> Needless to say I opened up the bench power supply to find that the trans=
former leads to the=20
> banana jack had it's enamel coating melted... I found out later that the =
DC ground was
> actually tied to the AC ground....... 145volts on the tested circuit and =
the bench PSU banana jack was hooked to AC ground too.......
>  =20
Most of the bench PSUs i've used have always had three jacks for each=20
supply, positive negative and ground (with ground being tied to mains=20
ground), if you want a floating supply you just use the positive and=20
negative if you want a supply tied to ground you can tie it to ground=20
youself.
>
> 1) Do I need to check ALL DC circuit to determine if it is tied to AC gro=
und?
>  =20
It's pretty normal for DC grounds (on all sorts of equipment) to be tied=20
to mains ground. Pretty much every desktop PC will have it's DC ground=20
tied to mains ground as does every osciloscope i've used.

It would probablly be wise when working on unknown equipment with a=20
connection to the mains to check for voltage relative to mains ground=20
before hooking it up to your bench gear. If there is voltage relative to=20
mains ground you should then test further to determine the impedance of=20
the equipment.

Getting a mains isolation transformer with a floating output is a good=20
idea if working on mains powered gear both to reduce the risk of damage=20
to equipment and to reduce the risk of shock to yourself.
--=20
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