National Aeronautics and Space Administration

www.nasa.gov

C1 C2

0.1μF 10μF

Non-polarized Polarized

� CWRO9 & CWR11 capacitors identify 

polarity by a beveled edge in the case 

and/or a polarity bar marked on the 

case (“+” or a stripe adjacent to the 

anode termination).

� CWR06 capacitors typically identify 

polarity by a small projection “nub” in 

the center of the anode termination.

� Exceptions or variations to these 

conventions may exist.

Conventional schematic capture 

symbols for capacitors.

Examples of polarity marking methods for tantalum capacitors.

Polarized capacitors continue

to be installed incorrectly 

So why does reverse installation continue to happen even 

though we’ve had hard lessons in the past? Probably the most 

significant reason is that NASA’s parts derating policy masks 

the problem. NASA usually puts a part in an application that 

has significant margin on its forward operating voltage rating 

vs. the application forward voltage. When such a derated part 

is installed in reverse that large margin often results in no 

immediate indication or failure. This is in stark contrast to 

commercial terrestrial designs where applications with much 

smaller margin can result in immediate energetic failure.

A second significant factor in all of this is the polarity marking 

standards in surface mount capacitors aren’t “standardized” 

and are often at odds with one another. Does the black 

band mean positive or negative? Depending on the marking 

convention, it could be either.

One way a reverse installation error can be introduced as the 

design evolves is if a part, such as a capacitor, is changed 

from non-polarized to polarized without a proper update of the 

schematic and assembly drawings. In a recent occurrence, 

the failure of the power supply in a ground hardware simulator 

was the result of an abnormal voltage caused by leakage in 

two polarized capacitors installed in reverse polarity. Similar 

capacitors in the flight units on the ISS are also installed in 

reverse polarity but have not yet resulted in failure.

The capacitor components, which are polarized tantalum 

devices, were erroneously specified on the schematic with 

a generic, non-polarized capacitor symbol. These capacitors, 

originally 0.1 microfarad (μF), were later changed to 10 

μF, which necessitated a change from a non-polarized to a 

polarized part. The capacitor value was changed in the 

schematic and in the parts list without changing the part 

symbol. Accordingly, the translation from schematic to 

assembly drawing arbitrarily designated the improper polarity.

In another recent instance (different hardware), an onorbit failure was experienced due to a reverse polarity solid 

tantalum capacitor. Possible confusion due to differences in 

part polarity marking conventions may have contributed.

Best Practices for avoiding

reverse installation 

1. Ensure there is a procedure to review the parts list and 

verify in the various drawings that the polarized parts are 

installed or represented with the correct polarity. 

2. Account for changes from non-polarized to polarized parts: 

review and change schematic drawings as required to ensure 

proper part polarity.

3. Never use non-polarized symbols to represent polarized 

components in drawings.

4. Recognize that the potential exists for certain components 

to be changed from non-polarized to polarized during design 

evolution. 

5. Ensure assembly and inspection personnel are cognizant 

of the allowable variations of polarity markings for polarized 

capacitors.

References

NESC-RP-13-00874, Reverse Polarity Capacitor Installation 

Anomaly on the International Space Station (ISS) Expedite the 

Processing of Experiments to the Space Station (ExPRESS) 

Logistics Carrier (ELC) Simulator, Jan. 2015.

NASA Lesson Learned 981 “Reverse Polarity Concerns With 

Tantalum Capacitors,” June 12, 2000.

NASA Engineering and Safety Center Technical Bulletin No. 15-01

Even though NASA’s Lessons Learned Information System has an entry on the reverse installation of polarized 

capacitors, this error keeps reoccurring and is a “lesson not learned.” The purpose of this bulletin is to discuss 

some of the reasons this keeps happening as well as offer best practices to prevent this error in the future.

Preventing Incorrect Installation of Polarized Capacitors