[Info-vax] VMS and the Internet of Things (IoT)

[Chris]

On 09/13/16 12:50, John E. Malmberg wrote:
> On 9/13/2016 6:14 AM, Chris wrote:
>> On 09/12/16 18:55, johnwallace4 at yahoo.co.uk wrote:
>>
>>> The smart meters being rolled out in the UK are required to
>>> have, as well as the remote metering stuff, a remotely
>>> controlled power-off switch. No UK law currently permits use
>>> of this off switch, but that can be changed at a few hours
>>> notice when the state of emergency arises.
>>
>> Forgot to mention that, but does raise an interesting
>> question from an engineering pov. They need to be able to
>> switch a 60-100 amp load, the usual incoming fuse rating
>> here in the uk. They can either use an electromechanical
>> contactor / relay, or a solid state switch. A relay of
>> that rating is physically bulky, with large silver or silver
>> alloy contacts That solution would drop insignificant
>> voltage, but would need to be always on, wasting ~10Va each.
>
> There are electro-mechanical switching systems that consume no
> power in their steady state. It increases the cost of the switch slightly.
>
> One solenoid turns the switch on, one turns it off.
>
> In the case of something just used for an emergency power off, you only
> need a solenoid to turn it off and have a human operated reset switch
> turn it back on.
>
> Regards,
> -John
> wb8tyw at qsl_network
>

Agreed, a latching relay would get the job done, but there's still the
contact problem, which would need to be quite substantial at the current
rating. As for manual reset, I doubt that will happen as one of the
reasons for the power off capability is to allow disconnection where the
bill hasn't been paid. Brave new world indeed...

Chris