Insulation Systems, and double insulation ...

[tallison]

I'm searching for some good explanations and examples of basic, supplimentary, reinfroced, and double insulation. This pertains to the safety standards(UL, CSA, IEC...), in general. I've read the definitions in the standards but some good examples sure would help. I'm also interested in different ways of making a product double insulated. I can't seem to find any good books or articles written on this subject....do you know of any or can you help with explanations? Thanks, James

 

[CurtB]

Below is some reference information that I had. Hope it helps.

In any isolation scheme, there is a certain amount of insulation required to create the isolation barrier. IEC 1010 calls this basic insulation. If a breakdown in the insulation could cause dangerous current to flow through a human body, basic insulation is not enough safety protection. IEC 1010 gives the designer several insulation improvement options. Two of the options are double insulation and reinforced insulation. Double insulation is basic insulation plus some supplementary insulation (for example, another basic layer). If the basic insulation breaks down (single fault), the supplementary insulation keeps the user safe. Reinforced insulation serves the same purpose as double insulation except that the basic and the extra insulation cannot be tested separately.
-Isolation and Safety Standards for Electronic Instruments by National Instruments

 

[tallison]

Hi CurtB, Thanks for your reply. I appreciate it. Your response is very much like the definitions in the CSA, UL, and IEC safety standards. I'm really searching for specific eplanations, examples, and such. Do you have any specific examples of Basic insulation as it applies to an electronics box that has a 120V power supply cord as it's input?
Is Basic insulation the insulation sheathing on the SJT power supply cord, the PCB creapage/clearance of the opposite polarity 120V line and neutral inputs, the plastic enclosure that keeps the end user from touching any voltage inside the box (the enclosure has safety screws on it), or something else. Your examples are welcomed. By the way, do you work for National Instruments? If so, do you know Ken R.? I used to work with him at IOtech, in Ohio.
Thanks for your help. It's difficult to find anyone who has experience with insulation systems...James

 

[welshwizard]

Picking up on some of CurtBs points

Single insulated hand tools etc require a cpc earth wire as the safety conductor
If the earth wire breakes then the safety conductor is lost increasing the users risk of electric shock

Double insulated tools do not require an earth wire as the protection against electric shock is provide by the basic insulation plus the supplemetary insulation

They can still have a metal case to provide mechanical protection even though they are unearthed

Often used in high risk locations such as construction sites
because of greater risk from shock by indirect contact
My terminalogy is British