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Old 15-11-2013, 21:48   #1
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Power load on 30A

After returning from vacation, I turned on my heater and this was the result.

According to Compass Marine, "Contrary to popular misconception a 30A or 50A shore power circuit should NEVER be continuously loaded to 30A or 50A! Circuits should only ever be used at up to 80% of the rating. On boats I prefer to use 70% due to the corrosive environment we are in. This was a result of multiple AC heaters used on-board and a poor/dirty/corroded connection which resulted in high resistance, heat and physically melting of the inlet and wire."

I recently bought my Hunter 34 and as the Winter winds up, I'm running more load on my 30a system - heaters, lights, etc… I replaced my cord and receptacle with a Smart Plug. I obviously want to prevent this in the future. Should I be able to run two electric heaters in addition to lights, TV, etc., or is that asking too much?
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Old 15-11-2013, 23:13   #2
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Join Date: Jan 2013
Location: South Texas
Boat: Newport 28 & Robalo 20
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Re: Power load on 30A

Quote:
Originally Posted by Steve Olson View Post
After returning from vacation, I turned on my heater and this was the result.

According to Compass Marine, "Contrary to popular misconception a 30A or 50A shore power circuit should NEVER be continuously loaded to 30A or 50A! Circuits should only ever be used at up to 80% of the rating. On boats I prefer to use 70% due to the corrosive environment we are in. This was a result of multiple AC heaters used on-board and a poor/dirty/corroded connection which resulted in high resistance, heat and physically melting of the inlet and wire."

I recently bought my Hunter 34 and as the Winter winds up, I'm running more load on my 30a system - heaters, lights, etc… I replaced my cord and receptacle with a Smart Plug. I obviously want to prevent this in the future. Should I be able to run two electric heaters in addition to lights, TV, etc., or is that asking too much?
He!! yes that's asking waaay too much!
A standard household electrical heater generally has a high heat rating of 1500 watts (some are 1200w and less).
1500 watts of power at 120 volts draws 12.5 amps ( W = V x I ).
You have TWO heaters drawing 12.5 amps each (at max output), that's 25 amps of the nominal 30 amp dockside service available (that's the 83% load point).
Add in a few other of your goodies and you're well over the 30 amps that might be available.
Discount for the resistance of the feeder wiring, plug connections, panel connections, circuit breakers, house wiring, etc., and you're ready to burn the effen marina down for the holidays. Ho-Ho, Ho...
I'm glad you're in the PNW and nowhere near my boats.

A boat is not a house.
Most new houses today have 400-800 amp entrance feeds, slightly older ones have 200-400 amp service, really old ones just 100 amps. Still far more power available at home than aboard.
It's different, get used to it before something really bad happens.
I'd suggest you read some of the BoatUS articles online, they have a very good safety magazine; and as an insurer they find most boat, and subsequent marina fires, are caused by exactly the root cause(s) you have displayed here.
Sorry to be so harsh sounding, but it's dang serious bidness (and I've seen a few too many crispy critters...).
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