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Old 11-05-2017, 10:01 AM   #21
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Originally Posted by Seevee View Post
Diver Dave,

That's the same question I'd ask. (and good paper of wiring diagrams).

Seems like the common "house" wiring would be better for a marina, all single phase. And don't understand why Wye is better. Same wires, less power. What am I missing?

Also, I still can figure out where the 208 comes from.
If you have 120 from neutral to Phase A,
and 120 from neutral to Phase B,
Then why wouldn't you have 240 from Phase A to Phase B?
In 3 phase, each phase is 120 deg out of phase with each other. In a center tap 240/120 (our houses), each "leg" is 180 deg out of phase. To calculate leg to leg voltage, with 180 deg out of phase, its a simple 2 x. With 120 deg out of phase, its square root 3 x each leg. So, 120V is square root of 3 (1.73) into 208.
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Old 11-05-2017, 10:06 AM   #22
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Also, I still can figure out where the 208 comes from.
If you have 120 from neutral to Phase A,
and 120 from neutral to Phase B,
Then why wouldn't you have 240 from Phase A to Phase B?
Because in 3 phase, the phases are staggered 120 degrees.

We are all most familiar with our home power which is the result of a center tap transformer on just one of the 3 phases that run down the road. That center tap transformer steps down the phase on the road to 240V, and with the center tap provides two legs that are 180 deg out of phase with each other. When one is peak negative, the other is peak positive. That's why they add up with simple addition.

With three phase, each phase is staggered by 180 deg, so when one is at it's peak positive, another is on it's way negative, and the third is on it's way positive. But neither of the other phases is fully positive or negative yet. That's why they only measure 208V. The relationship between the different phases is based on vector math with sines and cosines and other things most people avoided in school, or have since been trying to forget.
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Old 11-05-2017, 10:08 AM   #23
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To refresh the why Y is better:

Each primary wire phase, (there are 3), drives 120V loads. If there is any 120V load imbalance, the neutral takes the diff. current (similar to 240/120 split in your house).

In delta, there is no "neutral" wire feed. It's 3 wire primary, not 4. The good news is that you have 3 sets of 240V outputs at the transformer. I could center tap each of the 3 phases to d=get my true 240/120.
BUT, for safety, you need to supply a grounded neutral. I can only ground to earth one point on a transformer secondary. So, only one set of 240/120 could be used for a boat. One primary leg is supplying zero % of the load.

The good news is that IF you used delta, the boats actually get 240/120, but from a cost view, its bad news for the folks buying these assets, since they are not used efficiently.
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Old 11-05-2017, 10:30 AM   #24
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The relationship between the different phases is based on vector math with sines and cosines and other things most people avoided in school, or have since been trying to forget.
Its a sad life I have. It's fall outside, crappy overcast and rain and cold all day. the boat is winterized, my season is shot. For fun now, I try to remember trig...
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Old 11-05-2017, 10:49 AM   #25
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It's economics. With a 3 phase transformer on shore or out on the docks somewhere, the output is three 208/120V circuits. That will service more slips at a lower cost.

hmmm, not true for the 1 billion homes on the planet? But true for a few thousand marinas with a similar demand for service?

In all my travels, I have come across 1 house with 3 ph service. We have entire multi-square mile neighborhoods supplied with single phase. Efficiency is high on the list for utility distribution. Few residential areas have even 3 phase available.

so, my fundamental question remains. Who on a dock wants 3 phase??
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Old 11-05-2017, 11:08 AM   #26
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As much as this has created a lot of comment it must be remembered that a marina upgrading or providing a new installation must plan for what is being manufactured today plus planning for future capacity. It is not economically feasible to try to accommodate the odd vessel with 15 year old 240 volt compressors (that may be replaced in a year or two) when all the other newer vessels have 230 volt or 120 volt compressors that work within the parameters of the installation. We see this every day in so many products. Planned obsolescence is a fact of life and technology does not go backwards.
On a three year old dock of 14 seventy foot slips we used a 150 KVA 208wye transformer (homebuilders use this for up to 24 new homes). The only low voltage complaint was from a 20+ year old Viking 60ish sportfish. His B&B was broken and he did not want to spend the money to replace it.
All the rest of the vessels were much newer Searay, Neptunius and Princess vessels that had no issues at all.
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Old 11-05-2017, 12:25 PM   #27
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My experience is with 70 and smaller boats. All the 240v needs have always been provided by two 120v hots and a single neutral. I have never run into 3 phase.

I find this discussion most interesting. I could easily have spent all my time on a 208v wye dock and never known.

Isolation transformers are rare in my world and have all been 120v so I was unaware of the 208v issue. I will file this info away for future use.

The only time I have ever needed 3 phase has been in manufacturing to operate electric motors that are under constant high torque such as big compressors.

Great discussion!
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Old 11-05-2017, 01:29 PM   #28
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If you buy a significant amount of power every month, three phase is cheaper by the KW than single phase 110 or dual phase 240. $$$ talk which is probably why they used it.
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Old 11-05-2017, 01:40 PM   #29
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ld dock of 14 seventy foot slips we used a 150 KVA 208wye transformer (homebuilders use this for up to 24 new homes). The only low voltage complaint was from a 20+ year old Viking 60ish sportfish. His B&B was broken and he did not want to spend the money to replace it.
All the rest of the vessels were much newer Searay, Neptunius and Princess vessels that had no issues at all.
OK, still here trying to get a handle on this info. One point though, if 1 out of 14 homeowners had this issue with the utility, that is a huge issue. You would have 93 thousand Hydro One customers complaining, keeping that same percentage!

So, I looked up three 24k BTU marine air systems up, (at random), to check on the rated line voltage. This would be a good method, I think, to see if the marine industry is truly on-board with a 208/120 mains system. Here are the results:

Marinaire MSBA16C2; listed at 208-230V/50-60Hz; these guys are on-board! but, this was a 16kbtu model.

Aqua-Air SIG24C; listed at 230V ac, 50/60Hz. You can get an option for a 208-230V, 60Hz, or a 200-220V at 50Hz. So, you have three different order options even in the 200V space. Good luck!

Mermaid M24; listed at 220V; since 220V is not a typical, modern rating anymore (even europe has accepted now 230V, N America has long moved from 220 to 240V), I'll assume they are walking between 208 and 240 and they are simply in the middle. On the other hand their ad intro says this, which is confusing "As stated, Mermaid is an international company and we manufacture all of our air
conditioners in either 120V or 240V, 50/60-Hertz or 240V 50-Hertz configurations. So, I'm not sure what their rating actually is.

btw, the correct way to spec equipment is a Voltage and Frequency rating, which is the normal, expected voltage, and could be a range. So, 120-240 is rating range. In addition, you need to spec an allowable range. Either in % or total. So a rating of 120-240 with +/- 10% means you guarantee operation from 108 to 265. If you rate at 120/240, that means 108 to 132 OR 206 to 262V. The hypen vs slash is meaningful.

With that reseach done, it does seem POSSIBLE to get a "world wide" ac system in your boat. But, it doesn't seem likely unless you have an engineer doing the specs. And, these are new units, not what you have.
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Old 11-05-2017, 01:47 PM   #30
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If you buy a significant amount of power every month, three phase is cheaper by the KW than single phase 110 or dual phase 240. $$$ talk which is probably why they used it.
The marina is buying 3 phase and is billed accordingly. I'm supposing these dockside transformers are not utility owned, but marina owned. Therefore the marina is determining what voltage they shall give you, not the utility.

Gary, is this correct on the ownership?
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Old 11-05-2017, 01:55 PM   #31
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When it comes to AC, everything I see are reverse cycle heat pumps and they are all 120v.

I'm guessing down south reverse cycle heat pumps are not adequate for AC. Still I would expect the AC units to use two 120v hot legs still by passing the need for a single 208v hot wire, or is there something I am missing here.
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Old 11-05-2017, 02:11 PM   #32
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The marina is buying 3 phase and is billed accordingly. I'm supposing these dockside transformers are not utility owned, but marina owned. Therefore the marina is determining what voltage they shall give you, not the utility.

Gary, is this correct on the ownership?
Correct, the utility owns the main input transformer and each dockside transformer is marina owned.
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Old 11-05-2017, 02:16 PM   #33
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When it comes to AC, everything I see are reverse cycle heat pumps and they are all 120v.

I'm guessing down south reverse cycle heat pumps are not adequate for AC. Still I would expect the AC units to use two 120v hot legs still by passing the need for a single 208v hot wire, or is there something I am missing here.

No, two 120 volt hot wires from a 208 wye transformer will give you 208 volts because they are only 120 degrees out of phase if you have 230 volt compressors. If you have 2 120 volt units each one will get 120 volts because they are reacting with the neutral, not another leg even though they may be drawing from two different hot wires. A balanced load.
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Old 11-05-2017, 02:34 PM   #34
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A search on line of what marinas have is pretty much futile. I did see this one from Miami beach Marina, space for 400 boats, the largest to 250 ft.

"30amp/50amp/100amp single phase/100amp three phase, 480 volt"
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Old 11-05-2017, 02:41 PM   #35
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So I have ran into problems with 208. I have two different marinas that have 208 that I have gone to. A marina in Pensacola where I have no problems. However, at St. Pete Municipal they have 208 and if there is more than 2 boats on the transient T dock I have sufficient voltage drop that I can only run one of our AC units. Maybe two if they are small. We have five units and usually run three at a time. They tried to put us closer to the transformer but would have needed to move a bunch of boats. Ran the generator and they gave us a partial refund.
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Old 11-05-2017, 03:02 PM   #36
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Gary; are docks limited to 600V feeders? I found this 150kVa unit:

Marina Electrical Equipment -GTX™ UNIT SUBSTATION
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Old 11-05-2017, 03:13 PM   #37
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If you are measuring the power to your boat and it is lower than 120, it is probably because you are overloading your service. Unplug everything and measure the input voltage, then start plugging everything back in. As soon as you measure a voltage drop, I believe its 10%, you are done. More load than that and you are risking a failure and a fire. Try feeling how hot your shore power plug is too, if you feel any heat and there is no way to measure voltage, you are risking a failure and fire so unplug some devices. This is especially true in the winter heating time when your boat will not be used for long times.

Hot water tank?
Space heater?
Vent fan?
Battery charger?
Cell phone charger?
Lights?
Fridge?
Water pump?
Ais?
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Old 11-05-2017, 05:07 PM   #38
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I was trying to understad why I have never run into this 208v issue in B.C. Canada. Then it dawned on me. We can never find more than 50a 125v outlets. Thats why we use step up transformers, so even if we found a 50a 125/250v outlet we are seeing 120v on both panels and 240v from the step up transformer.
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Old 11-05-2017, 05:46 PM   #39
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So I have ran into problems with 208. I have two different marinas that have 208 that I have gone to. A marina in Pensacola where I have no problems. However, at St. Pete Municipal they have 208 and if there is more than 2 boats on the transient T dock I have sufficient voltage drop that I can only run one of our AC units. Maybe two if they are small. We have five units and usually run three at a time. They tried to put us closer to the transformer but would have needed to move a bunch of boats. Ran the generator and they gave us a partial refund.
Undersized wiring, corroded connections or a Marina adding a "few" more towers to a chain without upgrading the feeds can all contribute to line loss. It happens all the time.
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Old 11-05-2017, 07:29 PM   #40
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That's what the dock master said, that they added to many feeds. Almost all my big systems, AC, pumps, and so on are 220, not 120. This according to the dock master is a problem at the T head. I have no problem at other marinas. I could watch my 208 which read about 205 go down to 202 when other boat AC kicked on. That was before I put any of my loads on. Frustrating but they did make good and gave me a reasonable refund.
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