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Old 10-07-2020, 07:28 AM   #1
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Surge amps on 110v outlet

I am considering small heaters in my two engine bays (one heater per bay). I have 110v outlets with 15 amp circuit breaker. The total amps used by two heaters running at the same time are only around 9 amps. But the surge amps would be close to 20 or 25 amps for around 1 second or somewhere around 10 to 13 amps per unit surge. Of course, that assumes both heaters come on at exactly the same time.

I've done a search for info and understand it might depend on whether these are slow blow circuit breakers, but frankly I'm not sure how to tell if they are.

I'm curious whether anyone has insight whether this would likely trip circuit breakers and leave me without heat, or whether I should go with a different, lower amperage option. The units turn on by thermostat, so they would have to come on at exactly the same time to exceed my amperage. Each unit will be plugged into a different outlet, but the outlets are on the same circuit.

Thot's appreciated.
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Old 10-07-2020, 07:52 AM   #2
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I suspect the surge you are speaking about is when the heating elements are turned on cold they have a lower resistance which causes more current for maybe a second or so. That is different from the inductive surge starting a motor causes which is more difficult to deal with.

The bottom line is that the surge shouldn't trip any normal breaker.

Curious, where did you get your surge numbers?

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Old 10-07-2020, 08:35 AM   #3
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The bottom line is that the surge shouldn't trip any normal breaker.

Curious, where did you get your surge numbers?

David
Thanks David,

I'm looking at different heaters (I haven't purchased yet). In one case the surge number and time was from the manufacturer and in another case I had surge numbers for slightly larger units, so I estimated what they would be for the smaller unit.

I just got a comment from a dirt electrician (co-workers dad) who said land based slow-blow is 2x for 10 seconds. I assume that would mean a 15 amp breaker would trip if 30 amp for 10 seconds. If that's the case with mine, I'm golden.
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Old 10-07-2020, 09:01 AM   #4
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Is this a winterizing? If so use an extension cord and plug the second heater into a different circuit.
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Old 10-07-2020, 09:12 AM   #5
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Is this a winterizing? If so use an extension cord and plug the second heater into a different circuit.
That's way down the list of my preferred options. I really want to avoid that for a host of reasons that I don't type fast enough to list.
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Old 10-07-2020, 09:28 AM   #6
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What kind of heaters are you talking about?

Resistance heaters, 2 that are worth a crap are going to be more than 9 amps running unless block heaters or low wattage engine room/ locker/cushion heaters.

Compressors..... say on heat pumps may do what you are saying, there are capacitor kits to help with that surge.
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Old 10-07-2020, 09:32 AM   #7
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Not sure what kind of heaters you are contemplating, but based on experience, I feel that block heaters on the engines (oil pan pad or immersion) with some sort of thermostat control are a far superior solution. Good for the engines and keep the whole space around them nice and toasty.
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Old 10-07-2020, 09:32 AM   #8
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You have two different engine bays? Bummer. A point against cats.

I am only guessing.

The object is to keep the engine room equipment from freezing. Someplace between 38 and 45 F

Do you have engine block heaters?

If in theory both heaters turn on at the same time, reduce the thermostat setting on one of the heaters.
I would suggest ceramic heaters or oil filled radiator type heaters. That will totally eliminate the 'top over' accidents. Yea yea, I know. they have tip over switches but, ....

Put a small 12vt fan in each ER so as the equalize the temp.... not blowing on a heater.
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Old 10-07-2020, 09:33 AM   #9
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How many watts each are these heaters and are they high/low power settings?
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Old 10-07-2020, 09:48 AM   #10
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If you can set the temperatures operating range slightly different for each heater, they will go on and off at slightly different times, thereby avoiding the risk of a combined surge.
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Old 10-07-2020, 10:10 AM   #11
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My first choice is something like a Camfrano Pali (400 watt, 3.4 amp, 9 surge amps) or Xtreme 450 watt or 300 watt heater. The 450 watt is 4.5 amp running and 13 surge and the 300 watt is 3 amp running and I can't find surge - although I have a message in to them asking).

To the best of my knowledge, they don't have adjustable thermostat settings.

This is why I'm asking the question. So I can determine if my first choice works.

My second choice is a magnetic engine block heater. But that doesn't really accomplish what I want effectively. Which is why I asked the question on how circuit breakers operate.
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Old 10-07-2020, 10:51 AM   #12
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Either a engine block heater or a circulating water heater. Had both on my Bronco when I worked in northern Alberta Canada. The coldest I saw it was -46F. When I started the Bronco in the mornings, it did not take long for the heater to start working. SMILE
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Old 10-07-2020, 12:04 PM   #13
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Quote:
Originally Posted by Bkay View Post
My first choice is something like a Camfrano Pali (400 watt, 3.4 amp, 9 surge amps) or Xtreme 450 watt or 300 watt heater. The 450 watt is 4.5 amp running and 13 surge and the 300 watt is 3 amp running and I can't find surge - although I have a message in to them asking).

To the best of my knowledge, they don't have adjustable thermostat settings.

This is why I'm asking the question. So I can determine if my first choice works.

My second choice is a magnetic engine block heater. But that doesn't really accomplish what I want effectively. Which is why I asked the question on how circuit breakers operate.

You should be ok with two of those <500 watt heaters on the same outlet as long as your wiring is good. Why not try them out now before it gets cold and check the wiring connections for hotspots.
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Old 10-07-2020, 12:14 PM   #14
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I talked to the guys who make the Xtreme heater. He said the surge amps were for a fraction of a second. So even if they both kicked in at the same millisecond (not real likely) they wouldn't trip the circuit breaker.

I'll definitely check them out before winter hits, I just didn't want to buy the units if there were not going to work for me. I think Archie and DavidM are right - I'll be fine...unless I'm not.

Thanks, guys.
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Old 10-07-2020, 12:20 PM   #15
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Quote:
Originally Posted by Bkay View Post
I talked to the guys who make the Xtreme heater. He said the surge amps were for a fraction of a second. So even if they both kicked in at the same millisecond (not real likely) they wouldn't trip the circuit breaker.

I'll definitely check them out before winter hits, I just didn't want to buy the units if there were not going to work for me. I think Archie and DavidM are right - I'll be fine...unless I'm not.

Thanks, guys.
With my luck, that millisecond would still be too long LOL
Of course, check it out.
Did the builder of Xtreme Heaters mention anything about a thermostat? i would think it must have at least a high temp shut down.
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Old 10-07-2020, 12:33 PM   #16
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Did the builder of Xtreme Heaters mention anything about a thermostat?
They have a factory set thermostat that turns on at 40 and off at 50. Frankly, I won't even turn them on until I see an extended period below freezing predicted. I'm not really trying to keep the engines warm (since I'll winterize them anyway), I'm trying to keep the engine bay from getting too far below freezing.

As I think about it, even if the factory setting was perfect, the two engine bays will never be the exact same temperature due to different equipment installed in them. Of course, I guess the engine bays could be the exact same difference as the thermostats. I'll take that chance.
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Old 10-07-2020, 01:07 PM   #17
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https://www.boatbilgeheaters.com/ Twin Hornet.
Going in to 3rd winter with mine.
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Old 10-07-2020, 01:16 PM   #18
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If you can set the temperatures operating range slightly different for each heater, they will go on and off at slightly different times, thereby avoiding the risk of a combined surge.
That is a fine idea. Although circuit breakers take a lot more overload to trip off than the instantaneous surge current with a running current of 9 amps still far below the max rating. If it works at home, it will work at the boat, if these are 110 vac heaters.
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Old 10-07-2020, 03:06 PM   #19
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https://www.boatbilgeheaters.com/ Twin Hornet.
Going in to 3rd winter with mine.
Looks like that will solve the problem.
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Old 10-07-2020, 03:19 PM   #20
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I used plug in electric resistance heaters last winter in Toronto and never observed any issues with surge demand. First I've heard of this. No problems running 3000w on 30a shore power, or 1500w on a 15a house breaker. I've used several different heaters with the same observations.
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