Voltage leak on Isolated neutral electrical gremlin

82angelfan

Member
Location
Hesperia, Ca
Please help explaining problem to owner.

Private Surgery center, 3 ORs. See attached Picasso Style drawing.

We built a private surgery center with three identical ORs. Each OR has an Isolation panel that is a combination normal power, critical power, separate feeds from critical system and normal system.

The panel is fed with Single Phase 480V 30amp to a 2pole main that then feeds a step down transformer to 120V. Neither coil is grounded, though the can and the branch circuits are attached to a ground bus, that jumpers both have per NFPA99 and 517 in code book. The Neutral from the secondary is completely Isolated. I believe this creates an ungrounded Neutral. The Secondary feeds a single phase panel, where A is 120 hot and B is Neutral. All branch circuits are fed from 2 pole 20 AMP breakers. There is a LIM module in the panels that monitors voltage, and more importantly leakage. Each OR also has a completely Isolated DATA system with Router, Switch box, and computer, linked to Monitors, booms, and data ports. All of this equipment is in a cabinet and plugged into a power supply similar to those used in IDF racks.

When using a meter, I get 124V hot to neutral, but a combination of that voltage from hot to ground and neutral to ground at the receptacles. When I plug in my Greenlee plug tester it reads OPEN GROUND.

My problem arises in only one OR. OR1 works the same as described above until that OR's Router AND switch box are plugged in. It has to be both, each has their own power supply. When plugged in, my greenly tester now reads as "good ground", both yellow lights on, but leakage voltage now RAMPS UP until alarm sounds on LIM. It only does this on critical side, so I am assuming the voltage is leaking through the neutral, not the ground. It also dues not RAMP UP UNTIL I PLUG IN MY TESTER at any critical receptacle or circuit.

I have checked all my connections, the issue is isolated to that one circuit that powers the data equipment but bleeds in to the other circuits. I have plugged the suspected equipment into a different circuit with same result.

Does anyone have any insight to what could be causing this. I am convinced the power supply has an issue, but could be the router or switch box. Why would the issue only happen when BOTH are plugged into the power supply. If one or the other is plugged directly into the wall, there is no issue.
 

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There is no neutral in Isolation Power Systems, you have two 60V legs. The LIM should alarm when the system is faulted to ground. Your plug in tester should never show what it considers correct wiring. Read 517.160 for more information.
 
Please help explaining problem to owner.

Private Surgery center, 3 ORs. See attached Picasso Style drawing.

We built a private surgery center with three identical ORs. Each OR has an Isolation panel that is a combination normal power, critical power, separate feeds from critical system and normal system.

The panel is fed with Single Phase 480V 30amp to a 2pole main that then feeds a step down transformer to 120V. Neither coil is grounded, though the can and the branch circuits are attached to a ground bus, that jumpers both have per NFPA99 and 517 in code book. The Neutral from the secondary is completely Isolated. I believe this creates an ungrounded Neutral. The Secondary feeds a single phase panel, where A is 120 hot and B is Neutral. All branch circuits are fed from 2 pole 20 AMP breakers. There is a LIM module in the panels that monitors voltage, and more importantly leakage. Each OR also has a completely Isolated DATA system with Router, Switch box, and computer, linked to Monitors, booms, and data ports. All of this equipment is in a cabinet and plugged into a power supply similar to those used in IDF racks.

When using a meter, I get 124V hot to neutral, but a combination of that voltage from hot to ground and neutral to ground at the receptacles. When I plug in my Greenlee plug tester it reads OPEN GROUND.

My problem arises in only one OR. OR1 works the same as described above until that OR's Router AND switch box are plugged in. It has to be both, each has their own power supply. When plugged in, my greenly tester now reads as "good ground", both yellow lights on, but leakage voltage now RAMPS UP until alarm sounds on LIM. It only does this on critical side, so I am assuming the voltage is leaking through the neutral, not the ground. It also dues not RAMP UP UNTIL I PLUG IN MY TESTER at any critical receptacle or circuit.

I have checked all my connections, the issue is isolated to that one circuit that powers the data equipment but bleeds in to the other circuits. I have plugged the suspected equipment into a different circuit with same result.

Does anyone have any insight to what could be causing this. I am convinced the power supply has an issue, but could be the router or switch box. Why would the issue only happen when BOTH are plugged into the power supply. If one or the other is plugged directly into the wall, there is no issue.
Leakage current Router and switch power supplies trick your tester show good ground.
Also your plugged in tester add leakage current for LIM alarm
Replace Router and switch power supplies medical grade(low leakage power supplies .
 
.Does anyone have any insight to what could be causing this. I am convinced the power supply has an issue, but could be the router or switch box. Why would the issue only happen when BOTH are plugged into the power supply. If one or the other is plugged directly into the wall, there is no issue.

I presume there is a network cable between router and switch.

What sort of cable is this ( cable type, shielded or no, cat rating, etc)?

How is the room network connected to the rest of the building?

How do the line to ground voltages change when different things get plugged in?
 
There is no neutral in Isolation Power Systems, you have two 60V legs. The LIM should alarm when the system is faulted to ground. Your plug in tester should never show what it considers correct wiring. Read 517.160 for more information.
Ah, I did not consider this. As soon as you said it, it makes sense. Thanks
 
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