Problem of the week? Lets just say problem of the month!

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©Honorary Essex Boy™
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OK guys as promised this week I start the new refurbishment of a surgery, all the existing electrical supplies will be removed apart from the 16mm twin and earth for the upstairs flat.

The survey pictures are here.Manchester-20120504-00051.jpg

The new installation will be compliant with both MEIGaN and the HTM06 and of course BS7671.

The service head will not be changed it is not metal, and the neutral has been confirmed as linked and not fused. The box beneath the meter is where all the cables enter the meter outlet, at present there are 3 16mm tails connected to each terminal!

The first part of the project is to get the surgery up and running, so a new lighting circuit and surgery power supply will be installed via a new distribution board, keeping all connected services until a later date.

From the incomer to the surgery isolation is 20m, the cables will run in the cellar and up the wall in trunking to the isolator switch and earth reference bar, the position of this is on the wall just outside the surgery door.

So first questions given the above details in order to comply with medical locations what would be your cable choice? and perhaps why?

Second question the above flat is currently protected only by the distributors fuse, its overall run can not be verified other than to say it is installed within the fabric of the building and probably at a depth less than 50mm, how can we retro protect this with 30mA RCD and maintain the required protection? Remember single and double pole RCD's and how they differ.

Third and final question for tonight, there is a x ray to be fitted in the surgery the manufacturer requests that it is supplied from a 10amp 30mA RCD, remembering that this is a medical location and the required touch voltages required what would be your cable choice for this?

Remember also that cables can be of a lesser CSA because of the earth bonding, all services and final connections will be labelled individually to the earth reference bar.

Good luck and do not worry, its posted in the student and learning section because we are all students, I included.

Manchester-20120504-00047.jpg

Manchester-20120504-00048.jpg

Manchester-20120504-00049.jpg

Manchester-20120504-00050.jpg

 
1. Are we talking about the mechanics of the cable or are we talking about the csa of the cable? Also is this cable choice solely for the cable from incomer to the DB or is it a cable choice for all equipment installed in the surgery?

Mechanics of the cable:

"HTM06

15.20 Multi-core LV distribution cables should have a

black outer sheath to denote their voltage rating."

And according to figure 39 of HTM06 cables should be double insulated?

2. Not just a single pole stand alone rcd unit?

3. going to say 1mm because table 4d1a show a current carrying capacity of 11A, the 10A RCD will protect the cable from any damage. Unsure as to what to do with the touch voltage so going to stick with this answer for now (although i have an inkling it is to do with 411.5.3?)

are tails to be upgraded to 25mm?

thats all i have for now......

 
The cable from the DB will go directly to an isolator switch, from the isolator switch all sockets and the medical equipment with exception of the lighting will be wired from this. Which presents a problem for the x ray, having its own circuit as per manufacturer's instructions.

The requirements state that the DB should be in near to the medical location, but does not give an example of what is "near", so it could be argued that 20m is indeed near. Providing local isolation is present.

 
Where's everyone else? Forum seems a bit on the quiet side. I'll give it another day or two and continue to play :)

 
Down here i am reasonably familiar with our version of your MEIGaN. our standard is called AS/NZS 3003/2011 "Electrical installations - Patient areas". I am having problems with the terminology.

we basically have two types of patient areas. one must comply with a "Body protected area" which really is a area where the patient is in a Doctors consultation room, examination rooms, mothers to be etc etc. the other is the "cardiac protected areas" this is where actual op/theatres, ICU, , High dependecy units. Basically enviroments where the likelihood of instruments being in contact with the insides of your body is greater. It is in the Cardiac protected areas where we pay closer attention to earthing. What i did find interesting in comparison to your post was that in any patient area (in AUS) the RCD devices must be located in the same room and rated at a 10mA trip. you mentioned 30mA.

 
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