about ?SOLATED power systems

[turkoman]

hello, I wonder if we must bond ?SOLATED Power system common earth bus to the main grounding busbar of a hospital or just earth this common IT EARTH bus to directly? which one is true. can u explain for me the final stage of earthing of the IT systems....

 

[davidbeach]

Ground is ground and ultimately all ground must be bonded together. If you truly have an isolated power system, it doesn't have a ground (earth) bus; that's the whole point of an isolated system.

 

[turkoman]

but we make grounding for receptacles at operating rooms???

 

[EEJaime]

An isolated ground system for a data system is different from an isolated power system for a surgury suite which uses flammable anesthetics.

The data systems' isolation is where the receptacle device has an isolated ground terminal that has an isolated grounding conductor connected to it, but which is isolated from the equipment grounding path that bonds the outlet box, conduit, panelboard can, etc.... This isolated ground conductor which terminates at an isolated ground terminal bus in the panelboard which is not electrically bonded to the panelboard can, but which is routed back through the distribution system all the way to the service entrance where it is bonded to the equipment grounding system. So a typical circuit run would include an ungrounded, current carrying conductor, ('hot' conductor-color coded); a grounded circuit conductor, ('neutral' conductor- usually white), and equipment grounding conductor, ('ground'-usually green); and an isolated ground conductor, ('isolated ground'-we use green with oranges stripe).

An isolated power system in a hospital setting is one where the neutral conductor is routed through the second pole of a 2-pole circuit breaker and the ground leakage currents are monitored by a line isolation monitor that trips the system with the slightest indication of leakage current.

We used to put these in all OR's but they are rarely used now as the use of flammable anesthetics has fallen out of favor with most of the surgical community. Current high tech hospitals we have done in the past 15 years have not been equipped with these.

 

[turkoman]

? ask you of operating rooms for example, how do you make grounding of the receptacles here? you say IT doesnt need grounding but if there is a ground fault on the circuit of the receptacle and no one cares about this fault seen on the LIM and one touches the other line accidentally he will get schocked all right? ?f you look up bender' catalogues it shows equipotential grounding of an IT SYSTEM in the operating room, but i think it doesnt consider there the latest stage of grounding, ? mean if we bond the local grounding section (i mean equipotential grounding) to the main grounding system? do you have any idea?

 

[EEJaime]

Again, the equipotential grounding system is a different animal than the IT system ground or an isolated system ground. In an OR or a critical patient bed, all conductive surfaces which may come in contact with a patient, or with someone whom may be in contact with the patient, must be bonded together to form an equipotential ground system. These have nothing to do with whether or not the power system feeding the equipment, IT or otherwise is using an isolated ground system.

If you have an isolated power system wherein the neutral conductor and the ungrounded conductor of each circuit are protected by a circuit breaker and a line isolation monitor. ANY fault seen by the LIM is immediately interrupted. No current can flow and all conductors are de-energized.

If by some odd occurance there is a fault between the ungrounded conductor and some other ground point, whether it be the equipment bonding conductor, an equipotentially bonded surface or conductor, or a piece of equipment, and the LIM sees current on the ungrounded conductor, but not the return path, then again the LIM will trip the circuit and de-energize the circuit and patient and personnel are protected.

I hope this helps. I have no idea what you mean by "the latest stage of grounding". The way we install the equipotential grounding system in an OR is by providing a Room Reference Ground Point. Which is a ground bus in a small panel where all grounding in the room is bonded to one point. The ground conductors from every outlet-normal and emergency, metal box covers, equipment and bed frames, med gas column or headwall unit, all grounding jacks, everything that may come in contact with the patient-is bonded together. I don't know if I am addressing the specific question in your mind. I hope so.

Regards,
EEJaime

 

[turkoman]

dear ejaime, i think we cant agreeWe have for all ORs 1 isolation transformer ok? in fact it is in theory nonsense to make a grounding right in this system because isolation transformer wont be earthed anytime ok? now when we have a ground fault on our OR branch circuit the LIM will alert us ok?? after this if we dont clear the fault by intervening so the second fault (on the other line of the circuit)will turn into short-circuit ok? at least what we apply in hospitals is this. My real question :
yes all the equipments made equipotential by bringing all them to the ground on the panel right? but what about bonding this bus? we make it tied with hospital basement earthing system or we earth it seperately with an electrode seperately or we just leave it as it is? excuse me i am not so experienced about

 

[Dknecht]

Hello gentlemen. I design, test and install Isolated Power Systems for hospitals. (Bender/Isotrol Systems) And EEJamie is correct regarding this topic. The key is the equal-potential point. All the equipment is bonded to the same point (typically in the ceiling, refer to Bender MGM - master ground module) so that the resistance between any conductive surface is less than 0.1 Ohm.

If you have any additional question regarding isolated power: design, function, testing ect. feel free to shoot me an email and i will post in forums if necessary

 

[waross]

or we earth it seperately with an electrode seperately

Do not use a separate ground rod. A major fault elsewhere in the building or even on the grid outside the building may cause a potential gradient in the earth. This could allow a step or touch potential in the area that you ae trying to protect. It is also contrary to code.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Dknecht]

EEJAMIE

"...LIM will trip the circuit and de-energize the circuit and patient and personnel are protected."

This is incorrect the LIM is a monitor not a contactor. The LIM will never de-energize the circuit... this is one of the main advantages for isolated power.


Think of it this way:
On a 1-ph system the LIM really only needs 3 connections to monitor. L1 (orange), L2 (brown), Gnd (green). There is no neutral. On a balanced isolated 120VAC system if you measure the voltage you should read:

L1-L2 = 120VAC
L1-Gnd = 60VAC
L2-Gnd = 60VAC

The LIM monitors the impedance (Z) value between L1/Gnd and L2/Gnd. The lowest value between the two is taken and the current that could flow from L1/Gnd or L2/Gnd is calculated (I=V/Z) and displayed on the LIM.

If I was to take a piece of wire and connect Gnd to either, L1 or L2, the isolated power system would become a grounded power system, no breakers would trip and power would continue. The only way you would know that the isolated power system became a grounded system is the alarm of the LIM.

 

[rbulsara]

Turkoman:
What is the latest? The latest is in the NEC code and IEEE standards.

Let us separate the two issues. IT equipment (or so called orange isolated grounding receptacles) and the isolation transformers used for Operating Rooms (OR). Those are two totally different applications.

1. For IT or computer equipment grounding refer to IEEE- Emerald Book for sensitive system grounding. It is very clear there there is not need to argue. For those orange receptacles called isolated ground receptacles needs to be installed per NEC 250.146. This isolated grounding method is NOT ungrounded nor do they call for two separate grounding systems. Eventually all grounds are bonded to the service grounding electrode system. There is no such thing as isolated IT earth permitted.

2. For Operating Rooms (OR) isolating transformer, NEC 517.160 and other related sections there. The secondary of OR isolation transformers can be ungrounded (it is optional), but there is still an equipment grounding conductor that needs to bonded to equipment enclosure and system grounding bus (electrode), see NEC 517.19(E)and (F). LIM alarms on the first ground and depending upon the nature of the second ground OCPD of those secondary conductors could and shall open. The first ground makes the system grounded, hopefully limiting the leakage current as stipulated in the NEC. Plus the isolation transformers and LIM systems need to meet other criteria in the NEC 517 and shall be approved for such use.

Here again, there is no separate grounding electrode system permitted. Do not confuse ungrounded systems with isolated systems.