fraser gilmour wrote
I went to really interesting meeting last week with some home therapy providers from round the country. I was the only tech there and it was interesting to hear the clinicians take on what's required for installing the equipment. One seemed to suggest that they don't have an electrician visit and simply plug a four way extension lead into an existing mains socket to run the equipment? I've always taken the view that the existing wiring needs to be tested to ensure the quality of the earthing at the very least.
We may also be the only ones who install battery backed up lighting for powers cuts? A lot of our patients live in rural areas which are possibly at higher risk of this but I'm prepared to accept this is overkill, anyone else considered this?
Hello Fraser,
I believe that you are correct in your belief that the wiring requires checking.
As you say, to verify adequate earthing and bonding, plus, I believe that the circuit to be connected to should be verified for defects.
For example, take a ring final circuit, it could have many latent defects, perhaps the most serious would be a lack of earthing or an open circuit in one of the ring conductors.
Now the engineering behind a ring is that current can flow in both directions from source to load thus load sharing both legs of the ring from the circuit or overcurrent protective device (MCB/Fuse generally in the "fuse box"/Consumer Unit) to the load.
The hazard posed by open circuit ring is perhaps best explained by an example.
A ring circuit by definition starts at the OCPD, travels to each socket looped at the socket and terminates back at the OCPD.
Imagine this drawn as a ring with the MCB at the bottom.
Traversing around clockwise, if there were to be a break in the current carrying conductors between the last device travelling clockwise around the ring and the return to the MCB, then basically you have a very long radial circuit.
This is likely to be protected by a 32A circuit breaker, and likely wired in 2.5/1.5 flat twin & cpc in a domestic environment.
This cable has a maximum current carrying capacity (CCC) of 27A in free air the installed capacity could be well below that.
Now if the socket chosen for your medical equipment is said last device on the ring (now radial) and the CCC has say been reduced to 24A due to installation conditions, which is acceptable in a ring, perhaps the ring is the only one serving the property, the MCB will never trip carrying 34A, it will trip in about 10,000 seconds at about 37A.
Now the rated current of the cable is at 70 deg C, it has PVC insulation, which will begin to degrade when run at this sort of temperature.
So, running a cable above it's installed capacity will result in the cable eventually reaching a temperature above it's maximum allowable, additionally due to the Joule heating effect I^2R, as the temperature of the cable increases as does it's resistance, and thus the energy dissipated in heat, etc. and thermal runaway commences.
Now, IMHO, if a Health Trust is providing equipment into a patients home, then they have a duty of care to ensure that the equipment is safe, and can be used safely.
If there is a circuit with such a failure mode, and a plug in machine (NXStage) is plugged in then depending on its' power rating, noting that it runs for a long time, if the circuit is already faulty and heavily loaded, this additional long term load, could potentially cause circuit thermal failure.
Now whose responsibility this is, would not be my decision to make, but, would the Trust be negligent in allowing the device to be used on a faulty circuit?
Would the Trust be culpable in the event of a second fault in the circuit?
Does such a machine require a functional RCD?
If so who tests it every 3 months in accordance with manufacturer's instructions?
Just some food for thought, sorry it's a long post!
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