Convert 2 x 30A to 50A

[Richard Carlisle]

I have a 16K cruisair on the bridge. Had a AC guy take a peek at it and he said it was doing all it can do. He said he could install a 27K unit if I had 50A. Would also not burn up 30A cord ends and would be able to run everything on the boat while on shore power. The two sides on the panel have breakers for shore and generator. The shore breakers are 30A and the generator breakers are 50A. I don’t have to manage power on the generator, but on shore power I do.

So the million dollar question. Has anyone converted 2 x 30A to 50A? Seems pretty straight forward. Electrician said he would just install a 50A receptacle, then to a junction box with a couple 240 breakers for future 240V installs, like bridge AC, then up to the existing panel. Each leg of the 50A 240V would feed one side of the existing panel. They would replace the 30A shore breakers with 50A breakers

I think one variable he missed was the isolation transformers. I’m guessing without looking at them that I would have to upgrade those as well.

Biggest annoyance is that we have to shut down the salon AC to run the microwave, unless we are on the generator. Currently I can run both downstairs AC’s and the bridge on the genset. On shore power I can only run the downstairs.

Some of this may me a non issue once we get to MD. Down here in FL the heat and UV component is brutal.

What are your thoughts?

 

[ttmott]

First, the boat shouldn't have any issues with the two 30 amp feeds to operate anything. I assume you are tripping the boat's transfer circuit breakers?? If so I'd change out those breakers with new. Circuit breakers do, over time, become prone to trip at lower loads.
If you want to change the shore power system to a dedicated 50 amp feed then that feed needs to be appropriately protected at the transfer switch/breakers. If one side of the transfer is 50 amp for the generator then you then can up-rate the shore power circuit breaker/transfer switch to 50 amps.
The only other thing I'd look at is how the loads are balanced between the two 30 amp legs; did someone change things around? Even if you did uprate to 50 amp shore power you still want a balanced load.
Now the generator - your's is probably a 120 volt generator that when the transfer switches are on generator the two AC legs in the power panel are joined as one. This lends to no value added to provide for 240 volt split phase future additions at a later date.

 

[ranger58sb]

Biggest annoyance is that we have to shut down the salon AC to run the microwave, unless we are on the generator. Currently I can run both downstairs AC’s and the bridge on the genset. On shore power I can only run the downstairs.

I'd have thought you'd be able to run everything -- except maybe the bridge AC if that was an aftermarket add-on -- with twin 30A shorepower.

When we last had twin 30s, the ACs were powered by the second shorepower line. Or, there was an option on the panel to run "some" stuff (including an AC) on only one 30A line, but that also meant some power management was required.

I think I wouldn't leap to the 50A solution... at least until I fully understood why the twin 30s aren't acting like being sufficient.

-Chris

 

[Richard Carlisle]

My only reason to go to 50A is to have 240V which is required for AC larger that 16K, but my desire for a larger AC might dwindle once we get to MD. It’s brutal here in FL.

Loads are balanced pretty well. Salon AC is on line 1 and fwd AC is on line 2. Brindle AC is also on line 2, so when the fwd and bridge AC’s are on there is an issue. They will run fine but the start surge from either will trip that 30A transfer breaker on line 2. Salon AC and microwave is on line 1. When I run the microwave it will trip the line 1 transfer breaker. DISCLAIMER: I replaced the microwave with one that may draw more than the original. If you have replaced your microwave with something energy efficient, please share the make and model. Mine easily pulls 20A and when it is running and the AC compressor kicks on, pop goes the breaker.

Good idea changing the breakers. Do they make a slow blow breaker? Something that will ignore momentary surge currents?

 

[ranger58sb]

My only reason to go to 50A is to have 240V which is required for AC larger that 16K, but my desire for a larger AC might dwindle once we get to MD. It’s brutal here in FL.

Loads are balanced pretty well. Salon AC is on line 1 and fwd AC is on line 2. Brindle AC is also on line 2, so when the fwd and bridge AC’s are on there is an issue. They will run fine but the start surge from either will trip that 30A transfer breaker on line 2.

A bud put two ACs on their bridge; perhaps two 12s or a 16 and a 12 or whatever might be another way to get there from here (vs that 240V thing).

There are "smart start" things for ACs. I dunno much about 'em, but they apparently keep units from starting at the same time.

-Chris

 

[Skybolt]

@Richard Carlisle you seem to think 50A@240 means two legs of 240v, it's not. it's two legs of 120v@50A each. That is what would be feeding the boat. Once at the panel you can do what ever you like and add on a 220v outlet or the like.

Not sure what the gauge wire you have feeding the panel, but that would have to be upgraded to at least #6 wire. If you have isolation transformers then they would need to be replaced with a 12KVA unit for the 50A service.

When I first got my boat it was twin 30's and I kept burning up cords. I immediately changed over to 50A and it's been just fine ever since. I did have to change the wire feeding the panel. I used #4 wire, but that is over kill I think. I also had a new electric panel made up to be ABYC compliant, but also to fix any wiring issues for the newer GFCI stanchions. So far so good.

Regarding the AC unit's, most, if not AC units up to 16K can be found at 120v. Once you go over that to a 24K or larger then they are 220v.

I have a a standard house over the over microwave on my boat, it's not energy efficient that I know of. But I also ran new wire to the galley for the new stove top as well, both the stove top and microwave are 20A lines.

Here's the question, if you run on the generator does everything work fine? Or do you have issues there as well?

 

[ttmott]

@Richard Carlisle you seem to think 50A@240 means two legs of 240v, it's not. it's two legs of 120v@50A each. That is what would be feeding the boat. Once at the panel you can do what ever you like and add on a 220v outlet or the like.

Not sure what the gauge wire you have feeding the panel, but that would have to be upgraded to at least #6 wire. If you have isolation transformers then they would need to be replaced with a 12KVA unit for the 50A service.

When I first got my boat it was twin 30's and I kept burning up cords. I immediately changed over to 50A and it's been just fine ever since. I did have to change the wire feeding the panel. I used #4 wire, but that is over kill I think. I also had a new electric panel made up to be ABYC compliant, but also to fix any wiring issues for the newer GFCI stanchions. So far so good.

Regarding the AC unit's, most, if not AC units up to 16K can be found at 120v. Once you go over that to a 24K or larger then they are 220v.

I have a a standard house over the over microwave on my boat, it's not energy efficient that I know of. But I also ran new wire to the galley for the new stove top as well, both the stove top and microwave are 20A lines.

Here's the question, if you run on the generator does everything work fine? Or do you have issues there as well?

The issue is his generator is probably 120V single phase. If 220V HVAC systems are added they can only be used on shore power unless he changes the generator. There is no practical reason to have split phase electrical service other than the higher current service.
They make HVAC systems from 8K to whatever BTU operating on 220V. They do not make HVAC systems over 12K BTU (correct me if I'm wrong) that operate on single phase 120V.

Regarding the Soft-Start for the HVAC - These are large capacitors that supplement the inrush current during compressor start. They will definitely help the situation. The total Run current is well within the circuit breaker ratings regardless what is operating.

 

[Richard Carlisle]

@Richard Carlisle

Here's the question, if you run on the generator does everything work fine? Or do you have issues there as well?

Yes, I can run everything on the genset. 50A transfer breakers on the genset. I know I’m looking at new wire to the panel and new isolation transformers. Did you omit the isolation transformers? If I get rid of the transformers, this seems pretty straight forward. 50A receptacle, 6GA to the panel, done. Isolation transformers add another layer of complexity.

 

[Skybolt]

The issue is his generator is probably 120V single phase. If 220V HVAC systems are added they can only be used on shore power unless he changes the generator. There is no practical reason to have split phase electrical service other than the higher current service.
They make HVAC systems from 8K to whatever BTU operating on 220V. They do not make HVAC systems over 12K BTU (correct me if I'm wrong) that operate on single phase 120V.

Regarding the Soft-Start for the HVAC - These are large capacitors that supplement the inrush current during compressor start. They will definitely help the situation. The total Run current is well within the circuit breaker ratings regardless what is operating.

Yeah, I had to split my generator into 220v to do what I did. I also had to re-balance the loads for that and what made me ultimately make a new electric panel.

I have a 16K@120v in my salon, and a 12K@120v in the fwd SR - self contained Cruise air. I think they also make an 18K in the 120v configuration as well, not sure though. Also my units are ~8yrs old as well. But that might have changed these days to your point.

I was also going to add the soft start box's on mine to be nice to my generator. The right box will also stager start the units.

 

[Richard Carlisle]

Regarding the Soft-Start for the HVAC - These are large capacitors that supplement the inrush current during compressor start. They will definitely help the situation. The total Run current is well within the circuit breaker ratings regardless what is operating.

Agree, the start surge seems to be a problem. Any links for soft start devices?

 

[Skybolt]

Yes, I can run everything on the genset. 50A transfer breakers on the genset. I know I’m looking at new wire to the panel and new isolation transformers. Did you omit the isolation transformers? If I get rid of the transformers, this seems pretty straight forward. 50A receptacle, 6GA to the panel, done. Isolation transformers add another layer of complexity.

My boat is an 88' and never had the isolation transformer(s). For 50A service the isolation transformer is a single 220v unit that should be at least 12KVA. I don't really have the room for that so I haven't added it as yet. I did fix my boat to it works fine with GFCI stanchions.

I made up a test plug of sorts, that has a hot tub 50A GFCI breaker in it that trips at 10ma. Dockside GFCI's are 30ma trip. It did take a while to hunt the ussies down and fix them, but now my boat is fine so I don't have to worry about the isolation transformer right now.

The thing you will need to do is, probably make up the test cord that I did to test out the boat. Unless you already have a GFCI stanchion at your slip. Isolation transformers remove most issue(s) with the boat and the dock, they do not correct bad wiring in the boat itself. They will allow you to think everything is just fine when it may not be. Not saying you have any issues, just saying they will surface if you do.

EDIT: Yep they still make the 16/18K self contained in 120v https://wateryachtsolutions.com/marine-air-conditioners/self-contained-units/

 

[Skybolt]

Agree, the start surge seems to be a problem. Any links for soft start devices?

These are single unit soft starters https://wateryachtsolutions.com/marine-air-conditioners/soft-starters/

My stager start link was dead. I'll take a look tonight for the one I was going to get. The soft start is probably just as good to do.

 

[quality time]

@SKybolt any chance you'd loan out your test plug? I'm 50/50 for tripping the new GFI's at transient marinas but don't have a way to troubleshoot at my home dock.

 

[Skybolt]

@SKybolt any chance you'd loan out your test plug? I'm 50/50 for tripping the new GFI's at transient marinas but don't have a way to troubleshoot at my home dock.

Absolutely, PM me and we'll figure it out.

 

[ranger58sb]

Agree, the start surge seems to be a problem. Any links for soft start devices?

Another thought: the newer ACs we've installed -- replacements for originals -- seemed to be much more efficient than the older ones that had been in place.

The replacements have been 120VAC 16K BTUs Dometic DTGs starting in approx 2017 I think, another in 2019, both for 2002 Marine Airrrr Vector Compact 16K originals. And then more recently, a 12K BT unit in this boat, replacing a 2006 Cruisair Stowaway 12K unit.

All of those have re-used the original control panels, and CTM makes apparently-comparable units that do that too.

Perhaps a newer unit on your bridge would be more effective...

And if you don't have a hatch on the stairs to your bridge, maybe installing one of those might help, too.

Combine all that with soft-start things...

Although, just now it occurs to me I'm also surprised you maybe don't already have soft-starts. Or at least similar effect? Our AC control panels have some settings that can keep units from starting at the same time...

-Chris

 

[Richard Carlisle]

Definitely don’t have soft starts. My amp gauges peg when a compressor kicks on. Replacing AC units is on the short list. Mostly because they are old and I do t want to lose AC on 2 week trip. I also figured the new ones were more efficient. Kind of surprised they don’t build a soft start into the new ones from the factory.

 

[Richard Carlisle]

It’s not just starting at the same time. The spike from one while the other is running is enough to pop the transfer breaker.

 

[Scott215]

How many watts is your microwave that will tell you what it's pulling

 

[Richard Carlisle]

How many watts is your microwave that will tell you what it's pulling

Manual says 8.7 amps, which shouldn’t be a problem. Could have had a compressor spike while the microwave was running. I’m thinking soft starts on all AC’s will solve my problem.

 

[Scott215]

If it doesn't have a high amp draw a startup it shouldn't be a problem it's like at home running a toaster and a microwave or a toaster and a Keurig machine on the same plug, too much amp draw at one time