Quick electrical question

[S Viemeister]

I've seen two-seaters, where one was short and child-sized.

[ARW]

I won't.

It will just leave the Pandas to starve to death and the Asians nothing to build shit houses with.

[ARW]

There is a maximum VA for shaver sockets in bathrooms of 50VA (in the zones).

[John Rumm]

Well spotted!

BS 7671 (18th) does not seem to say much directly, but does call up BS EN 61558-2-5:2010 "Safety of transformers, reactors, power supply units and combinations thereof"

So I dug out a copy of that, and it does include the spec stating that:

"6.102 The rated output shall not be less than 20 VA and shall not exceed 50 VA."

However earlier the section "3.1.101 shaver transformer" states:

"isolating transformer for fixed installation and with a limited output, designed to supply electric shavers, toothbrushes, and similar appliances rated 50 VA or less used in a bathroom. It supplies only one shaver, or the like, at a time"

Which seems to be talking about a supply to only a single appliance, putting what we are discussing here somewhat out of scope.

Still, 50VA would probably be adequate for three - although that particular range I linked to only goes down to 60.

(the rest of the doc is not really relevant dealing with design proving and how to hit your transformer with a hammer etc!)

[Dave Plowman (News]

Be interested to know how you got 60Hz from a UK isolating transformer.

[Andrew]

My Grandfathers farm had an outside privy like that. There were two holes, one adult size and one kiddy size.

[ARW]

Not uncommon for urinals in some places - takeaways motorway services etc. Never seen it as a seat.

A lot have places have moved away from separate male and female toilets to unisex toilets. No pun intended but it has pissed a lot of the staff off. They still use them as male of female.

[alan_m]

Isn't your problem that you have purchased 3 separate items with faceplates wider than the back boxes. You cannot even glue 3 standard back-boxes together as they require a gap between them to accomadate the face plate overhang.

[Roger Hayter]

Is an electrician entitled to say that a plain socket fed from a separately mounted isolation transformer *is* a shaver socket for regulation purposes? Two faulty items fed from the same isolation transformer could have 240v between them, but not wrt earth. But seeing bathrooms tend to involve wet hands I wonder if you should have a separate remote transformers (or at least separate secondary windings) for each socket?

[Roger Hayter]

Is there a current limit written into the regulations, or is current limiting just a serendipitous feature of the cheapest possible single shaver transformer?

[Max Demian]

That's for the Three Bears.

[Max Demian]

I use brushes with removable batteries but use NiMH ones charged externally. But I find that the switches fail very soon. I get £5 brushes now, but even the original Braun/Oral-B ones didn't last very long.

[John Rumm]

There is no limit specified in the wiring regs (BS 7671) themselves, but they do call up a BS doc [2] that specifies the characteristics of the shaver point transformers. (see my response to Adam's post in this thread)

The specifies the allowable VA rating for a transformer[1] supplying a single shaver outlet to be in the range of 20VA to 50VA.

So you could argue there is a de-facto upper limit of a little under

220mA depending on supply voltage, and using the 230V output on the socket. So not really relevant from a safety PoV (since that is more than adequate current to be lethal), but it does impose a substantial limitation of the range of devices that could theoretically be powered from such a supply. [1] It includes electronic SMPSUs as well as traditional transformers [2] BS EN 61558-2-5:2010 "Safety of transformers, reactors, power supply units and combinations thereof"

[John Rumm]

Well to be fair, you could glue three together so long as you glue a spacer between each and the next to allow for the width of the faceplate. :-)

Not sure if the OP specified the wall construction where this collection of sockets are to be installed?

[NY]

Nah! If it was for bears, it would be "in the woods" since that's where they shit.

[Theo]

What does it say about SMPSUs? Are they covered by the 20-50VA limit?

For example, could I pick a (say) 48W multiport USB charger brick and wire that to a suitably IP rated wall plate of USB sockets? And rely on the SMPSU as isolation? Or alternatively a USB wall socket (that didn't have a mains socket as well).

Presumably this is how SELV works and that's taken to be OK?

Theo

[Dave Plowman (News]

Before the days of RCDs and when electrical musical instruments could be very crude, when these were used in TV etc studios, each and every instrument was fed with its own isolating transformer. Since microphone bodies usually provided a very good path to ground.

The reason for individual transformers being obvious. If you split the output from one to two devices, and one has a body at 'line' and the other at 'neutral' you get the full 240v between them.

Of course such a combination of faults might be rare, but you have to allow for it - or simply take your chances.

[GB]

Internal house wall. Tiled, with plasterboard behind.

[John Rumm]

I would expect any bathroom appliance / shaver to be double isolated and non conductive anyway, but yup the plugs are not polarised, so in theory the possibility exists.

(probably a moot point anyway since the OP has three separate isolated sockets)

[John Rumm]

So three deep dry lining boxes then - I would leave at least a couple of inches between them, otherwise the thin vertical strip separating them would potentially be very weak.