Water heater current draw

[dmksails]

I have an Atwood model EHM-6 water heater. It runs on shore power. When I switch it on, my AC amp meter goes to 15. Seems like a large draw. Can anyone confirm what this heater should draw? Can't find info on Atwood docs

[john61ct]

Why would you think that's high? Using electric to provide heat takes a lot. If it used less it would be cooler and slower.

[SecondBase]

Atwood specs a 15 amp switch. You're pushing the edge of the spec. FWIW sorry to say but I personally would consider it a possible fire hazard until you can prove otherwise from someone more experienced in this area.

http://www.atwoodmobile.com/manuals/...2011.19.07.pdf

[PaulinOz]

from web site: 120 volt / 1400 watt incalloy heating element.

P (watts) = E (volts) x I (current)

Should draw approx 13 amps.

[wiekeith]

Originally Posted by dmksails

I have an Atwood model EHM-6 water heater. It runs on shore power. When I switch it on, my AC amp meter goes to 15. Seems like a large draw. Can anyone confirm what this heater should draw? Can't find info on Atwood docs

I just copied the below from a UK online brochure - equates to about 12A.

EHM6 - Electric water heater with heat exchanger - 1400 watt /120 VAC

[wiekeith]

Ops, PaulinOz beat me to it

[GordMay]

Originally Posted by wiekeith

I just copied the below from a UK online brochure - equates to about 12A.

EHM6 - Electric water heater with heat exchanger - 1400 watt /120 VAC

Right.

“Each Atwood electric water heater is equipped with a high quality 120 volt/1400 watt Incaloy® heating element ...”
➥ Marine Water Heaters - Atwood Mobile

1400W ÷ 120V = 11.66 Amps

[alley]

My 2-cents...

First question to ask is whether the ammeter is accurate. I have a number of ammeters that give very different results for the same current. If the ammeter is accurate, then make sure there is not another load that is showing in addition to the water heater.

[Brewgyver]

Originally Posted by SecondBase

Atwood specs a 15 amp switch. You're pushing the edge of the spec. FWIW sorry to say but I personally would consider it a possible fire hazard ...

That's a bit rash. First, the typical panel-mounted AC ammeter is NOT ver accurate, especially at the low end of its range. Second, its reading the total current draw for the boat, which almost certainly inclludes loads that may not be apparent, like the battery charger, inverter, etc.

The way to properly assess the current draw of an individual load is with a good quality True RMS ammeter, clamped on to the conductor feeding only that load.

En electric water heater is a simple resistive load, it doesn't fluctuate in normal use, unlike inductive loads like fridges and A/C. As long as it's connected using properly sized wire and circuit breaker, even the failure mode is statistically very safe. Most of the time when the element fails it goes open, not even tripping the breaker, just stops heating.

[MB750]

Sounds about right. Converting electricity to heat is convenient, but inefficient.

Look at the water heater in your house for reference. (if your boat isn't also your house).

[SecondBase]

Originally Posted by Brewgyver

That's a bit rash. First, the typical panel-mounted AC ammeter is NOT ver accurate, especially at the low end of its range. Second, its reading the total current draw for the boat, which almost certainly inclludes loads that may not be apparent, like the battery charger, inverter, etc.



The way to properly assess the current draw of an individual load is with a good quality True RMS ammeter, clamped on to the conductor feeding only that load.



En electric water heater is a simple resistive load, it doesn't fluctuate in normal use, unlike inductive loads like fridges and A/C. As long as it's connected using properly sized wire and circuit breaker, even the failure mode is statistically very safe. Most of the time when the element fails it goes open, not even tripping the breaker, just stops heating.

I defer to Brewgyver who has more knowledge on this topic.

[foufou]

Not only is heating water with electricity convenient but is also efficient; nearly 100% efficient. A little bit of resistive loss in the wires feeding the beast. It might be costly or environmentally unsound...

[a64pilot]

Electric resistant heating, water, air or whatever is converting nearly 100% of the electricity to heat, but it is inefficient, if it weren't then there wouldn't be so many heat pumps sold.
It is efficient to some extent, just however we don't usually recognize the tremendous amount of energy in heat.
A typical SUV at highway speed has a stupendous amount of kinetic energy, easily enough to destroy buildings etc, but use the brakes to stop it and you convert nearly 100% of that enormous kinetic energy to heat the brakes, and yet they don't glow red

[mitiempo]

100% efficient for me and my neighbors as we do not pay for dockside power.