Isolation Panel - Hospital or Surgery Room

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short circuit faulted

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Columbia SC
Had a service call yesterday on a isolation panel for a surgical suite. Found problem to be loose wiring connections causing OCPD to open.
However I have never run across a panel arrangement of this nature. Transfomer mounted in panel with 277V input / output 59.5 Volts on a "phase". Circuits connected to tandem circuit breakers providing 120 V between the two.
Having seen this group in action, I know someone can explain the concept to me. Thanks in advance and have a good day!

Steve
 
Re: Isolation Panel - Hospital or Surgery Room

Isolation panels with isolating transformers are ungrounded systems, hence, no grounding (or neutral) conductor. This is done to prevent leakage currents from finding a conductor directly to ground which can endanger patients or attendants in contact with equipment in the room.

Current will not flow from either line conductor if it touches ground, current will only flow when the conductors touch each other, thus eliminating the millions of paths to ground that can occur if a conductor insulation fails or a screw comes loose in a piece of equipment.

A current as low as 100 mA can cause a heart attack, so it pays to find a way to eliminate all those dangerous paths to ground in a surgical suite when someone has a piece of electrical equipment inside a patient's chest.

Square D has a good piece of literature on it which I used to first learn about them at:

http://ecatalog.squared.com/pubs/Electrical%20Distribution/Medical%20Products/Hospital%20Isolation%20Panels/4800/4800CT9801.pdf

Trenton E. Schaaf, E.I.T.
E/B/E, Inc.
Houston, TX
tschaaf@ebeemce.com
 
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