Nickel Chromium (Nichrom wire) shorting?

[Hotown]

Hi all,

We are using nichrom wire at my work to keep some of our outdoor components from freezing. The problem is that when power is turned on to the loop (via plc) the voltage across any components that share a ground with the wire loop is reduced, in some cases to half the original voltage (24V DC).

My thinking is that the resistance through the wire is extremely small compared to the other components, thus causing a short when the wire is powered. Is this correct? If so, what should be done to solve this problem?

Thank you for your help

 

[IRstuff]

duh...?

you need bigger or alternate grounding.

have you no EEs to go and measure the current draw? this really doesn't sound like complicated problem.

TTFN

Eng-Tips Policies FAQ731-376

 

[IRstuff]

Since you mentioned shorting, one problem, of course, is that nichrome, like all metals, stretches when it gets hot, so if it's not properly isolated/insulated, it can droop and short out to any protruding metal.

TTFN

Eng-Tips Policies FAQ731-376

 

[itsmoked]

Is this bare nichrome?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Hotown]

We have no EE's. We all have very limited electrical experience and are learning as we go, so I'm sure it is a very simple problem. The draw on the loop is 1.7 amps at 24 VDC.

Let me make sure I'm clear in our setup. Currently, all components run by our 24VDC output module are grounded together on one rail, which is jumped to the common of the output module. When the nichrome wire is powered, the 24V output module essentially becomes a 10-16V output module.

IRstuff, are you suggesting that we run the nichrome wire loop to a seperate ground, such as an earth ground?

The nichrome is not bare. It is wrapped with fiberglass sheathing then heatshrinked to keep moisture out, so I don't believe shorting in the wire is an issue.

 

[itsmoked]

It sounds like you are waaaaaaay over drawing from your 24VDC source and it is dropping voltage in your switching device or your supply is sagging.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Comcokid]

I go with itsmoked.

How much output current is your 24VDC module rated for?
How is this 24 VDC module powered?

Your common ground wire (or ground return path).
How long is it? (A few feet or several hundred feet)?
What gauge wire is it? (32 AWG or more like 20 AWG)?

 

[kenvlach]

As stated above, you are drawing too much load for your miniature power supply-supply wiring.

If not damaging the supply side and if the reduced heat output is sufficient, no problem, at least w.r.t. the nichrome.
Once upon a time, I used nichrome shunt wires across resistance furnace winding taps to modify the temperature profiles of tube furnaces. To lower temperature in one zone, I'd use a shorter shunt (lower [Ω]) to draw off more current from the heating element.