Low Dock Voltage

[luckydave215]

The marina I'm in (for the last 8 years) was just rebuilt, new floating concrete docks, electrical, plumbing, the works. Even most of the the pilings are new. I think we have the highest slip rent in the harbor, as we are the closest marina to the open ocean, about two miles.
The fly in the ointment, is that to save $ (smaller wire) the contractor built the electrical system as three phase 208v. All the slips are single phase. What this means to me, is low voltage coming to my dock box 50A single phase service. There are more problems than just that, as last weekend the voltage was 177. It's never higher than 193-195.
Result? My salon AC (digital controller), bridge freezer, air compressor, and cockpit freezer won't start unless I fire up a genny. Real nice at $21.50/ft.
The marina's electrical contractor just tried to blow smoke up my a$$ when confronted. When I mentioned I'm an engineer he got real quiet. Caught red handed trying to BS me, and knew it.
Of course with no empty slips in San Diego, the marina owner's attitude is "pound sand mo fo, buy a buckboost transformer"
Now where did I leave that dynamite?

 

[Angela]

I don't always fully understand the electrical stuff, but I'm always eager to learn, and I'm wondering about some things, after reading your comments.....

I have a single 50 amp service line coming to my boat, but I have two transformers in the genny room. At some point, I want to upgrade to the digital thermostats. Does having transformers mean that I won't be affected by low voltage if there low voltage? My volt meter currently registers 212 and that's what it has read every time I've looked at it which is often.

We do have power issues on this dock and the marina either has or is still waiting for Florida Power to install a second transformer for the marina.

The boat's transformer breaker has tripped twice since I've been here (but that was when I was running all 3 AC compressors, 5 AC units, the dryer, etc. - probably a little too much!). The dock's power has gone out a lot (yeah, probably my fault. LOL).

I don't completely understand the concept of the transformers other than what I've been told - "they provide clean power" whatever that means.

Will I be able to use digital stuff?

Ang

 

[luckydave215]

The transformers on your boat are "isolation transformers". They protect your underwater metal from stray juice from neighboring boats, and will "clean" your power somewhat. The only way to really clean your incoming power is to convert it to DC, and then "chop" it back into full sine wave AC with an inverter. More trouble than it's worth.
You shouldn't have any trouble running digital AC controls at 212 volts, as long as your controls are set up to allow +- 5% voltage. That's a menu setting.

 

[Pete]

First and most important, the equiptment on you boat wants 240 volts. That is the design point of the equiptment, and very important for motors. Most equiptment will operate at plus or minus 10% of this 240 volts. 216 volts is the lower limit. Lower than this and motors will over heat and fail sooner than normal. The lower the voltage the worst the situation and on average the shorter the life of the motor.

Transformers do nothing to clean up power. The transformer isolates your boat from the dock power neutral and ground wire which helps a lot with electrolysis. The way Hatteras wires isolation transformers creates a magnetic link (transformer) only to the shore power. No path for DC, the cause of electrolysis. Some boats have a second transformer, as mine does, to boost the 120 volt 50/30 amp shore power input to the 240 volts required by your boat.

The bottom line is you need 216 volts in your boat to run your equiptment, else you will accelerate the failure rate of all AC motors, most notably your air conditioning compressors. If you do not have at least 216 volts, preferably more, approaching 240 volts, you need to solve this problem.

You do not want two phases of three phase power. There is nothing the electric company can do to make this acceptable to the needs of a 240 volt boat.

Pete Drez

 

[Pete]

Forgot two points in the prior message.

First, the low voltage shut down on the digital air conditioning controls is a safety feature, much as you have a low oil pressure shutdown on a generator. You can set it a low as you like using the menu function of the control, but then you allowing your compressors to run at voltages as low as you have set. Your compressors need 216 volts, minimum. If you set the safety shut down lower than this, then the controls will operate the compressors below their safe voltage. Just like setting the low oil pressure shut down on your generator below the safe pressure for the engine.

Second, to determine the voltage on your boat, you need a good volt meter. Either buy or borrow a good electricians hand held meter and read the voltage in one of you normal outlets with the air conditioners running. Double whatever you read at the electric outlet and that is within a volt or two of what your compressors are receiving. Is it 216 volts or greater? If lower, fix the problem.

Pete Drez

 

[TedZ]

This is very confusing.

Four wire 208 gives nominally 120 VAC, i.e. one leg to ground. (208 / sq. rt. of 3) Two legs do not give 240 VAC in any way nor 216 or anything else as the power on two legs is 120 degrees out of phase. (3 x 120 = 360!) Something is going on as a single phase motor will not run on two legs of a 208 service. Nor will a three phase motor for that matter. It will grunt and "2 phase."

Just a little bit of info. The modern standard is 230/460 for three phase power. 10% less than 230 is 207, hence the selection of 208 for four wire three phase voltage plus the convenience of getting single phase voltage in tolerance. Three phase motors are supposed to run + or - 10%. Many have trouble at full load...check the nameplate but probably no one runs 3 phase equipment anyway. At least no one i know.

The reason 230 volt three phase is not used for single phase circuits is the hot leg to ground voltage is about 130 vac, outside of the 115 VAC + or - 10% tolerance.

Buck - boosting (autotransformer) two phase power is usually an option on only one leg. You can use two obviously but you have to watch the phase relationship. Phase correcting equipment is common but gets a little complicated.

I just thought the above was a little misleading...maybe mine is worse!!

Ted

 

[Avenger]

Let me preface this by saying that I'm not an electrician, nor do I play one on TV. My experience with this stuff is: There is single phase 110V, single phase 220, and three phase 220. Yes, I know there is 440V also, but outside of a factory I've never seen it. All voltages are nominal, most 110V is 123 or more on a voltmeter. Single phase 110V consists of a hot and a neutral plus a "ground" for safety. To make things run you really only need the hot and neutral. Next, single phase 220V. Two hot legs 110V each, combined makes 220V, used to have a neutral only (3 wires), today has neutral and ground (4 wires). Neither is necessary for function, the two hot legs will run the load by themselves. Last we've got three phase. You'd need quite the yacht for this stuff. There's a couple of ways to do this, the system in my building has one 220V leg and two 110V legs when measured leg to ground. Put the meter across any two legs you get 220V. We find this convenient since you can use the two 110V legs for single phase 220V equipment. The other way is 220V on all three legs (I think, haven't actually seen it to measure it so I'm not 100%). Again something most of us will never use on our "yachts." I've never heard of "two phase." Although, from a laymans perspective the term would make more sense than "single phase 220V" with the two hot legs.

Power is all about Wattage, Watts equals Volts X Amps. A transformer trades Amperage for Voltage, you can't make something out of nothing.

Does this help or am I just making it worse?

Ignore the part about three legs of 220, corrected in later post

 

[TedZ]

Oh boy!

One of the reasons they have changed voltage values is to avoid costly mistakes and for safety. It is better to get away from 110 / 220 terminology.

Two phase occurs when you try to get power off of two legs of a three phase circuit. IT SHOULD NEVER BE DONE!

Transformers are AC voltage to voltage devices. Because of the volt amp product there is a change of ampacity but that is because the voltage changes in a constant volt amp relationship. The voltage varies as the turns ratio of the transformer (wrapped around an iron core). If the primary has 100 turns and the secondary 10, the voltage will be 10 times less...i.e. a 12 volt transformer fed by house current.

Your building has a single phase service and it works exactly as you say. But i understood there was a discussion of 208 service which is three phase. Two legs of a three phase service is not usable power without phase correction. 240 VAC power is single phase...the two legs do not make it two phases!

Just be careful with the 208 service at the marina. I don't want you to hurt any equipment, or worse.

I'll shut up now!

Ted

 

[Pete]

We are going to get this subject very technical which probably will not help the less technical members make decisions, but here goes. First, motors are designed by todays standards to perform at plus or minus 10% of the name plate voltage. Read the name plate and subtract 10%. That is the point you should not drop below if you want decent life from the motor. 240 volt nameplates need 216 and 230 nameplates need 207. I am not aware of any single phase 220 volt nameplate equiptment being installed on boats, but feel free to correct me.

All the AC voltages that we discuss are RMS (Root Mean Square) numbers. What we have with 120 volt AC is a sine wave that varies from zero to 170 volts. The RMS value is 120. When you use two legs of single or split phase power the two legs are 180 degrees out of phase yielding an RMS value of 240 volts. When you take two legs of three phase 120/208 RMS you get 208 RMS because the phases are 120 degrees out of phase as opposed to 180 degrees. Each phase varies from zero to 170 volts, but the phase angle is different, thus the RMS voltage is less (208).

Not sure if that help clear up the subject or not. But, for those that do not want to get an indepth understanding, the bottom line is only the RMS voltage matters to your boat. Single phase, split phase, three phase, you do not care. You want no less than 90% RMS of name plate voltage on your air conditioners, when they are running steady state.

BTW, the reason you can not solve the problem with a three phase 208 supply voltage is, the electric company could crank up the transformer so you get 240 two phase power, but in doing so would take the single leg voltage from 120 RMS up to 139 volts which way too high. Most of these installations set the 208 RMS to 216 which yields a 125 single leg RMS. This give a tolerable single and two phase RMS. The problem is the line drop coming down the dock which quickly gets the two phase voltage too low for our equiptment.

Again, get a good volt meter, turn on your air conditioners, measure the voltage at an outlet in your boat, double that reading and make sure it is at least 90% of the name plate voltage on your air conditioning units. If it is less, fix the problem, or get ready to buy compressors sooner rather than later.

Pete Drez

 

[TedZ]

Sounds great but of course the motors care about the phase angle. Their synchronous speed is a physical construct built into the motors with the pole configuration...at least the motors we usually use.

It's covered!

Ted

 

[Avenger]

Yep, it's gotten way more complicated than it needs to be. A correction to my earlier post. I just measured panel voltage in the building next door and they have three legs of "110"V actually about 126V from leg to ground, "220"V from leg to leg. My building has an apparently unusual arrangement that I think they call High Delta or something like that. No electrician I've ever spoken to can tell me what it is, including the guys from the utility. But we pull the two low voltage legs for single phase service and have been doing it for quite a while. We've never cooked anything, and the 3-phase equipment is happy with it too.

Re: the term "two phase"... that's what I thought. We've blown a few fuses when that's happened to us because of faulty contactors. Per Pete's discussion though I still think it makes more sense to call it two phase (two phases 180 deg. apart from each other) however I'm not going to try to change the way the world does it.

The 110, 120, 208, 240 thing. I really wish the industry would make up its mind. But thanks for explaining that, I've always wondered why everybody has a different take on what voltage things are. Now that you've got me going on this I'm going to pull out the Fluke meter and the oscilloscope and try to see exactly what this looks like. Thanks for "clarifying" that.

 

[Pete]

TedZ, as to your question about phasing, single phase motors, which we all have on our boats, are not sensitive to the phase angle difference of 120 dergees versus 180 degrees. They are sensitive to the difference RMS voltage between the two leg. If 240 RMS voltage was available at an 120 degree phase angle they would run just as well as with 240 RMS 180 degree phase angle power. Three phase motors are a completely different story as they rely on exactly 120 degrees between phases to achieve their power.

Pete