I'm most likely going to install an isolation transformer and am unsure whether there needs to be a breaker installed inline before the transformer? My 480DB had a breaker but I see some installation manuals online showing one and others that do not. Hubbel seems to be the only choice for 15kVA anymore and their manual isn't clear either IMO.
quality time
I've been going through this with an inverter upgrade. The issue is if you want to comply with the ELCI breaker requirement in the ABYC electric specs. You have to read carefully and look at your installation to tell if you need this or not.
Turns out Blue Sea Systems make such a beast specifically for this application. Its Blue Sea Systems SMS panel Part #3120. Its about $625 retail.
My bitch is it doesn't really fit anywhere I would logically like to put it.
![1714083774847.png]( "1714083774847.png")
Turns out Blue Sea Systems make such a beast specifically for this application. Its Blue Sea Systems SMS panel Part #3120. Its about $625 retail.
My bitch is it doesn't really fit anywhere I would logically like to put it.
The problem with all of this is this, if you have a problem and actually need the isolation transformer to fix an issue then the right thing to do is fix the issue causing the need. I went through this and now have zero issues with any GFCI powered dock.
An isolation transformer is a good thing to have but only after the real issue is fixed.
But to answer your question, yes you need a breaker system before the transformer. The one Dave mentioned is the right one to get.
An isolation transformer is a good thing to have but only after the real issue is fixed.
But to answer your question, yes you need a breaker system before the transformer. The one Dave mentioned is the right one to get.
First - there is no need nor a requirement for a ground fault device (ELCI) on the main power coming on the boat.
Second - as the isolation transformer and wiring to it does require circuit protection and a disconnect consequently a circuit breaker between shore power and the device. This is a code requirement.
The isolation transformer is classified as a power source. Consequently, your boat's systems on the load side of the transformer (secondary windings) must bond the neutral and ground conductors (center tap of the secondary windings) at the power source (isolation transformer or primary ground buss). That bond must be one place only which is typically the main ground buss on the boat.
The shore power ground conductor must bond to the isolation transformer iron core yet be completely isolated from the boat's systems - all the systems. This is to ensure is if there is a fault in the primary windings (the shore power windings on the isolation transformer) it is grounded to the shore power system. This makes marine isolation transformers rather unique.
Assuming your boat is a split phase system 240 / 120 volt AC then the shore power neutral will not be used and needs to be capped off in that circuit breaker location. The isolation transformer primary is split phase 240 volt (hot - hot) windings with the shore power ground bonded to the iron core. The secondary is also split phase 240 volt on each end of the windings with a center tap. The center tap is the neutral and ground for the 120 volt services. It is important to balance to the best extent possible the 120 volt loads across both sides of that tap.
Second - as the isolation transformer and wiring to it does require circuit protection and a disconnect consequently a circuit breaker between shore power and the device. This is a code requirement.
The isolation transformer is classified as a power source. Consequently, your boat's systems on the load side of the transformer (secondary windings) must bond the neutral and ground conductors (center tap of the secondary windings) at the power source (isolation transformer or primary ground buss). That bond must be one place only which is typically the main ground buss on the boat.
The shore power ground conductor must bond to the isolation transformer iron core yet be completely isolated from the boat's systems - all the systems. This is to ensure is if there is a fault in the primary windings (the shore power windings on the isolation transformer) it is grounded to the shore power system. This makes marine isolation transformers rather unique.
Assuming your boat is a split phase system 240 / 120 volt AC then the shore power neutral will not be used and needs to be capped off in that circuit breaker location. The isolation transformer primary is split phase 240 volt (hot - hot) windings with the shore power ground bonded to the iron core. The secondary is also split phase 240 volt on each end of the windings with a center tap. The center tap is the neutral and ground for the 120 volt services. It is important to balance to the best extent possible the 120 volt loads across both sides of that tap.
While the ELCI breaker is not required, ABYC does recommend having one. The other part of that standard is to a breaker with in 10' of the power entering the boat. One of the reasons Sea Ray put the power receptacle(s) on the side of the boat way back when.
Short version - https://shop.pkys.com/ABYC-standard-for-ELCIs-explained_b_50.html
Additionally- with the addition of an isolation transformer the boat becomes it's own power source consequently, there is no need for the galvanic isolators. Also, your boat will become rather immune to power surges and sags. The isolation transformer becomes a great buffer to shore power issues. Since the boat will be isolated from the shore power neutral and ground things get really simple in switching.
The down side is if you should slip where there is 120 volt AC shore power and it is not split phase providing that 240 volt differential then you will get zero volts from shore power.
Here is a graphic of a typical arrangement for an isolation transformer (disregard the inverters).
![Image]()
The down side is if you should slip where there is 120 volt AC shore power and it is not split phase providing that 240 volt differential then you will get zero volts from shore power.
Here is a graphic of a typical arrangement for an isolation transformer (disregard the inverters).
I’m no expert at all, the info above is so comprehensive. but as a layman just adding , my transformer (very different system but still an isolating transformer) , has an inbuilt breaker. Just an McB, I know this as I tripped it a couple of weeks back trying to run too many appliances at once.
For future reference, you can buy the Blue Sea ELCI breaker separately, but so far they don't make a standard panel mount and back cover for this this, like their other shore power breaker panels, so mounting become a custom job.
Like I said, I think it's a good idea, and if I can work it in I will. Retail is about $350, vs about $100 for a standard double pole breaker.
![1714139702033.png]( "1714139702033.png")
Like I said, I think it's a good idea, and if I can work it in I will. Retail is about $350, vs about $100 for a standard double pole breaker.
The short answer is Yes.
You have no control over the dock circuit protection even though that installation is prescribed by NFPA. The boat must protect it's self.
You have no control over the dock circuit protection even though that installation is prescribed by NFPA. The boat must protect it's self.
@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.
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.
Attachments
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
![Image]()
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.
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.
![splitphase.jpg]( "splitphase.jpg")
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.
Just wanted to follow up on this thread and say that we have fixed the neutral/ground cross on the boat so will not be installing an isolation transformer at this time.
The only thing that we intentionally did was replace the galvanic isolator with a failsafe model. The previous unit had a monitoring system with LED fault lights which we disconnected. My mechanic built a test box and the boat now holds on a 6ma GFI and we just finished a 10 day trip with stops at three marinas with new GFI pedestals and no issues.
The only thing that we intentionally did was replace the galvanic isolator with a failsafe model. The previous unit had a monitoring system with LED fault lights which we disconnected. My mechanic built a test box and the boat now holds on a 6ma GFI and we just finished a 10 day trip with stops at three marinas with new GFI pedestals and no issues.
Interesting thread. I am currently planning the addition of a Victron inverter system with 2 x 330Ah LiFePO4 Batteries, a MultiPlus 2000VA inverter/charger and all the associated pieces (exactly the diagram below, minus the solar for now).
![Image]()
This came out of a separate initiative to replace the starter/house batteries, which are combined on my boat (https://clubsearay.com/index.php?th...php?threads/battery-replacement-deep-cycle-or-dual-purpose.117369/#post-1488837), leading to my decision to separate the house bank.
I will start a separate post on this shortly to not hijack here, but the relevant part is the ABYC electrician I am talking to has recommended a 30A ELCI on the output of the inverter. The Blue Sea 1190 is on the bill of materials right now.
There are no other ELCI breakers on the boat so I am questioning the need. He is researching with the ABYC org...it will be interesting to see what they say.
Also relevant to this thread, to avoid the issue of bonding the neutral / ground, my plan is to power only a couple select AC circuits from the inverter by separating their hots and neutrals out of the main AC panel (remove them from the hot bus bar across all the breakers), and feeding them from new, dedicated (to the inverter) hot and neutral busses co-located in the main panel. The main ground (green) from the inverter chassis will go to the main boat ground with, if I understand correctly, the inverter will take care of properly bonding/un-bonding the chassis/neutral connection as required.
This came out of a separate initiative to replace the starter/house batteries, which are combined on my boat (https://clubsearay.com/index.php?th...php?threads/battery-replacement-deep-cycle-or-dual-purpose.117369/#post-1488837), leading to my decision to separate the house bank.
I will start a separate post on this shortly to not hijack here, but the relevant part is the ABYC electrician I am talking to has recommended a 30A ELCI on the output of the inverter. The Blue Sea 1190 is on the bill of materials right now.
There are no other ELCI breakers on the boat so I am questioning the need. He is researching with the ABYC org...it will be interesting to see what they say.
Also relevant to this thread, to avoid the issue of bonding the neutral / ground, my plan is to power only a couple select AC circuits from the inverter by separating their hots and neutrals out of the main AC panel (remove them from the hot bus bar across all the breakers), and feeding them from new, dedicated (to the inverter) hot and neutral busses co-located in the main panel. The main ground (green) from the inverter chassis will go to the main boat ground with, if I understand correctly, the inverter will take care of properly bonding/un-bonding the chassis/neutral connection as required.
Nice system. I have almost the identical system installed except I used the 3000VA version. Just currious why the 200VA version? I sized mine to be able to run the microwave and coffee maker simultaneously. 2000VA might be a little limiting in practice...just a thought.
Space and proximity are always an issue. Too bad, the other benefit of the 3000VA is a 120A charger or 50% larger/faster, and that's always a big bonus with a big battery bank.. Charge batteries faster and load your genny up more.
Not sure why batteries cant go in engine room? You're diesel and there are likely 5 more in there. Look forward to your thread
Not sure why batteries cant go in engine room? You're diesel and there are likely 5 more in there. Look forward to your thread
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