OT-electrical w/Metal content

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.

LLoyd

Reply to
Lloyd E. Sponenburgh
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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.

i
Reply to
Ignoramus25009

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

LLoyd

Reply to
Lloyd E. Sponenburgh

Seems consistent with the possibility of a thermal overload somewhere...

i
Reply to
Ignoramus25009

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

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

Reply to
Jeff Wisnia

"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."

Reply to
Leo Lichtman

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.

Reply to
Tim Shoppa

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?

Reply to
Robert Swinney

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 Sw> Ping Bruce - this thread's going to Hell in a handbasket! Can you help us

Reply to
Martin H. Eastburn

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

Reply to
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

Reply to
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.

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Reply to
Bruce L. Bergman

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