Focomat 11C rewire

[rknewcomb]

Hi,
I need to rewire a Leitz Focomat 11C. The wires in this are before the days of polarized plugs so this maching has only a two prong plug to go into the wall outlet.
Once i exposed the wires in the actual lamp housing I can that is has three wires, white, black and red. The red is the ground because it is connected to the outter case of the lamp house.
First thing: The white wire goes to the center of the lanp, Usually the black is the hot wire and one would think that it should be going to the center.
Second: why would they have a ground wire (red in this case) if the whole maching only has a two prong plug for the wall? The cord that goes from the enlarger to the wall outlet looks original as does the plug on it.
I can get new wire and just replace them one at a time until the whole thing is rewired just like it is now, but doesn't that make the enlarger outside subject to getting electrically hot if a wire ever thouches the metal? and why the red ground wire if only a two prong plug?
thanks for your help.

 

[richard ide]

However it was hooked up before; it would be a good idea to use a 3 wire cord and plug and ground the housing.

 

[archphoto]

Could it be that the original plug has been changed in the past ?

For new wiring: hot > center of the lamp, return > outside of the lamp and earth to earth if you have a socket for it.
The need for an earth-wired-socket exists in wet places with a tiled floor and/or sink with running water.

If you have a darkroom without running water don't worry too much, just wear shoes, that will insulate you enough.

Peter

 

[rknewcomb]

Thanks for the help!
The original wiring has the black (hot) wire going to the outside metal of the lamp socket - that just didn't seem like a safe idea.
I still don't understand the red ground wire when the enlarger has only a two prong plug.
Oh well...

 

[Steve Smith]

The original wiring has the black (hot) wire going to the outside metal of the lamp socket - that just didn't seem like a safe idea.
I still don't understand the red ground wire when the enlarger has only a two prong plug.

If it only has a two pin plug then the live and neutral could be either way round depending on how you plug it in.

It would only be a problem if you can touch the metal part of the bulb holder when in operation.

I don't understand why an earth lead would be red. In the UK, red used to indicate live. I do understand why it would have an earth lead though. All exposed metal parts should be connected to it.


Steve.

 

[Bob-D659]

Older equipment usually had a screw on the chassis somewhere that you attached a separate external earthing or grounding wire. Older specification residential power distribution systems in europe and north america were two wire systems without a ground wire so the cords and wall sockets were only two pin. My Durst 659 is built this way, in fact so is/was my house as it was built in 1948.

Internal wiring colours in older equipment were usually whatever the maker used. Electrical code wire colours usually apply to the wall connect cables, not to internal wiring.

 

[rknewcomb]

Older equipment usually had a screw on the chassis somewhere that you attached a separate external earthing or grounding wire. "

That is the way this is. The red wire ends up attached via a screw to the heavy metal column.

So, should I attach another grounding wire to this screw and run it to a ground?

 

[Bob-D659]

That will do it. Helps keep the dust away as well.

 

[Arvee]

The old rule, here in the US, and I think it is still the same, was:

Black>brass>hot
White>copper>neutral
Green>ground.

The 'metals' refer to the metals used for each prong on a conventional 3 pronged plug.

It has been a long time but occasionally I would see plugs using a 'white' metal as well but I don't remember if this is substituted for the copper or the brass prong.

And now, of course, we have the larger prong to make sure the 'hot' line gets attached to the hot line.

-Fred

 

[Steve Smith]

I have always thought it strange that the neutral is at earth potential.

In the UK (and the rest of the world I think) the standard supply is around 230v. If you work on a building site and use power tools here you have to use 110 volt tools via an isolation transformer. The transformer also places the earth at a mid point between the output. That means that the maximum voltage relative to earth is only 55 volts which is relatively safe.

I don't know why this centre tapped earth system was never introduced domestically.



Steve.

 

[rknewcomb]

The old rule, here in the US, and I think it is still the same, was:

Black>brass>hot
White>copper>neutral
Green>ground.

The 'metals' refer to the metals used for each prong on a conventional 3 pronged plug.

It has been a long time but occasionally I would see plugs using a 'white' metal as well but I don't remember if this is substituted for the copper or the brass prong.

And now, of course, we have the larger prong to make sure the 'hot' line gets attached to the hot line.


In this enlarger the black wire is going to the outside of the lamp bulb socket. Since this is all run off of a two prong both sides the same size plug, one can't tell for sure I guess that Leitz used the black or white wire as the hot. Depends on which way you insert the plug into the wall outlet.
If this were just a lamp, it would be easy to fix. The focomat 11C has a on/off switch, a timer socket, and a small light box built into the base board. I'm a little afraid to start reversing wires to get the black going to the lamp socket center because I might end up making something else hot (like the outside of the lightbox).
I may just rewire it exactly as it is but run a ground wire from the metal column to an external ground.