Fuse wire question

Mr.Generous

I've had shocks off HT leads, they aren't especially painful so surely nowhere near fatal. I'd take 10 ht lead shocks over 1 mains shock any day. Explain that one please...

FreeBear

Mr.Generous wrote: »

I've had shocks off HT leads, they aren't especially painful so surely nowhere near fatal. I'd take 10 ht lead shocks over 1 mains shock any day. Explain that one please...

It is the volts that jolts, and the amps that kills.

You can take a shock from an HT lead which is in the order of 20,000V to 40,000V, but it is very low current. You can also get a shock from a low voltage source (e.g. a 12V battery), but if the current is high enough, it will kill.

High voltages and high currents, if they don't kill, do all sorts of really nasty damage to the human body.

Kernel_Sanders

Risteard wrote: »

you may be interested to note that the single phase supply voltage is actually 230V, not 240V. (It hasn't been 240V for around 22 years.)

It has. I may well have had 240V in my house in the last 22 minutes. I have a plug-in monitor, and the voltage varies between 228V and 245V. You'd be surprised at how much voltage can fluctuate in a single minute.

[Deleted User]

FreeBear wrote: »

It is the volts that jolts, and the amps that kills.

It's a commonly heard maxim, but it's a bit misleading because it implies that voltage and current are independently variable, which they aren't. The ratio of voltage to current is the impedance (of the body in this case). If a high voltage supply produces little current it's because it has a high source impedance, in which case the voltage isn't actually high once the body is connected to it.

It's correct though that the safety or otherwise of electricity passing through the body is determined by the current, about 20mA being the safe limit. In the case of car HT leads, they're quite a high impedance source, but another factor is that it's only a very short duration pulse unlike the mains, which is continuous.

Apodemus

Kernel_Sanders wrote: »

It has. I may well have had 240V in my house in the last 22 minutes. I have a plug-in monitor, and the voltage varies between 228V and 245V. You'd be surprised at how much voltage can fluctuate in a single minute.

My recollection is that the the permitted variation around the quoted network voltage is 230 +10% or -6%. So the maximum can quite legally be 253v. In fact I've heard it argued that the change from 240 to 230 really never happened as the old voltage was completely within range and the higher the voltage the less transmission loss there is, so companies prefer to be in the upper portion of the range.

Gloomendoom

Apodemus wrote: »

My recollection is that the the permitted variation around the quoted network voltage is 230 +10% or -6%. So the maximum can quite legally be 253v. In fact I've heard it argued that the change from 240 to 230 really never happened as the old voltage was completely within range and the higher the voltage the less transmission loss there is, so companies prefer to be in the upper portion of the range.

The voltage drops with load, hence the variation as kettles etc are turned on and off up and down the street.

Heedtheadvice

Ok guys and gals. Surely we all know that the modern spec is 230 +- and that gives a practical range that may be experienced..........That commonly varies around the historical nominal 240......Or even any other figure you wish to nominate with a different range that gives the same result.

It still remains that the correct spec is as Risteard posts, and it is still defined as Low Voltage by electrical definition. It should just be understood by the lay person that "low" does not equate to "safe" neither does it equate to insignificant.

Cue, end of off topic discussion?

Back on topic, surely it would be a good opportunity to fit a new unit compete with appropriate circuit breakers and get the fault fixed? It could be that the fault might just not blow the fuse and leave some exposed metalwork live risking injury?

[Deleted User]

Apodemus wrote: »

My recollection is that the the permitted variation around the quoted network voltage is 230 +10% or -6%. So the maximum can quite legally be 253v. In fact I've heard it argued that the change from 240 to 230 really never happened as the old voltage was completely within range and the higher the voltage the less transmission loss there is, so companies prefer to be in the upper portion of the range.

They wanted the voltage standardised across Europe, but didn't want the huge cost of changing the whole grid, so they widened the tolerances. We have 240V ±6%, and Europe 220V, so they introduced a standard of 230V ±10%, so that both systems fall within tolerance without the need to change anything.

http://www.schneider-electric.co.uk/en/faqs/FA144717/