I would like to know if anyone in the group has been involved with the AGENCY APPROVAL of a product containing a water-cooled live electrode or coil, and what had to be done to make this safe in the eyes of the agency. My company is occasionally involved with this sort of thing, and some feel that we are being overly conservative and perhaps unnecessarily burdening our products with extra cost. To date we have only CE-marked such products and have had no third-party involvement.
Partial list of concerns: (1) Is it considered necessary to completely isolate the water-cooled live component from circuitry by locating it in a separate chamber? (2) Single-fault safety when circuitry is in the same enclosure as the coil -- if the tube ruptures and the box fills up with water, this is a hazard as water is rightly considered a conductive element. Drains are sometimes used to avoid this, but there is still the problem of water spraying. Splash guards and the like may be used but this involves some expense. Is copper tubing considered inherently unsafe, i.e. something that is expected to rupture? (3) If we use de-ionized water (and stainless steel tubing to avoid the copper corrosion problem), can we assume the water acts as a protective impedance? Could we prove this by filling the chamber with de-ionized water, applying RF, and measuring the leakage current? How much RF leakage current is permissible? (4) Are water fittings considered inherently unsafe? We have been unable to find any agency-approved fittings. (5) Has anyone considered (or accepted) putting a ferrite around the water tubing to form an inductor, thus limiting the RF current in the water? Or coiling the tubing to create an air-core inductor? (6) I once received an RF burn from an experimental system with a water-cooled cathode. This was in a crude garage shop atmosphere (not our company). The cathode was immersed in water that was sourced from a faucet, so it was ordinary tap water. The supply was 400kHz, 5kW. The water supply hose was ordinary garden hose. Between the faucet and the cathode were two lengths of garden hose with brass fittings. I inadvertently touched the fitting that connected the two hoses together, about ten feet from the cathode. The only grounding at the time was whatever was achieved at the faucet. We later provided some grounding at the fittings and supplementary grounding at the faucet. All this prompts the question: Is it considered sufficient protection if the bulkhead fittings are fitted to a grounded enclosure? Are starwashers or the like required? (7) Is it necessary to provide a SUPPLEMENTARY ground for the enclosure containing the water-cooled coil/electrode? (8) What if, instead of running water THROUGH the coil, the entire coil is IMMERSED in water in a metal enclosure? Would double ground connections be sufficient, assuming the leakage current is within allowable limits? (9) Is it allowable to connect neoprene hose to the coil? I have some doubts about neoprene's capacity to withstand RF fields. What hose materials would be considered safe/reliable? (10) Is a drain required? If so, must it be large enough to drain the water at the maximum rate at which it could accumulate, or is the pressure relief provided by the drain sufficient? Then there's the question of equipment orientation . . . must a drain be provided to serve each potential physical orientation of the installed equipment? These are just a few of the questions that have come to mind as I've considered water-cooled systems in the past. I would appreciate your inputs on these and other related issues you may think of. Thanks for your time, Jeff Jenkins Senior Regulatory Compliance Engineer Advanced Energy Industries, Inc. Fort Collins, CO USA 80525 Opinions are my own and not necessarily shared by Advanced Energy Industries, Inc. or its affiliates. --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
