Isolation Transformer Installation

[dtfeld]

@quality time

Hopefully we haven't completely hijacked your thread without providing some useful info

I've been looking for the best way to implement a new shore power connection w/ELCI, and Peter @ PKYS pointed me to a nice solution today. Its a Blue Sea custom panel that is panel mountable. I love that solution, but still have question as to suitability for my mounting location. PM me if you want more info.

As far as a breaker and should you go ELCI, it's just not that much money to do it right up front. I'm going to add it for resale/survey proofing.

 

[ttmott]

@quality time

Hopefully we haven't completely hijacked your thread without providing some useful info

I've been looking for the best way to implement a new shore power connection w/ELCI, and Peter @ PKYS pointed me to a nice solution today. Its a Blue Sea custom panel that is panel mountable. I love that solution, but still have question as to suitability for my mounting location. PM me if you want more info.

As far as a breaker and should you go ELCI, it's just not that much money to do it right up front. I'm going to add it for resale/survey proofing.

Isn't this apples and oranges? In your situation from our previous discussions your shore power will run into a Victron Quattro inverter/charger right? Consequently, the Quattro will switch/transfer the shore power directly to the boat's electrical system. So an ELCI circuit breaker would be effective for the entire boat.
In the case of an Isolation transformer and an ELCI installed between the boat's shore power cord and the isolation transformer then only the circuit between the ELCI and isolation transformer would be protected by the ELCI. Nothing on the boat on the load side of the isolation transformer would be protected. So in @quality time application only a couple of feet of wire/cable is protected by the ELCI - value added??
To be clear an ELCI on the primary side of a transformer will not function as a ground fault device for the secondary side of a transformer.

 

[hughespat57]

Hey Dave - I wanted to follow up and clarify - These requirements ABYC, NFPA, etc are not retroactive unless specifically stated. So, if the ELCI requirement was adopted in 2015 for example then vessels built after that adoption would need to be compliant but nothing retroactive. There is an interpretation that if a retrofit is beyond XX percent then the latest code / standard is in effect but I've never seen that in print; maybe @Skybolt or @hughespat57 or someone else has.
So, to install or not to install to the latest code? These are your choices. I tend to bring things up to current standards if I'm replacing as you know - but in this case with an isolation xfmr the value just isn't there. Now if you were to install the ELCI device after the isolation xfmr or after the inverters/transfer devices then there may be some added safety value.

I agree.

Let's start with understanding both NFPA and ABYC these are both "standards" organizations not legal authorities. They create "best practices" and "minimum recommended" standards.

NFPA becomes the "law" for land (buildings) only when a set of standards is adopted by a legal authority, a municipality, county, state etc. into building codes. They will adopt a specific year of the codes as the codes are always being improved.

ABYC has been codified by reference of specific sections into the law by the USCG changes to Federal Regulations. These primarily apply to manufactures as the minimum level of new designs.

Of course both can be applied by insurance companies as minimums for getting coverage, buts that's on a per company opinon basis.

Any professional electrician marine or land based should be doing upgrades per the latest standards. That does NOT mean the entire building or vessel needs to be brought up to the latest standards. Just the current work. i.e. if a breaker fails the replacement breaker only needs to match the standard at the time of manufacture. On the other hand if an entirely new electrical panel is installed it should meet the latest standards.

Let's focus on the devices and design.
GFCI and ELCI/RCD functions are often built into a Circuit Breaker or breaker panel, but they server two distinctly different purposes. Consider them as two separate devices when designing.

CB protect against overloads, an over load cause wires to heat, which can lead to fires.
CB are fire protection devices.

GFCI/ELCI/RCD are to limit any current in the grounding circuit. Any current flowing in the ground circuit indicates a fault in the attached circuit or device. If I touch a hot wire or device with one hand and with my other lean on a metal sink or equipment the GFCI trips.
GFCI/ELCI are human protection devices.

The isolation transformer is neither. It's primary purpose has always been to "isolate" the vessel electric from the land electric. Mostly for galvanic protection.
You still need CB and GFCI where appropriate on both sides of the transformer.
Isolation transformers predate modern ELCI/RCD and are a legacy method.

You really don't need both. A modern Galvanic idolator on the grounds and ELCI on the lines provides the same level of safety.

But if you choose to install you still need CB and GFCI at various points.

An ELCI would be desired before the transformer (land primary side) as it protects against ground faults thru the water back to the land based source. See electric shock drownings.
GFCI should be used on the vessel (secondary side) to protect humans.

 

[dtfeld]

Isn't this apples and oranges? In your situation from our previous discussions your shore power will run into a Victron Quattro inverter/charger right? Consequently, the Quattro will switch/transfer the shore power directly to the boat's electrical system. So an ELCI circuit breaker would be effective for the entire boat.
In the case of an Isolation transformer and an ELCI installed between the boat's shore power cord and the isolation transformer then only the circuit between the ELCI and isolation transformer would be protected by the ELCI. Nothing on the boat on the load side of the isolation transformer would be protected. So in @quality time application only a couple of feet of wire/cable is protected by the ELCI - value added??
To be clear an ELCI on the primary side of a transformer will not function as a ground fault device for the secondary side of a transformer.

Good question. I can't say I completely understand an ELCI that doesn't have a neutral running through it, but I'm assuming that it looks at the balance between L1 and L2 (and assumes any imbalance is leakage).

My system has an autotransformer (not isolation transformer) downstream of the inverter, so an ELCI on the incoming shore power would only provide protection for the system through to the connection to the autotransformer. Since the whole idea of the autotransformer here is to balance the load on the primary coil, I wouldn't think the ELCI would provide much value added, and it would be acting mostly as an expensive overcurrent protection device.

 

[Skybolt]

...

I intend to add a ELCI for this reason alone. If its a little safer, all the better.

Of course the real issue is fitting in the new hardware were none was ever intended to be installed.

When I replaced my electric panel I also had wanted to add an ECLI as the main breaker. But no room to do so. I don't see that as an issue for resale. Someone who cares about that isn't buying a 20yr old boat. JMO.

 

[hughespat57]

Some specifics to doing a shore power upgrade to 220/240 volt with ELCI that I did on my 300. Location was a small challenge.
300 shore upgrades
120V x 30A = 3600 watts (dual 30A would be 7200 watt)
240V x 50A = 12,000 watts

I think it was covered but there is often a misconception that when using split 120v panels that the neutral would need to be able to carry 100A. In the worst case of imbalance between two 120v panels only 50A would ever be on the neutral.

This seems counterintuitive because people think of it like a DC system. If I had two 50A positive legs I would need a return ground that can handle 100A. 50+50=100

However AC is just that, cyclic current/voltage flow. And the two hot legs are 180 degrees out of phase. So as soon as you start drawing power from both 120v panels only the imbalance current needs to flow on the neutral.

If each panel was drawing 120v 30A that must be 60A right? No.
The neutral would have 0A flowing.
Each Hot leg would have 30A flowing, returning on the other Hot leg as that leg goes to the opposite potential (AC). It's a hard concept.

 

[dtfeld]

Yes and no. This is why a the autotransformer neutral is rated at 28A continuous. It only really cares about the difference between the two legs.

 

[ttmott]

Again, for @quality time - An isolation transformer does not have a copper path through it; that's actually the basis and reason to have one. Consequently, a ground fault protection device like an ELCI installed on the shore power will not do anything nor protect anything on the other side (the boat side) of the transformer.
Also, a ground fault protection device does not protect anything on the utility supply side (upstream) of it. So, it makes no economic sense to have one on the boat for that few feet of wire to the isolation transformer.
Now if you wanted the ultimate protection for a boat with an isolation transformer then an ELCI on the dock pedestal which will protect from the service receptacle to the isolation transformer. Then another ELCI on the secondary side of the transformer and that will protect the boat. However, if the boat has a generator and/or an inverter then the boat isn't protected when running on the generator or inverter. It ends up being a complex quagmire that isn't really worth the effort and cost for a boat that wasn't initially designed for it.

 

[ttmott]

So, regarding the neutral conductor and the current it needs to support.
Current reverses 60 times a second (US) and the neutral carries that same current. If you disconnect the neutral will anything 120 volt operate - of course not.
In a 240 volt situation the two split phase hot legs are out of phase (that current reversing is exactly opposite) and the neutral will tend to reduce in current (cancel) as 120 volt devices are used on each phase. This is why we like to balance the 120 volt loads. The neutral, of course, is not used for any 240 volt devices.
If you should have two 30 amp shore power cords and they are plugged into the dock and by chance are the same phase then the neutral must carry all of the return load. This can tax a single neutral conductor should, for example, multiple 120 volt HVAC units are running - however, each 30 amp shore power cord has it's own neutral so there is no issues.

 

[dtfeld]

For simplification ( great discussion, but we did get off into the weeds concerning breakers, and standards etc).

You really have 3 choices.

1. No breaker between the shore power inlet and your isolation transformer - Assumes the pedestal breaker will protect from the pedestal to the transformer. Cost $0.

2. Basic over current breaker between the shore power inlet and your isolation transformer - Adds a little bit of over current protection from the breaker on your boat to your isolation transformer. Cost $100-$150.

3. ELCI Breaker - Adds current leakage protection from the shore power inlet and your isolation transformer. Meets the current ABYC requirement Cost $350.

For my money I'm a #2 or #3 cause I don't trust marinas to maintain their equipment. Then its just a matter if you want to voluntarily meet the newest requirement. If you think that's a good idea, go with #3. Considering the cost of a 15KVA Isolation transformer, this will be a rounding error in the budget.

 

[ttmott]

For simplification ( great discussion, but we did get off into the weeds concerning breakers, and standards etc).

You really have 3 choices.

1. No breaker between the shore power inlet and your isolation transformer - Assumes the pedestal breaker will protect from the pedestal to the transformer. Cost $0.

2. Basic over current breaker between the shore power inlet and your isolation transformer - Adds a little bit of over current protection from the breaker on your boat to your isolation transformer. Cost $100-$150.

3. ELCI Breaker - Adds current leakage protection from the shore power inlet and your isolation transformer. Meets the current ABYC requirement Cost $350.

For my money I'm a #2 or #3 cause I don't trust marinas to maintain their equipment. Then its just a matter if you want to voluntarily meet the newest requirement. If you think that's a good idea, go with #3. Considering the cost of a 15KVA Isolation transformer, this will be a rounding error in the budget.

There must be a disconnect on the boat between the shore power and first device which will be an isolation transformer. That disconnect is typically a circuit breaker. Item 1 is a negative.

 

[dtfeld]

I would agree #1 is not a real solution. But I'd bet there are a lot of old boats running around in this configuration.

I remembered seeing this in the Victron Inverter manual. While you might not get much bang for the buck on a short run between a shore power inlet and the isolation transformer, adding an ELCI downstream would protect the rest of the boat.

Seems a requirement reading this.

 

[Skybolt]

I would agree #1 is not a real solution. But I'd bet there are a lot of old boats running around in this configuration.

I remembered seeing this in the Victron Inverter manual. While you might not get much bang for the buck on a short run between a shore power inlet and the isolation transformer, adding an ELCI downstream would protect the rest of the boat.

A breaker must be installed between the power entering the boat and the first device it touches and must be installed within ten feet of that. on the older Sea Ray's like mine, the power entered the boat on the side of the electric panel so they didn't need to install more breakers. In that case the panel breakers were sufficient to satisfy the requirement.

Not having a disconnect breaker to protect the boat is not a wise move and why the newer Sea Rays have them in the swim platform compartment. ELCI breakers are usually in the main panel. But I have seen new installations of iso-tranformers have them near the transformer.

 

[ttmott]

Single Phase and Split Phase AC Power in North America
It seems there is some confusion on how alternating current works in America - This graphic may help some -
The green line is a 120 volt "hot" wire and the red line is the neutral. The voltage shown is actual peak voltage in a 120 volt system but we measure what is called RMS (root mean square) and that is around 120 volts. Note that the differential between the peaks of the green hot leg and the red neutral is 170 volts and it oscillates positive and negative that 170 volts about the neutral 60 times a second. That is your 120 VAC 60hz.

Now note the purple line - it does the exact same thing about the neutral but is is oscillating exactly opposite from the green line. It is "out of phase" from the green line or what it typically known as "split phase" or 180 degrees out of phase.

In this graph the green line is L1 hot, the purple line is L2 hot, and the red line is Neutral on our boats. The actual wiring on the boat is L1 is Red, L2 is Black, and Neutral is white.

Look at the differential between the green line and the purple line - when one is positive at 170 volts the other is negative 170 volts. If you measure between the two you get 340 volts or 240 VAC RMS.

This is why there is no use of the neutral in 240 volt systems as we get the differential potential between the two hot (L1 and L2) conductors.

Ground Fault detection - First of all Ground Fault detection is about current (amps) not potential (volts). For 120 volt systems the voltage reference is always to the neutral so a 120 volt ground fault device compares the current (amps) on the hot leg to the current on the neutral leg to ensure it is the same. If it isn't the same then, obviously, current is leaking somewhere else and the ground fault protection device trips the system off line. For 240 volt as we explained the current must be equal (oscillating between the two hot legs) across the two hot conductors if not equal the leaking to somewhere else. For systems that use the two hots and neutral 120/240 volt systems (homes and many of our boats) the ground fault device simply makes sure what ever current is supplied is returned across the three.