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Old 11-14-2011, 04:15 PM   #1
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electric heater current draw


here's the situation:
I recently bought a portable heater. (an infrared type) the specs say it draws 12.5 A. ok,so I've got it on a 20 A circuit. all should be fine,right? well, occaionally, when you first turn it on in the morning (I suspect because the filaments in the lamps are real cold) the current draw is enough to pop the breaker. so my "assistant" trudges downstairs and resets the breaker,then all is fine. (maybe because that initial surge of "juice" through the filament warmed it enough so it'll be ok the next time)
to save a trip downstairs to reset the breaker, I theorize that I can replace the outlet the heater's normally plugged into with a 15A GFCI. that way,if a breaker's going to pop,it'll probably (I hope) be the one on the GFCI and not the one downstairs and the normal running current won't trip the GFCI. is this theory sound?

tnx,

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Old 11-14-2011, 04:52 PM   #2
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GFIs do not trip due to overloads. They look for an imbalance in current between the hot and neutral.

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Old 11-14-2011, 05:57 PM   #3
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The heater should not be tripping a 20 amp breaker if the heater is the only appliance on the circuit. Did you run a new branch circuit from the panel to this receptacle so you are certain there is no other load?
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Old 11-14-2011, 06:31 PM   #4
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electric heater current draw


The theory about a cold filament drawing more current does not make much sense. In general, the resistance of a filament changes very little with normal temperature change, and typically the resistance is higher as the temperature increases. It is certainly the case that an induction motor draws substantially more current upon startup than when it has come up to speed, however it is unlikely you have a large induction motor in your heating unit. It may be that there are just enough other appliances on the circuit that you are close to trip level anyway, so upon fan startup you are just over the limit. However, this does not explain why resetting the breaker would allow the unit to work on the second try. Perhaps one of the electricians on the site can explain.
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Old 11-14-2011, 06:38 PM   #5
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electric heater current draw


My theory is that the heaters in the breaker are weak. All of that in-rush current is tripping the breaker. One the heater in the breaker is warmed up it holds.
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Old 11-14-2011, 07:05 PM   #6
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Quote:
Originally Posted by Daniel Holzman View Post
The theory about a cold filament drawing more current does not make much sense. In general, the resistance of a filament changes very little with normal temperature change, and typically the resistance is higher as the temperature increases. It is certainly the case that an induction motor draws substantially more current upon startup than when it has come up to speed, however it is unlikely you have a large induction motor in your heating unit. It may be that there are just enough other appliances on the circuit that you are close to trip level anyway, so upon fan startup you are just over the limit. However, this does not explain why resetting the breaker would allow the unit to work on the second try. Perhaps one of the electricians on the site can explain.
That is correct....resitive load do not change with temp....at least any significant amount....same thing for a light bulb...the startup current is basically the same as operating current.

For reference....(I'm assuming the space heater uses nichrome wire), the resistance will increase from 6-10% going from cold to 2000 deg. I really doubt your space heater is getting to 2000 deg....it's most likely running in the 600 deg range....which equates to about a 2-5% increase.

In terms of your breaker....it is seeing "at most" an additional 1.25A of current. In reality....it's most likely around .3-.5A on initial startup.

The only way to know for sure what the problem is, is to connect a clamp on amp probe at the breaker. It's either a weak breaker or you also have some other loads.....I'm going to lean toward "other loads".
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Old 11-14-2011, 09:49 PM   #7
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GFIs do not trip due to overloads. They look for an imbalance in current between the hot and neutral.
ok,I'll take your word for that. suppose I take a regular old "single pole 15A breaker",mount it in a box along with a standard outlet,plug the heater into that and plug the box into my outlet?

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Old 11-15-2011, 06:33 AM   #8
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electric heater current draw


You need to try and fix the problem instead of covering it up.
If the breaker is tripping, then somewhere you have a problem.
Look for loose connections in the circuit.
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Old 11-15-2011, 09:32 AM   #9
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If you don't want to use an ammeter and if the defect can be reliably reproduced, there is another way to troubleshoot this that is almost as good.
It might even be better since it doesn't involve test instruments.

Since there is a very low likelihood that more than one of your CBs is bad, try the heater on other outlets that are served by other circuit breakers. After the third time you should have a pretty good idea of what's going on.


Last edited by Yoyizit; 11-15-2011 at 09:41 AM.
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