# hook up 20 year old generator using interlock kit



## Gyrobog (Feb 18, 2019)

I have a 20 year old generator, 5000w, with about 20 hours on it. see the pic I want to use it through a generator interlock device (SD-H200A Square D Generator Interlock Kit). 

The circuit breaker panel has the dryer circuit breakers in exactly the correct location for that interlock kit. The dryer socket is unused since we have a gas dryer, and the socket is located in what is now part of the kitchen. In other words, I have an unused dryer socket wired to the 30 amp circuit breakers on the main circuit board that line up properly for the generator interlock kit.

I want to run the generator output to that dryer socket. 
--- When the utility power is on, that dryer socket would be cold, since the generator interlock device would not allow those circuit breakers to be closed (hot). 
--- When the utility power goes out, the interlock device would be moved to shut off the utility power main circuit breakers, and close what used to be the dryer circuit breakers, thereby connecting the dryer socket to the main circuit breaker panel.

I need to know a good way to run the generator output to that dryer socket. The old generator does NOT have a twist connector, it just has sockets that look pretty much like a standard 120V socket except for one of the blade slots being a T. Three holes for three conductors, like the dryer socket. See the pic

= Should I make a fancy extension cord? 
= Should I remove the old style generator output sockets and replace them with a more up-to-date twist connector, then build or buy that fancy extension cord? 
= Should I just bite the bullet and sell the generator for cheap and buy a new generator with a twist socket? (I am considering this option because this generator is LOUD. The new inverter generators are really quiet and have electric starters) I'd still have to run a cable of some sort from the twist socket on the inverter generator to the dryer socket. 
= Do the twist sockets have four conductors or three? The dryer socket has three.


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## Gyrobog (Feb 18, 2019)

Upon further research, it appears there would be problems hooking up a generator to a 3-prong dryer socket, even if the dryer socket was being switched on and off by a generator interlock,... and,.. even though the generator only has three prong outlets. See the pics in the first post for the type of 3-prong plug on the generator.

My original idea was to forget about those 30 amp dryer circuit breakers being dryer circuit breakers, and just use them as if they had been installed specifically for use with an interlock kit. I have the interlock kit, and it will work correctly by allowing only the house feed OR the dryer circuit breakers to be on simultaneously. 

I may have to forget about using the 3-prong dryer socket and just install an external L14-30R socket going to the existing dryer circuit breakers. That's a bummer because the existing set up with the dryer socket would have been so convenient. The dryer socket is about 10 feet from where the generator will be. Running the wiring from the external L14-30R socket to the circuit breaker panel is about 30 feet and will be more of a challenge to route the wiring.

The generator only has three-prong outlets. That's why I thought it would be handy to just run a 3-wire cable with a dryer plug on one end and a small three-prong 240V plug to match the generator on the other. See the pics in the first post for the type of 3-prong plug on the generator.

Any clarification on this issue would be greatly appreciated.


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## motormonkey (Jul 10, 2016)

You are correct that a 3-conductor 240-volt-only type circuit is not suitable for a proper 120/240 generator hookup. (no current carrying neutral) You need four conductors (ground, line, line, and neutral) to properly bring power from a generator to your house circuit.


You'll have to modify the generator to install the proper receptacle (L14-30R) and isolate neutral and ground. You'll also have to install a suitable 4-conductor generator receptacle (L14-30FI) outside your house and run a suitable four-conductor cable from that to your breaker box. Since the dryer circuit isn't in use, just disconnect the dryer wires from the dryer breaker and connect the genny circuit to it (and definitely install the interlock kit!). Ready made four-wire extension cables for use between the genny and the house are available at any decent home center.

A lot of this was covered in this thread:
https://www.powerequipmentforum.com...1622-generator-without-twist-lock-outlet.html


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## tabora (Sep 6, 2018)

Opinions vary ( see other thread referenced above ), but since it's only a 20amp 240V output, I would not hesitate to connect it to the properly interlocked dryer circuit breaker and the bonded panel neutral/ground bus bar, WITHOUT a separate ground rod. This assumes that the generator outlets are not GFCI, which I do not believe is the case on your generator. To quote another forum's moderator:
_In a normal circuit yes it would be a problem to have a bonded neutral and ground [on the generator], but in a temporary generator feed it is much less of a concern. It is more of a theoretical issue, but given that your generator cord is going to have an insulated ground conductor, even that is somewhat implausible. You will have created a parallel neutral feed, but since we're talking a main panel, neutral and ground really are the same thing at that point. The generator being bonded is sort of like the service entrance mast or meter socket box in that the neutral and ground are bonded at multiple points through them. The neutral is technically an insulated conductor running through the mast, but it's sometimes bonded at the top of the mast where the ACSR drop lashes, bonded in the meter can to the metal box, sometimes bonded via a bonding bushing, and bonded again in the main panel; the steel framework is electrically indistinguishable from the neutral conductor itself. Adding the generator frame to what bonding already exists in the service entrance really is not a big leap._​


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## tabora (Sep 6, 2018)

Gyrobog said:


> The new inverter generators are really quiet and have electric starters.


Yes, but a quality 240V electric start inverter generator IS NOT cheap... There are actually very few, of which the Honda EU7000is @ $4500 is the most common: https://www.northerntool.com/shop/tools/product_200640183_200640183


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## RedOctobyr (Aug 8, 2018)

IF you can get by with 110V power, then yes, there are nice inexpensive inverter options. But for now, like tabora said, 220V inverter choices are limited, and expensive. 

If HF makes a good 220V inverter unit at some point, that would get my attention. For now, my pair of little EU2000i do a great job. Quiet, clean power, and great on gas.


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## Gyrobog (Feb 18, 2019)

tabora said:


> Yes, but a quality 240V electric start inverter generator IS NOT cheap... There are actually very few, of which the Honda EU7000is @ $4500 is the most common: https://www.northerntool.com/shop/tools/product_200640183_200640183



How about this one?

https://www.homedepot.com/p/Briggs-...h-Briggs-and-Stratton-Engine-030675/301871650


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## Gyrobog (Feb 18, 2019)

recoil start, though


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## RedOctobyr (Aug 8, 2018)

Impressive price for the specs! 5000W continuous, 6500W starting, 240V output, inverter, and $1,200. 

Assuming it holds up and is reliable, that sounds pretty good.


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## tabora (Sep 6, 2018)

Gyrobog said:


> How about this one?
> https://www.homedepot.com/p/Briggs-...h-Briggs-and-Stratton-Engine-030675/301871650


Non-electric start, as you mentioned, and only 20A at 240V, so all you're gaining is quieter operation and some fuel economy over your Powermate.

And for what it's worth, the neutral and ground are also bonded on this one... And it appears that Consumer Reports may have it on their naughty list.


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## RedOctobyr (Aug 8, 2018)

Saw this one one HD's site: 

https://www.homedepot.com/p/Champio...Generator-with-301-cc-Engine-100519/308252910

Very similar specs. 5000W/6250W, 240V output, inverter. Even cheaper, at $875! 

Champion had earned a good reputation with their smaller inverter generators, when people were using them for a hobby of mine. This unit looks more like a conventional generator, they call it "open frame". So it's also louder than something like an enclosed Honda (or the Briggs). 

But if it performs well, maybe that's acceptable. No reviews on HD's site yet, unfortunately.


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## Gyrobog (Feb 18, 2019)

RedOctobyr said:


> Saw this one one HD's site:
> 
> https://www.homedepot.com/p/Champio...Generator-with-301-cc-Engine-100519/308252910
> 
> ...


Also it has 30 amps available.

I wonder how reliable Champion products are, generally.


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## tabora (Sep 6, 2018)

Gyrobog said:


> Also it has 30 amps available.


 Nope! 5000watts only gets you 20.8A continuous... Same as the Briggs and your current Powermate. It's a 30A outlet, but the math is simple: 5000W / 240V = 20.83A

It takes 7200W continuous to give you a full 30A. That's why generators larger than 7500W will generally have a 50A outlet.


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## Gyrobog (Feb 18, 2019)

*will this wiring work?*

I surely appreciate all the comments here.

That said, and as I think Tabora said, it should be acceptable to hook up a generator with a 3-prong 240v output to a circuit breaker panel that has a 3-prong input in the form of an unused 3-prong dryer socket.

I looked at the mass of wiring in the circuit breaker panel, and I can see that the three wires (red, black, white) coming from the dryer socket go to a dual 30amp breaker (the red and black wires) with the third wire (the white one) going to the ground buss. Is it normal for the white wire from a 3-prong dryer socket to go the the ground buss, or should it be on the neutral buss? That socket has never been used. There are only a few white wires connected to the ground buss. The rest of the white wires (25 or 30 of them) are connected to the neutral buss.

Please see the attached drawing for what I think I know about the situation.


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## motormonkey (Jul 10, 2016)

That three-prong dryer outlet was intended to supply power only to a 240 volt load. The current path in a 240 volt circuit is through the two line conductors. That third pin is a ground conductor. It is connected to any exposed metal parts of a generator or an appliance. It is there only to protect users if these metal parts should become shorted to a live electrical line. Using it as the current return path for a 120 volt circuit could create a situation where there is voltage present on these exposed metal parts.



If you want to supply power to a 120 volt load, you must have a separate insulated, and isolated, neutral conductor to serve as the current return path.


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## tabora (Sep 6, 2018)

Gyrobog said:


> Is it normal for the white wire from a 3-prong dryer socket to go the the ground buss, or should it be on the neutral buss? That socket has never been used. There are only a few white wires connected to the ground buss. The rest of the white wires (25 or 30 of them) are connected to the neutral buss.


Based on how you describe it, it sounds like the two buses (you called them neutral and ground) are both mounted directly to the distribution panel case, and are therefore the same bus. You should confirm whether that is the case (likely) and if so, what you describe should work fine.


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## Gyrobog (Feb 18, 2019)

tabora said:


> Based on how you describe it, it sounds like the two buses (you called them neutral and ground) are both mounted directly to the distribution panel case, and are therefore the same bus. You should confirm whether that is the case (likely) and if so, what you describe should work fine.


 
Here are a few pics to illustrate how the circuit breaker panel is set up. The installation here was done in 1994 when the house was built. I bought the house in 1997 and had a electrical contractor run a 240v line to an additional box in the workshop for a welding outlet and an A/C outlet. 


The dryer socket is unused, so the breaker is selected off in the pics. 


I'm just trying to give you a more specific idea of the situation here to verify that running a 3-conductor cord from the generator to the dryer outlet would power the house safely when the generator interlock switch had the utility power disconnected and the dryer circuit breaker on.


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## motormonkey (Jul 10, 2016)

That cable running from your dryer socket is a 12-3 cable or maybe a 10-3 cable. That means that it has three insulated 12 or 10 gauge conductors. The red and black conductors are the 240 volt line, and the white conductor is serving as a ground. What is normally used for a 240 volt circuit today is 12-2-G (or 10-2-G), which means it has two insulated 12 or 10 gauge conductors and a ground conductor, which is not insulated.

There is nothing wrong with using 12-3 or 10-3 cable like that for a 240 volt circuit, as long as you remember that the white conductor is serving as a ground, and not a current carrying neutral.
The three-conductor dryer circuit you have was intended to only supply power to a 240 volt appliance, where all of the current flows only between the two line conductors, and it is appropriately called a 240 volt circuit. *A circuit that will supply power to 240 volt appliances and 120 volt appliances is called a 120/240 volt circuit, and should be a four-conductor circuit with a separate neutral to carry the return currents from 120 volt loads.* This cable is called 12-3-G, (or 10-3-G) with three insulated conductors and one bare ground.

The ground and the neutral busses in your box are bonded together, either in the box or at the meter box, and it's perfectly acceptable to intermix neutral and ground conductors at this point, but only at this point.


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## Gyrobog (Feb 18, 2019)

motormonkey said:


> The ground and the neutral busses in your box are bonded together, either in the box or at the meter box, and it's perfectly acceptable to intermix neutral and ground conductors at this point, but only at this point.


 
I attached the pics in my previous post in an attempt to show that while the box was manufactured with the neutral and ground busses bonded together at the bottom of the box, things were modified when the house was originally wired. The pic shows how the ground buss screw (or rivet, whatever) that attached it to the heavy short buss at the bottom of the case was drilled out in order to separate the ground buss from the neutral buss. The ground buss is attached to the circuit breaker case. The ground buss is not directly attached anymore to the neutral buss. I don't understand why this was done, but the pics show it was done.


I'm trying to find out how this might affect wiring the generator (through an interlock kit) to the house.


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## motormonkey (Jul 10, 2016)

Trust me. Neutral and ground are supposed to be bonded together at a single point somewhere in the power path into your house. It may not be at that point you pictured, but it should be somewhere. Some electrical codes dictate that ground and neutral be bonded together in the meter box instead of the breaker box. The fact that neutral wires and ground wires in your breaker box are intermixed on the two busses would tend to confirm that they are bonded somewhere close by. If you have doubts about this, you should have a competent electrician look into it.


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## Gyrobog (Feb 18, 2019)

motormonkey said:


> Trust me. Neutral and ground are supposed to be bonded together at a single point somewhere in the power path into your house. It may not be at that point you pictured, but it should be somewhere. Some electrical codes dictate that ground and neutral be bonded together in the meter box instead of the breaker box. The fact that neutral wires and ground wires in your breaker box are intermixed on the two busses would tend to confirm that they are bonded somewhere close by. If you have doubts about this, you should have a competent electrician look into it.


 
I trust you. I'm a AE, not an electrician.


Still, I can't see why, when they built the house, the electrician drilled out the attachment screw that attached the ground buss to the neutral buss, then moved the ground buss away from the column of circuit breakers, and then attached the ground buss to the metal case. See the pics showing where the attachment screw was drilled out so the ground buss could be separated from the solid metal piece that attaches to the neutral buss. If it is all still electrically attached, why do this?


I am still trying to sort out how to use the three wires going from the dryer outlet to the circuit breaker box to hook up the extension cord to the three-prong generator output. The three wires from the dryer outlet go to the circuit breaker box ganged circuit breaker (red and black wires) and to the ground buss (white wire). See the pic


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## motormonkey (Jul 10, 2016)

> ...I can't see why, when they built the house, the electrician drilled out the attachment screw that attached the ground buss to the neutral buss, then moved the ground buss away from the column of circuit breakers, and then attached the ground buss to the metal case. ...


The only person who can answer that question is an electrician.



> ...I am still trying to sort out how to use the three wires going from the dryer outlet to the circuit breaker box to hook up the extension cord to the three-prong generator output. The three wires from the dryer outlet go to the circuit breaker box ganged circuit breaker (red and black wires) and to the ground buss (white wire). See the pic...


The short answer is that you cannot _safely_ use three wires for a properly grounded 120/240 volt circuit. You have to have four separate conductors; two hot wires to supply the voltage, a neutral wire to carry the return current from any 120 volt loads, and a ground for electrical safety. That third white wire in your circuit is not a neutral, it is a ground. Although you may be able to get by with using a ground conductor as a neutral, it is not safe.


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## Gyrobog (Feb 18, 2019)

Okay, let's say I give up on using the dryer socket. How do I safely hook up my generator (3-hole 240v output) to the house?


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## tabora (Sep 6, 2018)

Frankly, @Gyrobog it's time for you to stop speculating and get a locally licensed electrician to get things hooked up for you. @motormonkey and I disagree on what we think is acceptable in your situation, but we are not there to be able to test continuity and bonding. Hooking up a generator is pretty simple, but you have a slightly non-standard situation that requires local, knowledgeable hands-on. I've wired 1/2 dozen buildings and 4 generator switches, but I'm just a digital systems engineer. See again my post 4 re: bonding.


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## Gyrobog (Feb 18, 2019)

Maybe I'll take some local classes on how to be an electrician.


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