IBM IBM 35 Master Clock Electrical Connections

[Terry$]

I just completed a restoration of a 1941 IBM 35 Master Clock. Everything works great and looks awesome but I have questions on the electrical connections on top of the clock. I’m hoping someone can share a photo of the top of their 35 for comparison.

1. The black painted strip with stenciled numbers/letters designating connection terminals was worn away and I’d like to restore it to original. I can probably figure it out by metering the connection points but would like to have a picture of an original if possible.

2. The Bussman Fuse block for the power connection should have a cover of some kind to prevent inadvertent touching or shocking. In 1941, maybe no cover was thought to be necessary but for safety sake in today’s world a cover would be needed. Again a picture of some original may clear this up.

Attached are a couple of photos of my clock top for reference. Any help from an IBM 35 owner would be greatly appreciated.

 

[Steve Neul]

To me it doesn't look like it's wired right. I've never seen anything which the neutral wire was fused. Instead I think since the Master Clock is wired into and controlling other clocks the second fuse is for that purpose.

 

[TQ60]

Maybe...but...

This clock may be before current standards were in place.

Yes, it should be series circuit so only fuse on one side.

But this was before safety grounds were common.

Also, many places only had 110 volts, the other side wet to the other house.

So having a fuse on both sides insures that if either side gets a short it can open a fuse.

We have seen many odd power related things, electricity can take many different paths.

In this clock the hot wire Maybe goes to a switch for the winding actuator and maybe transformers or other switches for remote units.

The neutral is likely not switched and acting as common return.

If a remote device gets a wire that Maybe touches something hot and is connected to the return the path would be back through the neutral or common.

That fuse protects that alternate path.

 

[Steve Neul]

Maybe...but...

This clock may be before current standards were in place.

Yes, it should be series circuit so only fuse on one side.

But this was before safety grounds were common.

Also, many places only had 110 volts, the other side wet to the other house.

So having a fuse on both sides insures that if either side gets a short it can open a fuse.

We have seen many odd power related things, electricity can take many different paths.

In this clock the hot wire Maybe goes to a switch for the winding actuator and maybe transformers or other switches for remote units.

The neutral is likely not switched and acting as common return.

If a remote device gets a wire that Maybe touches something hot and is connected to the return the path would be back through the neutral or common.

That fuse protects that alternate path.

It wasn't the safety ground I was referring to. In that day there was only two wires for single phase110 circuit and only the hot lead was fused. At the time the other wire was considered a ground which today is called a neutral. The purpose of a fuse is to burn before the electrical wire does. It's there just to protect the wire.

 

[Terry$]

Thanks for the feedback on the wiring and fuse. Based on some wiring diagrams that I’ve found online it’s wired the way it was manufactured. I agree that two fuses would be unnecessary today but in the industrial age, they decided it was necessary. Inside the clock, the AC wiring goes to a 3 terminal strip, one directly to the winding motor, one feeds into the motor switch and the third returns from the other side of the switch and feeds power to the motor. I really don’t think it’s wired incorrectly, it’s just the way they did it back then. These clocks were also advertised as 110 or 220 AC or DC input so maybe the extra fuse relates to that option. I’ve read they use a resistor of some kind for the higher voltage input. Anyone have an pics to share of another IBM 35 top?