There is no such thing as 'RMS power'. The product of RMS voltage and
current which are in phase is average power. In IEC standards, voltages
and currents are RMS, and powers are average, unless otherwise stated.
The first dashed item is fairly well worded, The second and third are
not well worded. If your conclusion is about the first dashed item, it
would be more correct to say that the power /after /30 s (for an
unspecified time period) exceeds 15 W.
The second dashed item says 'has a power', which is vague. It probably
means 'dissipates more than 100 W', but at least the observation time is
specified.
The third dashed item is very different from the others. 'Available
power' is the maximum power that can be extracted from a source, not a
power dissipated in a load. So you have to look at the open-circuit
voltage V and source resistance R (maybe impedance if it's not purely
resistive) of whatever is feeding the potential PIS and calculate the
available power V^2/(2*R).
But the committee might not have meant that.
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
Rayleigh, Essex UK
On 2018-11-15 17:45, James Pawson (U3C) wrote:
Hi folks,
I seem to be more take than give at the moment, my apologies.
IEC/EN 62368-1 classifies ignition hazards as a *Potential Ignition
Source (PIS)*
/A //resistive PIS //is any part in a PS2 or PS3 circuit that:///
/– dissipates more than 15 W measured after 30 s of normal operation; OR//
//NOTE During the first 30 s there is no limit.//
//– under //single fault conditions//:/
/-- //has a power exceeding 100 W measured during the 30 s immediately
after the//
/introduction of the fault if electronic circuits, regulators or PTC
devices are used, or/
//-- //has an available power exceeding 15 W measured 30 s after the
introduction of the//
/fault.//
My questions:
1. It would makes sense to me that these powers are defined as rms
power. This would be the power that causes heating over time. For
instance a GSM module that takes bursts of 10W for at a 1/8 duty
cycle isn’t consuming 10W, rather 1.25W. The standard does not
state explicitly if these are given as Wrms.
2. If the above is true then I’m assuming that it would have to
exceed 15Wrms continuously for 30 seconds to be classified as a
Resistive PIS?
Can anyone help clarify this?
Many thanks!
James
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