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  • Author Author: shabaz
  • Date Created: 13 Jul 2014 2:30 PM Date Created
  • Views 3630 views
  • Likes 4 likes
  • Comments 17 comments
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Mains power control

shabaz
shabaz
13 Jul 2014

(This post was prompted by seeing a recent kickstarter project that some people may wish to use for direct mains control.).

 

It may be obvious, but using prototyping strip-board is not advisable for mains control.

It may not injure you, but may kill others who use the project, leaving you morally and legally liable.

Some less obvious things to non-engineers are things like strain relief, flame retardant materials, poor crimps, insulating barrier requirements and use of badly rated/designed cheap components that will never be compliant.

Here are some examples of designs not compliant in at least Europe (these images are reduced in resolution/cropped for fair use):

image

 

image

If you want to directly switch mains power, then avoid this type of design too, it is from a recent kickstarter claimed suitable for reflow oven use with a Raspberry Pi:

image

image

 

Here is another example of a UK product called the Mains Switch Widget - this extract is from the user documentation (extract is legal under fair use):

image

The above rings alarm bells for several reasons. The text in the user documentation snippet above states "this will help to anchor the connections in place" - is this valid according to standards in Europe? According to my understanding the method of clamping has to be well defined, so suggesting that hot glue is not essential but _may_ be used to help is confusing and not well defined, because either the method of clamping is sufficient to comply, or it is not. Also, how does a user know if it is secure? A cable tie can be tied by some people weakly, and by others more securely. Users will not know the test to apply to ensure it is compliant.

Also, the cable tie is wrongly applied to the cable in the photo above, since it should be further back from the unsheathed end. Note that this is not my photo, it is the photo from the product documentation!

 

Furthermore, for safety, since this is a permanently attached mains cable, the earth connection in the opinion of several engineers, should be the last to be stressed if there is any issue with the clamping of the cable.

 

When these points were raised with the creator of the Mains Switch Widget on this forum, the text silently changed in the user documentation - see here:

image

However, it is difficult to see how a documentation change can improve the situation much. The photo still shows the same length wires and cable tie too close to the unsheathed end.

 

Do check out the comments to the post below, for useful information.

A safe solution that requires no wiring is the Energenie modules - at £16.95+VAT for two of them, it appears well priced and safe. It is also cheaper than the Mains Switch Widget. I tried the Energenie modules out, and it was easy to get them working and controlled by the Raspberry Pi and with other microcontroller boards (they can be controlled via a remote control or via the Raspberry Pi etc.).

image

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Top Comments

  • gadget.iom
    gadget.iom over 10 years ago +2
    In terms of physical design this approach seems to be safer:
  • gadget.iom
    gadget.iom over 10 years ago in reply to shabaz +2
    Indeed. From an electrical safety perspective they seem far superior. A non-electrically minded person can use them without resorting to any mains wiring, and if the relay and wiring/traces are rated over…
  • mcb1
    mcb1 over 11 years ago +1
    Shabaz Looking at them ...(and cringing) they aren't compliant in New Zealand (or Australia) either. The middle one doesn't even have strain relief, and the least they could have done is made the earth…
  • gadget.iom
    gadget.iom over 10 years ago in reply to shabaz

    Indeed. From an electrical safety perspective they seem far superior.

    A non-electrically minded person can use them without resorting to any mains wiring, and if the relay and wiring/traces are rated over 10 amps there may be no need for an internal fuse.

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  • shabaz
    shabaz over 10 years ago in reply to gadget.iom

    Hi Paul,

     

    I agree too - sure they are more expensive but the C13/14 connectors save a world of issues. Many people don't use them however, and resort to "interesting" configurations as we have seen in recent days posts.

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  • gadget.iom
    gadget.iom over 10 years ago

    In terms of physical design this approach seems to be safer:

    image

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  • gadget.iom
    gadget.iom over 10 years ago in reply to Problemchild

    John Alexander wrote:

     

    Not sure if the chip is an Optoisolator or controller not that this would help the free wire situation on some Vero

     

    It looks like the device is an ATTiny 45 microcontroller. http://pleasantsoftware.com/developer/3d/reflow/comment-page-1/

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  • shabaz
    shabaz over 10 years ago in reply to gadget.iom

    Ouch!

    Added to the hall of fame:

    image

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