Shore Power Undersize - 12 gauge for 30 Amps

[captstu]

Hi, I was installing my new 2500 Watt inverter today. The process involves removing the shore power wire from the breaker panel, connecting it to the inverter "Line In" and connecting the "Line Out" to the shore power breaker.

In this way, when there is shore power present, the inverter senses it, turns itself into a charger, and all is gravy.

The Shore Power input is rated at 30 Amp and is typically connected to a 30 Amp protected outlet at the marina.

The inverter puts out a maximum of 27.5 amp and "consumes" most of the balance with its internal battery charger - at least for the first few minutes of charging.

All is good.

Unfortunately, the wire from my shore power plug on our 2010 R-25 was quite warm when I started removing it from the breaker. I examine the wire and was surprised to find that it, and all the AC wiring, was 12 gauge. On checking further, I found the wire was warm over its entire length! A fire waiting to happen.

12 Gauge wire is rated at 20 Amp maximum current. It just won't handle 30 Amp - or even 27.5 Amp - a value you are likely to meet or exceed when the air conditioning, hot water heater, and possibly a stove element are all working simultaneously. While such a load will eventually trip the shore power circuit breaker or your boat's master circuit breaker, it may burn your boat to the waterline first.

I don't know if Ranger still wires their 30 Amp shore power plugs with 12 Gauge wire. I suggest you check - I changed mine over to 10 Gauge as required - it is a simple change you might want to consider so you can sleep better at night.

Curious - in the inverter equipped boats provided by Ranger, is the inverter on the shore power circuit or the generator circuit?

 

[Red Raven]

Hi, I was installing my new 2500 Watt inverter today. The process involves removing the shore power wire from the breaker panel, connecting it to the inverter "Line In" and connecting the "Line Out" to the shore power breaker.

In this way, when there is shore power present, the inverter senses it, turns itself into a charger, and all is gravy.

The Shore Power input is rated at 30 Amp and is typically connected to a 30 Amp protected outlet at the marina.

The inverter puts out a maximum of 27.5 amp and "consumes" most of the balance with its internal battery charger...

Hi Stu,

I’m a little confused by your post. The Inverter/Charger, when in inverter mode (DC in and AC out), pulls DC power from the batteries and not the shore power. When in charging mode it only pulls enough AC shore power to run the Battery Charger (AC in and DC out). The AC mains shore power for all the rest of your systems do not run through the inverter. It runs direct to your AC panel and bypasses the inverter/Charger. Thus the AC input to your inverter/Charger needs to be rated for the battery charger draw only and not the 30 amps that is rated on the shore power breaker. There Is a separate DC input to your Inverter/Charger for the inverter function.

Does this help? Maybe I am missing something.

 

[captstu]

Tracy and/or Curt,

There are two issues in my post. Let me try to split them apart.

1) Undersize wire: As delivered, there is a wire that is connected to the shore power inlet plug on the starboard forward outside of my R-25. The other end is connected to the circuit breaker labeled "shore power". All of the shore power used by all the R-25 equipment including the air conditioner, hot water heater, battery charger, and stove run thru that cord. The plug and shore power cable delivered with the boat are rated at 30 Amps, as is the shore power circuit breaker on the boat and "typically" the marina. If you turn on all the major appliances, the 30 Amp breaker will trip - protecting the wiring. BUT, the wire is rated at only 20 Amps (12 Gauge) and gets quite warm when my air conditioner is running. If I run the air conditioner and stove at the same time, the boat draws nearly 30 Amps - and eventually, the wire will burn. I urge you to check the shore power wire and report if it is, also, under rated for the expected load. The shore power cord (the external cord) is 10 Gauge and is correct for the load. I am replacing the short piece of 12 Gauge on the boat with the required 10 Gauge.

2) The second issue, question actually, is where the inverter goes in the circuit. According to Promariner (and other inverters I have seen in operation), the inverter is placed between the shore power plug and the shore power circuit breaker. That way, the inverter can sense the presence of shore power and automatically turn off the inverter and bridge the LINE IN to ther LINE OUT on the inverter panel. the result is much the same as the lock-out control used on the R-25 to prevent the "shore power" and "generator" circuit breaker from being on at the same time.

The lock-out on the Promariner inverter (Automatic Transfer Switch) eliminates the need to turn the inverter off and on and turn the built in battery charger in the inverter off and on.

Since the Promariner 2500 typically used by Ranger is rated at 27.5 amps, it requires 10 gauge wire.

The battery charger inside the inverter is quite different from the built in charger that is happy with 16 gauge wire for the alternating current side of the supply.

Hope this clears up my concern????

 

[dclagett]

12 gauge wire should be able to handle 30 amps. The table I have for marine applications shows 12 gauge will handle up to 55 amps depending on the temperature rating of the conductor insulation. Also if the wire is bundled, which it would be for shore power (3 wires), it would only have 70% of the rated capacity. The jacket on your cable will provide temperature rating for both dry and wet applications.

On my RT25SC the cable from the shore power input connection to the main shore power disconnect circuit breaker with ELCI is 12 gauge. That cable run is about 3.5 feet. From that circuit breaker to the AC panel which is a much longer cable run the cable size is 10 gauge.

In your case with the cable being warm I would be somewhat concerned about voltage drop and it’s affect on what you are trying to power. If you are comfortable checking the voltage with systems running I would make sure the voltage is within the allowable range of those systems. If you are not comfortable get a good marine electrician. If the voltage does drop to the systems near or below their lowest acceptable voltage it is time to upgrade the cable.

 

[BB marine]

First, you are correct the incoming 30amp line is unprotected from shore power plug to ELCI and should be a minimum of 10ga. This line runs from shore power plug to the ELCI then to the power panel where the 30 amp breaker is located. The lines coming out of the panel can now be down sized to 12 gauge because the breakers are all 15amp or 20 amp. The only questionable one is the marine air which requires a 25 amp breaker for start up.It too should be 10gauge. I am going to the boat today to work on some projects and confirm that there is a 10 ga coming in but I actually think it is 12ga. I just installed an isolator at the ELCI and didn't question it at the time. I made my connections at this terminal block. This is Line in ( from shore power plug and load line (to the power panel).


When I installed a 2000w Kisea inverter with transfer switch I elected not to use the transfer switch. I wired the inverter separate from shore power and used the Blue Sea selector switch Shore Power/inverter/Generator. I was worried that if shore power was lost and the inverter switched on with hot water heater, charger, and a few other 120V devises on it would rapidly deplete my battery capacity . I used 10 gauge from the inverter to the power panel and wired it directly to the selector switch. Battery power comes from the house and thruster battles thru a separate battery switch. This provides many checks to insure that power management is used with the inverter.

Power switch to turn on inverter and monitor battery voltage


Power panel with inverter wired directly to selector switch by passing transfer switch


Battery switch with House and thruster batteries paralleled. this switch provides power to the inverter.

The auto transfer switch is a nice feature. I was afraid that it would result in dead batteries for me. I'm old school manual is better then auto :shock:

 

[knotflying]

A thread by coincidence. I will be re-wiring my combo promariner inverter/charger I have 10 GA wire coming in from the shore power and 10 GA going out of the inverter to the panel. My plan is to have the shore power go directly to the AC panel. I will then use a breaker from the top portion of the panel and run AC back to the inverter. I will then split the rest of the panel to run only off of the inverter/charger. This way the concerns of loosing shore power or having the high draw items on the inverter is eliminated. If shore power is not present or fails the inverter circuits stay on, but the water heater and air conditioner will not work.

 

[HRowland]

If you look at the ABYC Ampacity tables it is possible for 12G wire to be used for 30A provided the insulation is rated for a high enough temperature. If sheathed and in a bundle it looks like 105C temp rated insulation is required. This is HOT! While technically allowed by ABYC I would sure like to see 10G used to keep things cooler and provide less voltage drop.

I have a slip at the end of a dock, during the summer when a lot of air conditioners are running, the AC voltage can sag to 105VAC or less, I sure would want to minimize the drop in the ships wiring. 30A shore power cables are typically 10G.

Howard

 

[captstu]

I look to the ABYC for DC regulations and to the National electrical Code for AC safety regulations.

the NEC requires 10 Gauge for 30 Amp, 12 Gauge for 20 Amp and 14 Gauge for 15 Amp.

Why take a chance for $5 worth of wire.

After having learned from this thread (thank you everyone):

I plan to replace the wire from my shore power outlet with 10 Gauge.

It carries 22 Amps routinely when we are on shore power and away from the boat - to power the air conditioner and small dehumidifier. Makes no sense to try to prove the NEC wrong.

Since the inverter I am installing is rated at 27 Amps - when carrying shore power without interruption - I will not install it on the shore power circuit:

I plan on connecting the Generator to the Inverter "Line In" and the Inverter "Line Out" to the panel circuit now labeed "Generator".

Voltage drop is not an issue - it is under 2% at maximum load - a lot of voltage for a low volt DC circuit, but not so much on household power.

 

[dclagett]

I was surprised when I found 12 gauge wire from the shore power receptacle to the main circuit breaker on my boat, about 3.5 foot run. When I looked up the specifications for marine wiring it meets the requirements for 30 amps. I would bet that most if not all RT25s are wired that way. Also when I run my AC with shore power I do not notice any voltage drop at the panel meter. I boat on the Chesapeake and my AC runs constantly at the dock when the boat is being used.

I have not checked if the 12 gauge wire coming in is warm when my AC systems are on. I suspect that it is not with only a 3.5 foot run and no noticeable voltage drop, however I will check this coming season.

 

[Red Raven]

Tracy and/or Curt,

...

2) The second issue, question actually, is where the inverter goes in the circuit. According to Promariner (and other inverters I have seen in operation), the inverter is placed between the shore power plug and the shore power circuit breaker. That way, the inverter can sense the presence of shore power and automatically turn off the inverter and bridge the LINE IN to ther LINE OUT on the inverter panel. the result is much the same as the lock-out control used on the R-25 to prevent the "shore power" and "generator" circuit breaker from being on at the same time.

The lock-out on the Promariner inverter (Automatic Transfer Switch) eliminates the need to turn the inverter off and on and turn the built in battery charger in the inverter off and on.

Stu, Thanks for the clarification. I was not aware you had an Automatic Transfer Switch in your inverter/Charger. That explains why mains power is routed through the inverter. Our inverter is separate from the battery charger and we manually switch over to the inverter when desired. No AC input to the inverter. My confusion. Sorry about that!

I’ll go out and check the wire size of our AC input. I have never noticed any issues with voltage drop or heat.

Curt

 

[BB marine]

A thread by coincidence. I will be re-wiring my combo promariner inverter/charger I have 10 GA wire coming in from the shore power and 10 GA going out of the inverter to the panel. My plan is to have the shore power go directly to the AC panel. I will then use a breaker from the top portion of the panel and run AC back to the inverter. I will then split the rest of the panel to run only off of the inverter/charger. This way the concerns of loosing shore power or having the high draw items on the inverter is eliminated. If shore power is not present or fails the inverter circuits stay on, but the water heater and air conditioner will not work.

This is actually the right way of doing it to prevent battery drain in the event of a power loss. Our Cutwaters Power panel was actually wired that way. When the power selector switch was in the inverter position it powered up one side of the panel Outlets and Microwave and a accessory circuit. When I installed the 2000W/4000W Kisea I changed the wiring configuration in the panel to have the Inverter power the whole panel. We cook with electric stove top, I like to be able to turn the hot water heater on in the morning while at anchor, and We use the marine air( Fan only ) when cruising when it is raining. (It helps circulate air in the pilot house and berth area). Having the transfer switch is a good feature. In my application I decided not to use it.I take the extra few minutes to turn every thing on and monitor usage. The inverter is a great option without a generator. We have it on always when cruising, The D3 Volvo has a 180 amp alternator along with the three bank batteries linked into the Pure sine wave inverter we maintain a constant 120V with power management and minimal battery draw down.

If you look at the ABYC Ampacity tables it is possible for 12G wire to be used for 30A provided the insulation is rated for a high enough temperature. If sheathed and in a bundle it looks like 105C temp rated insulation is required. This is HOT! While technically allowed by ABYC I would sure like to see 10G used to keep things cooler and provide less voltage drop.

I have a slip at the end of a dock, during the summer when a lot of air conditioners are running, the AC voltage can sag to 105VAC or less, I sure would want to minimize the drop in the ships wiring. 30A shore power cables are typically 10G.

Howard

When looking at the tables 12ga meets the ABYC requirements it is not going to burn up and cause a fire. It is not an industry standard though. Marine 30 amp service installation is 10 ga coming in and 12ga for distribution feeds in 15 or 20 amp circuits. 25amp should be 10ga. Another industry standard is if a component of the electrical system has an amperage draw close to the 30 amp service another dedicated service should be installed. A marine air unit has a start up amperage draw of close to 25 amps and it is in a service with ,stove, microwave, Hot water heater, battery charger, and 6+ outlets and all of this is installed with 12ga wire. It really should be two 30 amp services using 10 ga wire. Take a look at your shore power plug if its like mine it has some burn marks on it.Remove and inspect your on board shore power connection, If its like mine were it has loose lugs . First thought is they didn't tighten it at the factory. Maybe , but there is a better chance that it is loose because of expansion and contraction of the lugs getting hot. It may be with in ABYC specs but not to marine industry standards. Great boats, a little better QC goes a long way!

 

[dclagett]

When looking at the tables 12ga meets the ABYC requirements it is not going to burn up and cause a fire. It is not an industry standard though. Marine 30 amp service installation is 10 ga coming in and 12ga for distribution feeds in 15 or 20 amp circuits. 25amp should be 10ga.

I hate to belabor this point but I am wondering what marine industry standard you are quoting? Is it written or basically a practice? I have read both ABYC and ISO standards and as I interpret them they agree with the way RT wired the Tugs. If owners are adding equipment then the owners may need to beef up the wiring. While using my AC systems and monitoring my AC panel voltage I have not seen any noticeable voltage drop implying the wiring is adequate for my boat configuration. I also would not expect the wires to be hot or warm since any heat generated in the cable would show up as a voltage drop at the AC panel.

As far as the shore power connector burn/melt marks are concerned, this is a common problem with this type of connector and not isolated with RT boats. It is a major cause in boat fires. The problems are as you say a loose connection within the boat connector, however the main problem is when the shore power cable is attached to the boat connector people are not seating it properly and/or not using the clamping ring. When I purchased my RT in 2016 the boat connector had burn marks. I immediately replaced the boat connector in 2016 and when I removed it this week to install a smart plug the old boat connector looked new. The smart plug will give me the confidence I have connected shore power correctly without fiddling around with the old style setup.

 

[HRowland]

This is ABYC E-11 AC and DC ELECTRICAL SYSTEMS ON BOATS, TABLE VI – B - AC & DC CIRCUITS – ALLOWABLE AMPERAGE OF CONDUCTORS WHEN UP TO THREE CURRENT CARRYING CONDUCTORS ARE BUNDLED, SHEATHED OR IN CONDUIT.

If larger bundles are used then the current rating is reduced, 10G would be required. There are multiple tables in the spec ranging from single conductor up to bundles of over 25 conductors. At very high conductor counts even 10G is not adequate for 30A. The tables cover multiple insulation temp ratings and installation inside/outside of an engine room.

Howard

 

[dclagett]

Sorry last post on this subject.

The ABYC table shows a 12 gauge conductor allowable amperage with 105 degree C insulation and outside of engine space is 45 amps. With 3 wires in the bundle, which is what we have, one needs to de-rate the amperage by .70 which gives 31.5 allowable amperage. That is the written down standard for both ABYC and ISO. If there is a different standard for boats I would like to read and understand it.

 

[knotflying]

Sorry last post on this subject.

The ABYC table shows a 12 gauge conductor allowable amperage with 105 degree C insulation and outside of engine space is 45 amps. With 3 wires in the bundle, which is what we have, one needs to de-rate the amperage by .70 which gives 31.5 allowable amperage. That is the written down standard for both ABYC and ISO. If there is a different standard for boats I would like to read and understand it.

Not to sound challenging here, but if I had the option of going 12 GA Versus 10 GA I wouldn't go with the smaller gauge to save a few pennies? I can see a manufacturer doing it because a few pennies on a lot of boats adds up. However, if it were my boat and it had 12 GA on a 30 amp circuit I would switch it out. When it comes to safety I like to err on the side of caution. Just my two cents, and if you get enough two cent comments you can go 10 GA! :lol:

 

[BB marine]

Sorry last post on this subject.

The ABYC table shows a 12 gauge conductor allowable amperage with 105 degree C insulation and outside of engine space is 45 amps. With 3 wires in the bundle, which is what we have, one needs to de-rate the amperage by .70 which gives 31.5 allowable amperage. That is the written down standard for both ABYC and ISO. If there is a different standard for boats I would like to read and understand it.

You are right! It follows the ABYC requirements , it is not going to cause a fire and it will work with a very limited safety factor. It works Ranger/Cutwater has manufactured many boats using 12ga wire Line in. The industry standard when wiring a boat is when amperage load limit is close use next larger size wire ( safety factor) especially in a boat.This is what was taught at any training session I went to. The marine environment is hard on equipment, including electrical equipment, corrosion causes resistance in current flow. How many times have you seen corrosion on electrical connections in a boat? Heat causes resistance to increase. I'm not sure where your wiring is in your Tug but in my 26 Cutwater the 30 amp 12gauge load line runs right above my engine it gets warm in that compartment. Vibration causes connections to come loose. Loose electrical connections increases resistance. A boat tends to have a few vibrations. I would be surprised if you asked any certified marine technician what size wire he or she would run to a 30 amp panel they would not say 12GA. Safety factor !!! I may be wrong here but I think most would say. 30 amp service 10ga unless it is a long run then install 8ga, 20 amp service 12ga , 15amp service 14ga (most manufactures do not use 14ga they run 12ga on a 15 amp circuit. You are 100% right 12ga is acceptable.
There are many publications, but I thought I would use one that Ranger Cutwater uses Blue Sea.
AC Circuits: For each AC Feed and Branch circuit, the ABYC table below lists the minimum wire size.
ABYC E-11 Table IV 105°C (122°F) Wire

29 amps 14ga

38.3 amps 12ga

51 amps 10 ga

68.0 amps 8 ga

This ABYC table is for wire with 105°C (122°F) insulation rating and no more than 2 conductors bundled together. It is not suitable for sizing exible shore power cords. The values will allow conductors to reach their full 105°C (122°F) rated temperature.
Many experts in the marine electrical industry recommend using wires that are one or two sizes larger than shown in the table above to reduce the operating temperature of the wire.
For more information go to http://www.bluesea.com

 

[captstu]

It is only a 4’ run from the shore power inlet to the 30 Amp breaker. I’m swapping out the 12 for 10 gauge. If the lugs are loose, it is most likely from overheating. This is a common cause a fire in older aluminum wire homes. I suspect it is the major cause of failure of the inlet plug. Why take the risk for 10 bucks?