OT: need some clarification

[theripley]

Hi,

So, I have a heating element @ 10kW capacity. Since heaters are resistive load (fix I assume), given a constant voltage hence, I will have constant current though out the operation. My assumption based on the above statement is, given a range of 1-100 C (being 100 C the maximum temp it can attain, for example), the current will be equal on 99 testing points (@ 1 C graduation).

If so then, why a need for a fuse/ circuit protection as indicated on Electrical standard?

 

[Mickey]

The fuse is there to protect the wiring not the heater.

What if you have a short ?

 

[theripley]

The fuse is there to protect the wiring not the heater.

What if you have a short ?

For example, my temperature set value is only 50 C (heater capacity is 1-100 C as previously posted) & my thermostat (controller) fails, meaning the contact (NO) continuesly shorts even after reaching 50C. It heats up continually upto its maximum then the heater burns out.

What protection can I add to prevent this occurence if the fuse/ circuit protection is suppose to be protecting the wire only?

 

[Ned_Flanders]

Most heating applications have two thermostats - a control stat and an over temperature stst (With manual reset). These are wired in series.

If the heater were to develop a short circuit, the fuse/overload would trip but as Mickey says, the wiring standards are concerned with protecting the wiring and not the appliance.

 

[theripley]

If the heater were to develop a short circuit, the fuse/overload would trip but as Mickey says, the wiring standards are concerned with protecting the wiring and not the appliance.

At what point will the heater develop such condition? Is it only due to mis-wiring?

 

[Mickey]

A short can occur in the wiring also within the heater itself.

There is no particular point just a malfunction within the wiring/equipment. S*** happens.

markie's, second thermostat I call a "High Temperature Shutdown". Normal stuff in an industrial environment. In fact even
my home force air furnace has one.

 

[leitmotif]

Fuses are there to protect the line.

If this is a 10 kW heater I would have a double thermostat setup. One thermo controls the normal ON OFF switch. If this one fails shut (NOT shorted) then depending on how much heat can be dumped to the heat sink from the heater you have a runaway and possible overtemp situation.

The second ie over temp controls another switch which will shut the whole thing down. A common setup can be seen in your home hot water tank.

Generally heater failure is an open heater - at least from what I have seen. Most shorts will result in an open sooner or later.

Dan Bentler