How to properly connect a 120v portable generator to off-grid power center

Hill_Country · March 2015

I have a Yamaha ef2000is 120v portable gas generator (very similar to the Honda EU2000i) that I am planning to use to help charge our off-grid solar system (to be installed) when we have multiple overcast days in the winter. I have a pre-wired MMP (Magnum Mini Panel) power center that's integrated with the Magnum 48v 4400 watt inverter (MS-PAE4448 )and this allows me to connect a generator to the MMP and use the Magnum Inverter's PFC (Power factor corrected) staged battery charging capabilities. Since the Yamaha generator is a portable generator, I'd like a setup where I can both plug-in and un-plug the generator whenever we need to charge the batteries. To this end, what's the best way to go from the Yamaha's duplex outlet-style AC plugs (2 20 amp, 120v outlets) to the MMP's "AC In/Gen" connection that allows me to plug in and unplug the connection? As a reminder, this is an off-grid system...so there is no grid tie at all.

I've been informed that using an extension cord that has been "hacked" to have two male ends is not code compliant, nor is it very safe. And I can't use a GFCI style outlet to plug in to as the input for the AC In. So it's looking like I need to use some sort of manual transfer switch? I want this to be as simple and straightforward as possible, but safe as well.

Any suggestions? Remember, this is for a portable, 120v small gas generator on an off-grid system with a Magnum Mini Panel/Magnum Inverter pre-wired power center and I'm going for the "plug and play" style of connection. Ideas?

Thanks!

mike95490 · March 2015

you can "buy" a pre-made transfer switch that does this, or use a small breaker sub-panel with a "interlock" so only 1, of a pair of breakers (or 2, of 4 in the case of 240VAC) is able to be connected. google circuit breaker interlock kit. The parts vary according to the panel and brand of breakers.

Hill_Country · March 2015

Thanks Mike! In addition, I did some more researching and with the MMP (Magnum Mini Panel) it already includes a dedicated "AC In/Gen" circuit breaker that allows you to switch the AC source on/off, so it doesn't look like the actual switching/circuit protection, will be the problem here.

Back to part of my original question...what's the best way to actually make the connection between the portable Yamaha generator (ef2000is) and this "AC In/Gen" connection point on the MMP? Do I rig up a "generator cord" so that one end has a normal male 20amp outlet connection, while the other end has a more traditional generator connection type into some sort of separate, dedicated box? This is where I'm stumped as to what is the best solution given the portable nature of the generator.

Thanks!!

BB. · March 2015

If the AC wiring inside the building is done correctly (transfer switch/etc.)... Then the generator connection should be unpowered by anything in the house... So you can use an outdoor plug type receptacle:

Attachment not found.

-Bill

Alaska Man · March 2015

My Yamaha Genny is plumbed right into the Inverter/Charger. It senses in coming AC and automatically switches the inverter off, lets the AC pass through to the distribution panel and kicks the charger on. All I do is plug in to the genny once she is running. I use a "Hacked" Extension chord, with the stripped end wired to AC IN on the Xentrex, works great.

Hill_Country · March 2015

Thanks BB and Alaska Man! Very helpful!

I checked with our sales/support rep. at NAWS (always very helpful and prompt!!) and he recommended something very similar to what Alaska Man suggests. He recommended that we use an SO or SOOW rated cord (S = Severe Service Cord, O = Oil Resistant Outer Jacket, W = Weather/Water Resistant), preferably 10 awg, with a male end for plugging into the Yamaha ef2000is, and then hardwire the other end into the MPP in the "AC In/Gen" connection. This seems to be the most straightforward and safest. However, I do like the idea of being able to remove the extension cord when it's not needed, but we'll see.

BB. · March 2015

One minor thing to watch out for... Heavy cord plugged into a genset with lots of vibrations. You may end up damaging the receptacle on the geneset from constant motion.

Try to make sure that you don't have a lot of weight on the cord/plug and possibly use a cable clamp or similar to hold the cord fixed relative to the genset.

Using a light weight 2 foot cord set to keep loads off the outlet may help extend receptacle life (don't want a "heavy" 10 AWG SO cord trying to lever out of the outlet).

-Bill

Hill_Country · May 2015

As an update, I chose to hardwire one end (female end) of a 12AWG extension cord to the Magnum Inverter's AC IN, while the other end of the extension cord is simply left as is with a male plug end. I just keep the extension cord coiled up when not in use.

Brian · July 2015

Hi Bill, I want to plug My inverter, from battery bank, which is three prong into the generator outlet that you have pictured which has four prongs. What is the correct wiring sequence? Thank you, Brian

BB. · July 2015

You can look up the NEC plug type for the wiring standards--Here is a small list.

http://www.nooutage.com/nema_configurations.htm

What is the type of genset you are connecting too? 120 VAC? 120/240 VAC? What current? etc.

-Bill

lkruper · July 2015

Brian wrote: »

Hi Bill, I want to plug My inverter, from battery bank, which is three prong into the generator outlet that you have pictured which has four prongs. What is the correct wiring sequence? Thank you, Brian

I recently decided to put a manual transfer switch on my cabin to use with my 110v 1600w inverter generator. The transfer switch has a four prong 220v input but the generator has the three prong 110v outlet. I ordered a adapter cord that takes the hot from the 110v and bridges to both hot sides of the 4 prong connector. Therefore both sides of my generator will be powered by the 110v cord. The company I ordered it from said they sold lots of them after hurricane Sandy.

I have not yet installed the switch, but I am confidant it will work.

inetdog · July 2015

lkruper wrote: »

I recently decided to put a manual transfer switch on my cabin to use with my 110v 1600w inverter generator. The transfer switch has a four prong 220v input but the generator has the three prong 110v outlet. I ordered a adapter cord that takes the hot from the 110v and bridges to both hot sides of the 4 prong connector. Therefore both sides of my generator will be powered by the 110v cord. The company I ordered it from said they sold lots of them after hurricane Sandy.

I have not yet installed the switch, but I am confidant it will work.

The biggest thing to worry about (as long as you do not have any 240V loads) is if the wiring system uses MultiWire Branch Circuits (MWBC). These circuits take two opposite phase hot conductors (L1 and L2 and combine them with one shared neutral to provide essentially two 120V circuits but using three wires instead of four. Also called the Edison Circuit from his introduction of it (for DC).
The problem is that when you drive both hot wires from one generator 120V supply the current in the neutral can become twice what it can safely be.
An electrician can easily tell you if you have this potential problem.

vtmaps · July 2015

inetdog wrote: »

The biggest thing to worry about (as long as you do not have any 240V loads) is if the wiring system uses MultiWire Branch Circuits (MWBC). These circuits take two opposite phase hot conductors (L1 and L2 and combine them with one shared neutral to provide essentially two 120V circuits but using three wires instead of four. Also called the Edison Circuit from his introduction of it (for DC).
The problem is that when you drive both hot wires from one generator 120V supply the current in the neutral can become twice what it can safely be.
An electrician can easily tell you if you have this potential problem.

Yes, but.... his generator only supplies 1600 watts at 110 volts, so therefore he will not encounter this MWBC safety issue.

On the other hand, his generator does have a 3 prong twist lock receptacle. If that is a 30 amp receptacle (such as on a honda generator that may be coupled to another generator) and he does use two generators at some point in the future, then he could run into the serious safety issue that you describe.

--vtMaps

How to properly connect a 120v portable generator to off-grid power center

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