UL voltage rating, is it RMS?

It definitely will not be the rms value as the peak voltage is dependant on the waveform form factor. rms value gives you the DC heating effect voltage into a resistive load. I suspect it is the peak voltage rating.

So a 10kV peak to peak poor form factor a.c. waveform whose rms voltage is 230V is perfectly ok on 300V rated cable?

Lol.

As always the problem of specifying complex technical data to the 'average user' rears its ugly head.

It's more usual to rate stuff like "250V AC/450V DC"to allow for the above.

The standard for testing cables, BS EN 50395 deals with such issues as follows: "Unless otherwise stated the test voltage shall be ac of approximately sine wave form and of frequency between 49 and 61 Hz. The ratio of peak value to r.m.s value shall be equal to sqrt 2 with a tolerance of +/- 7%. The values quoted are r.m.s. values."

John

According to BS EN 50525-1 completed cables for general use that are rated at 300V line to neutral are tested at 2kV rms for at least 15 minutes. Individual cores are tested for at least 5 minutes at 2kV if the insulation is >0.6mm thick and at 1.5kV if <=0.6mm. There is a lot of harmonization of standards, so UL is probably very similar. John

Thanks all, the cable certainly looks the part for carrying mains voltage. As it ahppens the requirement (making a long lead for a toothbrush charger) has now disappeared but it's still of interest.

Can one reasonably requir/mandate a three amp fuse in the plug on the end of the cable? If not then how do you make sure it's not overloaded? It's certainly not a requirement that all cables (on a UK plug top) can carry 13 amps safely.

Mandate, probably not... you could obviously fix a label etc.

In most cases that is something you control at the appliance end. i.e Is there any plausible non fault[1] scenario where the appliance that normally draws (say) 150mA could suddenly start to sustain a draw of 13A?

In the vast majority of cases the answer will be "no".

So an overload is only one of the over current situations that you design for, the more important one (typically) is dealing with fault currents. Also fault current protection *must* be at the source end of the supply, whereas overloads protection can be controlled by design and selection of equipment at the destination end of the circuit.

For an appliance protected by a fuse[2] you are not protecting the cable for 13A, but more likely from >100A - typically for a very short duration. Possibly counter intuitively, a 13A fuse will often protect a "3A" flex in these cases. (you can check this using the Adiabatic check as described here: