How do Edison Bayonet light fittings work?

[TulTrak]

I wasn't really sure which section to post this in, another forum might have been best but someone might be able to help.

I've been restoring two old lamps with standard bayonet fittings. When checking the switch I got a reading of almost 0 ohms between one mains terminal and one of the light bulb contacts, but no connection whatsoever for the other. This is the same on both fittings yet when tested with a bulb they work!

Any idea as to what's going on?

Thanks

 

[brightspark]

theres no such thing as edison bayonet fittings . eddison invented the eddison screw fitting. ES BULBS george lane fox invented the bayonet cap fitting. bc

 

[rtbcomp]

Not exactly sure where you were putting the test meter, but was the switch set to "on" when you did the test?

 

[wookie]

I wasn't really sure <snip>
Any idea as to what's going on?

Yeah ! you don't know what your doing...







Ok seriously, Stop poking around with that meter before you kill yourself, you obviously don't know what your doing.

However if you want to play and or learn here goes... apologies if I'm teaching granny to suck eggs but I have no idea what you know, if anything....

1) Unplug the light from the mains.

2) Switch your meter ON and set it to test continuity/resistance (as low as possible setting, your lowest setting might also bleep if it detects a good connection)

3) Make sure the meter leads are in the 'common' and resistance/voltage holes, NOT amps, and test your meter by touching the two meter leads together to check the meter is working.

4) you do a test by holding one meter lead on a connection and the other on another point to see if there is an electrical connection between the two points your touching, so try the following...

5) hold one lead on the neutral pin on the plug and the other lead on one of the 2 pins in the bayonet socket, you should get 0 ohms if not try the other pin in the bayonet.

6) now test live pin on the plug to the other pin on the bayonet socket, you should alternate between 0 ohms and infinity often shows as "OL" as you work the switch

7) now test earth pin to the metal body of the bayonet socket, not always connected, might be only 2 core wire.

8) finally you can check for safety that neither live or neutral have a connection to the earth pin and the metal body of the bayonet socket.

Hopefully you understood all that and are still alive, NEVER test anything that is plugged in, even if it is switched OFF unless you really know what you are doing.

Hope that helps you

 

[Master-of-none]

Some designs are made with a "unique safety feature" [that] ensures that whenever the bulb is removed, the exposed terminal brass plungers are cut off from the live supply.http://www.amazon.co.uk/Brass-Safety-Switch-Holder-Shade/dp/B007MPBSTI

 

[piman]

Hello TulTrac,

if I understand you correctly what you have checked is the switch works OK, and only switches one line, which should be live, the second contact is the neutral and is not switched.

Alec

 

[TulTrak]

Thanks everyone.

"theres no such thing as edison bayonet fittings" Thanks for correcting me Brightspark!

Wooshie, thank you for being concerned for my well being, however your post feels like it was written to make me look like an idiot, so thanks for that as well. I'm perfectly comfortable using all the features of my multimeters.

I was confused because one terminal was switching as expected, but the other was NEVER zero ohms. Master-of-none, that is a nice feature on the item you linked, that I hadn't heard of. These fittings are pretty old and had no earth so I doubt they have a feature like this.

I have now reassembled the fitting and fitted an earth. It is working fine I just don't know how one of those terminals is connecting!

And sometimes you do have to test on live equipment... as long as you are able to take sufficient precaution... (in this case I was testing that everything was safe)

I have another the same to finish, so maybe I'll yet figure out how it works.

Thanks all

 

[the snooper]

Wookie, thank you for being concerned for my well being, however your post feels like it was written to make me look like an idiot, so thanks for that as well. I'm perfectly comfortable using all the features of my multimeters.

Thanks all

I don't think that would have been his aim but it could have been written better, in fact it had no bearing what so ever on your question given that you had already used the meter as stated in your post and all you were asking is why you got no reading on one terminal

 

[DanielW]

You don't say what lamps they're,a standard table lamp does not have an earth unless its of metal construction like brass,steel,ect if its just a table lamp with a ceramic,or none conductive body then it does not have an earth.

 

[DanielW]

I've been restoring two old lamps with standard bayonet fittings. When checking the switch I got a reading of almost 0 ohms between one mains terminal and one of the light bulb contacts, but no connection whatsoever for the other. This is the same on both fittings yet when tested with a bulb they work!

Any idea as to what's going on?

Thanks

I'm assuming the switch is on the lamps flex? if so the reason you did not get a reading/connection whatsoever is the circuit was open,that is the lamp completed the circuit when you plugged the bulb in.

To test a lamps wiring just put the probes on nuetral and live terminals of the plug without the bulb,if there's no continuity then plug the bulb in and if there's contuity then the lamp is fine if there's still no continuity after bulb plugged in then the fuse needs checking.

 

[normspanners]

It is possible that the switch, if double pole is not actually making proper contact when tested because there is no current flowing the contacts may have/ probably arced in the past and have dirtied the actual tips but when the bulb is in place and switched on at the mains ,current will flow MAKING the contacts arc slightly and forcing the connection.
Test meter lead probes are notoriously difficult at making the trip, even on soldered joints sometimes, so dirty contacts are no better.

 

[wookie]

thank you for being concerned for my well being, however your post feels like it was written to make me look like an idiot, so thanks for that as well. I'm perfectly comfortable using all the features of my multimeters.

Well I did put "apologies if I'm teaching granny to suck eggs but I have no idea what you know" near the top of my post.

I didn't know if your problem was an actual problem with the light you were testing or because you weren't using the meter correctly, so I tried to provide as "idiot proof" instructions as possible, I am NOT calling you a idiot.

The reason I offered such basic instructions was I remembered the attempts to trouble shoot a switched mode power for a vintage computer on another forum I go on, after about 10 messages back and forth with some rather strange readings being reported by a novice using a multimeter following the directions offered, somebody realised he was testing the psu with it powered up and was poking around near heatsinks that were at mains voltage

 

[TulTrak]

To test a lamps wiring just put the probes on neutral and live terminals of the plug without the bulb,if there's no continuity then plug the bulb in and if there's continuity.

I like this approach, compared to checking of the two holder terminal seperately.

The lamp is an old brass lamp. I assume from a time before earth was deemed necessary.

It's very similar to this

And OK Wookie, thanks