Re: Substrate heaters

> From: "shaji (s.) bhaskar" <bhaskar at bnr_ca>
> In message "Re: What's this plant? & Substrate heaters", you write:
> >
> >I must
> >caution you (and all) that amperages more than a few milli-amps can be
> >quite *fatal*!  <snip>
>  24 volts will not hurt (See Erik Olson's and Eith Brummett's
> postings).
 [precautions deleted]
Yes, in general 24 volts will not deliver a fatal jolt if the skin is
dry and unbroken. If however, the skin is wet or moist, the skin's
resistance is considerably lowered! If in addition, there is a crack
in the skin's surface, then wet skin offers almost no insulation for
the interior of the body is also filled with water and electrolytic
conductors. What I'm saying is, we can cover any exposed connectors
and conductors to make this safe for children or those not familiar
with our precautions. As for having a 24v electrified tank; the fish
would probably be ok :) but I'd rather not have it. Tank grounding and
a ground fault safety is a sensible precaution.

Enough about safety. The other consideration is so that any DIYS heater
builders don't blow up their power supplies or transformers. The
insulation on wire wrap is rather thin and is designed to be easily
removed. It takes very little to damage it and we need a rugged design
to protect against mechanical abrasion. Consider removal and reuse,
heavy rocks put in for decoration, wear and tear, not to mention the
scratches and dings of construction.

The use of a layer of electrical tape. Low cost. Yeah, you gotta wrap
it on there. This is mechanical protection. You wouldn't need to do this
if you put the whole thing in a PVC tube. The thing is, you can't
count on electrical tape for a water tight seal. 

The use of a PVC tube. Yeah, you're gonna pay $10-$20 for this.
Installation is easy if the tube is flexible and large enough
to allow the cable to slide in easily. I'm suggesting the thin wall
stuff that's cheaper and you can easily pinch it together with
your fingers unlike the rigid tubes we use for gravel and pump
siphons. Since the amount of heat to be transferred per sq. inch of
PVC is low, the temperature differential will not be significantly
high. I'm a mech. eng. myself, so I guess I want to build things
tough and rugged and tend to view electrical stuff with caution. :=)