Hooking hardwired boiler up to small 120V generator

[MikeInMass]

The power around here goes out pretty frequently in the winter. So I'd like to be able to have our gas boiler and its hot water circulator pumps run from a generator.

If the boiler plugged in to an electrical outlet, that would be easy: unplug it and plug it into an extension cord running to the generator. But it's hard-wired into the wall, one 120V 15 amp circuit for the boiler and pumps.

Also, it's a high-efficiency boiler, and won't run from a conventional generator; it shows error messages and shuts down. I am told that it would run from an inverter generator, so I picked up a small inverter generator that I'd like to use. The generator has two regular 120 volt outlets.

The house has a generator hookup and transfer switch. But it uses a different connection for a much larger conventional generator (pictured).

I don't have the budget to buy a larger inverter generator that has the kind of connection matching the house's generator hookup, and even if I did, Murphy's Law dictates that my wife is usually home alone when the power goes out, and she wouldn't be able to haul anything bigger up the stairs.

Is it feasible to use some sort of adapter cable with the house's generator hookup and transfer switch to run just the boiler circuit using this small generator?

Or do I need a totally separate solution? For instance, could the boiler and pumps, instead of being hardwired, be connected to a normal power cord that could be unplugged and plugged into the generator during a power failure? Or is there some requirement that they be hardwired?

I'd appreciate any advice before winter comes in and the lights go out. Thanks!

 

[zeke67]

I don't know wether it is code for a boiler but many other permanently installed devices are often (but not always) wired with a cord plug. Ranges, dishwashers, garbage disposal. The cord and plug can serve as the disconnecting means in line of sight with the device. If you do it, do so professionally with a premed cord plug, the correct clamp, etc. Don't put a repair plug on a piece of Romex. It needs to remain on a dedicated circuit. The extension cord for e-use should be rated for the amps the boil will draw.

I suggest learning more about why a conventional rotating generator won't run your boiler. An inverter generator is effectively synthesizing a 60HZ sine wave whereas a conventional synchronous generator makes a pure sine wave. If you have tested it with a generator you own already, you may have a frequency issue that could be fixed with a proper tune up.

 

[aandpdan]

Make an adapter cord.

On the generator end use a NEMA 5-20P
On the house end use a NEMA L14-30R

At the house end you tie the X and Y terminals together, they go to the "hot" lead. Connect the neutral lead to the W terminal and then connect the ground.

You'll be running your house off of just one leg. All 120 volt loads will work. The only real concern would be if you have any multi-wire branch circuits but with that generator, the output isn't high enough to worry.

I use such an adapter when I don't need my larger generator.

As the the high efficiency boiler, mine (Munchkin) works fine with a conventional generator. Some manufacturers make upgrades if needed but give it a try first.

There are also single circuit transfer switches if you want to go that route.

https://www.jackssmallengines.com/jacks-parts-lookup/part/honda/32314tf151w?msclkid=076ea1eb0ea01b3fa08dfe80530d88c5

 

[MikeInMass]

Thanks, guys! One question:

Make an adapter cord.

On the generator end use a NEMA 5-20P
On the house end use a NEMA L14-30R

Hmm, it seems like I can't use a NEMA 5-20P on the generator end, because the generator only has regular 3 prong receptacles like you'd have in a house, I think "NEMA 5-15". I assume I can do what you suggested with a regular NEMA 5-15P plug -- is that correct? Thanks again!

 

[wyliesdiesels]

Yeah use a 5-15p instead of a 5-20p.

I would look into why the boiler wouldnt run on the conventional generator. Maybe voltage sag or freq was off?

 

[mike93lx]

My furnace plugs in (well the transformer does). I would have no problem converting one to a plug in order to facilitate running off backup power. It will also allow you to add a surge protector, which would be a good move too

 

[aandpdan]

The generator you had pictured shows the 5-20R. You can use the 5-15P.

My understanding of the boiler issue has to do with grounding. Some of the flame sensors can have issues.

 

[510ebl]

I had a similar issue with my water heater. The term is harmonic distortion. Your main gene might have 10%, your boiler requires less than 5% for example. Inverter genes often have less than 3%.

I just bought a 7000W inverter gene that connects to the 30A twist lock like yours. It also protects the other electronics in the house, like the computers, TVs, the new fridge, etc. And of course my furnace.

I recommend looking into one sized for your application as a future purchase.

Meanwhile, a dedicated transfer switch for the boiler is a good idea for under $100. (Like in post #3)

 

[MikeInMass]

Thanks to all you guys for the great ideas and suggestions. This is a great forum and I am glad to be here.

 

[Sawdust_]

I have a honda generator that I hook up to my gas boiler when I lose power for extended periods. Right now I use an extension cord with the female end cut off and when I lose power I manually wire the cord to the boiler at the junction box but I hate doing so.

Turns out there is a transfer switch available for the exact condition we find ourselves in:

https://www.homedepot.com/p/Reliance-Controls-Furnace-Transfer-Switch-TF151/202216476

 

[Stuart in MN]

Turns out there is a transfer switch available for the exact condition we find ourselves in:

https://www.homedepot.com/p/Reliance-Controls-Furnace-Transfer-Switch-TF151/202216476

You could also just buy a double pole switch and the suitable receptacle, and mount them in a box to get the same thing for less money. The generator should have a circuit breaker on its output so a second one won't be required.

 

[theoldwizard1]

People make things SO HARD when they don't have to be !

Get some 12/3 cord. Install a 5-15P or 5-20P male on one end. Install an L14-30R on the other end. JUMPER THE L1 to L2 INSDIE THE L14-30R HOUSING ! Plug in to the existing inlet.

Yes, this is safe ! If you have any 240V appliances hooked up (well pump, etc) to that transfer panel, they will not run !

Most portable generators are un-bonded and as some have pointed out, "modern" furnaces/boilers don't like this. But or make a generator bonding plug and plug it into the open 5-20R on the generator.

 

[wyliesdiesels]

People make things SO HARD when they don't have to be !

Get some 12/3 cord. Install a 5-15P or 5-20P male on one end. Install an L14-30R on the other end. JUMPER THE L1 to L2 INSDIE THE L14-30R HOUSING ! Plug in to the existing inlet.

Yes, this is safe ! If you have any 240V appliances hooked up (well pump, etc) to that transfer panel, they will not run !

Most portable generators are un-bonded and as some have pointed out, "modern" furnaces/boilers don't like this. But or make a generator bonding plug and plug it into the open 5-20R on the generator.

no. portable generators SHOULD be bonded from the factory since most of the time they are used as a separate system not connected to an existing electrical system. The bonding is required for breakers to trip when there is a ground fault.

 

[theoldwizard1]

no. portable generators SHOULD be bonded from the factory since most of the time they are used as a separate system not connected to an existing electrical system.

Some are, some are not.

The bonding is required for breakers to trip when there is a ground fault.

When using one of those transfer switches, L1 and L2 AND N are disconnected from the PoCo. I ASSUME ground is not disconnected (correct ?)

The problem I was trying address is that modern heating equipment will not operate if neutral and ground are not bonded.

 

[mike93lx]

Some are, some are not.


When using one of those transfer switches, L1 and L2 AND N are disconnected from the PoCo. I ASSUME ground is not disconnected (correct ?)

The problem I was trying address is that modern heating equipment will not operate if neutral and ground are not bonded.

There is no Poco ground. Your house only has two hots and a netrual coming in. Everything else is your's

 

[Stuart in MN]

Before you guys get too deep into arguing, remember that his boiler runs on 120vac 15 amps.

 

[Schu338]

What about just using a spdt "selector" switch? Mount a box near the boiler with a male plug pigtail hanging from it. Wire the common of the switch to the boiler and 1 side to POCO and other side to male pigtail. All neutrals together as well as grounds together. Could actually just use a 3-way switch, but I would probably prefer a "center off" switch. Just make sure to wire before the boiler emergency switch.