[guest]

Check this out:

http://www.youtube.com/watch?feature=player_detailpage&v=NRog9L2Y2f4

 

[BBQ]

Check this out:

http://www.youtube.com/watch?feature=player_detailpage&v=NRog9L2Y2f4

Nice!

I have some Scotch 33 and some Tek screws I can fix it!

 

[chewy]

Nice!

I have some Scotch 33 and some Tek screws I can fix it!

I did that to my muffler, last I saw it was going end over end on the highway.

 

[Meadow]

Nice!

 

[FrunkSlammer]

Backstabbed Receptacle Causes Catastrophic Electrical Failure

 

[Fredman]

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

 

[Zog]

Check this out:

http://www.youtube.com/watch?feature=player_detailpage&v=NRog9L2Y2f4

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.

 

[220/221]

Check this out:

http://www.youtube.com/watch?feature=player_detailpage&v=NRog9L2Y2f4

I'm pretty sure it was caused by an SE service or romex in a commercial building.

 

[CopperSlave]

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

 

[BBQ]

I'm pretty sure it was caused by an SE service or romex in a commercial building.

Poor 220/221, that was a terrible thing his scoutmaster did to him with a piece of SE cable. He was never the same after. :no:

 

[Big John]

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

:laughing: Caused by the ubiquitous "short circuit." Doesn't matter what happened: "Must've been a short."

 

[CopperSlave]

: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.

 

[Big John]

Ubiquitous...that is a 2 Dollar Word right there. Biggest word I know is mayonnaise.

I like to trot them out once in a while. Makes me feel like a big man.

 

[Sky Seattle]

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?

 

[Zog]

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.

 

[Awg-Dawg]

Measures the gazin and gazout current of a transformer.

I love technical jargon.:thumbup:

 

[guest]

I love technical jargon.:thumbup:

BTW another term for the differential relay is "gizmachie." :thumbsup:

 

[don_resqcapt19]

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?

 

[Zog]

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?)

 

[guest]

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.