Hi Bill:
SPDs, regardless of configuration, are notorious for being
prone to failure, either short-circuit or open-circuit or
any value of resistance between those two extremes. (One
cannot predict the energy the SPD will be required to
dissipate.)
From a safety point of view, all such failures must be
accounted for such that the safety of the equipment is not
compromised by any failure of the SPD.
If the SPD should fail open-circuit, then expected
transients that are therefore not attenuated, must not
cause the insulation to fail. Hence, the insulation must
pass the hi-pot test without the SPD in place.
As for the requirement for the GDT to pass the hi-pot test...
??? I don't have any rationale for this.
Best regards,
Rich
On 5/10/2013 10:11 AM, Bill Owsley wrote:
I'm running into a dilemma. Not being a Safety Engineer myself, but
rubbing elbows with them...
On a piece of ITE equipment, I need some surge suppression for
worldwide markets with one annoying requirement for 4 kV, otherwise
just 2 kV line to earth, and using either plugable cords or permanent
connection, whichever is worse.
Now the Safety guys tell me that MOV's alone cannot bridge the
insulation (Basic or Functional, I forget.) between primary and
earth, when using one of power cable options mentioned above.
But a proper qualified (GDT) gas discharge tube can do the bridging.
So we figured to use them in series.
On a quick and dirty bench test it works to 4 kV.
Then the Safety guys pull out the rest of the story and point out
5.2.2 which seems to indicate that the GDT is to meet the Hi-Pot test,
1500 vac.
Previously, section, 1.5.9.4 (?) indicates that the surge protection
devices can be removed during the Hi-Pot test.
But now I have a Surge suppression circuit that has to withstand the
same Hi-Pot as the rest of the board.
Question is how does a surge protection circuit protect the board when
it has to meet the same Hi-Pot test?
In other words, when a surge comes along, which is going to break over
first?
The surge protection or the board?
Is the purpose of surge suppression is to keep the clamped voltage
below a problem level?
What am I missing in this?
Thanks...
- Bill
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