575/588 - undervoltage issue?

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undervoltage issue?

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Forum Name: 575/588
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Topic: undervoltage issue?

Posted By: Black Diamond
Subject: undervoltage issue?
Date Posted: 10 June 2025 at 16:14

I'm in a discussion with my marina about the shore power voltage coming onto my boat. My 575 has a 125/250 50 AMP connection, but is only seeing between 208V and 212V coming from the dock. Things seem to be working properly, but I'm worried the constant undervoltage is going to cause damage. My research finds lots of reference to potential undervoltage issues, but none of them are specific as to WHAT might be damaged and how.

Does anyone have thoughts or experience on this?

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Rick
S/V Black Diamond
Hanse 575 Build #192, Hull# 161
Newport, RI

Replies:

Posted By: Arcadia
Date Posted: 10 June 2025 at 19:53

Rick, it sounds like the marina is using a 3 phase 208 supply to provide the two legs of power that our 50 amp cable needs. The problem with this is the you only get 208 volts between any two legs of a 3 phase supply. The equipment on the Hanse will run on 208 but it will not be happy and will be under powered. I would also imagine that the appliance outlets would only give 104 volts. Check it out next time you’re onboard. 3 phase 208 is very common in commercial supplies. However most marinas will provide a SINGLE phase 240 to the shore power outlets. What surprises me is that this has not come up a long time ago at the marina.

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Leon / ARCADIA
2018 Hanse 588
Sag Harbor, NY

Posted By: Black Diamond
Date Posted: 10 June 2025 at 21:51

it is three phase 208. On this dock. We moved docks two years ago to take advantage of some better protection in gales. The other dock had a different setup.

My understanding is that 208V is a three-phase voltage and 240V (split-phase) is a single-phase voltage. In North America, 240V is derived from a single-phase source with a neutral connection. This creates two 120V legs, mostly for appliances that require more power, like electric dryers and ovens. Simply put, it's different from 208V by design.

Given that I'm not roasting a turkey in an electric oven on the boat, I'll assume that my needs are still going to be met. Unless someone can tell me the long term danger of using 208 vs a higher voltage. Apparently I have been using 208V for 2 years now and not noticing. :-)

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Rick
S/V Black Diamond
Hanse 575 Build #192, Hull# 161
Newport, RI

Posted By: Arcadia
Date Posted: 10 June 2025 at 22:15

Mostly correct. Single phase or split phase as you say, is actually derived from a single leg of a three phase service. A single transformer will take one leg of the three phase service and create the two legs of 120 which will also give 240 across those same two legs. Most transmission lines in the us both residential and commercial is three phase. As I mentioned before, you can’t be getting more than 105 volts at your outlets in this situation. And only 208 to everything else.

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Leon / ARCADIA
2018 Hanse 588
Sag Harbor, NY