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Re:Substrate heaters

In message "Re: What's this plant? & Substrate heaters", you write:

>Re: Substrate heaters
>
>When you first described your design for the UG heater, I envisioned wrapping
>the wire wrap in a tight spiral around the clotheline wire so that the whole
>thing resembled a long flexible heating cable, as opposed to something that
>looks more like a loom with lots of thin wires woven back and forth.

The "spiral around the clothesline" is what I have been planning to do
all along.

>I must
>caution you (and all) that amperages more than a few milli-amps can be
>quite *fatal*! The power supplies and transformers which you are planning
>to use are capable of delivering *lethal* currents. Normally when you wire
>your house, a building inspector comes to check things over and there are
>strict codes to follow. What we are suggesting violates all sorts of things
>you would never do in your home. For safety sake, you *MUST* ensure that
>there is adequate insulation. Especially if you have children (or anyone
>else) even the terminal connections should be enclosed. (Imagine tiny
>wet fingers *shudder*!) Wire wrap usually comes on a spool of some sort so
>winding may be tedious but not impossible.

I take such concerns quite seriously.  I have an EE background that is
adequate to accomplish this job with high confidence that it will be
safe.  24 volts will not hurt (See Erik Olson's and Eith Brummett's
postings).  A more serious accident could occur if the transformer
failed in a manner that brought supply voltage into the tank, and at
the same time, there was a failure in insulation of the heater.  This
is unlikely, but there are things you can do to reduce the risk -
turning off the electricity before working on the tank, installing a
GFI, grounding the tank, wearing shoes with insulating soles, etc.

>How about this design:
[deleted, see original posting in archives]

This is a fairly elaborate scheme.  The effort involved is high enough
that, I for one would rather just buy a commercial product.

-Shaji