Completed Project Why does my 125V 15A power extension cord trip when a 1500W heater is connected to it?

Thread Starter

Rahulk70

Joined Dec 16, 2016
504
Hello everyone,

I've a Martin Industries-Kingston Series space heater 120V 1500W with two modes of operation LOW and HIGH. LOW mode is around 750W I guess and HIGH is 1500W. I've plugged this to a 120V 20A outlet and it works fine but the wire from the heater is too short from my work table so I wanted to extend it. From the wall outlet I have no issues running at both modes.

But since I wanted to extend the length of the heater I made myself one from an outlet box, 20A NEMA outlet and a wire. Unfortunately that wire wasn't able to handle more than 10A so can only run in LOW mode. So, I used the 125V 15A power extension cord (picture below) with circuit breaker. But even on this the breaker on the power cord trips after 15 seconds.I meant the breaker on the power extension cord not my wall circuit breaker. My wall outlet voltage is 121.8V. So, theoretically it should draw around 12.3A at 1500W only right? In the morning its so cold its unbearable, I need to run in HIGH mode:D

Thanks in advance.
 

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wayneh

Joined Sep 9, 2010
16,390
I’ll speculate that the cold amp draw is enough to trip the breaker. Resistive elements, like light bulbs, have a much lower resistance when cold and draw much more current very briefly before they get hot. In this case it’s lasting long enough to trip the breaker.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
504
I’ll speculate that the cold amp draw is enough to trip the breaker. Resistive elements, like light bulbs, have a much lower resistance when cold and draw much more current very briefly before they get hot. In this case it’s lasting long enough to trip the breaker.
Hi,
So, if I connect the heater to my wall outlet directly and run it at HIGH mode for like 5 minutes and immediately plug it to my extension cord will it solve the initial higher current draw issue? The heater resistance should be much higher by now right?
 

Sensacell

Joined Jun 19, 2012
2,567
I would not expect the breaker on an extension cord to be terribly accurate, current wise.
12.5 Amps is close enough to 15 for all intents and purposes, for sure they will err on the low side.
Use an extension without a breaker.
 

tcmtech

Joined Nov 4, 2013
2,867
A lot of cheap power strips have really weak or overrated breakers or undersized breaker in them. I have found a few 15 amp one that had 12.5 and even 10 amp breakers in them.

Try a different outlet strip and see what happens. Or just buy a short appliance cord which is basically just a short (4 - 8 feet) heavy gauge extension cord designed specifically for higher power devices.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
504

wayneh

Joined Sep 9, 2010
16,390
Hi,
So, if I connect the heater to my wall outlet directly and run it at HIGH mode for like 5 minutes and immediately plug it to my extension cord will it solve the initial higher current draw issue? The heater resistance should be much higher by now right?
It might. A lightbulb goes dark (and cool) awfully quickly but a heater element might retain enough heat. This is not a practical solution really, just an experiment.
 

mcgyvr

Joined Oct 15, 2009
5,394
I guess you are right. Had a bad experience in the past but this one is all metal. But anyway I've managed to find a thick wire from an old A/C. I'll try to make a power extension with this.
Note that its may also be a UL/Safety violation to run that heater from any extension cord (see manual)..

And your power strip breaker is likely just a cheap and inaccurate device as stated above..
 

Audioguru

Joined Dec 20, 2007
11,249
Look where the "15A" extension cord is made. It might be cheap junk that trips at 14A.
The "15A" heater might also be made there and draw 16A.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
504
Look where the "15A" extension cord is made. It might be cheap junk that trips at 14A.
The "15A" heater might also be made there and draw 16A.
I agree with your first statement "Look where the "15A" extension cord is made. It might be cheap junk that trips at 14A.". It is Chinese made and hence this issue. Tried another similar cord which I used with my PC and its acc ,Taiwanese made which is double the price of the Chinese junk and it didn't trip.

"The "15A" heater might also be made there and draw 16A". No, its a fantastic American made heater from the 70's (Picture 2 with specs). I had owned four Chinese made heaters in a span of 10 years and all of them are dead. Three quartz halogen and one nichrome wire type. I had thought of junking this one sometime ago, but I'm glad I didn't. We get what we pay for.
 

be80be

Joined Jul 5, 2008
2,042
Don't run a heater from a power strip even a appliance cord is a bad idea I see maybe 20 of these a year that burn up the problem is
the wall outlet in most houses are cheap. You then plug a heater in and they heat up making the outlet spring weaker the cord adds more resistance to the heater making it pull even more.
I've seen 100's of these burn up from the wall outlet to the heater most don't even trip a breaker do to poor wiring and bad outlets they are not making good connection and just simply heat up till there on fire or you smell the burning wire insulation.

Plus the fact that most power strips are poorly made don't help to.
Most of them are lucky if there 16 awg I've seen lots that where 18 awg.

Appliance cord come in 12 awg but if you did use one you need a good outlet that's rated for 20 amp $4 to $8 each not the cheap stuff most homes have.
 
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Thread Starter

Rahulk70

Joined Dec 16, 2016
504
Don't run a heater from a power strip even a appliance cord is a bad idea I see maybe 20 of these a year that burn up the problem is
the wall outlet in most houses are cheap. You then plug a heater in and they heat up making the outlet spring weaker the cord adds more resistance to the heater making it pull even more.
I've seen 100's of these burn up from the wall outlet to the heater most don't even trip a breaker do to poor wiring and bad outlets they are not making good connection and just simply heat up till there on fire or you smell the burning wire insulation.

Plus the fact that most power strips are poorly made don't help to.
Most of them are lucky if there 16 awg I've seen lots that where 18 awg.

Appliance cord come in 12 awg but if you did use one you need a good outlet that's rated for 20 amp $4 to $8 each not the cheap stuff most homes have.
You are right. The newer outlets are quite cheap. Its evident when you inspect the newer Leviton outlets and the old GE ones etc. The older ones are heavier, have spring contacts. I had made an outlet myself with a #12AWG (I replaced the 16/3 since its current limit is much lower) and a 20A GE outlet, though I need to change the plug tomorrow. My outlet and wiring with the heater connection is a 20A itself.
 

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Phil-S

Joined Dec 4, 2015
142
As a UK user, I'm not up to speed with what I assume is a US plug and socket arrangement.
Most UK versions of a heater like that would come with a fused 3-pin plug (BS 1360??) which makes a separate breaker (again assuming this is a straightforward thermal trip) unnecessary.
Are US plugs fused or not? If it's an extension with an RCD trip, then that's a different story (assuming it's not)
For a UK version of the heater running at 240V-AC, a 10-A fuse fast blow ceramic for 1500-W load would be sufficient. Obviously running at 120V-AC is going to pull a lot more current.
If it works in the wall outlet and not on the extension, then the extension is either overloaded or simply not good enough.
In terms of making up an extension lead, I would use some decent quality components and the cable would be at least 2.5-mm2 cross section for the live, neutral and protective earth. A lot of these very cheap made up outlets aren't worth the risk
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
504
As a UK user, I'm not up to speed with what I assume is a US plug and socket arrangement.
Most UK versions of a heater like that would come with a fused 3-pin plug (BS 1360??) which makes a separate breaker (again assuming this is a straightforward thermal trip) unnecessary.
Are US plugs fused or not? If it's an extension with an RCD trip, then that's a different story (assuming it's not)
For a UK version of the heater running at 240V-AC, a 10-A fuse fast blow ceramic for 1500-W load would be sufficient. Obviously running at 120V-AC is going to pull a lot more current.
If it works in the wall outlet and not on the extension, then the extension is either overloaded or simply not good enough.
In terms of making up an extension lead, I would use some decent quality components and the cable would be at least 2.5-mm2 cross section for the live, neutral and protective earth. A lot of these very cheap made up outlets aren't worth the risk
No, most US plugs are unfused like Wayneh has said. You are right, the breaker had tripped because I had used a Chinese power cord extension. Tried with another good quality Taiwanese 125V 15A power cord with breaker and it was fine.

The power extension cord that I had made and posted above with picture is using a 125V 20A GE outlet and 20A Air Conditioner 12AWG wire. Initially I had used a 16/3 TYPE SJ 16AWG wire which was only 16AWG and was getting warm so the 12AWG wire.
 
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