See I told you there is no such thing as Safe Isolation. No one has mentioned borrowed neutrals?

So I was taught, and teach, when testing rubber soled shoes, no metal jewelry (tape if unable to remove for religious or sentimental reasons), don't lean on anything, one hand in your pocket and don't touch the shiny stuff! And remember there are bold engineers and old engineers but very few old bold engineers! 

My 2 pole voltage tester issued to me in the Post Office was a Drummond Test lamp known as a tester 133A. Standard issue until an engineer used it on a lift and managed to pull in a relay causing a contractor to energize and the lift to move causing a near miss accident.  Testers withdrawn and ordered to be destroyed and a a Martindale issued as a replacement.

The years roll on and I leave the Post Office. Later an engineer had a 2 pole tester hanging around his neck working on an isolated machine leaning inside the machine  manged by some fluke to short a power factor capacitor, with a broken blead resistor, and discharge the capacitor in to the centre of his chest causing him to convulse and wet himself. Big inquiry and back comes the Drummond Tester to be used to discharge capacitors

So would your safe isolation procedure would have picked up the charged capacitor waiting to bite you?

As Inspector Clusoe said, "always expect the unexpected".

JP

Afternoon Chris

I do a few 710 inspections of operating theatres (Group 2 locations). I was doing an inspection in a famous London hospital and found a broken back box around an equipotential bonding point. Drinking tea with the theater nurses who were going to clean up and prepare the theatre for use and mention that they needed to get the defect fixed before they used the room. They said don't worry we never use them anyway. I said but you do open heart surgery in there and she said no one uses them.

Speaking to a colleague of mine he said the same.

So is this true that we have BS 7671 regulations to provide them but  they are never used? Also if you did use them what would you connect to them? Me thinking if the installation was fully compliant with 710 ( I have yet to see one) everything would be bonded anyway.

JP

"What would you connect to them?" Here is the back of a medical camera unit such as are used everywhere nowadays. I assume that the pin on the back (zoom in if you wish) relates to 710.415.2.1. I cannot think of a better way of creating trip hazards than trailing coils of G&Y across the floor of an operating theatre, etc.

Graham will probably be on in a mo to say that symbol of a triangle with a circle in it is not the right sort of ground symbol for equipment like that To me it would read as 'ground zero' on a circuit.

Anyway it is neither a safety nor a functional earth sign that I recognize.

I'm also not surprised that no one wants any more trailing wires that the minimum.

Mike.

mapj1 said:

Graham will probably be on in a mo to say that symbol of a triangle with a circle in it is not the right sort of ground symbol for equipment like that To me it would read as 'ground zero' on a circuit.

See pages 20 and 25 of the instruction book.

Thanks Chris

Assuming that an appropriate lead is available then a short lead from the bonding point to the light over the table would do the trick and avoid a trip hazard?

Can I push my luck and ask why everything the clinicians attach to the patient is connected to the medical IT system and why the table the patient is laying on is a 230V Class 1 appliance, albeit hopefully bonded to the EBB?

JP

Hi John. Would an IT socket  provide power to a table employed for patient examination or treatment in a Group 2 medical location. Additionally, the table should be a Class 1 appliance with earth protection and should be connected to the equipotential bonding bar (EBB) to minimize the potential difference between various metal parts that may contact the patient or staff.

Well that's a new one 'potential equilization conductor'

EEB then to supplement the ADS ;-)

Mike.

mapj1 said:

Graham will probably be on in a mo to say that symbol of a triangle with a circle in it is not the right sort of ground symbol for equipment like that To me it would read as 'ground zero' on a circuit.

But then again, he might come along and say "If it's not a protective or functional earth connection, say because the product has Class II or similar construction, but the terminal is used to prevent static build-up or help equalize potential (behind which is a normally unhazardous current, but one that might be uncomfortable for patients, or cause involuntary muscle reactions or a perceptive reaction) that might be caused by capacitances or leakage across the insulation of the class II insulation, then it really is the correct symbol IEC 60417-5021: ">www.iso.org/.../ui

mapj1 said:

Well that's a new one 'potential equilization conductor'

If you call 1977 new (date from the IEC 60417 entry linked above). Used on medical electrical equipment quite regularly, also seen it on other electronic systems where you might have a similar issue.

The wheelie bin is much newer. Its use (in EU and member-state legislation) is older than its entry IEC 60417 -6414, which was made in 2019.

Resus ward , medical bed head trunking. You can just about see the symbol.

As JP suggests, I bet that it has never been used.

I wonder whether this facility is present in order to comply with an international standard which might be more appropriate elsewhere.

As JP suggests, I bet that it has never been used.

I wonder whether this facility is present in order to comply with an international standard which might be more appropriate elsewhere.