About three weeks ago, my boss's home lost one 'leg' of the incoming 240.
Every other 120 circuit in the box was live, every other alternate one dead.
No 240 devices in the house worked.

I told him over the phone to throw the main off/on, then take a peek inside
to see if there was any sign of heating/arcing where the two legs come into
the main.

His main is bolted to the buss bars, and the incoming lines were tight, with
plenty of No-Ox on the joints... nothing loose. Cycling the main didn't fix
it. He called an electrician.

The pro told him to just wait... it was a power company problem. Sure
enough, about two hours later, the dead leg came on, and everything is OK
since.

Now... I know only enough about distribution to confuse me about this
problem. The transformer on his pole is single-phase in, center-tapped
secondary on the output. You CAN'T loose just one leg, unless....

Unless is later; because -- yesterday my son-in-law reported the same
problem. This time, I whipped over to his house with a DVM, and checked it
out.

Same thing... one dead leg. But the can on his pole is the same
single-phase in, center-tapped secondary affair out. HUH? Three hours
later, power was restored.

So... unless.... unless there is a thermal breaker of some type internal to
the transformer and separate for each leg, as opposed to just shutting down
the primary.

Both my boss's and son-in-law's cans have "cricket" disconnect breakers on
the primary side.

Does anybody know if a standard residential transformer has thermal breakers
on the secondary?

Oh... yeah... metal content. The can is steel. The wiring is copper. G

LLoyd

"Ignoramus25009" wrote in message
...
The center tapped secondary of a xfmr can be thought of as two
secondaries in series. Surely, one of them could fail. Do a mental
experiment, take a xfmr winding and imagine cutting a wire. You would
still have power in one half of the winding.

Or, possibly, somehow contact coule be interrupted after the xfmr, as
well.

Sure... but the power has been back on solid ever since, and the power
company didn't come out to 'repair' anything.

LLoyd

Lloyd E. Sponenburgh wrote:
About three weeks ago, my boss's home lost one 'leg' of the incoming 240.
Every other 120 circuit in the box was live, every other alternate one dead.
No 240 devices in the house worked.

I told him over the phone to throw the main off/on, then take a peek inside
to see if there was any sign of heating/arcing where the two legs come into
the main.

His main is bolted to the buss bars, and the incoming lines were tight, with
plenty of No-Ox on the joints... nothing loose. Cycling the main didn't fix
it. He called an electrician.

The pro told him to just wait... it was a power company problem. Sure
enough, about two hours later, the dead leg came on, and everything is OK
since.

Now... I know only enough about distribution to confuse me about this
problem. The transformer on his pole is single-phase in, center-tapped
secondary on the output. You CAN'T loose just one leg, unless....

Unless is later; because -- yesterday my son-in-law reported the same
problem. This time, I whipped over to his house with a DVM, and checked it
out.

Same thing... one dead leg. But the can on his pole is the same
single-phase in, center-tapped secondary affair out. HUH? Three hours
later, power was restored.

So... unless.... unless there is a thermal breaker of some type internal to
the transformer and separate for each leg, as opposed to just shutting down
the primary.

Both my boss's and son-in-law's cans have "cricket" disconnect breakers on
the primary side.

Does anybody know if a standard residential transformer has thermal breakers
on the secondary?

Oh... yeah... metal content. The can is steel. The wiring is copper. G

LLoyd



As my uncle Alec* used to say, "There's probably a "loose disconnection"
somewhere." G

Jeff (Whose uncle Alec wuz an "alectrician" you see.)

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."

"Jeff Wisnia" wrote: As my uncle Alec* used to say, "There's probably a
"loose disconnection" somewhere."
^^^^^^^^^^^^^^^
I love it. My father once explained away a mystery by saying, "It just has
that property, I guess."

Ignoramus25009 wrote:
Seems consistent with the possibility of a thermal overload
somewhere...

Just trying to wrap my brain around the concept:

Say there is such a thing as an overload cutout which opens one of the
two hots.

Say you have a largish 240V motor or oven connected between the two
hots.

Won't many of the (low current) devices on the opened circuit see
lower-than-normal-to-normal voltage through the motor?

Sounds like a bad idea. I know that after you get past the breaker box,
any circuits that share a neutral must have breakers that open both
poles.

Of course, all sorts of bad things can happen between the power pole
transformer and the entrance panel, for example having the neutral go
open!

Tim.

Ping Bruce - this thread's going to Hell in a handbasket! Can you help us
out here? What could happen in primary distribution (not from the pole pig
to the house) that would cause 1/2 of the 120V outlets and all of the 240V
to go dead?

Bob Swinney
"Leo Lichtman" wrote in message
...

"Jeff Wisnia" wrote: As my uncle Alec* used to say, "There's probably a
"loose disconnection" somewhere."
^^^^^^^^^^^^^^^
I love it. My father once explained away a mystery by saying, "It just
has that property, I guess."

Is this another faulty ground line - using the one on the pole and not at the house ?
e.g. - the power company is replacing lines - and reconnects the protective ground.

Martin

Martin Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
NRA LOH & Endowment Member
NRA Second Amendment Task Force Charter Founder



Robert Swinney wrote:
Ping Bruce - this thread's going to Hell in a handbasket! Can you help us
out here? What could happen in primary distribution (not from the pole pig
to the house) that would cause 1/2 of the 120V outlets and all of the 240V
to go dead?

Bob Swinney
"Leo Lichtman" wrote in message
...

"Jeff Wisnia" wrote: As my uncle Alec* used to say, "There's probably a
"loose disconnection" somewhere."
^^^^^^^^^^^^^^^
I love it. My father once explained away a mystery by saying, "It just
has that property, I guess."





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"Robert Swinney" wrote in message
...
Ping Bruce - this thread's going to Hell in a handbasket! Can you help
us out here? What could happen in primary distribution (not from the pole
pig to the house) that would cause 1/2 of the 120V outlets and all of the
240V to go dead?

Bob Swinney
"Leo Lichtman" wrote in message
...

"Jeff Wisnia" wrote: As my uncle Alec* used to say, "There's probably a
"loose disconnection" somewhere."
^^^^^^^^^^^^^^^
I love it. My father once explained away a mystery by saying, "It just
has that property, I guess."


Nothing can occur on the primary side to cause a center tapped transformer
secondary to lose power on only one-half of the secondary. Even if the
primary is disconnected and another source energizes one side of the
secondary, autotransformer action will energize the other side. It has to be
a secondary side problem. High current connections will sometimes heat up,
open, cool and then arc and weld themselves together. Unless someone was
working on the secondary lines, expect it to happen again.

Don Young

The center tap of the pole X'former is the neutral. When one of the hot
legs is lost, you only have 120 V. on one side of the Xformer. Pretty
common fault on rural lines.
Bugs

On 10 Feb 2006 05:37:45 -0800, "Bugs" wrote:

The center tap of the pole X'former is the neutral. When one of the hot
legs is lost, you only have 120 V. on one side of the Xformer. Pretty
common fault on rural lines.
Bugs

If you lose either hot leg on the primary of a Delta connected (Hot
to Hot) transformer, or either leg on a transformer connected Wye (Hot
to Ground) you get Zero output. Zip Nada, Bubkis. The secondary is
one coil for the 240V, center-tapped, and the tap is grounded to
derive Neutral for 120V loads. If there's energy coming from the
primary, both sides see it.

The fault had to be on the secondary side of the pole transformer
somewhere (toward the house) - intermittent secondary winding, bad
splice, loose lug, bad fuseholder going intermittent, wire going bad
and burning open, etc. And it can cool down and magically start
working again - but that can't last.

Get out your infrared non-contact thermometer (or an IR camera if
you are made of money) and start scanning all the connections - one of
them is going to be much warmer than the rest...

Oh, and power meters do go bad occasionally, don't discount that.

-- Bruce --

--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
Spamtrapped address: Remove the python and the invalid, and use a net.