Electrolytic Cap case touching Enclosure: Problem?

[rubix cube]

Is there a problem with the top of an electrolytic capacitor being in contact with the (grounded) chasis?  I'm presuming not, but I may be wrong. (It is a power supply bypass cap, and there simply isn't any clearance between the top of it and the enclosure).

[gez]

A minute spent with a multimeter would tell you. 

[rubix cube]

OK, thanks.  Unfortunately my layout only currently exists as a design inside a graphics program.  So if there's no potential difference, there's no problem right?

[gez]

OK, thanks.  Unfortunately my layout only currently exists as a design inside a graphics program.  So if there's no potential difference, there's no problem right?

If there's no potential difference between the case and the lugs of the cap, then probably not. 

I have to confess that I wasn't sure of the answer to your original question, so I just grabbed a handful of caps and tested them.  As I suspected, there's no continuity between the casing and either of the lugs.  However, when I tested for resistance I had some intriguing results.  Small values had infinite resistance, but large electrolytic caps showed a large resistance between one of the lugs (didn't matter which) and the case, which gradually increased with time.  This suggests that the cap was charging - the case acting as one plate of the capacitor. 

How does this answer your question?  It doesn't.  Paging R.G. Keen! 

[PerroGrande]

Back in the day, I would troubleshoot circuits with my Dad.  He had his version of the audio probe, which consisted of a small amp and speaker (about 2") in a little plexiglass box he constructed for the purpose.  It always fascinated me...

Anyway...

When testing for where in a circuit the audio died or became distorted, he would go from stage to stage, using the probe to see where things went haywire.  I distinctly remember being able to hear audio from touching this probe to the top of electrolytics that were used as coupling capacitors. 

I've seen other circuits where clearance with caps was an issue, and they *did* put some form of insulator between the top of the cap and the case.  I'd imagine that a couple of strips of electrical tape on the inside of the cover would do it.  I wouldn't recommend taping the top of the electrolytic, as it is designed to open-up in case of a major problem.

[petemoore]

  electrical tape, plastic sheet of film, or even a dob of hotmelt glue can be used to make a physical gap between any two conductive elements that might touch.
 I just imagine static electricity or any other charge and try to avoid anything near the circuit rubbing against a conductive'.

[gez]

When testing for where in a circuit the audio died or became distorted, he would go from stage to stage, using the probe to see where things went haywire.  I distinctly remember being able to hear audio from touching this probe to the top of electrolytics that were used as coupling capacitors. 

Interesting.  This suggests, then, that some signal would be lost if the case connected to the chasis (if at ground potential).

[rubix cube]

Thanks for the replies.  I initially thought "surely no problem", then "well I could just insulate it", then curiosity made me wonder!