eddy currents 1

[baaman]

We are upgrading a old service, OH to URD. New service is 2 phase 14.4 in a fiberglass transcloser. Primary URD is in 2 pipes,schedule 80 pvc. Transformers are on a concrete pad, 6" with rebar. Will we have trouble with eddy currents, because of the rebar in the concrete? Thank you, Bob

 

[rcw retired EE]

Only if the rebar encircles an individual conduit containing conductors for a single phase with no conductors from the other phase. Even then the induced eddy currents in the rebar would depend on the rebar loop resistance and the resistance of the rebar-to-rebar connections. Most rebar joints are only wire tied and not welded making a relatively high resistance joint.

Also, induced currents are not typically a problem until the currents are in the high 100's of amps.

Search the forum. There were some discussion on this a few months ago.

 

[rcw retired EE]

Here is one thread that discusses rebar and enclosure heating.

thread238-335961

 

[baaman]

Thank you, that answered my question. Bob

 

[ghostbuster7]

Note: the ferrous loop will still carry current even if the loop formed does not encircle this conductor

 

[waross]

But not much current. If the conductor is not encircled (closed ferrous loop), the air gap (or concrete gap) will drastically reduce the magnetic flux and so reduce eddy currents and the heating.

Bill
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