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Electrical Backup Power

Star Designing your electrical system so it can switch to generator power in a blackout.

 

Backup Power

General principle

You cannot just feed power from a generator back into your house wiring.  This would be very dangerous and may electrocute power workers who are working to restore utility power to your house.  It is necessary to have proper certified changeover switches that switch from utility power to generator power via a completely off state.  You could use a huge switch into your main panel for this, but a much better idea is to use lots of smaller switches on the circuits that you will actually need during a power outage.

Example things that need power during an outage include:

Well water pressure pump
Well submersible pump
Fridge/freezer
Lights
PC and home network for internet
TV
Fans etc for heating system
One or two small electrical heaters

Septic systems don't need to be powered during a power outage, assuming the outage only lasts a maximum of a day or two because the first tank has enough extra capacity without being pumped into the second tank.

In practice you will want to keep the total power usage to under about 4000 watts so that you can buy a mainstream economical generator.  Here are some guideline power usage figures...

Power usage guidelines

Generator

It is very important to get a generator that has a 230V (ie dual pole) output.

DuroMax Hybrid Generator

Champion generator 46514 Details are here .

I recommend buying two economically priced generators rather than one more expensive one so that you have redundancy rather than a single point of failure.  It is good to use a generator that can work with both gas (as per a car) and propane.

Generator Transfer Panel

Once you have decided which circuits will need power,  you wire from the generator transfer panel.  The generator transfer panel looks like and behaves like a subpanel.  The unit chosen needs to be able to accommodate arc-fault breakers.

TransGen Wiring Diagram

The best units are made by GenTran.  They do internal and external versions with various power handling capabilities.  Here's one I think is a good choice for outside use...

GenTran R200660 20-Amp 6-Circuit Outdoor Generator Transfer Switch for Generators up to 5000 Watts

Details are here (including installation instructions).

The instructions actually make it sound harder than it really is.  You feed the transfer panel from a 60A dual breaker in the Main Panel.  This goes via four 6-guage wires to the Transfer Panel.  Because the Transfer Panel is a Sub-Panel, the earth and neutral is kept separate.  All things that you want to be available for backup power you wire to the breakers in the transfer panel.

GenTrans generator panel 

For use inside your house you can use an internal version, but I chose to use the outside version even inside the house as it happenedto be less expensive.  Only the internal versions have power balancing meters, but that's not really needed.

Generator Transfer Internal Panel 

Here's the GenTrans wiring details (both internal and external) (click image for higher resolution)...

GenTrans wiring details

An interesting point is that all the circuits that you decide need power during an outage will always be powered by the generator transfer panel even when not using a generator.  To cater for the fact that you will not be as power conscious when not in a power outage, the generator panel can provide more power when not in generator mode.  The GenTran units shown above are fed with a dual pole 60 amp breaker from the main panel.  You need to make sure the maximum current you ever use when not in a power outage is below that dual pole 60 amps.

Exterior connection box and cable

If mounting inside then you will need a connection box on the outside of your house (the generator MUST be used outside because of exhaust fumes).  Mount the socket in an electrical box on the outside wall.

When wiring an L14-20 (or an L14-30) plug or socket, G is (green) ground, W is (white) neutral, Red and Black are the interchangeable Live1 and Live2 and go on the X and Y terminals.

https://smile.amazon.com/gp/product/B01JNWZN66/ref=ox_sc_act_title_1?ie=UTF8&psc=1&smid=A21SDU20CEFN4K   $74.95 + tax for 40 feet

Generator Cable L14-30 

For the transfer panel you may need to put an L14-20 plug on the end of the wire (instead of an L14-30 plug).  The wiring for an L14-30 plug is as per this diagram (from: http://www.smps.us/portablegenerators.html)...

L14-30 wiring diagram 

On the outside wall of you house you need...

Generator Wall Box L14-30   Wall box L14-30

Other details and my plot specific details

In my case because of the configuration of the wiring around my property, I need two transfer panels and two generators, ie two separate setups.  My main panel and my electricity meter are mounted outside on the driveway.  There are feeds from there to the well house and various out buildings, as well as a feed to the subpanel in the main house.  I use an external generator transfer panel and generator to power the well house and out buildings during a power outage.

Transfer Panel Breaker Uses 

External generator transfer panel in yard

Inside the house, next to the internal subpanel that does lighting and electronics, I use another generator transfer panel fed via an external connector box and another generator.  Note that the other house subpanel that powers the heavy current appliances does not have any power backup so none of these will be able to operate during a power outage.

The two generators are both 4000W and are interchangeable and movable.  If one fails then one generator will be used most of the time for the house, but moved to the outside transfer panel for 10 minutes whenever the water pressure has dropped (and the faucets stop working).  Note that even when both generators are functional, it is only necessary to run the generator on the external panel that feeds the well house occasionally and this will save gas.

Take heed of the fact that you can never exceed dual pole 60 amps even when not in a power outage.  Here are the calculations for the external generator transfer panel...

Well submersible pump             6A 230V (Dual pole)
Water pressure pump               10A 230V (Dual pole)
Power tools in the well house    14A 110V (Single pole)
Well house heater                     14A 110V (Single pole)

The Well house needs a 30A dual pole breaker.  That leaves only 30A for everything else fed from the external generator transfer panel.

During a power outage it is necessary to keep the well house power usage to under 20A dual pole or the generator circuit breaker (in the transfer panel or on the actual generator) will keep tripping.  If this happens then you will need to in the well house sub-panel turn off the breaker to the submersible pump and just rely on the stored water in the tank.  If the tank runs dry then turn off the breaker to the pressure pump and let the submersible pump have power for a while.

The septic system does not need to be fed from a generator transfer panel on the assumption that a power outage will be less than a day or two.  To allow for a more serious longer outage you would need to temporarily run wiring to one of the breakers on the transfer panel and temporarily turn off the breaker to the well house (or other 20A load).  You would do this every couple of days to pump sewage from the first tank to the second tank and out to the drain field.

It is not practical to have your garage (with lots of power tools etc) all powered from the generator transfer panel.  Instead you should pick a suitable 20A single pole (ie 115V) power outlet in the yard that is powered by the generator transfer panel and then run an extension cord if you need a particular power tool during a power outage.  Alternatively have a couple of special dedicated and marked sockets in the garage.  If it is an out-building without power tools then it is practical to feed it from the Transfer Panel.

 

My particular breaker configurations

Site main panel

 

Yard transfer panel

Name
 
Breaker
 
L1/L2
 
L1/L2
 
Breaker
 
Name
 
Near post power outlet
20 L1  
 
 
L1 15 (Unused)
Garage & modem
Cloth Sheds & Fountain 20 L2  
 
 
L2 15 (Unused)
Garage & modem
Wellhouse L1
 
30 L1  
 
 
L1 20 ICF Shed L1
Wellhouse L2
 
30 L2
 
 
L2 20 ICF Shed L2

 

High current house sub-panel

Name
 
Breaker
 
L1/L2
 
L1/L2
 
Breaker
 
Name
 
1 L1 L1
2 L2 L2
3 L1 L1
4 L2 L2
5 L1 L1
6 L2 L2
7 L1 L1
8 L2 L2
9 L1 L1
10 L2 L2
11 L1 L1
12 L2 L2
13 L1 L1
14 L2 L2
15 L1 L1
16 L2 L2
17 L1 L1
18 L2 L2
19 L1 L1
20 L2 L2

 

Low current house sub-panel

Name
 
Breaker
 
L1/L2
 
L1/L2
 
Breaker
 
Name
 
1 L1 L1
2 L2 L2
3 L1 L1
4 L2 L2
5 L1 L1
6 L2 L2
7 L1 L1
8 L2 L2
9 L1 L1
10 L2 L2
11 L1 L1
12 L2 L2
13 L1 L1
14 L2 L2
15 L1 L1
16 L2 L2
17 L1 L1
18 L2 L2
19 L1 L1
20 L2 L2

 

House transfer panel

Name
 
Breaker
 
L1/L2
 
L1/L2
 
Breaker
 
Name
 
Kitchen Socs Microwave
20 L1  
 
 
L1 15  Family Water Heater
Main Socs 20 L2  
 
 
L2 15  Family Water Heater
Kitchen Fridge
Extra Soc
20 L1  
 
 
L1 15 Server Basement
Bedroom Socs
20 AFCI L2
 
 
L2 15 Main Bed Base Lights
Base socs

Notes

(Gen) Kitchen Socs Microwave
    One bench (8 socs) fed from one GFCI
    Use plugin cooktop rather than main cooktop
    Kettle (13A)
    Coffee maker (10A)
(Gen) Main Socs
    Living room power sockets (plug in mobile radiator) (3 soc), TV etc (3 socs)
    Utility room (one twin soc)
    Socket in bathroom
(Gen) Kitchen Fridge
    Use twin power outlet
(Gen) Bedroom Socs
    One twin socket in each bedroom and landing (total of 10 twin socs)
    Sockets in bathrooms
(Gen) Family Water Heater L1
    One side of 2500W 240V 11A element for family hot water heater.
    Need to fit water heater with 2500W 240V elements.
(Gen) Family Water Heater L2    Basement Freezer
    Other side of 2500W 240V 11A element for family hot water heater.
    Need to fit water heater with 2500W 240V elements.
(Gen) Server Basement
    Internet switches, server PC & discs
(Gen) Main Bed Base Lights, Base Socs
    LED lights so not much power
    Just 4 special basement socs

Things that will not work in a power outage

Washing machine
Clothes dryer
Ovens
Induction cook top
Big hot water heaters
Hot water heat pump
In-wall oil radiators

Hot water heater

Need to fit water heater with 2500W 240V elements rather than the usual 4500W 240V elements.

https://smile.amazon.com/gp/product/B000BQR3FI/ref=ox_sc_act_title_1?ie=UTF8&psc=1&smid=A1JBXRJ2FT7YCD   $7.18

This will mean that the heat time (or rather recovery time) for the family hot water is a bit slow even when there is not a power outage.  This may be ok (suck it and see), particularly as there are 50 gallons of full temperature hot water available before recovery is needed.  If this is a problem then will need to buy an extra water heater that is dedicated to power outages.

 

 

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