A/C Question

[ADaily3224]

Air Conditioning Experts:

I was running both A/C units using one power cord with a splitter (Two 30 Amp connectors with one 30 amp cord). I know, not the best practice but up north here marinas provide one 30 amp plug per dock.
Normally if I'm not careful the breaker on the power source will trip, although running both A/C units usually wont cause this, today was especially hot and both units were running full time. At about 5:00 both A/C units shut down but the ship service stayed on. I checked my electrical panel, nothing tripped. I disconnected the power to the 30 amp A/C service receptacle and unscrewed the clear plastic fuse holder just below the lock on power cord receptacle. The fuse (FRN-R-30 Dual Element Time Delay D HRC I) was hot, but seemed intact. Am I on the right track? There were two fuses and there are two AC units, neither were working. I seem to remember that when one of these fuses burns out a orange neon lamp lights inside the clear plastic holder? I suppose I could have switched fuses from ship service to the A/C service but I didn't have time and the fuses looked fine although kind of warm. Is there another circuit breaker or fuse that I don't know about? The small separate A/C circuit panel's red power lamp was extinguished, another indication that power to the panel had been interrupted.
The A/C unit is a 1988 model, two units I think a 12,000 BTU and a 18,000BTU seems to be pulling 20 Amps with nothing else on.
Thanks, Tony D

 

[RTyler]

I've blown those fuses before and not had any visual indication that they were blown. I'd try replacing them and see what happens.

R Tyler

 

[MikeP]

Had EXACTLY the same thing happen yesterday afternoon with guests aboard - single (in this case) 50 Amp cable, 4 air conditioners running, microwave and assorted other items - lost AC power but breaker at shore did not trip. I shut off the breaker, pulled the cartridge fuse, checked it with a multimeter - dead. Put in new fuse - fine. I'm sure it's your fuse. Be sure to keep spares. As mentioned, there is no external indication that these fuses are blown.

I would expect the 50Amp shore breaker to trip before the 50 Amp time-delay fuse does but, oh well.

 

[labrador]

Had the same problem last year however when those fuses blow you lose all power not just the A/C which is what I believe you are saying. If the fuses blow at the power source there is no power to the ships service therefore if this is the case you will have to look elsewhere. Hope that's not the case.

 

[MikeP]

Oops, sorry - Lab is quite right - I see I didn't carefully read the initial post. I failed to notice the part where A/C units quit BUT the ships ac service, provided by the shore power, stayed on. Obviously if you still had power coming in, the cartridge fuse in the main shore power circuit is OK.

When this occurred did you get a warning light/audible alarm that you had lost A/C power?

 

[67hat34c]

Typical systems have thermal overload switches on the condensing unit, also the cooling pump will have an internal switch. sometimes there is also a cut out switch that will not allow the condensor to work if the cooling pump not working. Typical system has many safety features to protect system from damage if it gets too hot.

Do you have one cooling pump for both units? if so then if the pump is bad then possibly the system will not run.

also remember that although you claim 20 amp usage with your system, the start up amps can be 3 to 4x running amps. if both units happen to cut on at the same time then it could overload electrical systems. Although i would think it would trip breaker at the dock.

 

[Cobra29]

Had kind of the same thing happen about 2 months ago. My problem turned out to be that one leg of my 50 a, 220 v power cord was blown. Had power to ship's service but no a/c. After tearing everything up, checked power at the boat end of the cord and had nothing on one leg but fine at the box. Using the spare cord solved the problem.

 

[ADaily3224]

Thanks for the useful information.

In as much as someone has had the same problem I'll try the delay fuse first, there are two of them. If that doesn't work I'll check the other items listed. With the indicator light off at the A/C panel it seems like the issue would be the fuse although I thought there would be some sort of indication on the fuse or the holder. I had a Bertram and when a fuse blew it had a neon glow light that lit.

Tony D

 

[SKYCHENEY]

No glow light on mine. When the A/C's quit last week (4 units on one 50amp 220v service), I pulled both fuses. One was extremely hot. Tested them with a multimeter and that was the one that was blown. The other one was fine. So, I pulled out the box of fuses that the previous owner left aboard the boat. I tested those fuses before replacing the bad one and found that the first two out of the box were blown too. Apparently he never knew how to test fuses, so he would put new ones in and just throw the others back into the same box. Anyway, once I found a good fuse, all was fine and no problems since. I suspect that it will prove to be one of those fuses in your situation as well.

 

[Maynard Rupp]

We have 2 30 amp plugs on our 1986 36C, onefor ship service and one for AC. Each is protected by 2 fuses, one for the black 110volt line and one for neutral. We had our 2 AC units quit last week and found one of the AC fuses blown. I replaced it but noted thet all 3 of the other fuses had some corosion and green on the copper ends. After running the AC units for about an hour, I was amased to find that the power cord was quite warm. I pulled the fuses and couldn't touch them. Our AC panel showed about 27 amps current drain. I took all the fuses home and cleaned the ends with the wire wheel on my grinder. I coated all parts with ac-50, (a corosion inhibiter), and put it all back together. Plug stays much cooler now. We had all that corosion and this boat has never seen salt water. I wonder how bad most other boat's fuses look!

 

[Pascal]

what is the benefits of these fuses ? i have some old large fuseholders, disconnected near the panel in the ER and only rely on the circuit breakers for protection... either the one on the dock or the main breakers on the panel?

boats i had before (also with 220/50 shore) didn' have any fuse either....

seems like the breakers pop out nicely in case of an overload...

 

[UNIQUE_NAME]

i was wondering the same thing last year after loosing power to the air conditioners one HOT day. i only found them after looking at the wiring schematics.

i found this from d. pascoe

Main Circuit Protection Many people think that the circuit breakers on the dock protect their boat. They do not; they only protect the dock wiring. Your main circuit breaker protects your boat's systems. But what about that section of wiring and connectors between your main panel and the dock breaker? Well, the fact is that it is unprotected. which is why so many fires occur. Check out all the top end boats and you will find that they have circuit protection located directly at the shore connectors. Which is why we recommend that you should too. Having slow blow cartridge fuses installed directly at the connectors can go a long way toward preventing fires and burned up shore cords, particularly if you are a traveler and frequently rely on uncertain power supplies. Circuit breakers should NEVER be installed on the exterior of the boat. Only gasketed, water proof cartridge holders should be used.

i replaced the fuse and now carry spares.

 

[Pascal]

well if there is a short between the dock box and the boat panel (including the shore connectors) woudln't the breaker on the dock box blow?

i understand the need for extra protection between the shore power receptacle on the boat and the main panel, but i think safety guidelines only mandates a fuse or breaker where power enters the boat when the distance is greater than ?? feet... is it 6 ? i can't remember the numnber. Teh concern is indeed possible insuficient protection from sub standard dock equipment.

on the 53, the shore power connectors are within 3 ft of the electrical panel... my old fuses were next to the panel, leaving most of the run between connector and panel un protected.

my previous boat (37 express) had the shore connection at the stern, in a locker. it had a breaker next to the connector, sorta protected in that locker, and installed in a standard shore power chrome cover. it made sense because of the length of the cable run between the stern and the electrical panel

 

[UNIQUE_NAME]

i didn't know what the wiring length spec was and thought he was referring to hatteras' ("Check out all the top end boats") . plus my panel is 7 or 8' away from the connection.

 

[SKYCHENEY]

Pascal,
As with most items regarding safety, the standards have gotten more strict over the years. Your boat is probably just fine as it is, but the added protection of the fuses at the connection point to the boat was probably necessary to conform to updated electrical codes. Look at ground fault plugs, for example. They just keep finding more and more places where they think they are necessary (to meet the new electrical codes).

Or maybe, since the boat manufacturers want to limit their exposure to risk and since they don't know what you are plugging into or how many cords you have connected or their condition, they have chosen to add redundancy to the system. Hatt also added isolation transformers in later years, which I don't believe they had in the 1970 model. Just a little added protection.

 

[Pascal]

well, true... but the fuses are located (or were on my boat) riht by the main panel so they didn't add much protection... the wire run from the shore connector to the fuses would be the same as to the main breaker on the panel...

 

[ADaily3224]

Thanks everyone for the useful information. As it turned out it was the slow blow fuse, I see someone else has the same issue. I noticed in another post that someone wrote that if the dock voltage drops A/C units can pull more than the normal amount of amps at start up. While looking at my amp gauge voltage is always on the move, when demand is high, voltage is low.

Tony D