FAQ
TL;DR: Old Silesia/RIFA-style EMI filters use 2 Y capacitors to earth and are known to crack; “replace if found, always!” applies. [Elektroda, filipcichowskidev, post #21775596]
Why it matters: This FAQ helps bench technicians and restorers spot failing mains filters and choose safe, modern replacements, reducing shock risk and downtime.
Quick Facts
- Failure signature: cracked resin, moisture ingress, tar leakage/explosion, and rising leakage current in paper X/Y capacitors. [Elektroda, filipcichowskidev, post #21775596]
- Leakage limit reference: EN 50699 cites 0.75 mA under normal conditions for portable appliance testing. [Elektroda, filipcichowskidev, post #21778064]
- Field example: a lab PSU showed 10 mA between L–PE; swapping cracked RIFA parts for Würth fixed it. [Elektroda, filipcichowskidev, post #21775678]
- Recommended retrofit parts: polypropylene film X2/Y capacitors from WIMA or Würth Electronics. [Elektroda, filipcichowskidev, post #21775596]
- Cleanup tip: old tar potting removes with extraction petrol or WD‑40. [Elektroda, filipcichowskidev, post #21775596]
What exactly fails in old Silesia/RIFA mains filters?
Paper-dielectric X and Y capacitors absorb moisture after the resin case cracks. Leakage rises, leading to smoke, bangs, or tar ejection. The common‑mode choke usually survives. The EEVBlog rule of thumb quoted is “replace if found, always!” because these parts age poorly. [Elektroda, filipcichowskidev, post #21775596]
How much leakage current is acceptable during safety testing?
Use 0.75 mA under normal conditions per EN 50699 as a practical acceptance figure in PAT workflows. If you read values near or above this, investigate immediately. “Safety limits exist for a reason.” Replace suspect X/Y caps before returning the device to service. [Elektroda, filipcichowskidev, post #21778064]
I measured 10 mA from L to PE. What should I do first?
Isolate mains, discharge capacitors, and inspect X/Y caps for cracks or discoloration. Replace degraded paper capacitors with modern polypropylene film parts, then retest insulation/leakage. A real case showed 10 mA L–PE; replacing cracked RIFAs with Würth restored compliance the same day. [Elektroda, filipcichowskidev, post #21775678]
What are X and Y capacitors in EMI filters?
X capacitors connect across L–N to suppress differential‑mode noise. Y capacitors connect from L and N to PE to shunt common‑mode noise. Old paper types drift and leak; modern polypropylene X2/Y2 parts are safer and more reliable. [Elektroda, filipcichowskidev, post #21775596]
Why do these filters fail after years of service?
They operate hot and across the mains from power‑on to power‑off. Aging, voltage spikes, and poor historical materials accelerate dielectric breakdown. As one expert notes, components can fail “by themselves” after decades; this is a known lifecycle outcome. [Elektroda, 398216 Usunięty, post #21778433]
Are WIMA MP3 X2 or other brands immune to this problem?
No brand is immune to misuse or aging. Users reported a WIMA MP3 X2 that blazed and contaminated the supply. Select suitable class‑rated film parts, observe temperature and surge ratings, and locate them away from heat sources. [Elektroda, tos18, post #21778451]
Can modern equipment still show RIFA branding?
Yes. RIFA AB ended capacitor production in 1988; the brand moved through Evox Rifa and later KEMET (2007). You may still see RIFA‑marked stock or labeling even when supplied under KEMET. [Elektroda, gregor124, post #21779893]
Does older gear have to meet today’s safety standards?
Legally, equipment must meet the standards that applied at market entry. Current requirements do not retroactively bind earlier devices. Your workplace can impose stricter internal policies for continued use, though. [Elektroda, ArturAVS, post #21775715]
What’s the difference between common‑mode and differential‑mode noise?
Common‑mode noise appears on L and N simultaneously relative to PE; the choke and Y caps shunt it to earth. Differential‑mode noise exists between L and N; the X cap suppresses it across the line. [Elektroda, filipcichowskidev, post #21775596]
How do I retrofit a failed Silesia can filter with discrete parts?
- Remove the potted can and clean tar residue with extraction petrol or WD‑40. 2. Recreate the topology: common‑mode choke, two Y caps to PE, one X across L–N, all class‑rated film types. 3. Verify wiring, then run insulation and leakage tests before power‑up. [Elektroda, filipcichowskidev, post #21775596]
Are RCDs appropriate in TN‑C installations for these issues?
No. In TN‑C, protective earth and neutral are combined; RCDs are not applied. Use RCDs in TN‑S. A poster clarified their earlier mistake, noting RCDs fit TN‑S, not TN‑C. [Elektroda, filipcichowskidev, post #21781367]
I can’t source a 1990s IEC inlet filter from HP—what now?
Those combined switch‑socket filters can be hard to obtain. Consider bypassing the failed module and recreating the filter with discrete class‑rated film X/Y caps and a choke, observing creepage and wiring discipline. [Elektroda, filipcichowskidev, post #21775596]
Were RIFA capacitors common in Revox equipment?
Yes. Users report RIFA parts widely used in Revox gear, with some still not replacing them during service. Proactive replacement reduces future failures. [Elektroda, koko0, post #21779811]
What pre‑power checks should I perform on vintage mains gear?
Use an insulation tester before any live work, wear insulating gloves and goggles, and inspect transformer leads and sleeving. Replace degraded mains parts first, then power through an isolation transformer or variac. “A little paranoia never hurts.” [Elektroda, filipcichowskidev, post #21781219]
How do I clean up after a capacitor ‘tar bomb’ inside equipment?
Mechanically remove chunks, then dissolve residue using extraction petrol or WD‑40. Protect coils and delicate parts from solvents, and re‑varnish if needed. Finish by replacing the failed capacitors with polypropylene film types. [Elektroda, filipcichowskidev, post #21775596]
(note that this is just my opinion).
