Cold War EMP Protection

[jabrahams]

During a recent survey of Electrical Equipment in a repurposed Bunker at a Federal facility, I encountered what appeared to be several small capacitors, wired in series, terminated on branch circuit breakers on one end and terminated to the panel can on the other. This was in a 225amp 120/208 Volt Federal Pacific panel dating back to the Cold war. I was not able to get any nomenclature off of these little components such as Farad or Impedance Values. The are approximately 1/2" in diameter discs with leads out of either side. The circuit breaker itself was identified as "EMP Protection DO NOT REMOVE". Has anyone else encountered or possibly installed such a device? Would removal of the devise and installation of a modern MOV seem a better alternative?

 

[hbiss]

Those do sound like MOVs not caps. Interesting about the breakers marked "EMP protection". Did that come from the manufacturer or field labeling? If the bunker has been repurposed I would probably say you can just get rid of them, especially today.

-Hal

 

[jabrahams]

Those do sound like MOVs not caps. Interesting about the breakers marked "EMP protection". Did that come from the manufacturer or field labeling? If the bunker has been repurposed I would probably say you can just get rid of them, especially today.

-Hal

This was field labeling. I do believe this to be unnecessary at this point, and we are recommending replacement of the Panelboards regardless as they are 50 year old FPE. I've seen a lot of Panels and this is a new one for me. I wonder if any old timers recall installing these or designing this approach.

 

[mbrooke]

Those do sound like MOVs not caps. Interesting about the breakers marked "EMP protection". Did that come from the manufacturer or field labeling? If the bunker has been repurposed I would probably say you can just get rid of them, especially today.

-Hal

Theoretically they could be series capacitors to block large DC currents- though the OP describes them parallel. Its done on the neutral of power transformers to protect against geomagnetic storms and there is also series compensation of transmission lines (Cali has them) to control load flow.

 

[mbrooke]

This was field labeling. I do believe this to be unnecessary at this point, and we are recommending replacement of the Panelboards regardless as they are 50 year old FPE. I've seen a lot of Panels and this is a new one for me. I wonder if any old timers recall installing these or designing this approach.

Any pics? This would take the cake for the best pictures ever.

 

[junkhound]

Good of you to ask before removing the devices.

As for EMP, was part of the team that designed the EMP protection in Minuteman nuclear missile sites in the early 1970s, with upgrades stretching into the 90s.

Those thingys are MOVs as bliss already identified.

Only un-necessary if you want the Ruskies, Iran, or China to take over. :?

Don't recall the section of NEC that has the thermal equations as an option for current rating. One circuit has 18 AWG on a circuit with 10 AWG THHN otherwise, used as an EMP high reliability fuse, One junction box has a piece of 260C nickel plated wire made up with a short controlled length with bulky terminals, thermal analysis shows compliant with NEC. The wire link has a specific part number and is called out on all the facility drawings.

A few times an EMP uninformed hotshot USAF electrician in from the commercial world took the 18 AWG wire links out and put in a piece of 10 gauge. Ended up having to LABEL those boxes -- probably why the box you are working on has labels also, to prevent electricians from making the facility vulnerable to EMP.