20 Dec
2002
20 Dec
'02
9:10 a.m.
The MOVs used in these things fail by shorting. When they short, they put a short
directly across the AC line. Building one of these things without fuses or circuit
breakers in BOTH legs is just looking for trouble. You should report these incidents to
your state and local fire marshall, as many consumer agencies as you can find and the
store that sold them to you.
You need a protective device (fuse or circuit breaker but fuse prefered) in BOTH AC
legs since the power surge can be differeential (across the AC line) or common mode (where
the voltage increasses in both AC lines). Don't put a protective device in the ground
line!
FWIW I pick up old power supplies and surge protectors and save the MOVs out of them.
Then anytime that I work on a computer or other electrical device I add a MOV across the
AC line and a MOV between each AC line and ground. I also add fuses in each AC line ahead
of the MOVs. Even with these changes I still use surge protectors whenever possible, call
it double insurance. I live in the lightning capital of the world (central Florida) and
I've yet to lose a computer or TV to lighting despites numerous close hits. I've
lost plenty of MOVs and surge protectors though.
Joe
At 04:39 PM 12/19/02 -0800, you wrote:
Hi
I've just seen the third surge protector blow
up and this time, it almost started a real fire.
I've had two of these go up in smoke that were
in metal strips. These generally make a lot of
smoke but I think the metal spreads the heat enough
that the fire danger is small. Now, most of the
newer ones are made from plastic. The last one
that just burned, started a small fire on the back
side of a chest of drawers. Luckily, the chest
didn't stay lit. It did charcoalize one of the feet.
While these things come with a 15 amp breaker,
the MOV's fail and draw something less then what
is required to blow the breaker.
I wonder if any of the fire prevention groups are
looking into these time bombs?
Dwight