Friday, September 18, 2009, 5:18:41 PM, 2elnav wrote:

2nc> ----- Original Message ----- 
2nc> From: "Ken Bloomfield" <khtb at bellsouth.net>
>> 3.  You have described a delta winding at the shore utility end, but the 
>> phase relationship between the two hot wires must be 180 degrees apart, 
>> not the 120 degree relationship that you have mentioned.  There is the odd 
>> marina badly wired that in fact has the 120 degree relationship and 
>> appliances that need the actual 240 VAC (if any) will be unhappy.


2nc> REPLY
2nc> Ken  stopped short  too soon.
2nc> Many marinas  - especially those having been rewired or repowered by the
2nc> utility  company -  may in fact now have  3 phase power  going to each dock.
2nc> But only one phase per 120V  outlet
2nc> Except  now the 240V  outlets on a 50A 4 wire pedestal only delivers 208 V
2nc> instead of 240V.
2nc> The Smart Y connectors  will also detect this  120  phase angle  and also
2nc> reject a connection.

2nc> Arild

This would be an interesting topic for a survey. I wonder what
percentage of marinas actually deliver 120/208 3-phase power to the
dock outlets?

One of my yacht club's outstations delivers 600V 3-phase to the dock,
but that is stepped down to 120/240 by three single-phase
transformers. All dock outlets there are 30 amp 120V, so members
wanting 120/240 need a Y adaptor, and will get 240 volts, unless they
manage to connect to two 30 amp receptacles on different transformers.

Another outstation started out that way, but the docks were expanded,
and the new section is fed by a 600:120/208 3-phase transformer, which
has apparently upset at least one member who wanted 120/240 this summer.


-- 
Peter Bennett, VE7CEI    Vancouver, B.C., Canada
Ennos 31 "Honeycomb"
GPS and NMEA info: http://vancouver-webpages.com/peter 
Vancouver Power Squadron: http://vancouver.powersquadron.ca