Only 90V AC Shore power

[mml2112]

When 50A shore power cable is connected to MS400, either forward or aft, AC panel meter shows 90V. Tried another known good cable, still 90V. Generator produces 110V+ on meter. Pedestal on dock tests at 208V. Anything I should check? Isolation transformer?

 

[O C Diver]

Is that with a load (appliances running) or with out?

Ted

 

[sunchaser]

Work your way from the pedestal to and then onto the boat with a VOM. Several areas can be problematic. Borrow a power cord and connectors of known good voltage transfer if possible to eliminate that common problem.

Do you have an IT? Do you have a volt meter for each incoming leg? Keep in mind safety and look for scorch marks. Me- I’d just call a good marine tech once the easy stuff is checked out.

 

[Arc]

First simple test is to go to the outlets with a meter and verify actual voltage.

 

[Jc180]

My neighbor boat is a Mainship 400 and suffers from the same problem. Need to get a little technical to start: 208v at the pedestal indicates that the Marina power is a “wye” configuration vs a “delta” that would 240v. The Mainship isolation transformer divides either the 208 or 240 in half (transformer winding is “center tapped”) for hot leg to neutral voltage resulting in either 104 or 120 volts respectively. Without the isolation transformer, the wye hot leg to neutral voltage would be 120v, same as the delta.

So now more of a layman’s discussion. So from above, the best you can expect from shore power is 104. And if you have some voltage drop in boat wiring and then add load, under 100 easily. Would say 90 is lower than would expect, but upper 90s may be as good as it gets.

So the questions are why would Mainship deliver a boat with an isolation transformer wired this way? Why would the Marina not be a delta configuration? Don’t know. By the way, I own a Mainship, and love it, so not bashing Mainship.

We could have a vigorous debate about the benefits of an isolation transformer. But in this case it is a liability. Might consider bypassing transformer.

 

[twistedtree]

My neighbor boat is a Mainship 400 and suffers from the same problem. Need to get a little technical to start: 208v at the pedestal indicates that the Marina power is a “wye” configuration vs a “delta” that would 240v. The Mainship isolation transformer divides either the 208 or 240 in half (transformer winding is “center tapped”) for hot leg to neutral voltage resulting in either 104 or 120 volts respectively. Without the isolation transformer, the wye hot leg to neutral voltage would be 120v, same as the delta.

So now more of a layman’s discussion. So from above, the best you can expect from shore power is 104. And if you have some voltage drop in boat wiring and then add load, under 100 easily. Would say 90 is lower than would expect, but upper 90s may be as good as it gets.

So the questions are why would Mainship deliver a boat with an isolation transformer wired this way? Why would the Marina not be a delta configuration? Don’t know. By the way, I own a Mainship, and love it, so not bashing Mainship.

We could have a vigorous debate about the benefits of an isolation transformer. But in this case it is a liability. Might consider bypassing transformer.

This


This is how a 240V split phase isolation transformer works. And "Y" dock power is very common, as is this exact problem. I think any boat wired this why should have a boost function in the transformer. Many have the winding taps to accept wither 240V or 208V input and create 120/240V output using a simple switch. Others are fancier with voltage detection and automatic switching.

 

[sunchaser]

My neighbor boat is a Mainship 400 and suffers from the same problem. Need to get a little technical to start: 208v at the pedestal indicates that the Marina power is a “wye” configuration vs a “delta” that would 240v. The Mainship isolation transformer divides either the 208 or 240 in half (transformer winding is “center tapped”) for hot leg to neutral voltage resulting in either 104 or 120 volts respectively. Without the isolation transformer, the wye hot leg to neutral voltage would be 120v, same as the delta.

So now more of a layman’s discussion. So from above, the best you can expect from shore power is 104. And if you have some voltage drop in boat wiring and then add load, under 100 easily. Would say 90 is lower than would expect, but upper 90s may be as good as it gets.

So the questions are why would Mainship deliver a boat with an isolation transformer wired this way? Why would the Marina not be a delta configuration? Don’t know. By the way, I own a Mainship, and love it, so not bashing Mainship.

We could have a vigorous debate about the benefits of an isolation transformer. But in this case it is a liability. Might consider bypassing transformer.

So we don’t have an IT. We have a 208 pedestal with BC Hydro saying the wye connection is likely better for marina use than a Delta. Your thoughts?.

 

[twistedtree]

So we don’t have an IT. We have a 208 pedestal with BC Hydro saying the wye connection is likely better for marina use than a Delta. Your thoughts?.

Tough to say without a basic wiring diagram of your shore power setup. There are just so many variations, and obviously we guessed wrong the first time...

 

[rslifkin]

Assuming that it's tapped from a 120/208 3 phase feed, you will likely see 120v phase to ground, 208v phase to phase. Most likely the pedestal will be wired with a 50A outlet having 2 out of 3 phases on it. So with no IT, you'll get 120v on both legs, but any 240v loads will only see 208v.

 

[STB]

I'm not sure why wye vs delta matters here. Both are 3-phase transformer configurations that produce 208v between any two phases since, in either case, the phase are 120-degrees apart.

For reasons of efficiency, 3-phase power is used in most industrial and commercial settings. It also can deliver more consistent power since the ups and downs of the phases balance out. This is important for heavy motor loads, etc.

Single phase power is commonly used for residential use. Two single phase 120v supplies 180 degrees apart have a 240v difference. Thus is why homes get 240v.

Single phase power is usually used for terminal delivery to residential just for the simplicity and reduced expense of the wiring, breaker box, etc. Most residential loads, even motors, aren't three phase, unlike large industrial motors which, for reasons of efficiency, not wanting a big starting cap, etc, are 3 phase.

As an aside, as I understand it, residential single phase power is normally derived via transformers from a single phase from distribution 3-phase power by center tapping a transformer winding, giving two legs 180 degrees put of phase, so the 120v gets doubled to 240v.

I'd imagine that most marinas are 3 phase. That the common case for non-residential delivery in the US. And it makes sense for large pumps and big boats.

If mainship uses an isolation transformer that commonly divides across two 120v legs (120 degrees out of phase) to get 104v, it would be easy to call that a blunder, but that's not quite the whole story.

What's the alternative? Imagine configuring it for the common case for commercial marinas -- and then someone parks at a residential dock with singe phase service. Now the transformer is delivering 277v to systems designed, in some cases, for as little as 208v. That ain't good.

They'd need to pony up for the expense, complexity, and reduced reliability of an auto variable transformer. Or, they'd need to provide a switch to select among taps -- which a user could set wrong, putting things back into the unsafe 277v to 208v appliance situation.

This situation is common to more than mainships.

Most of the larger boats at my marina have step-up transformers to solve exactly this problem, especially with AC units. I attached a few quick photos.

I'd recommend adding one by your shore power pedestal. It's the common solution to a common problem.

I'd also recommend figuring out how 104v is becoming 90v or how 208v is becoming 180v. 13% loss is a lot. I suspect high resistence connections somewhere -- somewhere getting hot and that might get hotter, perhaps?

 

[STB]

I just read this thread a little more carefully on my computer vs my phone.

If there is no isolation transformer, then something is off if it isn't 208 hot-to-hot and 120v hot-to-neutral, within some reasonable amount of voltage drop for the load. 90v from 120v is not a normal or reasonable drop.

I'm with Arc and Sunchaser. Start with a meter at the pedestal. See what you have there. Then at the other end of the shore power cord. Then at the back of the shore power inlet. Then going into the main panel, then into the main breaker, then out of the main breaker, then at the main busbar, etc.

A lot of things could be going wrong along the way. I always bet on a bad cable (likely just connector and maybe a little bit of wire at the end), a bad outlet on the shore power pedestal (or associated internal wiring), or a bad shore power inlet (inlet side or wiring side, or associated wiring). They get exposed to weather, salt, mechanical loading, chronically high loads, overloads, etc.

I think the 3-phase thing was a little bit of an excursion given that there isn't a transformer.

 

[OldDan1943]

Okay, let’s go over this again.
You have 120 volt at the pedestal, you plug in the cable, the other end of the cable, you have ? Voltage?

We are all accepting, you have cleaned and inspected the contacts at both end of the cable???

Next, clean and inspect the boat’s shore power receptacle, you have 120vt out the back of the boat’s shore power receptacle.
The first breaker, you have 120vt in and out of the breaker?

So far, nothing feels hot?

You have the standard shower power connector and not a “smart shore power plug”?

 

[mml2112]

More testing

Thank you all for the education on electrical issues. The wiring at the pedestal is from about 20 years ago. The main ship 400 that pulled up next to me the other day had a brand new 50 amp cable so I tried his. I still got 90 volts on my leg one and leg two. He was getting 100 volts with his cable and his isolation transformer. I have not tested my isolation transformer yet in any way. I will do more voltage checks as described above with my mechanic. My basic question is:

Is supplying 90 volts to my panel a problem for the equipment on the boat?

 

[twistedtree]

Thank you all for the education on electrical issues. The wiring at the pedestal is from about 20 years ago. The main ship 400 that pulled up next to me the other day had a brand new 50 amp cable so I tried his. I still got 90 volts on my leg one and leg two. He was getting 100 volts with his cable and his isolation transformer. I have not tested my isolation transformer yet in any way. I will do more voltage checks as described above with my mechanic. My basic question is:



Is supplying 90 volts to my panel a problem for the equipment on the boat?

It you DO have an isolation transformer? And are using 50A 240V shore power? And on the boat have a panel that’s split between leg 1 and leg 2? And you panel meters for those legs shows 90V on each. And a sister ship shows 100V?

If all this is true then the earlier posts about isolation transformers and 120/208 three phase power are all applicable. Voltage per leg on the boat (output side of isolation transformer) will be half of the actual 208V input voltage. That’s 104v in a perfect situation. The 100V the sister ship sees sounds typical. The 90V you see is because of some additional loss. When you tried your neighbor’s power cord, we’re you plugged into the same dock outlet? If so then the loss is on your boat. If you are plugged into a different dock outlet the there could be dock wiring losses contributing to the problem.

90V is not good. Some appliances will be fine with it, but others will be stressed, especially HVAC.

I think that with a 240v split phase isolation transformer you MUST have boost capability somehow or another. If your isolation transformer can’t be wired with a selector switch to accept either 240 or 208 input, then an external booster should be used.

 

[OldDan1943]

Is supplying 90 volts to my panel a problem for the equipment on the boat?

I am not an electrician, 120 has a tendency to scare me.

90 volts to your panel is not per design and may prohibit the proper operation of all electrical down stream.

Inform the DockMaster, he has a real problem.
Just might be time to employ a marine electrician to trouble shoot the system.

In other words, 90vt at the pedestal sure ain’t helping and will at least shorten the life of every piece of electrical equipment on board.

 

[smitty477]

I am not an electrician, 120 has a tendency to scare me.

90 volts to your panel is not per design and may prohibit the proper operation of all electrical down stream.

Inform the DockMaster, he has a real problem.
Just might be time to employ a marine electrician to trouble shoot the system.

In other words, 90vt at the pedestal sure ain’t helping and will at least shorten the life of every piece of electrical equipment on board.

From first post...
"Pedestal on dock tests at 208V. Anything I should check?"

 

[OldDan1943]

From first post...
"Pedestal on dock tests at 208V. Anything I should check?"

Yes, get the dock-master involved.
Check all connections while the dock-master is watching. Might be time to shut the power off and tighten all the connections and/or replace the socket at the pedestal while ‘brightening’ the ends of the cable.
Corrosion can allow the output to look normal until a load is applied.
Take the 2 50ft shore power cables together and try a different pedestal.

It looks like you are doing the dock-master’s job. Send him the bill and ‘hope’.

 

[twistedtree]

Yes, get the dock-master involved.
Check all connections while the dock-master is watching. Might be time to shut the power off and tighten all the connections and/or replace the socket at the pedestal while ‘brightening’ the ends of the cable.
Corrosion can allow the output to look normal until a load is applied.
Take the 2 50ft shore power cables together and try a different pedestal.

It looks like you are doing the dock-master’s job. Send him the bill and ‘hope’.

By all indications the dock power is operating exactly as expected/designed. 208V is spot on for a 120/208 system.

 

[smitty477]

Yes, get the dock-master involved.
Check all connections while the dock-master is watching. Might be time to shut the power off and tighten all the connections and/or replace the socket at the pedestal while ‘brightening’ the ends of the cable.
Corrosion can allow the output to look normal until a load is applied.
Take the 2 50ft shore power cables together and try a different pedestal.

It looks like you are doing the dock-master’s job. Send him the bill and ‘hope’.

I do not agree.

 

[garmstro55]

First off, 90V is lower than it should be and not good for some appliances.

However, I found I was getting about 100+/- on my 400 at the marina due to the way the marina was wired, i.e. 120/208 wye. I found this writeup on Red Pearl's website which helped me understand it. I didn't like getting only 100v at my home marina all the time so I undertook the project as he did on Red Pearl.

Essentially, the Charles isolation transformer allows you to wire it to boost the voltage 15%, but it is not easily selectable. So, you need to add a switch and some wiring to select either "boosted" or "not boosted", depending on the situation at your marina and any transient marinas.

When I am at home, I am boosted and get approximately 115V. When I leave the dock for a transient slip, I flip the switch to "unboosted" and check my voltmeter when I get to the transient dock. If I get only 100V, I activate the boost.

A little inconvenient but I feel better that I am not damaging anything. I guess it cost me about $500-600 for the switch and the electrician.

 

[Jc180]

So we don’t have an IT. We have a 208 pedestal with BC Hydro saying the wye connection is likely better for marina use than a Delta. Your thoughts?.

Don’t know that wye better than delta but, Wye connection fine. You will get 120v hot leg to neutral and 208 hot leg to hot leg which is ok as well.

 

[Jeff F]

90V is not good. Some appliances will be fine with it, but others will be stressed, especially HVAC.

Agreed. Just to add, if this isn't related to the IT, wouldn't loading it up with HVAC or other major loads cause further voltage drop and likely failure to operate?



Sent from my moto g play (2021) using Trawler Forum mobile app

 

[twistedtree]

Agreed. Just to add, if this isn't related to the IT, wouldn't loading it up with HVAC or other major loads cause further voltage drop and likely failure to operate?

Yes, the low voltage will only get lower with loads. The IT creates a low starting point of 100V to maybe 104V. But any loads will drag that down, whether the loads are on the boat, or elsewhere on the dock. I think anything below 100V is asking for trouble.

 

[Osprey69]

First off, 90V is lower than it should be and not good for some appliances.

However, I found I was getting about 100+/- on my 400 at the marina due to the way the marina was wired, i.e. 120/208 wye. I found this writeup on Red Pearl's website which helped me understand it. I didn't like getting only 100v at my home marina all the time so I undertook the project as he did on Red Pearl.

Essentially, the Charles isolation transformer allows you to wire it to boost the voltage 15%, but it is not easily selectable. So, you need to add a switch and some wiring to select either "boosted" or "not boosted", depending on the situation at your marina and any transient marinas.

When I am at home, I am boosted and get approximately 115V. When I leave the dock for a transient slip, I flip the switch to "unboosted" and check my voltmeter when I get to the transient dock. If I get only 100V, I activate the boost.

A little inconvenient but I feel better that I am not damaging anything. I guess it cost me about $500-600 for the switch and the electrician.

So after we were browned-out at marinas (begrudgingly used the generator as the weather was dictating A/C) I had an ABYC electrician aboard who confirms the 208 vs the 240 our 48k BTU A/C monster needs is not being provided in many marinas and a boosted isolation transformer was needed to the tune of $8-10k.

Although that pays for a lot of diesel, I would rather not run the beast. So if I understand this post correctly, one could boost an un-boosted isolation transformer for many thousands less? Sounds too good to be true. What am I missing here?

 

[twistedtree]

Check out Ward's BB208/230-50W. Someone posted a picture earlier that might be one.

 

[STB]

That might have been a good question for the electrician.

But, I think so. You saw a few of the transformers lining my dock. Standard fix.

What's the downside? It doesn't solve whatever other(possibly worsening) loss (and maybe heat) you have going on.Transformers aren't perfectly efficient, so you'll be losing energy to two transformers instead of just one, meaning that you'll pay a little more for the usable electricity and the load sustainable at your panel will be a little less than what the pedestal, itself, can deliver. There are two parts that can fail vs just one. There is wire to maintain going in and out of it. You'll need to keep it bicycle locked so it doesn't get stolen. It clutters the dock. You'll need to remember to take it with you when you cruise. It'll be extra weight and take up extra space while underway.

Of course...it does give you the higher voltage you want, is a lot less expensive, and has a very minimal install (configure taps and splice in cable). And they can be bought in different configurations, and often field configured for different amounts of boost (or even buck, which is reduction).

And, I'll bet if you walk your dock, like mine, you'll see a bunch of them right there by the power pedestals keeping their owners nice and cool inside.

 

[Osprey69]

STB...thanks. Our home marina is fine for us. And we have no IT. It would be a temp volt boost when encountering the inevitable a 208v marina again in the future.

 

[twistedtree]

STB...thanks. Our home marina is fine for us. And we have no IT. It would be a temp volt boost when encountering the inevitable a 208v marina again in the future.

If you don't have an isolation transformer, and more specifically one that takes 240V in from the dock and outputs split phase in your boat, you are not subject to this particular problem. You might still have wiring losses in your boat, but you won't have 100V instead of 120V on the two legs.

 

[STB]

STB...thanks. Our home marina is fine for us. And we have no IT. It would be a temp volt boost when encountering the inevitable a 208v marina again in the future.

Very straight-forward choice then....

If you want an isolation transformer, and it is worth the money to you, get one that is auto variable or manually configurable for the boost.

If you don't want an isolation transformer, or one isn't worth the cost to you, get a simple boost transformers to use when needed. A unit configurable for an appropriate boost (or buck to go the other way and reduce) is, I think, normally about $1k, with very little installation needed (open up case, configure taps, splice in power cord, close up, plug in).

But, please, still figure out where and why your are experiencing thst voltage drop. Something coukd be heating up, burning insulation, getting worse, and headed for a fire.

 

[twistedtree]

So after we were browned-out at marinas (begrudgingly used the generator as the weather was dictating A/C) I had an ABYC electrician aboard who confirms the 208 vs the 240 our 48k BTU A/C monster needs is not being provided in many marinas and a boosted isolation transformer was needed to the tune of $8-10k.

Although that pays for a lot of diesel, I would rather not run the beast. So if I understand this post correctly, one could boost an un-boosted isolation transformer for many thousands less? Sounds too good to be true. What am I missing here?

This surprises me a bit because most "240V" appliances are rated for 208-240V for exactly this reason.