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.

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.

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.

To guard against this, use a ground fault interruptor to protect any outlets 
powering your aquarium.  It will provide complete safety, no matter what 
happens to the heating cable.

Paul Chapman
Saskatoon, Saskatchewan, Canada -35C -31F