Best Inverter for the Buck

[mitiempo]

Originally Posted by prroots

Thanks. I'm thinking I only need a 2 pole switch to switch hot and neutral. When in shore position, there should be no path from neutral to ground at the inverter since it's neutral has been interrupted. Likewise, when in inverter position, there should be no path from neutral to ground at shore since it's neutral has been interrupted. Is this not correct?

I don't understand why dedicated outlets are required (or recommended). It seems that the 2 pole rotary switch should do the job it was designed to do. In my case, it is impractical to use dedicated outlets although I understand that on smaller boats this may be practical. In this instance, the issue is not about saving money; it's about providing the needed functionality in a practical manner.

The transfer switch is a very bad idea in my application. It raises the possibility of draining my batteries flat. It seems that transfer switches are designed to provide critical backup, but that certainly doesn't apply in my case. Also, one must keep in mind that this is a non-critical application mostly used to run a few galley appliances such as our microwave. The cost associated with a marine grade inverter with transfer switch is just not justified. I do understand that integrating a standalone inverter into an existing AC system is more difficult to ensure that all requirements are satisfied; it's not a job for the light of heart

You are right, I have not addressed the issue of a breaker on the inverter side. The Samlex SSW-1500-12A inverter I'm favoring does have overload shutdown protection. I was hoping that would be sufficient.

With respect to the neutral to ground connection issue here is a quote from the Samlex manual:
The manual covers all ratings of the SSW series inverters. Since the above quote does not mention the 1500, it is clear that this model does internally connect neutral to ground. It also makes it clear that one cannot generalize as to whether inverters internally connect neutral to ground.

With respect to GFCI here is a quote from the Samlex manual:

so I'm thinking that issue is satisfied. Thanks again for your post.
Pete

A transfer switch internal to the inverter is never a bad idea - it accomplishes automatically what you are trying to create with a separate switch and also disconnects neutral/ground when on shorepower. If the inverter is properly connected through either a sub-panel or part of the main panel to the outlets there is no way to drain the batteries.

The overload protection in the Samlex is there to protect the inverter when you try to use 2000 watts and it only outputs 1500 watts. It is not there to protect the wiring as a breaker would so you really need one.

If the Samlex has a GFCI you don't need one but it is not a substitute for a breaker - they have different functions. GFCI's are designed to protect people after the outlet - not the wiring to the outlet.

The 2 pole switch doesn't break neutral and ground, but it takes the inverter totally off line which accomplishes the same thing.

[goboatingnow]

If the Samlex has a GFCI you don't need one but it is not a substitute for a breaker - they have different functions. GFCI's are designed to protect people after the outlet - not the wiring to the outlet.

Not so at all, In europe they are used exactly as was specified to protect cables AND people but they have this function built in ie RCBO. in fact I dont even see ordinary GFCIs for sale here anymore.

Mainly because the US has never seen much use for them as 110V is safe (er). But RCBOs are better and if the invertor has a RCBO function, thats fines.

dave

[mitiempo]

Based on that theory all a boat needs is a GFCI (RCD) and the breakers are redundant.

They do different things - GFCI's do not protect against overload or short circuit.

[goboatingnow]

A Residual Current Circuit Breaker with Overload protection (RCBO) combines the functions of overcurrent protection and leakage detection. An earth leakage circuit breaker (ELCB) may be a residual-current device, although an older type of voltage-operated earth leakage circuit breaker exists.

Almost everything this side of the pond is RCBOs havent seen a GFCI in years. RCBO are standard on every marine shore power post etc etc

dave

[mitiempo]

The Samlex inverter has a 5mV GFCI built-in - not a RCBO. It will trip when there is an imbalance of 5mV between hot and neutral. It does not offer protection from either short circuit or an overload that causes the wires to heat up. There should be a 15 amp breaker in the line to the outlets - just as there is when on shore power.

Were it a maine inverter with transfer switch it would be breaker protected through the sub-panel powered by the inverter.

[CarinaPDX]

This thread moves right along, even when I'm sleeping. It is interesting that it has drifted from the narrow question of which inverter to buy to the larger issue of what a proper AC system looks like. I think the OP has a pretty good idea of what is needed now. Some thoughts:

1) On this side of the Atlantic, adoption of the standards regarding RCBOs, called GFCI (5ma trip) and ELCI (30ma trip), are further behind than in Europe for both boats and marinas. However, they are happening now. (Edit: noted that GFCIs only trip on leakage, not overcurrent, while ELCIs generally (always?) include overcurrent breakers.) I have already got two boats in the last year here to add ELCIs to their circuits, and will be adding one to my boat soon (cobbler's children sort of thing). Potentially the addition of an ELCI complicates the discussion (and circuit design), not to mention adding cost, but I agree it should be a consideration here. (Example: Residual Current Circuit Breakers (GFCI and ELCI) - PN - Blue Sea Systems) Whichever way that goes, the outlets should be converted to GFCI style for the best protection.

2) I consider the galvanic isolator a minimum solution for the electroysis issue only, and would encourage stepping up to an isolation transformer instead for the reasons previously given. OTOH an ELCI does provide protection for some of the same problems as an isolation transformer. If you plan to cruise outside of North America, a step up/down isolation transformer is particularly useful.

(Dave: the question of why to ground a floating power source is a bit too much for this thread. Suffice it to say that it is in the standards, the powers that be judge that to be in balance safer, much electrical equipment design assumes a grounded neutral, and this is way over my pay grade.)

[mitiempo]

Originally Posted by prroots

Thanks. I'm thinking I only need a 2 pole switch to switch hot and neutral. When in shore position, there should be no path from neutral to ground at the inverter since it's neutral has been interrupted. Likewise, when in inverter position, there should be no path from neutral to ground at shore since it's neutral has been interrupted. Is this not correct?

I don't understand why dedicated outlets are required (or recommended). It seems that the 2 pole rotary switch should do the job it was designed to do. In my case, it is impractical to use dedicated outlets although I understand that on smaller boats this may be practical. In this instance, the issue is not about saving money; it's about providing the needed functionality in a practical manner.

The transfer switch is a very bad idea in my application. It raises the possibility of draining my batteries flat. It seems that transfer switches are designed to provide critical backup, but that certainly doesn't apply in my case. Also, one must keep in mind that this is a non-critical application mostly used to run a few galley appliances such as our microwave. The cost associated with a marine grade inverter with transfer switch is just not justified. I do understand that integrating a standalone inverter into an existing AC system is more difficult to ensure that all requirements are satisfied; it's not a job for the light of heart

You are right, I have not addressed the issue of a breaker on the inverter side. The Samlex SSW-1500-12A inverter I'm favoring does have overload shutdown protection. I was hoping that would be sufficient.

With respect to the neutral to ground connection issue here is a quote from the Samlex manual:
The manual covers all ratings of the SSW series inverters. Since the above quote does not mention the 1500, it is clear that this model does internally connect neutral to ground. It also makes it clear that one cannot generalize as to whether inverters internally connect neutral to ground.

With respect to GFCI here is a quote from the Samlex manual:

so I'm thinking that issue is satisfied. Thanks again for your post.
Pete

With the addition of a 15 amp breaker after the inverter and before the 2 pole switch I agree.

[44'cruisingcat]

Originally Posted by prroots

Thanks. I was going to wire one side of the 3PDT switch to the AC Outlet breaker of AC panel which is just 15 Amps. I noticed 3PDT switches rated at 15 and 20 Amps. In other words the switch will be selecting either shore power via the 15 Amp breaker or inverter.
Pete

I did something simpler: the shore power inlet is connected to a power outlet socket next to the inverter. All the boat's power points are lead to one plug, which when away from shore is plugged into the inverter, and on shore power is plugged into that socket.

[mitiempo]

Originally Posted by 44'cruisingcat

I did something simpler: the shore power inlet is connected to a power outlet socket next to the inverter. All the boat's power points are lead to one plug, which when away from shore is plugged into the inverter, and on shore power is plugged into that socket.

I would hope both the wiring and plug are rated for 30 amps for the shore power side.

[goboatingnow]

Originally Posted by mitiempo

The Samlex inverter has a 5mV GFCI built-in - not a RCBO. It will trip when there is an imbalance of 5mV between hot and neutral. It does not offer protection from either short circuit or an overload that causes the wires to heat up. There should be a 15 amp breaker in the line to the outlets - just as there is when on shore power.

Were it a maine inverter with transfer switch it would be breaker protected through the sub-panel powered by the inverter.

Sorry it has overload protection and your wires should be rated to carry the full inverter output, why do you need a breaker. The samlex manual seems to state that on overload you have to turn it off an on to reset, why add a breaker ( by all means do but its more voodoo electrics).

Dave

[goboatingnow]

Originally Posted by CarinaPDX

....

(Dave: the question of why to ground a floating power source is a bit too much for this thread. Suffice it to say that it is in the standards, the powers that be judge that to be in balance safer, much electrical equipment design assumes a grounded neutral, and this is way over my pay grade.)

Id love to know how you establish a proper AC ground potential afloat.! Connecting it to DC ground doesnt do it.

As to the powers that be, ABYC is not a regulator , In Europe RCD is and it does not require some a ground. There absolutely nothing wrong with floating power supplies as long as they are isolated. this is often the case in metal boats. with isolating transformers you do not have a grounded neutral ( you have onboard AC ground connected to traffo neutral, but thats not the same as grounded)

Dave

[mitiempo]

Originally Posted by goboatingnow

Sorry it has overload protection and your wires should be rated to carry the full inverter output, why do you need a breaker. The samlex manual seems to state that on overload you have to turn it off an on to reset, why add a breaker ( by all means do but its more voodoo electrics).

Dave

Yes it has overload protection as every inverter I have ever seen has. But I have never seen an inverter manual suggest breakers are not needed when hardwired into a system as this one will be.

Pete should ask a surveyor for his thoughts and check with his insurance company as well if he plans not to use a breaker to get their thoughts - it could prevent an issue like a refused claim in the future. The inverter is not designed to be hard wired into a system and shouldn't be without the proper safeguards.

As far as the connection between AC ground and DC ground on board below is part of an article in Professional Boatbuilder by Nigel Calder (April/May 2006). The article goes on to explain the ISO regulations and the unreliability of RCD's in practice.

[44'cruisingcat]

Originally Posted by mitiempo

I would hope both the wiring and plug are rated for 30 amps for the shore power side.

No, they are rated for 15 amps. At 240 volts.

[goboatingnow]

Originally Posted by mitiempo

Yes it has overload protection as every inverter I have ever seen has. But I have never seen an inverter manual suggest breakers are not needed when hardwired into a system as this one will be.

Pete should ask a surveyor for his thoughts and check with his insurance company as well if he plans not to use a breaker to get their thoughts - it could prevent an issue like a refused claim in the future. The inverter is not designed to be hard wired into a system and shouldn't be without the proper safeguards.

As far as the connection between AC ground and DC ground on board below is part of an article in Professional Boatbuilder by Nigel Calder (April/May 2006).

Yes a US centric article for a US centric readership. He has swung both ways when he writes in Europe.

My view is that RCBOs remove the need For the connection and this is consistent with legislation where I am. ABYC tends to be behind the times , it's only recently discovered ELCIs for example.

But hey fill the boat with breakers. knock yourself out.

Ps of the inverter isn't designed to be permanently designed in then don't use it so.

Dave

[mitiempo]

Originally Posted by goboatingnow

Ps of the inverter isn't designed to be permanently designed in then don't use it so.

Dave

That is what I have suggested all along.