Line Isolation Monitors

[mikeames]

Are line isolation monitors still the standard for places like Operating rooms? Or is that less common? I read sites like the following and I don't quite follow the logic of how a GFCI is a replacement? LIMs are for isolated systems and warn but don't disconnect, obviously we know GFCIs. Anybody have experience on this? Also how does a LIM work? Does it just compare current on L1 and L2 of the secondary of the isolation transformer or does it do more?

Line Isolation Still Important

Has there been a change in the recommended use of line isolation monitors? We had an alarm today and we were told by our engineering department to

www.apsf.org

 

[roger]

Actually Isolated Power Systems have been on the way out for probably 20 years or more. In reality they were a hold over from flammable anesthesia days. You are right that when an LIM went into alarm it would not trip the device/circuit but the medical team would need to abandoned it or the equipment so it would essentially be the same as a GFCI tripping and taking the device out of service. The LIM is looking for a fault of any kind that would be over .006A, could be line to line, accumulative leakage, the system becoming grounded, etc...

 

[mikeames]

Actually Isolated Power Systems have been on the way out for probably 20 years or more. In reality they were a hold over from flammable anesthesia days. You are right that when an LIM went into alarm it would not trip the device/circuit but the medical team would need to abandoned it or the equipment so it would essentially be the same as a GFCI tripping and taking the device out of service. The LIM is looking for a fault of any kind that would be over .006A, could be line to line, accumulative leakage, the system becoming grounded, etc...

So they do use GFCI in the OR?

 

[jim dungar]

So they do use GFCI in the OR?

I wouldn't be surprised. Nowadays most OR equipment runs off of battery power so there is time to find an active receptacle.

I mean if backup power was so absolutely critical, surgery wouldn't be started while running only on a single generator.

 

[roger]

So they do use GFCI in the OR?

I have heard some locations do.

 

[garbo]

Retired from a large 500 bed hospital.When they remodeled maybe 16 of the original 1970's era OR'S they replaced the two LIM panels for each OR that had believe a 10 KW isolation transformer ( about 10 years ago ) with similar models. Every OR always registered at least 1 million of leakage and would alarm around 4.6 to 4.8 milliamps. Majority of the times they went into an alarm was due to defective warming blanket. We had a special box with several switches & pots that we attached our digital VOM meter to test LIM S every month to test them. Safe thing with LIMS is their is no true grounded conductor ( yea neutral ). They center tap the 120 volt transformer winding and ground that point so maximum voltage to ground always measured approximately 56 to 64 volts.Told us that in most cases safer to have an OR circuit go into an alarm rather then having it trip out ( if it was on a GFCI ). Will have to talk to one of my old coworker to see what protection they are going with in OR'S in new under construction hospital.

 

[roger]

They center tap the 120 volt transformer winding and ground that point so maximum voltage to ground always measured approximately 56 to 64 volts.

Actually neither winding is tapped, the system is two wire. The core is grounded but the windings float.

What you are describing is an article 647 system, three wire 60V L-N 120V L-L