[time-nuts] Thunderbolt power supply open heart surgery

[Dave Ackrill]

Lux, James P wrote:

>> I do not know why they run it so high, maybe they think they will
>> sell more power.
>> The problem is that many appliances have a 240 or 250 maximum, dual
>> power supplies for 110 V
>> switch to take 220 V.
> 
> That's actually pretty unlikely. 110V might be what it says on the label,
> but in reality, nominal line voltage in the US is 120V, at least at the
> meter. There's a difference in the "service voltage" and the "utilization
> voltage" in most cases, for instance, 230V electric motors are operated on a
> 240V service.

It can make a difference where you are on the network as well.  Having 
been an Engineer with an electricity company here in the UK, and worked 
for a time in the planning office, the designs are based upon ensuring 
that the people at the far end of the feeders from a substation get 
their electricity within the stated minimum and the ones nearest the 
substation within the stated maximum.

In the UK we now have a +/-10% limit from a nominated 230V (single 
phase) supply.  So, nearest the substation you may well see up to 253V 
and the farthest away could see 207V.  As has already been said, at 
times of high demand the voltage will tend to be lower than at low 
demand times.  In order for the supply to be deemed to be out-of-limits 
the minimum or maximum must be reached for a significant period of time. 
  So, if it dips below 207V for only a brief time every now-and-then it 
doesn't count as being out-of-limits either.  Same applies to over limit 
as well.

Dave