# Generator install - unique home wiring or not



## toofast (Aug 27, 2013)

I was not sure what to call this thread....so here we go.

I bought a Generator that would power 10 - 20 amp circuits in my house.  We live in the country and often lose power, especially in the dead of night in the winter...plus I travel.  So wife does not love getting up in the middle of the night in a snow storm to stay in a hotel with our 3 year old.

OK....now the problem.

The Generator Installer got everything set, then went to wire the 10 circuits and said OPPPS, you are in trouble.  I can only use "5" of the circuits you wanted, because the electricians when they built the house "cheated" and you don't really have dedicated circuits.  For example...my hot water tank is gas, but on its OWN 20 AMP circuit, however coming into the main panel is a 12 - 3 line, one of the hots feeding the hot water tank, and another hot feeding the foyer lights, sharing a neutral.  

So the way the generator is setup, he says I have to move BOTH circuits because the generator circuit takes control and I can't "split" the neutral.

Hopefully that made sense ?

With that in mind, what options do I have.  My neighbor who is a EE told me that I could CHEAT YET again, and it might not be CODE, but the way your house is wired you would never have an issue.  What he means is that I have 200 amp service with "dedicated" circuits in every room.  In the example above he said I could combine the hot water line and the foyer line (runs a single light with 4 40 watt bulbs) together and I would NEVER come close to overloading that circuit.  

He said I could do this with MOST of the circuits that are setup with this 12-3 shared neutral and I should be ok.  

That does not feel right, but it might be my only option.  I can't afford to re-wire my entire house.  Is there any other way to perhaps put in a junction box and somehow split that back out...meaning move the 12-3 into a box, then take two 12-2 and run one to the main (aka foyer) and then run the other 12-2 into the genny panel for hot water.  Or will this cause an issue with the neutral and when the genny kicks in all heck will break loose.

Ok...hopefully this is enough to get some guidance and of course if you need more details just yell.


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## toofast (Aug 27, 2013)

Ok, I did a bit more research and I THINK this is called multi-wire branch circuit (MWBC). 

Hope this helps.


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## JoeD (Aug 27, 2013)

You are correct. They are called multi wire branch circuits. They are legal and not cheating. It saves cable and expense when wiring a house.
He is correct that both of them must be moved.
I would not be following your neighbour's directions.


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## toofast (Aug 28, 2013)

JoeD said:


> You are correct. They are called multi wire branch circuits. They are legal and not cheating. It saves cable and expense when wiring a house.
> He is correct that both of them must be moved.
> I would not be following your neighbour's directions.



Yeah I agree with not listening to the neighbor.

As a side note...is there ANY WAY to split out these circuits...without rewiring the whole house ?


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## kok328 (Aug 28, 2013)

It is my understanding that in order to utilize a MWBC you have to share the neutral between the two phases of hot.


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## JoeD (Aug 28, 2013)

The only way to separate them is replace the 12/3 line from the panel to the point where it separates into two circuits With two separate 12/2 cables. The new cables do not need to follow the same route as the 12/3, as long as you get them from the panel the separation point. The old 12/3 can be abandoned in the wall.

EDIT. 
Actually you only need one 12/2 cable. The 12/3 can remain as one of the circuits with one of the hots simply being left unused.


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## bud16415 (Aug 29, 2013)

I don&#8217;t know much about backup generators but have a few questions based around what the OP said he had. 

If he has a generator capable of (10) 20 amp circuits the unit then should be large enough to power his whole house assuming he has a 200 amp service. Why would they isolate the power of individual circuits in this manner rather than one large switch that isolates the whole house? 

I understand the rational of doing that with a small unit sized to supply only emergency needs heat, water pump, fridge, and a few lights etc. Around here many people have a small gasoline unit sitting in the garage and will hook up some extension cords even if needed in the winter to keep the necessities going, and others have whole house natural gas rig outside with automatic transfer. I assumed the big units took the house off line and then fired up replacing the power.


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## JoeD (Aug 29, 2013)

20 circuits does not mean it is large enough to support the whole house. 
Also a 200 amp whole house transfer switch is much more expensive.


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## toofast (Aug 29, 2013)

Correct...my main panel has 42 20 amp breakers.  My Genny (if I ever get it going) will power most of the critical circuits but not all.

Keep in mind (although I am no expert) the total amps of the breakers installed nearly always exceed the service as these are not directly related.  Although it seems like it should be.  Perhaps an expert will explain this better.

As for my problem...I think I will try to FIX the circuits that I can get to - without tearing into the walls.  Hopefully it will give me enough to power the critical areas.


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## bud16415 (Aug 29, 2013)

How big is your gen, KVA rating? 

A auto disconnect for a whole 200 amp house is about $700 and a manual one is about $350 so ya pretty pricy.   

The reason the sum of the parts is greater than the whole I believe is that&#8217;s a max rating. No one would ever have every circuit maxed out at the same time. That&#8217;s kind of what your neighbor was suggesting. You said one of the items was your gas water heater? How much current could that draw? 

Do you have a well and pump? That would and should be a dedicated line now what other combinations and items do you want to break out?

If you do like JoeD said and use the 12 / 3 as a 12 / 2 for the lighting then it might not be as hard to run a new wire to your water heater. Other things might just work out the same.


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## gottodo1 (Aug 29, 2013)

They're right that the best way to solve it would be to run new 12-2, is that feasible? Crawlspace/attic access? 

What I've seen since I've moved to backwater is exactly what your neighbor mentioned doing. Here's the fun part right. Without rewiring you could just run some raw cables into your house and try what your neighbor suggested. You're not going to hurt anything everything has breakers that will prevent overcurrent conditions before anything bad happens. This assumes the genset people did their work right. If they told you about this problem instead of just "setting it up" they're probably descent enough.  If you're that concerned you could get an IR camera or use a thermocouple on the lines to see if the wires/breakers heat up. That's the only reason you have individual breakers is to save your *** if you pull too much current through the wire, the ways of doing this are of course innumerable. 

Personally I would much prefer if you fixed it the right way as will the next guy but, I'm getting a little over my hope to fix everything properly, as long as it works safely. Of course leaving notes/pictures of what you did that deviates from code would be really nice but also probably incriminating. After all NEC is there for 2 reasons, to stop you from killing yourself, and stop you from killing the next guy who owns the house. 

You seem pretty descent and I wouldn't fault ya much for doing it either way. The next guy will be glad to have the GenSet regardless.


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## Speedbump (Aug 31, 2013)

Even though I've always had an electric water heater.  I'm still trying to figure out why a Gas heater needs any electricity.


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## gottodo1 (Aug 31, 2013)

It could have a fan, and the ignition may also be electric.


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## Speedbump (Aug 31, 2013)

Man... I must be old school.  The gas heaters I'm familiar with had thermocouples and pilot lights.  A fan???  What would it need a fan for.  "I know it's going to be an intelligent answer, I just can't fathom why a water HEATER would need a fan."


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## speedy petey (Sep 1, 2013)

Speedbump said:


> Man... I must be old school.  The gas heaters I'm familiar with had thermocouples and pilot lights.  A fan???  What would it need a fan for.  "I know it's going to be an intelligent answer, I just can't fathom why a water HEATER would need a fan."



Many newer high-efficiency units have power vents and even make-up air for the combustion.


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## gottodo1 (Sep 1, 2013)

Yup, old school you are. http://www.rheem.com/product/residential-gas-water-heaters-power-vent, more efficiency. Moar Powar! I think some places require it by code for sidewall installs too.


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## Speedbump (Sep 2, 2013)

Well there is another one I learned today.


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## gottodo1 (Sep 2, 2013)

Nothing wrong with that man, I've learned a bunch since Joining this forum... Like owning a pneumatic stapler/nailer is the best thing since sliced bread.


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## toofast (Sep 4, 2013)

Ok trying to catch up....

Yes...Hot water tank is GAS, but it has a FAN to provide AIR - it uses VERY LITTLE JUICE - yet it is on its own 20 amp circuit (of course tied into the foyer light - which is 4 20 watt bulbs).  So I should be able to tie those together into one new circuit ?  No way will it overload the 20 amp breaker - the total draw is like 5 amps.

Same story on other circuits...

Furnace is GAS, but of course has a blower - that is on its own 20 amp circuit - tied in with dining room lights (4 60 watt cans) that is NEVER USED.  I can certainly tie these together ??

Guess my house was over engineered...or is there HUGE CODE violations potentially facing me.


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## gottodo1 (Sep 5, 2013)

I don't know about the violations bit, but sometimes those motors when turning on and off can put noise on the line with other items that share the same neutral due to their inductive nature and if you don't correct the Power Factor (and who does in their own home?). This could cause the lights to dim (especially CFL bulbs, not sure about LED), these fans probably aren't high enough load for that though, I've seen larger motors  cause electronics to turn off or restart. I've installed a electric tankless water heater that made all the CFLs flicker in the hosue when it was chopping the current, when it didn't need to be hard on. 

Drawing from your Gen you should be totally fine with what you've described.


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## toofast (Oct 17, 2013)

Ok, so as a follow up - the licensed genny guy came in and did his stuff.  He followed the rules related to the multi branch circuits, etc.  

I was doing some testing to make sure all the label are correct and I am having a MINOR issue (I THINK).

I had a multi branch circuit that controlled the furnace fan (furnace is gas) and the living room lights.  So he moved both circuits over to the genny panel (each on its own breaker) and tied the shared neutral together.  All seems on the up and up....

However...now for the life of me, I can't get the living room lights to shut off (via the breaker).  I turn the new genny breaker off for the furnace and that works fine.  Then I turn off the circuit for the living room and heck the lights are still one.

Now it gets weird....so I decide to make sure the hot is indeed turning off with the breaker, and it is.  YET SOMEHOW the lights are staying on.

I assume I have a PROBLEM somehow with the neutral back feeding, but even if I turn off BOTH CIRCUITS (furnace and living room) I still get the lights to stay on...yet furnace is out.   ?? Is there a way to test for this safely? Any other clues ? 

Or is everyone as lost as me


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## nealtw (Oct 18, 2013)

With that breaker turned off turn off all the breakers one by one. If the light goes off, turn the first one back on if the light comes back on you have a connection somewhere that should not be connected.


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## JoeD (Oct 18, 2013)

Call him back and ask him what he did. It could be an honest mistake that needs a quick fix.


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## gottodo1 (Oct 18, 2013)

I'd go with Neal's approach before calling (unless he'll come out for free), I wouldn't be surprised if it's a house issue, I found an instance where loose THHN had been spliced together in the basement of a friends house once. What was that thing called that they used in Europe back in the day to have 30A circuits, ring wiring... where you used the wire as the ballast resistor to dissipate any difference between the two hot wires (because there's always some phase difference)... Ha, look at this and you'll feel better about the wiring in your house. http://en.wikipedia.org/wiki/Ring_circuit


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