Home Generator & Backup Switching

This blog is from 2014 updated in Feb 2018.

A few years ago just before Christmas we had an extended power outage, not only didn’t the telly work :-(,  but all the food in the fridge/freezer was nearly spoiled which would have been a disaster, it was at that point I decided to install an external power inlet point for a petrol generator and some form of switching.

I decided early on that I only needed the essentials to be on the generator backup, this included the heating, lighting, kitchen power circuit and cooking, it was important that I confirmed which circuit breaker control which circuit, this is important as I need to isolate high current consuming circuits so as not to overload the generator when online.

The generator I bought was a Honda 3kVA manual pull start unit off eBay (it later transpired that it wasn’t a genuine Honda, you’ve got to love shysters), which should be plenty big enough, if we need to heat water for hot drinks we’ll use the gas hob kettle rather than the electric one so as not to overload the genny, I can keep an eye on actual consumption due to a digital power monitor which is incorporated into the transfer switch enclosure.

As the generator is a manual pull start their was no point having an automatic power transfer switch, so I built a manual one.

So, outside in the meter cupboard is a 16A switched male socket inlet, this has been modified with a power indicator which illuminates when the generator is running, the generator plugs into this external outlet via small lead, two things to note, first that the petrol generator is outside so that fumes can’t get into the house and secondly that the power lead from the generator to the house uses a female socket to ensure that no exposed pins can be touched with the generator running, removing any shock risk.

From the external socket a 4mm cable feeds into one side of a power transfer switch, this switch has a capacity of 125 amps and is a break before make type, this will ensure that it is not possible to back feed power to the generator from the utility supply during the manual switching operation.

The supply from the utility company also go to this transfer switch, the output of the switch goes to the consumer unit and from here to each of the circuits in the house.

Operation – under normal conditions, the transfer switch is set to utility supply, this is confirmed by an LED, on a sustained power outage, the generator is hooked up and started, the switch on the external socket inlet is turned to on and the generator power available LED is lit.

Non essential circuit breakers in the consumer unit are turned to the off position, once done, the transfer switch generator power available LED is checked, and if lit, the transfer switch is operated to import power to the consumer unit from the generator.

Restoration of utility supply is indicated by an audible tone which obviously is switched off in normal utility power operation.

original
Original electricity cupboard
moded
Supply company lowered the isolator to make room for the generator intake switch.
generator intake
Generator intake.
switch
125A break before make transfer switch.
panel display
Digital Volts, Amps, Kw and frequency meter.
switch
Transfer switch mounted next to garage dado power consumer unit.
boxed up
Transfer switch fully installed.
consumer
Consumer modified to RCBO and remote power off to garage supply
smart
Smart meter installed August 2017
Generator plugged in
Generator plugged in on test.

System on test, instruction by the consumer unit, give the startup and shutdown process including which breakers to turn off before changing over, the transfer switch panel meter is used for monitoring load to make sure the generator is not overloaded.

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