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.

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?

David

DavidM said:

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

Curious, where did you get your surge numbers?

David

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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.

Is this a winterizing? If so use an extension cord and plug the second heater into a different circuit.

tiltrider1 said:

Is this a winterizing? If so use an extension cord and plug the second heater into a different circuit.

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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.

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.

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.

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.

How many watts each are these heaters and are they high/low power settings?

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.

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.

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

Bkay said:

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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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.

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.

Bkay said:

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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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.

OldDan1943 said:

Did the builder of Xtreme Heaters mention anything about a thermostat?

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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.

https://www.boatbilgeheaters.com/ Twin Hornet.
Going in to 3rd winter with mine.

Chrisjs said:

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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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.

lucky day said:

https://www.boatbilgeheaters.com/ Twin Hornet.
Going in to 3rd winter with mine.

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Looks like that will solve the problem.

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.

There is not a marine version of a HVAC breaker that I know of but Blue Seas has some good graphs of their breakers. Using their suggestion of 3x for inductive load gives about .5 seconds which should be sufficient.

For heating the interior while you are on board , the best I have found is the small (expensive) ceramic units.

They will operate at 500w while on and bump up to 1300w as the thermostat demands.

Since the cold is always coming in this is ideal, 500w keeps the temp more stable , the 1300 helps as required.

The "surge" you are referring to applies to the PTC heaters you mentioned. This really isn't a surge, but it max output that occurs until the temperature rises. Not sure what the time is, but it is certainly longer than what it normally considered "surge" or "inrush".

Box stores sell 120v std outlets rares for 20A , might stop the heater plug from getting hot.

We had used a Caframo True North heater in our ER. It’s quite versatile with 600, 900 and 1,500 watt settings, 2 speed fan and adjustable thermostat.

Heaters are typically resistance loads.

Like an incandescent light bulb, there is no inrush, and resistance increases with temperature.

So, if it pulls 9amps it will be 9amps or less.

The issue you could have is circuit breakers have a plus or minus 20% window from the factory.

So the 15a breaker could trip at 12a and be within spec. And most tend to be low.

I use a small oil filled home radiator heater. I set it in the er, and crack the hatch into the salon. The heat escapes into the boat and works great.

A heater will dry out the woodwork, so wax or oil it first.

Porgy said:

We had used a Caframo True North heater in our ER. It’s quite versatile with 600, 900 and 1,500 watt settings, 2 speed fan and adjustable thermostat.

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Thanks, I ordered a couple Camfrano Pali heaters.

Despite the interesting discussion above on what is or is not a "surge" and what type of load a heater produces, the manufacturer states the 400 watt model draws 3.4 amps with a 9 amp surge at start up for less that 1 second.

I'm making the bold assumption that the manufacturer knows what he's talking about.

Choices said:

I use a small oil filled home radiator heater. I set it in the er, and crack the hatch into the salon. The heat escapes into the boat and works great.

A heater will dry out the woodwork, so wax or oil it first.

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Thanks, my ER opens to the world, so cracking space into saloon won't work for me. I'm more concerned with plugging vents so I don't loose heat. But I also don't have any wood in the ER so I won't have any drying of wood to worry about.

OldDan1943 said:

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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Our Cummins/fleet fleet used h20 heaters.

My experience

I have not winterized my defever 49 in Annapolis for the last 10 yrs. I have one oil filled radiator in my engine room, one in aft state room and one in forward stateroom. Each plugged in to different outlet and the shore power is 30 amps. Not had any issues or concerns regarding freeze....touch wood! Do not jinx!