When was it 440 volt?

[ericmark]

As a lad many items which were three phase were marked 440 volt but since becoming an electrician it has been 415 and then 400 volt.

Since the volts are given as single phase I would assume:-
Single - Three
220 - 381
230 - 398
240 - 416
250 - 433
255 - 442
Now it seem most likely 440 was maximum voltage 440.6337 is three phase voltage plus 6% from 240 and 438.2089 is three phase voltage plus 10% from 230 volt. It would make sense to quote highest voltage on a warning label. But only guessing.

So any one know why it was called 440 volt?

 

[JohnW2]

So any one know why it was called 440 volt?

I can but guess that, back in those days, they 'rounded up' to the nearest 10V, hence 440V became the (rounded up) 3-phase equivalent of 250V single-phase (433V rounded up to 440V).

Kind Regards, John

 

[wundaboy]

Isn't it because that's traditionally near as dammit the highest tapping for the no-load voltage on standard distribution transformers?

Certainly around here (Swansea) that's what Western Power and formerly South Wales Electricity seem to have done - its quite common to see no-load single phase voltages between 248-252 at supply terminals in properties not especially close to the tranny.

 

[RF Lighting]

That's higher than the average I'd expect to find in my area, but not unknown.

Having said that a lot of old industrial premises in my area still display the 440V warnings.

 

[ban-all-sheds]

It would make sense to quote highest voltage on a warning label.

And to rate stuff for the highest voltage.

 

[westie101]

Interestingly all new transformers come with a 250V (single phase) secondary. (or 250/433 for 3 phase units) And have done for many years back to the older BEBS T1 spec and the more modern ES I35/1 spec)

When commisioning on large networks we do have to take into account keeping within limits at both ends of the network. (and the time of day we commision the substation forms part of this)