How high voltages are allowed ?

Yes, back in the '50s I remember getting a serious shock off a 90V battery which had been supplied to a cinema - presumably to provide a hum free supply for the sound amplifiers of that period. I used to have great fun striking carbon arcs between carbons salvaged from No. 8 Ever Ready cells.

In the UK, there's something like the "Electricity at Work" Regulations which talked about danger etc. and I think the HSE recommended using it in conjunction with a Code of Practice where voltages etc. were spelt out with a little more detail. Some European Codes of Practice were even more explicit, but it was always difficult trying to generate understandable Company Instructions which were easily traced back to legislation. There's different legislation dealing with the use of electricity in supplied goods.

I don't know of a limit. Appliances need to be designed to be safe, which can be done in a variety of ways, e.g. insulating the 30kV in a TV, limiting the current of the 30kV from a ioniser, etc.

Isn't it all defined in the IEE regs? SELV is isolated from earth, PELV isn't.

Protection from direct contact not necessary provided less than 25 V ac or

For bathrooms, swimming pools, saunas protection required at all voltages.

For "Other areas" no direct contact for SELV > 12 V ac or 30 V dc, or PELV >

Source, IEE on site guide Feb 2002 page 19

IEE regs applies to electrical installations. The OP appears to be refering to appliances, not installations.

Not sure offhand but the old PO telephone exchanges ran (safely) on -50 volt battery systems with +50 volt for certain circuits as well, giving 100 volt dc in places. Ringing current was driven by 75 volt ac which used to give you a right old bang when you got the little men up your arm. The 50 volt dc was not noticeble at all. The rack fuses were quite novel with sprung metal contacts held under tension by the fusewire. When the fuse operated the spring moved and contacted an alarm rail, operating a relay which controlled a rack lamp, a signal to a bell and extended a remote alarm to a desk in a central main exchange etc. I seem to recall fuses or other prompt alarms lit a red lamp, deferred alarms lit a yellow lamp, there was a green lamp but my memory is running out on that one. anyone fill in the details?

Any voltage you like. If they're more than 50V though, they're no longer ELV and will require the same sort of protection that's normally required for these voltages. You'll notice that the old 90v batteries used plug and socket connectors with no externally protruding contacts.

And the 3kV dry Zamboni piles for the old Tabby sets (war-surplus infra-red binoculars) from Henry's.

John submitted this idea :

The ringing voltage did give you a jolt, not because of the 75v, but because it was much higher due to the circuit inductance.

Under dry conditions, 75v ac can hardly be felt by the hand.

"John" wrote in news:dkturf$10u$ snipped-for-privacy@nwrdmz03.dmz.ncs.ea.ibs-infra.bt.com:

My feeling was that the ringing was more like +/- 75 volts, but very unregulated, so if you got across an unloaded circuit, I can confirm you got quite a tickle.

I also managed to get it off the screw that held the jack plug sleeve on, if you were plugging while someone was ringing

They usually brought up a central alarm, there were also lights on the fuse panels, (10 fuses per row I think, plus the fuse alarm fuse - that way lies madness), so a light on each panel and bay would quickly get you to the blown one

mike

In-station?

The green lamp indicated a "release" alarm. If for some reason an electromechanical selector jammed whilst trying to release, a hefty current remained in the release circuitry. This, if not attended to pretty quickly, gave a lovely smell of burning electromagnet :-) In the last years of Strowger, a very slow time delay fuse was fitted in the release circuit (by replacing an n-link) - this (sometimes) saved the electromagnet.

There was also a blue alarm lamp, which indicated a fault somewhere in the power room - almost always a "prompt" alarm.

You get a 50 volt shock to earth whilst working up a ladder and you could be easily dead. It is usually only a little tingle, but if you are sweaty you may react and fall. I've done it, but managed to grab something on the way down.

It was pretty bad getting hold of a Telex line, where the potential swung between +/- 80V.

It's said that early GPO linemen had the worst experiences, having to jam their arms and torsos between bare open wires in foul weather conditions atop an 80 foot pole, the wires carrying all sorts of voltages.

Just bear this in mind, all you IT-type people concerned about the odd bit-error on your outside fibre-optic lines :-)

I wish there was a UK source of 90V batteries for my wireless stuff. I do have a USA source of 67½V batteries - they are made in China anyway!

SNIP

Ah it comes back to me now Now you have jogged my memory, I recall going round freeing off stuck selector mechanisms. I'd completely forgotten the blue power alarms, I suppose because they weren't very common. I also recall (depressingly) wiper adjustment on 3000 type two motion selectors, Uniselectors, AC9s and 11s. The advent of Simultaneous Cut , Strip and Wrap terminations, reading ATW diagrams, cable running (and stitching) on racks not the scruffy grid mesh which came in around 1965 or just after. The canteen on the top floor of the exchange in the Stonebow in York and Ron the blind TO who adjusted dials by ear. I worked on the development team for TXe2 Reed/Electronic exchanges after that before moving out of exchanges and into Process Plant Engineering and onto building services when the economic downturn hit. Nostalgia is setting in.

SNIP

And they didn't work on scaffold towers or cherry pickers but had a stout leather belt around the pole and boots with claws. God knows what a present day HSE safety rep wouyld have made of it. Those guys took a certain sort of pride in working under adverse conditions!

They weren't especially "safe", but 50V was defined as the limit of safety for no better reason than the enormous cost (to the government purse) of changing all the existing telephone exchanges if the "safe" limit had been set at something lower instead.

Telex was 90V DC too, which certainly did give you a belt if you touched it.

There are a number of safety standards that apply to products sold to the general public, and whilst can't comment on all of them, a general guide is that SELV 60V DC / 42.2V ac is the limit for operator accessible areas. Unless access requires the use of a tool and suitable warnings are provided in the manual/on product, a battery compartment would be considered to be operator accessible, so no more than 60V dc can be available there under normal or single fault conditions.

Charlie

| Interesing conversation cropped up elsewhere on how high battery voltages | are currently allowed for 'consumer equipment'. | | Now you used toi be able to get 90v batteries for valve radios...and some | of the current crop of electric radio controlled models are pushing up to | 60v and above in the sort of 8-10bhp motor type arena (yes, they do get | that big) | | The question arose as to what legislation affects how high a voltage can be | used in equipment sold to punters...any one know what rules exist - there's | a low voltage directive or summat...but there must be other stuff relating | to high DC voltages in things? | | I know,because it threw me across the lab, that even 40V AC off a PA | amplifier loudspeaker terminal is a pretty massive jolt.. | | | URLs to laws, or recommendations would be ideal...

Safety is a matter of both voltage and current. You can have as much voltage as you like provided that the current is very low, a few milliamps. (30ma on 240V mains)

The "low voltage" directive is a bit of a misnomer as you will see here

MBQ