De icer question

[paulga]

No, locked rotor amps are what the motor will draw if the rotor is held fast. There will always be a spike in energy draw when the motor is started, but it only lasts a very small amount of time. Breakers have the ability to withstand that inrush current. Locked rotor current is what you measure after the inrush spike has leveled out but the shaft is jammed by something. So if the motor is on a 15 amp breaker and the shaft is jammed somehow, the breaker will trip as the locked rotor current is 20 amps. This is what you want to happen.

If the shaft is jammed, the rotor does not run. Should it be drawing zero current in that state?

 

[Bmarler]

If the shaft is jammed, the rotor does not run. Should it be drawing zero current in that state?

No. The motor will draw very high amps as it’s trying to start. I can’t explain how motors operate in a forum post, there are too many points to cover. If you really want to know there’s a ton of easily findable information. One google search will keep you busy for as long as you want.

 

[paulga]

Quite right. I had forgotten that. But best practice dictates circuit breakers limiting current to the rating of the receptacle and wiring. So installing a 15a rated GFCI outlet on a 20a circuit is generally a bad practice, and putting it on a 30a protected circuit is a very bad practice.

My solution was to start with an old 30a shore power cord with a burnt boat end. I cut off the bad connector, and attached a small 30a distribution panel with 15a current protected gfci receptacles. With this arrangement I powered two bubblers all winter. The panel stayed under cover in the cockpit of the boat. Photo attached for reference.

Again, I question the need for more than 15a of current protection.

if you do this set up now, do you have to purchase a 30a (10g) shore power cord, cut the other end to have 3 open wires, then connect to the 30a distribution panel? are there alternative methods?

 

[Jeff F]

if you do this set up now, do you have to purchase a 30a (10g) shore power cord, cut the other end to have 3 open wires, then connect to the 30a distribution panel? are there alternative methods?

Ask around. There are lots of 30a cords with failed boat ends out there. But otherwise, yes. I built a similar 50a 240v panel and used a brand new shore power cord.

I don't think this is a prudent solution to build on your own, but any electrician could build something similar. Parts are maybe $150. Seems like overkill for you, but it's worked well for me. Bonus for you would be having another outlet that you could run 1500w of heat on. As mentioned above vet any non-standard stuff with the marina.

Maybe the marina will install a 15a gfci receptacle for you? If not I'd probably follow the path of least resistance and use the Marinco adaptor, especially if the controller has 20a protection as I think you mentioned earlier. Hopefully you understand from this thread where it falls short, but if outdoors the risks seem small to me.

 

[Jeff F]

One more alternative is to power it from the boat, but I'm guessing you don't have excess power available there. Still might be worth considering. How big is the motor on the de-icer?

 

[paulga]

One more alternative is to power it from the boat, but I'm guessing you don't have excess power available there. Still might be worth considering. How big is the motor on the de-icer?

1/2 HP is a good size. the rated operating current is 5.6a, the same as a 700w heater

 

[Jeff F]

1/2 HP is a good size. the rated operating current is 5.6a, the same as a 700w heater

Can you fit it in to your onboard power budget? Where are you, btw? And living aboard?

 

[paulga]

Quite right. I had forgotten that. But best practice dictates circuit breakers limiting current to the rating of the receptacle and wiring. So installing a 15a rated GFCI outlet on a 20a circuit is generally a bad practice, and putting it on a 30a protected circuit is a very bad practice.

My solution was to start with an old 30a shore power cord with a burnt boat end. I cut off the bad connector, and attached a small 30a distribution panel with 15a current protected gfci receptacles. With this arrangement I powered two bubblers all winter. The panel stayed under cover in the cockpit of the boat. Photo attached for reference.

Again, I question the need for more than 15a of current protection.

are the connecting struts provided by the electrical boxes?

 

[paulga]

Can you fit it in to your onboard power budget? Where are you, btw? And living aboard?

it still fits, but not ideal. even a grinder will use 10a.

 

[Jeff F]

Don't try this at home!

 

[paulga]

Don't try this at home!

only to have a mental model. I would call for a local electrician's help for sure.

 

[Jeff F]

Show 'em this pic and they'll figure it out. Two hours would be generous to put that together.

 

[Bmarler]

are the connecting struts provided by the electrical boxes?

View attachment 159320

Those are conduit offset fittings. They allow you to have holes at different elevations.

 

[paulga]

Those are conduit offset fittings. They allow you to have holes at different elevations.

Thanks. That explains these struts connect with the boxes in an oblique way

 

[SIBERNUT]

Musta missed something. Thread started with bubbler and migrated into "Kasco", not the same thing.
Had REAL bubbler system, compressor noisy, PITA. Went to de-icer like Kasco.
Cripes, in the old days wed wait for the ice to form & pour a gallon of #2 around the boat