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Bandwidth Conservator
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Looks like the bolts were either never installed on that connection or they were not tight.
 

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Slave to the grind
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I'd bet a dollar to a donut that the local news station reported it as "A Transformer Explosion." :thumbsup:
 

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Slave to the grind
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:laughing: Caused by the ubiquitous "short circuit." Doesn't matter what happened: "Must've been a short."
Ubiquitous...that is a 2 Dollar Word right there. Biggest word I know is mayonnaise.:D
 

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Where would the relays be

Thats the "Blind spot", upstream of the LV side OCPD, the primary side OCPD (Fuses in this case) see nothing but a fully loaded transformer. Easily prevented with differential relays but that box is seldom checked on low bid installs.
I've not done line work, built plenty of services, what is a differential relay?
 

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Sky Seattle said:
I've not done line work, built plenty of services, what is a differential relay?
Measures the gazin and gazout current of a transformer and compares theoretically ratio, too much of a difference and it trips the upstream OCPD. Protects from the secondary winding of the transformer down to the next OCPD.
 
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Can you expand on that?
Device #87 - a protective relay that functions on a percentage or phase angle or other quantitative difference of two currents or of some other electrical quantities.

(See why I paraphrased?)
 

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Discussion Starter #20 (Edited)
Measures the gazin and gazout current of a transformer and compares theoretically ratio, too much of a difference and it trips the upstream OCPD. Protects from the secondary winding of the transformer down to the next OCPD.
Can you expand on that?
My understanding is like this:

Let's say the transformer's turn ratio is 10:1,
Primary current is 10 amps
Secondary current is 100 amps

Note that the primary/secondary current is 10:1

Now a short or fault on the secondary causes the current to rise sharply to 500 amps for example...now the differential is 50:1 so the relay initiates an upstream (primary) OCPD to trip. (my understanding also assumes that a fault will cause the transformer's core to saturate so that the primary current does NOT rise in a linear manner to the secondary current.)

That was a very oversimplified version as the relay has to account for inrush current and normal loading imbalance BELOW the set overload point.

Zog will elaborate and correct me on anything I messed up with that...

Edit: zog posted as I was typing..I like his answer better. :)
 
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