HHD electrical installation

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HHD electrical installation

fraser gilmour
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?
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Re: HHD electrical installation

Ian Wilde
Administrator
You're not on your own Fraser, we do it too.
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Re: HHD electrical installation

Matt Waite
In reply to this post by fraser gilmour
Not considered emergency lighting. In the event of a power cut they'd (currently) have to work by the light of the dialysis machine! I don't know of this ever happening...

As for the install we get an electrician to look at the property. They fit one or two twin RCB sockets with an electric meter (to monitor their consumption) either to an existing circuit to to a new one as they think appropriate. Not sure what would happen if the electrics were pronounced unsafe requiring a re-wire
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Re: HHD electrical installation

Terry Simpson
We also fit emergency lighting
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Re: HHD electrical installation

fraser gilmour
Good to hear I'm not the only one
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Re: HHD electrical installation

Andrew Gardner
In reply to this post by fraser gilmour
Some patients are dialysing at home with catheters, is so the equipotential connectors must be used as a redundant earth. With both earth's tested.
Interestingly many clinics installations  also don't use the equiptential connectors to add a redundant earth.
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Re: HHD electrical installation

Andrew Gardner
In reply to this post by fraser gilmour
Really the installations should be electrically safe for clinical environment, there is a regulatory standard for this and it also specifies dialysis environments specifically. IEC 60364 part 7-710.

An equipotential earth should be fitted.
All the room earths should be cross bonded and differential earth impedance checked.
Emergency lighting should be provided
A Ze test should be performed

My opinion is,  as the EP earth is for redundancy a second 3 pin plug with the earth used for redundancy should suffice as it serves exactly the same purpose as the EP lead.

Interestingly many main HD units don't have EP points fitted and this directly contravenes the standard. Even new builds I have seen recently.

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Re: HHD electrical installation

fraser gilmour
EP points can serve two purposes, to link medical equipment with direct patient connections so as to reduce any potential difference and ,as you say, to create a supplementary earth to protect patients in case of an earth fault. We had EP points retrofitted at two of our sites where it was possible, and to comply the points needed to be connected to the earth reference bar back at the board, not just linked to the earth at the mains outlet on the wall. This is because the earth fault could be between the wall socket and the board. Having a supplementary earth that just connects to the wall outlet at a home location would probably not comply with the regulations.
This subject is such a minefield, I can see what the regulations are trying to do but to comply with them fully you would need each piece of equipment either hard wired in or connected with a non standard plug, plus enough EP points to connect all the medical devices back to the earth reference bar on the domestic consumer unit. Anyone doing this?  
I'm surprised you are finding new build dialysis units without EP, can't see a good reason for that.
   
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Re: HHD electrical installation

Ian Wilde
Administrator
In reply to this post by Andrew Gardner
If you're going to put a ep earth in a home environment and do it properly then it has to be a separate earth all the way back to the fuse board.

Using one of the AK series machines with a detachable iec lead I can see where you can get an earth fail. If the power lead is hard wired into the machine and it has passed an electric safety test I don't understand how there could be a problem? Especially if you use a machine where the dialysate lines are also earthed internally.

A home environment is such an uncontrollable place to operate equipment you just have to try and cover all angles I guess.
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Re: HHD electrical installation

PaulS
Hello,

I have just joined the forum, thanks to the admins for letting me in.

I'll give you a potted introduction, so that it clears the air, and you can all see where I am coming from, because I'm not a Renal Tech, but, I do know a few! ;)

I'm a professional engineer, and member of the IET, I also run an NICEIC Approved Contracting company, and we do a lot of HHD installs for our local health trust, and we have seen quite a few issues over time, and I would like to hope that I can give you guys who are involved in HHD works the heads up on BS7671 and associated guidance and legislation to help you keep your patients safe and dialysing @ home, and maybe even help you to extend your home programmes for the benefit of the patients and, your budgets! ;)


I'll leave my introduction here for a few days, then I'll look to comment on the rest of the thread, if that's OK.
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Re: HHD electrical installation

Ian Wilde
Administrator
Welcome aboard Paul

Always nice to get another angle on the problems we face especially when dealing with providing facilities in the home environment.
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Re: HHD electrical installation

fraser gilmour
In reply to this post by PaulS
Great to have your input Paul
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Re: HHD electrical installation

PaulS
In reply to this post by fraser gilmour
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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Re: HHD electrical installation

fraser gilmour
Thanks for the example Paul, for the reasons you've illustrated I'd be surprised if any of my colleagues aren't employing electricians to test before an install.

We currently have an electrician create a metered spur from an existing ring, or use an existing radial to create a dedicated twin 13A outlet supply for the equipment we use, electrical works certificate is provided. As our equipment is not really portable and the patient wouldn't be reimbursed if they moved it to a different outlet we use standard 13A plugs and accept that we don't fully comply with particular requirements for medical devices used in the home environment. We class it as low risk but if a patient really wanted to there is nothing to stop them running a faulty or under rated extension lead to the equipment and plugging it in. We considered using 16A rated CEE plugs for the equipment but our electrician told us we couldn't spur off a ring with these, so it depends how close to the board the equipment is as to how difficult big a job this is. I have heard recently it's possible to use BS546 plugs and sockets on fused spurs, but haven't fully investigated this.
 
The other consideration is the requirement for equipotential bonding/supplementary earth, particularly for patients using direct cardiac connections. Our clinical policy is not allow patients to dialyse at home on these lines so we have never considered installing EP points. And as the equipment isn't transportable and the earth connection isn't regularly interrupted the risk of loosing the main earth is very low. Again it would depend on how close the main board is as to how easy this is to do.
Hard wired emergency lighting is also something we have moved away from. The equipment has battery backup itself and the screen of the equipment we currently use kicks out quite a bit of light, so patients aren't plunged into darkness in the event of a power cut. This light can then be supplemented with battery powered devices.
One other thing I'm looking at is periodic inspection of the electrical supply and an acceptable interval.