Overloaded? Not tripping...

Hello all. My first post in the forum so I hope this isn’t too much of a newbie question…
I have a question in regards to electric baseboard heaters and breaker size, so here we go;

I have 4 electric baseboard heaters (1500w, 2000w, 500w & 500w) with 2 digital thermostats in the living room and dining room all connected to a 20amp breaker. My question is, why hasn’t the breaker tripped?

From my calculations (1500+2000+500+500= 4500w/240v= 18.75a x 125%= 23.4 amps) wouldn’t this be an overloaded circuit?!

Thank you all and wishing everyone a fun, safe holiday season!

Are you sure they are on one circuit . What is the size of wire what is the size of the breaker .Are they on 240 volts \Much more info required did you take an amp load test .

Yes they are all on one circuit as when the breaker is shut off all the heaters and thermostats turn off.
12/2 wire(s), 20 amp breaker, 240v

Did not do an amp load test.

Did you take a picture of the dead front off and are they all tapped into the same breaker…? I had a similar situation recently with two (2) 1000 watt heaters double tapping a 20 amp circuit breaker and I’m still not certain if this is allowed. Presumably not all the heaters were on at the same time which is why it hasn’t tripped or simply burned up as a result of overloading or being defective in some manner.
I’ve heard that if they are in series it’s allowed…?

With the info given yes the breaker might shut off . Except heaters go off and on heaters do not necessary draw what the label says .
They might have to be on for some time to dump the breaker if they are only close to the posted load.
This is too close I would like to see two breakers .
what is the voltage supply if on the low side the current also will be low

Good thought in series the load drops considerably if I remember correctly 1/2 voltage = 1/4 amperage if both heater are same size .
Remember I have been out of the trade for about 25 years

Keeping it really simple, a 20 amp breaker can supply the current you are placing on it, which would be approximately as you calculated 19 amps. However, it is overloaded as per electrical code for continuous current.

I think I remember as constant load should be at 80% or 16 Amps for a 20 amp breaker .
You can not always go by listed load that is why an amp meter is needed . Most of this is above what a home inspector needs to know and have ,the equipment for .

Yes I did take a picture but don’t know how to post a pic here…there is only one black and one red wire going into the breaker.

So now after reading your last reply Roy I looked at the heaters data plates; one example Volts AC 240/Watts 2000/Amps 8.33 & below that Volts AC 208/Watts 1500/Amps 7.21

So if I do the lower voltage calculations (208 Volts AC instead of 240 Volts AC) it would be 1500w, 1125w, 375w, 375w= 3375w/208v= 16.23a x 125%= 20 amps

I have cranked up the heat in both rooms and have all 4 heaters blazing…still no tripping and hasn’t ever tripped since the home was built in 2008.

Strange no?!

As I said written load and true load can be different .Feel the wire near the breaker is it warm or hot Count the seconds you can keep you finger on the wire please .
Older heater do get tired and draw less current ,no big deal.
you power should be close to 240 volt do not be concerned on the 208 reading that is for industry or commercial use ., You need to get a volt meter at least not too expensive $20.00~

Breakers will hold more than their rated for a specified time according to their trip curve.

Unless you actually measure the load current you calculation is meaningless.

Unless all heaters in your case remain on for a long enough time it will not trip.


Wires are nice and cold…2008 construction so wiring & heaters not old. Battery is dead in my volt meter ;-)…will try get new ones tomorrow.

If we go by your chart Michael, this could explain my scenario…

So now the real question would be this (to everyone); should you come across this in a home inspection, what would you do/report/recommend?

I do not think I would have found this .Heater work no concerns in the panel move on Sounds like you are taking to much time on your inspections .Trying too hard I expect you will miss other things . Send me your phone # and a time to call… Roy What is your area .( Time zone )

A breaker will hold at 125% for over two hours which explains why the breaker is not tripping. Also the heaters cycle on and off so the maximum load is not being seen by the breaker.

It sounds like you are in Canada?

This all came to be during an inspection I did today where the owner had a dual energy furnace on 125 amp breaker and an A/C unit on a 100 amp breaker, so I did my calculations (according to the data plates on his appliances) to show him he was “over fusing”…

Then when I got home I decided to “play around” with my own heating (baseboard heaters) and thus, here we are…otherwise, I wouldn’t be looking at the data plates or measuring the sizes of the heaters to verify at the panel (too long process) and completely agree with you Roy, heaters work, no problem in panel, definitely move on!

Just thought this would be a good topic to explore…

I’m in Montreal (Eastern time) 514-968-8971

You went further then I ever did .
Not my job to do load calculations .It was installed by a qualified person looks fine works fine and I move on.

Wish we paid what you do for electricity . Too late to talk tonight do you want me to call tomorrow …all the best … Roy

Anytime is a good time for me…if I’m tied up, just leave me a message and I’ll call back as soon as I’m freed up.

Thanks again for everyone who took the time to respond and hope it helped anyone else that was curious too.

That’s the answer, with a 19 amp load on a 20 amp CB the breaker will never trip. The code regarding a continuous load is a different issue.

Just remember that the continuous load is listed for all the conductors shown in 310.15(B)(16). The values given in that table are indeed continuous loads. However, since we know that OCPD’s have limitations terminals have limitations and so on…

19 Amps on a 12 AWG under the perfect conditions of T310.15(B)(16) would be fine in terms of the conductor itself as again T310.15(B)(16) is based on continuous load values under the tables specific conditions…then the NEC adjusts or corrects accordingly based on ambient, # of conductors, condition of use which change those values given in the table as you know.

Now I would never say 19A on a 20A OCPD would never trip. In theory the trip curves would tend to support that but the ambient rise in heat at the point of termination will affect the OCPD in it’s thermal range. So at some point it will trip even if 19A is placed on a 20 OCPD…but when is the magical question, if the load is continuous at 19A for 3 hours or more…but more than likely a lot more as OCPD’s are robust and do maintain stability well under adverse conditions.

P.S. I have been told by a leading manufacturer of OCPD’s that the above is true, in that the 80% value (125%) is indeed to support the OCPD manufacturers and terminations on those devices. The continuous load effect does result in heat rise to which at some point it overtakes the ambient, and overtakes the long term threshold of the thermal component they will trip at some point…which ironically was the end data that supported FPE in saying they would eventually trip…due to thermal dynamics to the point it would be below thermal ignition points…basically the same theory so to speak.

I feel much better now! LOL!