RL's Question:- what are people doing about inspection, testing, rating and on-going maintenance of multi-socket extension blocks? Does anybody actually suggest the users purchase or use them? Is the use of them actually acceptable in these days or just a necessity? Do we turn a blind-eye to this practice or what?

This is our Trust Bio-engineering group's view:-


1. Advice on use of MPSOs

The advice we give to Trust staff on the use of mains extension leads with medical equipment is based on BS EN 60601-1-1:2001. The main requirements of this standard are:
· The use of MPSOs should be avoided as far as possible – priority should be given to the installation of additional fixed socket outlets
· MPSOs shall not be placed on the floor and shall be mounted to prevent ingress of fluids and mechanical damage
· Connection to a MPSO shall only be possible by use of a tool, or the multiple portable socket outlet shall be supplied by an isolation transformer.

2. Testing of MPSOs

Clinical Physics/EBME has responsibility for testing all MPSOs fixed to medical equipment systems. It was agreed that testing procedures would be written into local work instructions. These should include the following:
1. MPSOs should be tested annually in addition to the electrical safety tests of each individual connected equipment.
2. Visual inspection of mains plug, flexible cable and MPSO. Identify signs of damage, overheating, fluid ingress etc. Internal inspection of mains plug and MPSO cord security, polarity, connections and contacts, unauthorised modifications or daisy-chaining, switches, plug fuse size appropriate to cable etc.
3. Polarity and continuity test of live and neutral on each socket outlet. This is easily performed on the Rigel 266 with the use of a standard IEC lead. Otherwise a standard ohmmeter will have to be used.
4. Earth continuity (bonding) test between earth pin on mains plug and each socket outlet earth terminal and other accessible metal parts. This should be tested at 10A and the resistance should be less than 0.1 ohm .
5. Insulation resistance between earth and both live and neutral pins of the mains plug. The test should be performed with all switches on. The resistance should normally be greater than 20 Mohm .
6. Total medical equipment system earth leakage. The current should be less than 0.5 mA with normal and reversed mains connection with all units live. Test not applicable if isolation transformer is fitted.
7. If an isolation transformer is fitted to the MPSO, the following additional tests should be performed.
a) Transformer earth leakage (less than 0.5 mA) and enclosure leakage (less than 0.1 mA).
b) Insulation resistance on the secondary side of transformer should be greater than 20 Mohm with all switches on (primary side insulation resistance only is tested by 5 above). This will require construction of a special lead with a mains socket at each end to connect the MPSO to the safety tester. This should be clearly marked “Test Purposes Only”, each plug should be fitted with a 3A fuse and have the live and neutral leads connected together as a safety precaution against misuse.