Re: Dupla Cables (The whole message)

>From: chapman at SEDSystems_ca
>Date: Wed, 6 Mar 1996 10:36:48 -0600
>Subject: Dupla Cables (The whole message)
>Despite assurances that Didi received from the guy at the pet store, I'd still
>have "grave" concerns about running the 120 V heating cables in my tank:
>> the guy told me not to worry about it since the cable has a grounding wire
>> right along and that in case of failure the path of least resistance will
>> be the ground just in case that doesn't work, the wire has a fuse that will
>> blow really fast should the electric current choose the body. "After all,
>> people put powerheads in their tanks all the time"
>In the first place, electricity does not just take the path of least
>resistance -- it takes every available path.  You can see that this is true
>from your own experiences -- you can plug several different items into a
>power bar, and electricity flows into all of them, even though each has a
>different resistance.

Electric current actually take the path of least resistance. If one of your 
several items has a short circuit to ground, all the current will flow there and
none to the rest of your items. The sum of current to all items is equal to the 
input current. Something got to do with Kirchoff(sp?) Law.

>The purpose of the ground wire is to make a low resistance path to ground
>available so that if a fault occurs, a large current will flow and result in
>a blown fuse or circuit breaker.  If the cable has an internal fuse, as the
>salesperson implied, that is its purpose.  No fuse can tell if current is
>flowing through your body or not.

Partly true because the path to ground has the least resistance. All currents 
flow to the ground and none through your body. The ELCB would then trip. The 
fuse would blow only if the ELCB malfunction or the ground wire is open, as 
mentioned by the sales person.

>It is possible for a fault to occur that would only allow a little bit of
>current to flow to ground, preventing the fuse from blowing.  In this
>situation, a potentially serious shock hazard will exist.

ELCB would take care of that unless you don't have one. ELCB installation is 
compulsory in Malaysia. We have more confidence of the submerged powerhead, 
aren't we?