90 degrees
Thats what I said!
90 degrees
Must confess, when I was ill-educated, I have done that, but never got a shock.
Surely, there's no "connection" between the two pairs of pins until both pairs are connected to their respective lampholders?
Fairly common these days, but older fittings didn't have namby pamby safety features like that. Though I suspect it's more a case of being easier/cheaper to make "insert and rotate" tube holders than to make spring out holders.The majority of tubular lamp holders don't make the circuit until you rotate the lamp ...
You reckon? I have no idea, and have never seen such an animal. If there's literally only one connection to one end, that presumably must mean that there is no filament at that end (there ain't going to be a conductor going along the tube) - which would seem odd. Of course, 'instant start' tubes have/had no filaments at all (just used a high enough striking voltage to strike 'cold', like a 'cold cathode tube'), hence just one pin at each end, but it would seem pretty odd to have a filament at one end and not the other. Maybe, for some reason, it's a half-way house between 'ordinary' and 'instant start' - do they use 'special' ballasts?Oddly enough, some philips fittings have two wires to one filament, and only one wire to the other filament, so who knows what goes on inside the glass tube ... Wheres john he will know
On reflection, maybe - but that doesn't alter what I wrote, which was essentially about 3 connections to the tube, regardless of the number of pins.I read it as the tube still having 4 terminals, but the fitting only using 3 of them.
That's also my understanding - it's only the cathode (negative side, at that moment) which needs heatingThinking back <quite a few years> to physics lessons, I think you probably only need a heater at one end to strike up an arc - if the polarity of the applied voltage is correct.
Quite so.But since we use AC, and with a magnetic ballast/switch start fitting it's indeterminate which polarity the fitting would try and strike up on. Also, there's probably little saving to be had by making non-symmtrical tubes - so there'll have been no reason in the past to make 3 terminal fittings.
Interesting. It does sound a bit like the 'half way house' scenario I mentioned - with the 'ballast' (odd word, really, for an electronic one!) providing enough start up voltage for the tube to strike (and 'stay struck') with only one filament (at one end) working. It would be interesting to play and see if it would strike with no filament at all (i.e. just one connection at each end, but you'd have to experiment to find out which one at the 2-wire end!).The electronic ballasts have 3 lamp output wires so are non standard really. I have only seen them as 4 foot T8 fittings. The fittings use standard 4 pin tubes which seem to work fitted either way round.
This quote from Wikipedia suggests that they may well strike with no filament at all:It would be interesting to play and see if it would strike with no filament at all (i.e. just one connection at each end, but you'd have to experiment to find out which one at the 2-wire end!).
Low cost ballasts mostly contain only a simple oscillator and series resonant LC circuit. ... This principle is called the current resonant inverter circuit. After a short time the voltage across the lamp reaches about 1 kV and the lamp ignites. The process is too fast to preheat the cathodes, so the lamp instant-starts in cold cathode mode. The cathode filaments are still used for protection of the ballast from overheating if the lamp does not ignite.
Didnt quite get that bitThe cathode filaments are still used for protection of the ballast from overheating if the lamp does not ignite.
Yes, I meant with only one of the two wires connected at the 2-wire end - so just one wire connected at each end. However, as I said, one probably has to get the right one of the two wires (shouldn't matter with of the two pins it connects to).I will try that next time I find one, and also get the ballast info John W2 ... I would not know off hand as they are twist holders and as you would know the connections not active till you twist it, usually with both ends in. But i can easily just try various combos of twisting one end at a time also trying the lamp either way in each end EDIT Oh just realised i think you meant 1 wire at each end
I presume they mean that the 'ballast' will go on generating ~1kV (and potentially getting hot) until the tube strikes - so, just in case it doesn't start 'immediately' (with ~1kV,in 'cold cathode' mode),it almost certainly will start one the filament(s) have had a chance to warm up, thereby 'sparing' the ballast.Didnt quite get that bitThe cathode filaments are still used for protection of the ballast from overheating if the lamp does not ignite.
Indeed, with one like the Wikipedia described. If there's ~1kV knocking around until the tube strikes, you wouldn't get me changing the tube 'live' (even though I often would with a 'conventional' fluorescent). It might even strike 'through me'!So as per the OP .. Could that create a shock risk from the exposed pin or pins to earth via your body if the opposite tube end was in and connected
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local