Electrical Puzzle/Question

[John Keiser]

I live in a 50 unit condo serviced by its own 3-phase transformer. Each unit has a standard 200 amp breaker box [these are large condo units] which I assume is fed with a single 240v line. Yesterday the lights in the master bedroom and bath dimmed noticeably. These are fed off of 2 separate breakers. After cycling the breakers and still having dim lights I measured the outlets. Those outlets read 69v! [The outlets in other rooms were 120v.] The power company came [in the middle of the night] and changed the transformer. All is now normal. I was using a reliable digital meter. How do I account for 69v?

[gfretwell]

Bad winding in the transformer? That seems to be what the PoCo thought it was and they fixed the problem. BTW it sounds like you have 208 across the 2 hots in your panel. That is normal for 3p wye. With that much single phase load, I doubt seriously that you have delta (240v)

[Ralph Mowery]

As they changed the transformer you can assume it was bad, to state the ovious.

If only one side was low in voltage, then you could have a bad connection. As you did not seem to take the voltages off both sides of the line at the breaker box it could be one side would have about 150 volts on it and the other side had the 69 volts on it due to an open or loose connection neutral.

In other words, not enough information to give a very good answer. Just a couple of bad guesses.

[John G]

Based on the information that you supplied, it was a bad transformer that c aused the 69 volts.

If you had not found the cause, I would have suggested removing the two cir cuit breakers to see if there was any burning indication. Also to check fo r loose connections on the circuit breakers and the neutral bar. I also wo uld have suggested taking apart the outlets to check for loose connections.

John Grabowski

[clare]

bad "half" on your transformer phase - confirmed by transformer replacement solving the problem.

[George]

*Three men go to stay at a motel, and the man at the desk charges them $30.00 for a room.* They split the cost ten dollars each. Later the manager tells the desk man that he overcharged the men, that the actual cost should have been $25.00. The manager gives the bellboy $5.00 and tells him to give it to the men.

The bellboy, however, decides to cheat the men and pockets $2.00, giving each of the men only one dollar.

Now each man has paid $9.00 to stay in the room and 3 x $9.00 = $27.00. The bellboy has pocketed $2.00. $27.00 + $2.00 = $29.00 - so *where is the missing $1.00?*

[Mark Lloyd]

[snip]

It's very simple if you don't allow yourself to get mixed up.

Where's the money now? The hotel has $25, the bellboy has $2, the men have $1 each. That's $30. There's no missing dollar.

(the addition of $2 to $27 is inappropriate)

BTW, if you call the tail a leg, how many legs does a dog have?

[gfretwell]

$25/3 = 8.333 not 9

[Paintedcow]

4 if the dog is female. 5 if it's a male...

[Paintedcow]

Therefore, it;s no longer a puzzle.... The transformer was bad....

[John Keiser]

I knew the transformer was the cause; the puzzle was why 69v and not some other number? :)

[Paintedcow]

You should have asked the guys that changed the transformer...

[Phil Kangas]

"George" >

$30-$1-$1-$1-$2=$25

[John Keiser]

They responded at midnight [thank you Hawaiian Electric], the elevators had been disabled, and my curiosity grew overnight.

[clare]

Most lilely the one side had a shorted winding, shorting it pretty well in half.