In article , Iain Churches
wrote:

"Andy Evans" wrote in message
oups.com...
d) at least one connector must safely take 360Vdc (equals 250v AC
rating).

Morning Andy. That's odd. Most connectors and relays have a much
*lower* rating at DC than AC.

I was just doing a standard calculation as for capacitors - usually
about 1.4 to 1. Why is it different with connectors?

Odd isn't it. perpelexing too is that the same connector has different
ratings for different uses (military, broadcast or domestic)

The complications are due to variations in the anticipated range of
conditions of use, and in what effects/factors are regarded as setting the
limits.

e.g. For some items the main concern is a flashover or breakdown of the
insulation. The insulation may survive a 'brief' high voltage, but break
down after a given time if the voltage is maintained. Thus you may find
that an ac signal can have a higher peak level before breakdown than a
maintained dc.

Whereas for LF on some other items it may simply be that you need the
*peak* level of the waveform to be limited to the same level as the dc
maximum. Hence a factor of root 2 for sinusoids.

Some capacitors may suffer from internal dielectric loss dissipation
problems or plate conduction losses, so the max permitted ac might be
somewhat lower than the max dc. etc. Reason being to avoid overheating the
device. The expected environmental temperature will matter here as well.

Some connectors/cables may be rated for working under a pile of mud whilst
squaddies are jumping up and down on top of them. Others may not be
expected to cope with this. :-)


You have to be very wary. If your neighbour's world champion, best of
breed Rottweiler bites through your DC cable, it could cost you a pile
of the elusive spondoolicks.

Dunno if there us a mil spec for that yet... :-)

Slainte,

Jim

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