Darrell, Your equipment was still considered a Class I product. And, yes, all operator accessible parts must have Double or Reinforced Insulation from hazardous voltages. Class II equipment relies on this Double/Reinforced insulation system as well as on a continuous metallic or insulating material enclosure. The key word is continuous. Its like having two enclosures, either two metal skins separated by air that will not deflect under strength tests, or a single metal enclosure alongside a continuous insulating material that provides this Double/Reinforced insulation. Check 1.2.4.2 Definition section of Class II equipment in any of your IEC 950 derivative standards. However, Class II equipment must not employ a green/yellow earth wire, although a separate ground wire is allowed for equipotential bonding where required. Check section 2.5.2:
"Class II equipment (double insulated) shall have no provision for protective earthing except that it may be provided with a means for maintaining the continuity of protective earthing circuits to other equipment in a system. Such a means shall be separated from parts at hazardous voltages by Double or Reinforced Insulation." Tania Grant, [email protected] <[email protected]> Lucent Technologies, Communications Applications Group ---------- From: Darrell Locke (MSMail) [SMTP:[email protected]] Sent: Wednesday, December 01, 1999 1:50 PM To: '[email protected]' Subject: Re: safety ground wire I have in the past worked on a UPS project where we provided double insulation from all hazardous voltages to the operator interface, and a three pronged line cord with the green wire ground bonded to the chassis. In essence we had both types of protection which we thought was good. However, we received some confilcting views on this, especially concerning Europe. Some people said we could not have both. I do not remember the reasoning why. Is there anything prohibiting simultaneous protection schemes? Darrell Locke Advanced Input Devices ---------- From: Rich Nute To: [email protected] Cc: [email protected] Subject: Re: safety ground wire List-Post: [email protected] Date: Wednesday, December 01, 1999 9:19AM Hi Ken: > Thank you for your comprehensive answer. I am a little surprised that after > all the discussion in this forum on specs relative to the width of the > yellow stripe on the green wire that there is no rule on how or if things > get a green wire in the first place! The choice of whether to design any particular product as double-insulated or grounded is the manufacturer's choice. The rules are: If your product is grounded, it shall meet these requirements... If your product is double-insulated, it shall meet these requirements... We, HP, make both double-insulated and grounded computer peripheral products. We waffle back and forth between the two constructions, and are not consistent in our choice. Our primary motivation is cost. Two-wire seems to be lower cost (one less wire, etc.). But, the EMC filter seems more difficult to design. Then, we are concerned with worldwide distribution. The same two-wire plug can be used in many more countries than the grounded plug (i.e., Denmark, Switzerland, Italy). So, there are fewer power cords to stock. But, we already stock all of the grounded power cords. Finally, there is customer convenience. Two-wire works everywhere, grounded only works in a grounded environment. Japan residences are 2-wire. Many European residences have both grounded and 2-wire outlets in various parts of the home. Many homes in North America still have 2-wire outlets. So, there seems to be some advantages to 2-wire. On the other hand, grounded is a very familiar construction, and is easy and straight-forward for both design and manufacturing. No rule. Manufacturer's choice, but biased by competition and "inertia" of the product line. Vacuum cleaners are 2-wire; washers are grounded. Best regards, Rich ps: Yes, we do get hung up on issues such as the width of the stripe on the grounding conductor because this is a RULE. The choice of using a grounding conductor is NOT a rule. The only rule is that the product must be either grounded or double-insulated. --------- 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). --------- 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). --------- 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).
