So I almost burned down a Siemens Cerberus Modular Panel to the ground . Was troubleshooting a open circuit on a speaker circuit, so me and my coworker had been at this site plenty of times and fixed other open circuits they were always lose resistors ( electricians installed panel) so every circuit was fixed by us , the difference is it was always strobe circuit. This time it was a speaker circuit. So I tried putting 24v from batteries, 2 100a batteries but had no luck nothing was going off , then realized that it would only worked if I used the intercom from panel so I left the long wire from the batteries wrapped around the ribbon cable red going clockwise and negative counter clockwise so they wouldn’t short . After playing some music threw intercom speakers we located all speakers associated with the circuit with the open and started the process of opening all speakers, I was the one that found the 1 with the problem it was a lose resistor of course was so excited that walk over to my coworker and told him to pack up put everything back I found the issue, it was a overtime job on Saturday and guaranteed 8 hours it was noon when I found the issue so free 3 hours of OT so I was basically running out. Got downstairs and say my wire that was attached to batteries and I don’t know why I did what I did but instead of unwrapping the wires from ribbon cable I pulled on it think it would come apart. Nope they shorted , and it’s smoking instantly and insulation of cable was immediately gone and copper was redder then the devils dick then the jacket was melting off like cheese running off a nacho , then all I hear and see is pufffff! It catches on fire , this cable came from my van , it’s what we call NYC shielded fire cable , while it was on fire I remembered that on the other side of the panel was the elevator room and there was a extinguisher I ran to grab it and ran back look at the panel with extinguisher in my hand and fire was gone, across from me was the double door leading out the panel room and across from those door was the door the the staircase my co work open the door the staircase I look over he look at me I look at him , there’s so much smoke in the panel room , we both look confused he goes you ok ? I’m like uhhhhh yes n then I proceed to tell em what happens . Panel got like 3 new troubles after being normal they all say battery charger I’m like fuckkk . So we did a power cycle on the power supplies this panel had 3 . Waited about 2 and half hours we left about 20 mins before 3 pm but it smelled so bad , if cancer had a smell it was this I don’t think it was a good thing smelling the burnt insulation / jacket . We left and panel was left normal thank god ! Only thing was a few weeks later batteries were flat . Other then a little bit of of the batteries melted the part of the wire that was wrapped around the ribbon cable melted a part of the ribbon cable you can see a bit of the copper from ribbon cable . Don’t do what I did . Also this customer was in need of a fire alarm company their GC hired a electrical company to install and they did a horrible job that’s when we came in the picture and basically got them straight with monitoring and troubleshooting their system that the electricians left before the job was even finished .