Daily multiple mains failures - fed up with

[Boncuk]

Hi All,

living on the country side in Thailand is no fun considering electric supply. A thunderstorm some 20 miles away might cause mains to fail for several hours.

Building my new home an automatic switchover auxiliary generator is beyond my budget for now.

I decided to purchase a diesel driven generator supplying 5KW of power to take care of the most important items like refrigerators, water pumps, air condition and of course - PC (and last not least the TV to make my lovely stepdaughter happy).

Using a 4-pole double throw power switch I think switching from public mains to generator is the most economic solution for now.

Circuit explanation: As soon as mains fails somebody in the house will notice that and I'll throw the switch from "Normal" to "Emergency" - additionally start the diesel generator.

As soon as mains returns an alarm circuit will signal it to me, taking back the switch to "Normal" and switch off the diesel.

Is the schematic safe?

Regards

Boncuk

 

[Nigel Goodwin]

Seems rather over complicated?.

No need for any switches, just a mains AC relay and DPDT contacts - feed the relay coil from the generator, and then when the generator starts up it automatically switches over to the generator.

I did this at home years ago, with my 2KW generator only feeding certain circuits in the house, lights, TV, fridge etc.

 

[MRCecil]

Hi Boncuk

As soon as mains returns an alarm circuit will signal it to me, taking back the switch to "Normal" and switch off the diesel.

Is the schematic safe?

To answer your question, not completely. Attached is a diagram of a standard load transfer switch, and should be sized for the ampacity of the incoming power. As you can see, it is a DP3T (ON-OFF-ON). This gives one the ability to totally isolate the load, your house. Also to be safe, be sure to fuse your alarm circuits based on the wire size supplying them.

Nigel's approach is fine given you have a split buss main panel, but does have the possibility of backfeeding the incoming line from the generator if not on the low load split on the panel buss.

Disclaimer: My opinion is based solely on the US National Elec. Code, and I have no experience with foreign practices.

Good Luck!

 

[crutschow]

There is an arc-over danger when feeding high-voltage power to both fixed contacts of a double-throw relay (I once read about someone blowing a relay in this manner). As the contacts switch, an arc is generated. If the arc is sufficient it can arc to the other contact (depending upon the relative voltage of the two sine-wave peaks) and cause a short between the power line and the generator, definitely a no-no.

However if it's done as Nigel suggested, there should never be voltage on both contacts simultaneously, so that would be ok.

 

[mneary]

There is an arc-over danger when feeding high-voltage power to both fixed contacts of a double-throw relay (I once read about someone blowing a relay in this manner).

I still have the relay.

 

[Boncuk]

Seems rather over complicated?.

No need for any switches, just a mains AC relay and DPDT contacts - feed the relay coil from the generator, and then when the generator starts up it automatically switches over to the generator.

I did this at home years ago, with my 2KW generator only feeding certain circuits in the house, lights, TV, fridge etc.

Hi Nigel,

your suggestion is logical, but I'm missing an indication of "mains restored".

Burning diesel fuel for electric power is more expensive than public power.

Regards

Boncuk

 

[crutschow]

Do you need more than just a light connected to the mains power?

Certainly you could connect a mains powered relay to the generator shut-off.

 

[Nigel Goodwin]

Hi Nigel,

your suggestion is logical, but I'm missing an indication of "mains restored".

Burning diesel fuel for electric power is more expensive than public power.

It would be trivial to arrange an indicator on the incoming mains supply, another relay with the coil fed from the generator would be simple to connect. However, my experince of mains failures is that you soon notice other people have power back anyway.

 

[Boncuk]

It would be trivial to arrange an indicator on the incoming mains supply, another relay with the coil fed from the generator would be simple to connect. However, my experince of mains failures is that you soon notice other people have power back anyway.

That's a bit different here. On the country side single houses are not always built in clusters, but are 500m and more distant.