Isolation Transformer for 53MY

[tjshuler]

So the dock has been rebuilt...new water, pump out, and power. The 30mA GFCI's definitely do not like to play nice with a vintage Hatt. I put in an isolation transformer, but it was too large for the 50 amp, 240 VAC pedestal breaker. Magnetizing current for a cold transformer was too much for it. Moving to the other side of the boat, I tried separating the ground from the neutral, but apparently I have missed a connection. Kind of a moot point as the appliances in the boat such as refrigerator, ice maker, range, battery charger are old enough that they could leak to ground e.g. defrost cycle.

So, it is back to an isolation transformer. I do not have the time current curve of the pedestal circuit breaker. It is the initial in rush current that is my concern.

What size have you wise people successfully installed?

 

[SeaEric]

When I added the Hubbell isolation transformer on my 41TC, my electrician found the need to add a "soft start" device. IIRC this thing ramps the power up to the transformer. I'm not sure that's your issue, but I thought it was worth mentioning.

 

[Captain Ralph]

Or fix what ever is leaking current to ground.
In my dealings with this, it is usually some white & green wire tied on board, including the strapping at the gen-set and/or inverter.

 

[sparky66]

I think it would be unusual for a circuit breaker to not be able to handle the inrush from a standard transformer. What transformer are you using? It isn't toroidal, is it? The next thing to check is to make sure it is wired correctly to verify it isn't tripping on ground fault instead of overload.

 

[Pascal]

I don’t have one on my 53 being an early model but I have been thru the new Marina rebuild. Just disconnect the plugs for all older major appliances and find out which one is the culprit. Likely the range or fridge or washer.

It could also be a non marine inverter which will permanently bond N to G instead of having the bond only in inverter mode

I should not be the generator. Although it permanently bonds N to G , the rotary switch will disconnect N in shore position.

 

[Captain Ralph]

should not be the generator. Although it permanently bonds N to G , the rotary switch will disconnect N in shore position.

If correctly installed with a proper transfer switch.
I have witnessed DIY and factory issues here.

 

[tjshuler]

A little clarification... The GFCI is not tripping, the pedestal circuit breaker is tripping. These are newfangled circuit breakers that have the standard 2 pole circuit breaker, with a separate GFCI element so either the circuit breaker can trip due to overload or the GFCI will trip and correspondingly trip the circuit breaker.

When I initially plugged in a year ago after the docks were redone, the GFCI tripped. Older boats commonly have neutral and ground tied together. Electrons, not being very smart, don't know to just stay on the neutral and thus, the GFCI trips. I also have a refrigerator, ice maker, range that are older and probably have circuits that allowed leakage to ground. An isolation transformer is the most cost effective way to resolve this problem.

So, I got an isolation transformer, 15 kVA as 12 kVA is not a standard size. The inrush current when first turning on the circuit with no load trips the circuit breaker. The GFCI did not trip. The primary side of the transformer has no neutral or ground, so the GFCI should not trip. The ground and neutral are all connected together on the secondary side of the isolation transformer.

My question again is, what size isolation transformer's have you used that do not trip pedestal circuit breaker @ 50A, 230V . I am thinking that the 7.5 kVA should work, assuming I can get past the cold start problem.

Thanks in advance.

 

[tjshuler]

When I added the Hubbell isolation transformer on my 41TC, my electrician found the need to add a "soft start" device. IIRC this thing ramps the power up to the transformer. I'm not sure that's your issue, but I thought it was worth mentioning.

I have the Acme / Hubbell transformer also. Can you provide me more information of the soft starter that you used?

 

[Captain Ralph]

So you are explaining that the initial (turn on) in-rush of current to your transformer is tripping the breaker not a ground leak?

I am not an expert but been around many shore power issues and several different transformers, Never witnessed this before.

 

[tjshuler]

So you are explaining that the initial (turn on) in-rush of current to your transformer is tripping the breaker not a ground leak?

I am not an expert but been around many shore power issues and several different transformers, Never witnessed this before.

Correct.
The transformer is larger than it needs to be. Although the transformer will never be loaded to 100%, the magnetizing current makes the standard circuit breaker trip. I have generally used time delay fuses on primaries of a transformer like this with no issues. The circuit breaker time current curve is probably tighter than a Bussmann LPJ fuse and less tolerant of inrush. If I can get past the first second after energizing, we are home free.

 

[Boatsb]

maybe its time to call in a professional. I see problems and theres no way to do this remotely.

 

[Len R]

It may be an "Arc Fault" breaker, different than a GFIC. It might be time to consult an electrician.

 

[sparky66]

"The primary side of the transformer has no neutral or ground, so the GFCI should not trip. The ground and neutral are all connected together on the secondary side of the isolation transformer."

The shore power grounding conductor should be connected to the transformer shield. It might be, but just checking. Wouldn't affect inrush, though. For safety only.

 

[Boatsb]

The transformer must have ground. They usually do not have neutral on the input and some buck or boost the voltage. This is not a DIY project. There are true marine versions made for just this situation. Its not as simple as everyone thinks as the ground has to be connected in a proper fashion or it can be dangerous. You may also burn up zincs.

 

[Pascal]

Boats with isolation transformers don’t have a N wire in the in the shore power cord but they sure have a ground wire connected to the transformer.

 

[Captain Ralph]

I was locked out of HOF a while back for arguing some of these same ground & neutral wire specks here.
The other member was FOS but I was a junior and not savvy of the forum's scrotum pole.
If anybody requires any extra specs on different Hatterass vs after market isolation transformers, thoughts and ideas please PM me and we can share direct communications. Maybe resolve some of these wives tails that I fear are starting to form,, again..

 

[sparky66]

"Boats with isolation transformers don’t have a N wire in the in the shore power cord but they sure have a ground wire connected to the transformer."

That certainly isn't a blanket statement. Even my Hatteras with an isolation transformer has a grounded conductor(N wire) when connected to 30A shore power

 

[Cricket]

Sort of confused with "12kva isn't a standard size". We have a Charles 12kva iso-boost transformer which is designed for 50amp 240v installs, Charles is gone but other companies have entered the market with very similar direct replacement products. Also, as already stated green ground is hooked up to these units. Scott and Ralph, what's you go to Charles iso-boost replacement, just thinking ahead? Thanks.

 

[Boatsb]

Older boats do not have the grounding correct. There needs to be isolators on any shore power source. They can not be grounded to the vessels ground.

 

[Captain Ralph]

Scott and Ralph, what's you go to Charles iso-boost replacement, just thinking ahead? Thanks.

please review post # 16