EBME Forums Forums Maintenance Technical Assistance EST on 3 phase medical equipment

In Malaysia we adopt IEC60601 and IEC62353 standard. Can I said that EST only conducted during installation of the equipment and during PM we only need to check Protective earth continuity.

If we are still talking about permanently wired 3-phase equipment (such as x-ray systems), my answer would be:- yes.

Whilst not wishing to wander from the original topic, can I please make the point that when it is applied to medical devices, it is Electrical Safety Analysing - not PAT testing, that is for domestic stuff. Rant over.

When testing fixed wired or 3-phase equipment, a number of safety tests can be carried out by
powering the safety analyser from a normal mains supply provided this is at the same earth reference
as the fixed wired equipment (single or three phase)
Tests that can be carried out this way are:
o Point to Point Earthbond test this will be the main test.
o Enclosure leakage
o Patient Leakage
o Patient Auxiliary Leakage
o Patient Leakage Mains on Applied Parts.

Due to the fix connection of the device under test (DUT), the safety analyser is not able to measure;
Earth leakage nor will the safety analyser be able to measure under single fault conditions (unless the
earth and neutral are physically interrupted at the switch board or mains panel).
To measure Earth Leakage, a current clamp can be used provided the earth wire is separated from the Live and Neutral wires.

The 4th Edition of the IET Code of Practice for In-Service Inspection and Testing of Electrical equipment (2012) now excludes medical electrical equipment from the scope and refers the reader to 62353.

Permanently installed equipment, which 3-phase units would most certainly be, are covered in more detail within the 2nd edition of IEC 62353 (BS EN 62353).

The testing would include:

• Visual Inspection
  
• Measurement of Protective Earth Resistance
  
• Measurement of Touch Leakage Currents - Only for parts not connected to the Protective earth
  
• Measurement of Applied Parts Leakage Current - Only for BF and CF Applied Parts
  
• Functional test
  
• Evaluation of Tests and Documentation

As most 3-phase equipment has no BF or CF Applied parts and probably no conductive parts that are not connected to earth the testing is quite simple.

However, I would always want to be sure the electrical installation, providing the mains supply, meets the required standard (IEC 60364-7-710 or BS 7671 Section 710) so you can be sure there is adequate safety. This can be done by simply asking for the last tests certificate for the electrical installation (in the UK called an EICR). If not available then consider measuring the loop impedance (TN supplies) or testing the RCD (TT supplies) as a minimum.

IEC 60364-7-710 Special location ideally for critical area that fall under Group 2 of the standards, probably area like ICU,OT,CV Lab are in that category of installation with isolation system or well know as IT system ( Isolation Transformer are use to monitor leakage current and earth resistance. The current measurement always have to less than 5mA
as a set point and it wont trip for single fault condition but will give you alarm for fault.

Off topic! I think you meant the LIM (Line Isolation Monitor) there. The isolation transformer is there for ... er, isolation.

See this .pdf (for example).

60364-7-710 covers all medical locations and these are grouped into three areas depending on the use of medical equipment and the threat to safety discontinuity of the supply poses.

Medical locations of group 1 include areas where any medical electrical equipment is being used and specify things like the use of RCD protection on supplies up to 32A. Locations falling under group 2 would be those where the discontinuity of supply represents a threat to life, so the use of a medical IT system is often used.

The medical IT system has a maximum allowed leakage current of 0.5mA (500uA), so in the first fault to earth condition the current is limited to the 60601-1 single fault touch leakage of 500uA. The medical IT system is fitted with insulation monitoring that will alarm when the insulation is below 50K ohms.

Oh yes last time we call them LIM but due to standard IEC 60364-7-710 they call it as Medical IT system and in USA they call as isolated power system.

Check for local UK product Starkstorm IPS unit.

http://www.starkstrom.com/