Block Heater Replacement

[whaler23]

I have posted this issue before but now I have bought my replacement block heater
[http://cgi.ebay.com/ebaymotors/ws/e...=1,1&item=8038065132&sspagename=STRK:MEWN:IT]
and need advice on the wiring again. When I bought the boat both of the block heaters were wired directly into the hot water heater circuit. I.E. The only time I can run the block heaters I have the water heater on. Both block heaters are 1500W immersion type Zero Start and I need the best way to wire them this go around. I believe I have an open circuit on the panel but not sure of the ease of wiring them both together and getting to the back of panel. Any advice is appreciated.

 

[Genesis]

1500 W is a lot of power; that's basically all of a 15A circuit.

For two engines, you need most of a 30A shorecord! Be very, very sure you take appropriate care in how you wire this up, and that everything can take the load it will draw.

I recommend thermostatic control for high-wattage units like this - Kim Hotstart makes thermostats that connect to these heaters and go in the cooling system loop to cycle it appropriately.

 

[whaler23]

Last fall I replaced both shore power inlets and the fuse blocks right behind them with circuit breakers as an upgrade but have not touched anything else at this point. Wiring for the most part is all original with all hatteras labeling intact and well arranged. Will look into the thermostats and sep circuits.

 

[REBrueckner]

Ditto Genesis comments.
An alternative thermostat arrangement is an electric baseboard heating thermostat from Home Depot or Lowes. Each thermostat handles 2,000 watts. Cost is uner $20 each. It is activated by the air temperature and so should be placed adjacent to your engines in the engine room. I have a similar arrangement in my boat and am happy with it. Once the engine warms, surrounding air is quickly warmed, and switchs the thermostat off.

 

[SeaEric]

I have 2 separate breakers on my AC panel- One marked "Port Block Heater" and the other marked "Starboard Block Heater" This is probably the best power source set up.

 

[REBrueckner]

Seaeric has a good arrangement.
An alternative is to install a single 30 amp circuit breaker in place of a 20 amp. You can shut either block heater off via the individual thermostat setting if desired.

 

[whaler23]

"An alternative is to install a single 30 amp circuit breaker in place of a 20 amp. You can shut either block heater off via the individual thermostat setting if desired."

That's probably the best way for me to proceed, thanks for the advice, went to HD already and bought one thermostat for both heaters and will mount the stat in the middle on a floor support. I think I can do this.

 

[Nick]

The circuit breaker should not be changed from 20A to 30 A unless the wire conductor is appropriately sized to handle 30 amps. Even If you have have a 30 amp breaker in your panel and the heaters are both on simultaneously your branch circuit is pulling about 28 amps. NO GOOD. and what about your other loads on the same shore service, like the water heater and refridge and ...The water heater alone may be 1500 watts.

I found that even with two 750 watt heaters on our 37 with auto thermostats from Kimstart, and the other loads on the same shore service, I have to manually manage the load by shutting off the water heater and watching the use of things like a coffee pot and stove top and of course the hair dryer and the toaster. The 30 amp service just isn't enough for all the loads at the same time. If I don't manage the load, I blow the fuse on the 30 AMP shore service and can feel the heat buildup at the shore power connection.

I think the only way to use the two 1500 watt units on a 30 shore service(one in each block) is to have a controller that prevents both units from being energized at the same time, not just a thermostat.

Nick

 

[Genesis]

Shore power concerns were part of the reason that I went with the Wolverine Pad heaters.

They do not provide the quick heatup that the immersion heaters can, but they only draw 250w each - two per engine, or 1000w total. That's right around 8 amps, which is quite manageable....

And - they do the job.