Shore Power Question

When it comes to electrical systems aboard boats, Arild Jensen knows his stuff. Here's where to ask the simplest or most complex questions about marine electrics.

Shore Power Question

Postby Flatsflyer » Sat Jul 31, 2010 8:21 am

I have a 35' CT Trawler with two 30 Amp Power Inlets on the boat. As usual one is for the air conditions, one ids for the house. At home and most places I use a spliter from 50 Amp to two 30 Amp Power Cords. We just returned from 6 weeks in the keys and at several marina's the only power available was 30 Amp. I removed my spliter and hooked the two 30 Amp power cords appropriately. Then the problems started, the AC side would trip the circuit breaker after about two minutes. Both AC are cruiseAir, 16,000 BTU's. If I run one unit no problem, turn on the second unit and it trips the breaker. Got home and everything is fine (50 Amp) at my dock behind the house. Can the problem be that I taking on 60Amps rather than 50?
Posts: 7
Joined: Fri May 08, 2009 7:36 pm

Re: Shore Power Question

Postby Capt Alfex » Mon Dec 13, 2010 1:44 am

Using 2 air conditioners will need the full 30 Amps if they are both running. You cannot start them both at the same time normally. My boat has the same setup but with 10K and 16K units. If I start them both at the same time, both the compressors come on at the same time and blows the circuit breaker. I start one and wait until the compressor has started, then I start the other one.

Did you plug each 30Amp shore plug into separate power receptacles on shore or use the splitter?
Capt Alfex
Posts: 2
Joined: Sun Nov 28, 2010 1:41 pm

Re: Shore Power Question

Postby elnav » Mon Dec 13, 2010 12:05 pm

It sounds more like a problem related to undersized wiring causing excessive voltage drop. One of the characteristics of inductive motor loads is that as the voltage sags the current increases. This is especially noticable during start up when start surges drag the voltage much lower. Marinas with lon g dock wiring to feed to power pedestals are notorious for havin g brown-outs at the end of the dock where transient boats are often assigned for over night slips.

What starts out as 120V at the supply transformer may end up as 100 V at the far end even without a load plogged in. The as you plug in a big load like an air conditioner the surge current causes even greater voltage drop and this in turn leads the inductive load( comopressor motor) to pull even more current. At some point the breaker trips. The solution is easy but expensive. Run bigger wiring. If you do not have a problem its because that dock is wired with adequate sized supply wiring.
Arild Jensen
Custom electrical design for cruising boats
Telephone: 250 998 4474
Posts: 65
Joined: Fri Apr 10, 2009 4:54 pm

Return to Electrical Systems

Who is online

Users browsing this forum: No registered users and 1 guest