I have a 1950s low-voltage lighting system, as described in this question, and while tearing out the wires in the basement, I somehow disabled the entire system. By trial and error, I discovered that the system works again throughout the whole house if I bypass the component circled in red and labeled A. This is only one of the transformers in the system, but it appears that they are all connected somehow. I added the white wire circled in green and labeled B to bypass component A, and now everything works.

Picture of transformer box

The questions are...

  1. What is component A?
  2. Why is it blocking current?
  3. Is it probably safe to bypass it the way that I have? If not, what should I do?
  • 7
    \$\begingroup\$ Looks like a fuse holder to me. Replace the fuse in it. \$\endgroup\$ Aug 21 at 1:01
  • 6
    \$\begingroup\$ It kind of scares me that someone who cannot recognize a fuse is screwing around with this system and jumping wires. (All they did was to bypass the fuse with a wire.) \$\endgroup\$
    – jonk
    Aug 21 at 1:08
  • \$\begingroup\$ when you replace the fuse, might consider a smaller current one and moving to LEDs. \$\endgroup\$
    – dandavis
    Aug 21 at 21:05
  • 1
    \$\begingroup\$ the cabinet contents don't look 1950s. more like 1980s \$\endgroup\$
    – Jasen
    Aug 22 at 12:23

Component A looks like a fuse holder to me. So it would be blocking current because the fuse blew, and it would NOT be safe to bypass it.

Can you get to the other side of the panel that it's mounted to to see if you can open the fuseholder and replace the fuse?


It looks like a fuse holder and if you look on the outside of the panel you should see a removable cap - usually with a screwdriver slot - to allow you to inspect and replace the fuse without having to take the cover off the system.

enter image description here

Image source: Littlefuse.

The fuse is a protection device and the fine wire inside it is designed to melt and break the circuit if it's current rating is exceeded for a certain time. It should not be bypassed but should be replaced by one of the same size after the fault which caused it to how has been fixed.


Component A is a fuse holder, the thermal sleeves are put on after soldering the joints on the holder.

The type of fuse in this kind of holder is most probably a cylindrical classical fuse, where it will be irreversibly blown subject to high currents. It can be open by cutting the sleeve, and usually a lead, using a string, is at the top. opening that will simply allow you to change the fuse.

In previous experiences, I have had the wire cut from the middle (the white wire in your case), have those exposed parts of copper soldered to 2 ends of fuse (same rating used in the original one), having a tiny sleeve on each end to insulate the exposed bits. This works really good, but needless to say it's a short term solution, it's not neat, it's not nice and most importantly, not that safe.

Of course, my good friend, it goes with out saying, working with live voltage is extremely dangerous so if you don't have previous experience and this project involves handling live voltages, refrain from carrying on with your project.

  • \$\begingroup\$ Those are insulated spade-type quick connects. They looked crimped. There are no soldered joints on that fuse holder. \$\endgroup\$ Aug 21 at 1:56

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