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Switch from mains to genny?

 
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Vortex2



Joined: 13 Jan 2019
Posts: 1269

PostPosted: Sun Jan 13, 2019 3:00 pm    Post subject: Switch from mains to genny? Reply with quote

Is it legal to have a switch (professionally) installed to take house power from a generator instead of mains?

If so, any idea what the parts and labour etc costs might be?
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adam2
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Joined: 02 Jul 2007
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Location: North Somerset

PostPosted: Sun Jan 13, 2019 4:12 pm    Post subject: Reply with quote

Yes, perfectly legal so long as it is properly installed and fit for purpose.

It is VITAL that no interconnection can be made, even briefly between the mains and generator supplies.

The switch must therefore be of the "break before make" type whereby the mains circuit is reliably interrupted before the generator circuit is made, and likewise when switching back to mains.

A simple manually operated changeover switch costs less than £50.

An automatic changeover control will be a lot more costly, and is rather pointless unless the generator also starts automatically.

Unless you have a very small electrical installation, or a very large generator, the changeover switch would normally operate on only part of the installation that consists of the lower power but more important loads.
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Vortex2



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PostPosted: Sun Jan 13, 2019 4:26 pm    Post subject: Reply with quote

Thanks for that.

The MVHR, a Saniflo kitchen waste pump, LED lighting and fridge-freezer are key.

Cooker and washing machine less so.

THe MVHR has integrated immersion and air heaters, so that could be a problem.

Could be looking at say a 3.5kw genny.
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kenneal - lagger
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PostPosted: Sun Jan 13, 2019 6:15 pm    Post subject: Reply with quote

We have a time delay switches on our freezers so that they don't come on for about 15 minutes after our genny starts up to avoid a high starting load which would stop the genny. We have a number of freezers to keep our meat supplies (beef farmer) among other things cold.

We have a pumped grey water disposal system which sometimes comes on with the genny. That would be another candidate for a time delay start up if necessary. Your Saniflo and heaters pump might be a candidates for that depending on the size of your genny.
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adam2
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PostPosted: Mon Jan 14, 2019 4:24 pm    Post subject: Reply with quote

Installation of a changeover switch is relatively simple if it is connected immediately ahead of the consumer unit.
The drawback of this arrangement is that the WHOLE installation is changed over to the generator, and reliance must then be placed on the human factor to avoid use of high loading appliances.

A better arrangement is to install two consumer units, one "mains only" and one "mains and changeover to generator"

Connect to the second consumer unit those loads that you wish to use in a power cut.
All lighting
Refrigeration
TV, PC, internet router, cellphone charger, cordless telephone base unit.
MVHR fans.
Saniflow.
POSSIBLY the heat pump, but this may need a large generator.

As a simplified guide to sizing a domestic generator, I often suggest the following.
Allow 1kW in total for all the low loading appliances that you might reasonably want to use.
Add to this any larger loads like sewage pumps or heat pumps that you wish to use.
Then add another 3KW so as to permit of use of any one single heavy loading appliance.

This will allow use of an electric kettle, or a washing machine, or a microwave oven, or a portable heater, or a table top electric cooker, or a power tool, or a vacuum cleaner, but ONLY ONE such appliance at a time.

Also a generator needs to be oversized to start large motors such as heat pumps or power tools.
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vtsnowedin



Joined: 07 Jan 2011
Posts: 5822
Location: New England ,Chelsea Vermont

PostPosted: Mon Jan 14, 2019 6:28 pm    Post subject: Reply with quote

When the power goes out I run my own house with just two extension cords from my 4KW generator unplugging what I need from the wall sockets (and thereby from the grid) and into the cords.
Here they call the switch you describe as a "double pole -double throw switch". Closed right you are on the grid , closed left you are on your generator.
An educated owner could when he opens the switch turning off the grid go down his breaker panel and snap off the circuits his generator can't handle, clothes dryer , hot tub , freezer,water heater etc. and then close the switch left to connect to his generator.
He could switch on one at a time if he has the gen. capacity to keep the freezer cooled down as needed.
The only drawback is the possibility of forgetting to switch everything back on once the grid comes back up and with it disconnected you won't notice when it comes back on.
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adam2
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PostPosted: Sun Jan 20, 2019 3:55 pm    Post subject: Reply with quote

I have just looked out the details of a standby generator installation that I did some years ago.

The house was equipped with two consumer units, one for mains only circuits and for one for generator backup.

MAINS ONLY
40 amp---------------electric shower
40 amp---------------electric shower
40 amp---------------mains into changeover switch
32 amp---------------electric cooker
32 amp---------------ring circuit, kitchen and basement
32 amp---------------ring circuit, ground floor
32 amp---------------ring circuit, first and second floor
32 amp---------------to outbuildings
32 amp-------------- 32 amp socket
32 amp 3PHASE-----32 amp 3 phase socket
16 amp---------------immersion heater
16 amp---------------electric heater
Supply is three phase, 100 amp. All sub circuits are single phase apart from one 3 phase socket.

Generator backed consumer unit
6 amp---------------basement lighting
6 amp---------------ground floor lighting
6 amp---------------first floor lighting
6 amp--------------- second floor and loft lighting
6 amp---------------central heating
6 amp---------------security equipment
6 amp---------------outside lights
6 amp--------------essential power outlets, ground floor and basement
6 amp -------------essential power outlets, first and second floor and loft.
10 amp ------------fridge and freezer
16amp-------------one single 13 amp socket in kitchen. To allow use of just one heavy loading appliance.
All single phase.

The manual changeover switch is rated at 60 amps.
The diesel generator is rated at about 8 KVA continually, or 9 KVA short term. Push button electric start.

All socket outlets are standard 13 amp types. Those on "mains only" circuits are white plastic, those on the generator supply are red.

This arrangements permits almost unlimited use of the multitude of low loading appliances found in most homes, provided that such items are plugged into the red sockets.

Very high loading appliance like showers or cooker cant be used in a power cut.
High loading portable appliances can be used, but only one such appliance at a time via the single red socket on a 16 amp circuit.

Appliances to be used on red sockets.
computers
TV sets
cellphone chargers
internet router
portable lamps
electric blankets
clock radios
Christmas lights

Appliances NOT to be used on red sockets
heaters
hair dryers
any form of cooking appliance
kettles
power tools
vacuum cleaners
washing machine
tumble dryer
EXCEPTION, any one single such appliance may be used from the dedicated single red socket in the kitchen. If the appliance can not readily be moved to the kitchen than an extension lead will be needed.
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clv101
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PostPosted: Sun Jan 20, 2019 4:10 pm    Post subject: Reply with quote

adam2 wrote:
A better arrangement is to install two consumer units, one "mains only" and one "mains and changeover to generator"

Connect to the second consumer unit those loads that you wish to use in a power cut.
All lighting
Refrigeration
TV, PC, internet router, cellphone charger, cordless telephone base unit.
MVHR fans.
Saniflow.
POSSIBLY the heat pump, but this may need a large generator.


Yes, we use two consumer units. Not for a generator but for two different inverters. We have a 1.2kW inverter on 24/7 running IT, fridge, freezer... And a 6kW inverter for oven, hob, kettle, power tools etc which is only switched on when needed.
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vtsnowedin



Joined: 07 Jan 2011
Posts: 5822
Location: New England ,Chelsea Vermont

PostPosted: Mon Jan 20, 2020 2:03 am    Post subject: Reply with quote

Rolling Eyes I am at present working off my backup generator. The mains power cut out just as I was walking with a plate of pot roast in one hand and a fork in the other. Total darkness so had to be careful of where I set the plate down while looking for emergency light sources. It took about five minutes for me to start up the Honda 5KW generator and getting lights TV and computer back on. Cell phone links say about five towns are effected but no news as to what went out. It has been snowing for two days with temps below zero F but it was pretty much over so I'm thinking a car crash that took out a critical pole or something of the like.
Feeling a bit smug about our ability to deal with problems like this. Wink
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vtsnowedin



Joined: 07 Jan 2011
Posts: 5822
Location: New England ,Chelsea Vermont

PostPosted: Mon Jan 20, 2020 2:52 am    Post subject: Reply with quote

Well hat did not last long. All back to normal in less then two hours. Probably find out what happened with the morning news.
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ReserveGrowthRulz



Joined: 19 May 2019
Posts: 595
Location: Colorado

PostPosted: Mon Jan 20, 2020 8:40 pm    Post subject: Re: Switch from mains to genny? Reply with quote

Vortex2 wrote:
Is it legal to have a switch (professionally) installed to take house power from a generator instead of mains?

If so, any idea what the parts and labour etc costs might be?


Surprised this is even a question. Every one of these setups I've ever seen has this ability, to the point where I thought it was a requirement.
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adam2
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PostPosted: Mon Jan 20, 2020 10:46 pm    Post subject: Reply with quote

There is no requirement for a changeover switch, though use of same is often the best approach.

Alternatives include dedicated "generator only" circuits that are not energised normally, but are energised when the generator is in use.
Back in the old days this was the usual approach for lighting.
Dedicated circuits supply one or two lamps in each room, these lamps are not part of the normal room lighting and are not lit normally.

When the generator is running, all these lamps light. Cheap and simple and fool resistant.
Lamps of low power may be used, the intention not being to provide full normal lighting, but sufficient for essential work.
A common system in public buildings and some older, large shops.
Suggested lamp wattages.
Small store rooms, individual toilets--------------15 watts
Large store rooms, private offices-----------------25 watts
Corridors and passages ----------------------------25 watts, at every change of direction, near fire fighting equipment, fire alarm call point, and then as required such that no point is more than 5 meters from a lamp.

Stairs------------------------------------------------25 watts, so spaced that every step gets light from two different lamps, and that no point is more than 3 meters from a lamp.

Large open sales areas----------------------------60 watts, so spaced that no point is more than 5 meters away from a lamp.

Theatres, cinemas, concert halls and the like. A 60 watt lamp near each exit, and sufficient other lamps such that no point is more than 5 meters from a lamp. (100 watt or 150 watt lamps may be used at greater spacing if the ceiling is high enough)

Large open plan offices, 40 watt lamps near each exit, and sufficient other 40 watt lamps such that no point is more than 5 meters away from a lamp.

Alternate lamps in passages, stairways, and open plan areas to be on different circuits.
Lamps in stores, toilets, offices etc to be on a different circuit to that for the nearest lights outside such a room.

For a small or domestic installation, a few power outlets connected to the generator only is a cheap system.
It relies on the user unplugging appliances from the normal outlets and pugging them into the generator outlets.
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