Shore Power

[gsmallwood]

I only have 20amp service at my dock. I will only be running the heat and a bilge heater in the winter. Everything else will be turned off. Everything seems to be ok with just 20 amps. Has anyone experienced any problems not having 30amp service.

 

[Southpaw II]

So, do you have 1 20 amp service connection, or 2? 1 shorepower cord or 2?

 

[Presentation]

I only have 20amp service at my dock. I will only be running the heat and a bilge heater in the winter. Everything else will be turned off. Everything seems to be ok with just 20 amps. Has anyone experienced any problems not having 30amp service.

Boy that’s a short question with a long answer. I'll try to keep it simple.

We have plugged our boat into a 20 amp outlet. We have also popped the breaker on shore doing this.

Here is the issue. You can turn on your two items and wait a given amount of time and have the breaker not pop and get a false sense of security.

Here is why. Breakers have two tripping mechanisms. The over-load protection is made by connecting two dissimilar metals. This results in a time / current trip curve. The other mechanism is for short circuits. I'll focus on the first one only.

A 20 amp breaker should be able to pass 20 amps continually without tripping.

But apply 25 amps and it will take about 30 minutes to trip.

Give it 21 amps and it will take much longer but it will trip.

The question becomes ‘what is the maximum amps from these loads?’

Just for reference, the short circuit tripping mechanism is a field magnet. A short circuit results in a wire coil creating a magnetic field and pulling a mechanism. Neither mechanism opens the electrical circuit directly; they both cause a fast mate / fast break mechanism to trip.
The above is why traditional residential circuit breakers are referred to as thermal mag circuit breakers.

 

[The Bill Collector]

I only have 20amp service at my dock. I will only be running the heat and a bilge heater in the winter. Everything else will be turned off. Everything seems to be ok with just 20 amps. Has anyone experienced any problems not having 30amp service.

The question you need to answer is how many amps your two heaters draw... If they both kicked on at the same second, is that surge enough to trip your 20 amp breaker or are you still under 20 amps....?
(imo - i'm not an electrician)

 

[johngus]

I would check the draw with an amp clamp around the cord.If anywhere near 20 amps,i would not trust it to be OK.All you need is a little high resistance and trouble will come.You can also check the specs for the 2 heaters to see what is their draw.both running and on statrup.Either way,I would winterize the engines to be safe

 

[sbw1]

Heaters use amps. 20 is pretty slim pickin's. IMO you probably are shy of what you need.

 

[Southpaw II]

That's why I asked if the service was "1" or "2" 20 amp cords. If the load was split between the 2 cords, he's OK.

 

[melida]

I have 16 amps in my marina and always connected to shore power. Battery charger (AC converter) and refrigirator is always on and sometimes I want to boil water with using the 220v receptacles the test button is off individually.
On wednesday I'm gonna install A/C and heat 10,000BTU while max heating draws 0,85kw and max cooling 0,7kw 4Amps max.
So which of them can I use simultaneously ?
Thanks a lot.

 

[sbw1]

I have 16 amps in my marina and always connected to shore power. Battery charger (AC converter) and refrigirator is always on and sometimes I want to boil water with using the 220v receptacles the test button is off individually.
On wednesday I'm gonna install A/C and heat 10,000BTU while max heating draws 0,85kw and max cooling 0,7kw 4Amps max.
So which of them can I use simultaneously ?
Thanks a lot.

Here is a simplistic yet practical way of looking at this. You want to stay below the 16 amps on a continuous basis or you will heat things up and trip breakers. You can add up the watts of the things you want to run and divide that sum by the fixed volts delivered to your recepticle. The result of watts/constant volts=amps. Stay below 16 and you should be ok. The other way is to look at the amp meter on your control panel and turn things on. The constant draw should be less than 16 amps. The appliances that use the most power on your boat will be the hot water heater, the microwave, cook top, A/C at start (probably around 12-15 amps when running and making heat or cold air) and any heaters you have plugged into outlets. I'm not familiar with your power set up. If you have two 16 amp recepticles, you could probably run quite a bit with two power cords going into two different recepticals on the boat. The electrical engineers will probably have a more precise answer to your questions, but this approach works for me.

 

[gsmallwood]

I have 2 - 20amp lines coming onto my dock, but only have 1 ( the big yellow cord ) that goes from the boat to the dock.

 

[sbw1]

You need to add up the amps you need on a continuous basis. You may be ok with two shore power lines going into your boat with a heater connected to each power cord. Hard to say without knowing what you have.

 

[chazaroo]

Not sure if this helps but we have 20 amp shore power at our dock and keep the inverter, fridge and A/C on all the time with no problems.