CU, head and meter enclosures fire resistance

[JohnW2]

So volt drop limits are not so old radios don't produce a mains hum or motoris don't stall it is just to limit energy loose due to cables producing heat!

As you know, there are not actually any 'limits' (only 'guidelines'), unless there is a limit specified in the appropriate product Standard for the equipment in question. I can't say that I've ever seen/heard of a product Standard which specifies any such limit - and, even if it did, I presume that it would specify the limit as the minimum absolute voltage supplied to the equipment/product, not as a percentage below some arbitrary figure.

I know that you seem to disagree but, if if one goes with the BS7671 guideline (for non-lighting circuits), the implication is that the voltage supplied to equipment in the UK could theoretically be as low as 204.7 (216.2V minus 5% of 230V) - so, as I've often said, I do not think that anything sold in the UK could be regarded as 'fit for purpose' if it would/could/might not work satisfactorily at that voltage.

Kind Regards, John

 

[ericmark]

Equipment was sold when we had 240 volt and a 4% volt drop limit, so there was loads of stuff sold which was never designed to work with the voltage we have now. And with the old style voltage regulations once the voltage drops to a set point there is a ripple, which causes a mains hum.

With motors the limit is not so defined, how low the voltage would need to go before it over heated or stalled I don't know, one would hope some overload device would trip, and it has been a subject of debate as to what fault could cause danger, however I have been involved with a fire caused by the fan in a fan heater failing, but there were other factors, it was not level, so when it stalled the heat did not open the thermal fuse. And I suspect it had other faults.

I know under voltage release is possible, and one would hope is the voltage is very important there would be some safety system, and with socket outlets it is not normal for them to be loaded to the maximum, so I think the problem with volt drop does not really exist with sockets.

But with lights I have seen many times where fluorescent lamps have failed due to start due to volt drop. Even that is a thing of the past with electronic HF ballast used today.

 

[JohnW2]

Equipment was sold when we had 240 volt and a 4% volt drop limit, so there was loads of stuff sold which was never designed to work with the voltage we have now....

In addition to the fact that you are talking about quite a long time (more than 30 years) ago, things have not changed all that much.

When the nominal voltage was 240V ±6%, the 'minimum permitted supply voltage' would have been 225.6V. If the guideline max VD was then 4% (I have to take your word for that), to be 'fit for purpose' for sale in the UK, products would presumably have had to work reliably down to a voltage of 216V (225.6V minus 4% of 240V).

Kind Regards, John

 

[frank999]

Very interesting ... I am considering voltage drop on cables from Solar Panels, but that will be for another thread.