60s lamp overheating

[Tadmeister]

That was if he replaced the flex - then the regs wouldn't allow the plug to be refitted to the new flex.

Hi again,

My friend wants me to replace the cable and the plug. Would it be ok to use 6amp rated 2-core cable like this: -
https://www.ebay.co.uk/itm/2-Core-F...146026&hash=item2a94bb19d4:g:9vgAAOSw7z1aAcuf

Or will the 6A max current be a problem. Not sure how much current a transformer (220V to 12V) like this would draw...

The fuse in the plug is 13A.

 

[Avo Mk8]

Hi again,

My friend wants me to replace the cable and the plug. Would it be ok to use 6amp rated 2-core cable like this: -
https://www.ebay.co.uk/itm/2-Core-F...146026&hash=item2a94bb19d4:g:9vgAAOSw7z1aAcuf

Or will the 6A max current be a problem. Not sure how much current a transformer (220V to 12V) like this would draw...

The fuse in the plug is 13A

On a technical note, the current taken by your lamp would be in the order of tenths of an amp (If that), so the flex you suggest would work. The 13A plug must have a 3A fuse in it.

On an ethical / legal note, if you are updating, hence modifying, the lamp, you are personally taking over responsibility for its safety. The lamp would have originally gone through a (hopefully) rigorous design and testing regime, and shown to be safe according to the standards of the time. By changing anything now, you invalidate that original verification. If it's your lamp, to be used by you, you might feel you are happy to take the risk of your own handiwork backfiring. But if its going to someone else, or be used by them, it's totally your responsibility to make sure what is done is safe (and prove it).

This really means technical competence and workmanship done to the proper standards, and then testing the updated item (eg PAT). Not knowing if "replacing the cable" involves screw terminals, or soldering, or modifying strain relief cos the flex is different, or if adding an earth will improve safety, it's impossible to advise.

Be sure to keep safe, and keep the lamp safe too!

 

[Simon47]

I would temper that warning with my feeling that replacing the flex on a "like for like" basis, assuming that's practical (as you say, we don't know how the thing is constructed) would be "routine maintenance" rather than "modification". So the legal risk is much much lower - but you still need to be able to test it (especially IR since it has unearthed conductive parts).
I would be tempted to replace the flex with 3 core and earth the metalwork, upgrading it from a questionable Class II to a known Class I device - but again, that's without knowing how practical that would be as I've not seen anything but the two photos. I also have the means to test it, which I'm guessing the OP doesn't.

 

[Tadmeister]

On a technical note, the current taken by your lamp would be in the order of tenths of an amp (If that), so the flex you suggest would work. The 13A plug must have a 3A fuse in it.

On an ethical / legal note, if you are updating, hence modifying, the lamp, you are personally taking over responsibility for its safety. The lamp would have originally gone through a (hopefully) rigorous design and testing regime, and shown to be safe according to the standards of the time. By changing anything now, you invalidate that original verification. If it's your lamp, to be used by you, you might feel you are happy to take the risk of your own handiwork backfiring. But if its going to someone else, or be used by them, it's totally your responsibility to make sure what is done is safe (and prove it).

This really means technical competence and workmanship done to the proper standards, and then testing the updated item (eg PAT). Not knowing if "replacing the cable" involves screw terminals, or soldering, or modifying strain relief cos the flex is different, or if adding an earth will improve safety, it's impossible to advise.

Be sure to keep safe, and keep the lamp safe too!

 

[Tadmeister]

Hi again,

Thanks for all the help everyone.
Here's a short vid showing construction of the lamp - insides plus the wiring path.

It is mainly plastic but has the metal arm which is carrying part of the 12V supply to the lamp. There are 2 bolts attached to this and there is also a screw holding the base on.

There is also a retractable metal hanger which I forgot to mention in the first vid. I've shown it in this one...

The hanger is inside a plastic channel which is separate from the main compartment.

Should I earth the metal arm?

Cheers

Tom

 

[Avo Mk8]

Hi again,

Thanks for all the help everyone.
Here's a short vid showing construction of the lamp - insides plus the wiring path.

It is mainly plastic but has the metal arm which is carrying part of the 12V supply to the lamp. There are 2 bolts attached to this and there is also a screw holding the base on.

There is also a retractable metal hanger which I forgot to mention in the first vid. I've shown it in this one...

The hanger is inside a plastic channel which is separate from the main compartment.

Should I earth the metal arm?

Cheers

Tom

All credit to you Tadmeister for a thorough video. I just need to absorb the information!
Well done for that - I'm sure you'll get some suggestions!

 

[Tadmeister]

All credit to you Tadmeister for a thorough video. I just need to absorb the information!
Well done for that - I'm sure you'll get some suggestions!

Thanks so much!

 

[Avo Mk8]

Hi Tadmeister Tom

Just a few thoughts:

I guess the first task is to find some 3 core flex that will feed through the base! The strain relief bush you have is a type that I thought, once clipped on the flex, was supposed to push into the exit hole from the inside. But it doesn't look if there's room for that. I did wonder if some other original strain relief occupied that rebate where the wire comes out of the base.
If the bush you have is a type that clicks closed and stays closed (around a new flex) it should be OK to use. If you need another, Google is your friend.

I don't think it is practical or necessary to try to earth the sliding hanging bracket. It seems to have its own insulated pockets to sit in.

I suspect it is worth earthing the metal arm of the lamp, as it's connected to the secondary of the transformer to complete the circuit to the bulb. Opinions anyone? Transformer is providing isolated supply, presumably built with robust isolation pri to sec. But if transformer fails, earthing a good thing!

You need to somehow get a good connection to the arm, eg via a ring tag to the screw connecting to the transformer, or soldering to the existing tag. It's good practice to make the earth wire longer than the other mains connections, so that if the flex strain relief fails, and the cable were to pull out of the lamp, then the earth wire would be the last to disconnect/ break.

Looks like you are happy to do some soldering, so good luck with the restoration. If you can find someone with a Portable Appliance Tester, or equivalent test equipment, to check earth resistance and insulation resistance when you've finished that would be great.

 

[Tadmeister]

Hi Tadmeister Tom

Just a few thoughts:

I guess the first task is to find some 3 core flex that will feed through the base! The strain relief bush you have is a type that I thought, once clipped on the flex, was supposed to push into the exit hole from the inside. But it doesn't look if there's room for that. I did wonder if some other original strain relief occupied that rebate where the wire comes out of the base.
If the bush you have is a type that clicks closed and stays closed (around a new flex) it should be OK to use. If you need another, Google is your friend.

I don't think it is practical or necessary to try to earth the sliding hanging bracket. It seems to have its own insulated pockets to sit in.

I suspect it is worth earthing the metal arm of the lamp, as it's connected to the secondary of the transformer to complete the circuit to the bulb. Opinions anyone? Transformer is providing isolated supply, presumably built with robust isolation pri to sec. But if transformer fails, earthing a good thing!

You need to somehow get a good connection to the arm, eg via a ring tag to the screw connecting to the transformer, or soldering to the existing tag. It's good practice to make the earth wire longer than the other mains connections, so that if the flex strain relief fails, and the cable were to pull out of the lamp, then the earth wire would be the last to disconnect/ break.

Looks like you are happy to do some soldering, so good luck with the restoration. If you can find someone with a Portable Appliance Tester, or equivalent test equipment, to check earth resistance and insulation resistance when you've finished that would be great.

Thanks again for all your help. I can squeeze some 3 core 0.5mm 3 Amp flex cable through the aperture in the base. Do you think that'd be ok?

I've also got some 2 core 6amp flat cable which fits a bit better but I think the earthed option is probably safer.

I'm definitely ok to solder - I've built guitar pedals and a Fender valve amp in the past. I have quite a bit of experience in this area but don't have any formal electricians' training so I'm in the process of learning the various rules and regulations.

I don't have any PAT testing equipment but I have a decent multimeter. I could test the current going through the cable...

 

[Avo Mk8]

0.5mm flex is rated at 3A, so 'compatible' with a 3A fuse in the plug, though as we all know it takes a lot more than 3A to blow the fuse!
BS1363 the standard for plugs seems to say 0.5mm can be fused at 3A.
As suggested previously, the lamp is only going to take 1/10ths of an amp - it's fault current that's the issue. In practice I think your 3 core should be fine.

 

[Tadmeister]

0.5mm flex is rated at 3A, so 'compatible' with a 3A fuse in the plug, though as we all know it takes a lot more than 3A to blow the fuse!
BS1363 the standard for plugs seems to say 0.5mm can be fused at 3A.
As suggested previously, the lamp is only going to take 1/10ths of an amp - it's fault current that's the issue. In practice I think your 3 core should be fine.

Thanks again. I think I can get the strain relief bush on the new cable but there is absolutely no room in the exit hole to wedge it in there so it will have to be just inside, stopping the cable from being pulled out (as it was with the old cable). However the fit is so tight with the 3-core that I don't think the cable would budge anyway.

Could I ask one more question? Inside the housing I would like to attach the new neutral wire to the end of the old neutral wire (which I have cut and you can see dangling in the vid). This is because the wire attaches to the rotary switch, which is right up inside the case, behind the transformer and so taking the old wire out completely and soldering the new one directly to the rotary switch is going to be a nightmare.

My plan was to splice (as in merge the strands) and solder the 2 wires together and apply 2 layers of heat shrink over the join. Is that the best way or is there an issue with the lasting insulation of heat shrink?

Cheers

Tom

 

[Avo Mk8]

Thanks again. I think I can get the strain relief bush on the new cable but there is absolutely no room in the exit hole to wedge it in there so it will have to be just inside, stopping the cable from being pulled out (as it was with the old cable). However the fit is so tight with the 3-core that I don't think the cable would budge anyway.

Could I ask one more question? Inside the housing I would like to attach the new neutral wire to the end of the old neutral wire (which I have cut and you can see dangling in the vid). This is because the wire attaches to the rotary switch, which is right up inside the case, behind the transformer and so taking the old wire out completely and soldering the new one directly to the rotary switch is going to be a nightmare.

My plan was to splice (as in merge the strands) and solder the 2 wires together and apply 2 layers of heat shrink over the join. Is that the best way or is there an issue with the lasting insulation of heat shrink?

Cheers

Tom

If you put the sleeving on the flex, make a mechanically sound joint and solder it soundly - i'm sure you know how to make a good joint, and then shrink two layers, I would judge that satisfactory. The alternative would be a crimp, but it's a fine gauge wire for that method.

 

[Tadmeister]

If you put the sleeving on the flex, make a mechanically sound joint and solder it soundly - i'm sure you know how to make a good joint, and then shrink two layers, I would judge that satisfactory. The alternative would be a crimp, but it's a fine gauge wire for that method.

Brilliant. Thanks again.