Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Chris Wilson
 
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Default Mains failure gennie switching

I am looking for advice on the easiest way to wire up a modified
electrical distribution panel here at home, to allow a generator to be
fired up and take over power supply to the house during one of our fairly
frequent mains failures. Ideally I would like a self powered contactor to
isolate the mains input to the board and make available a socket into
which the generator output is left plugged. Once power is re-established
from the mains this socket would be automatically isolated and the mains
takes over the running again. I need to (obviously...) avoid the scenario
where both mains and generator are connected at the same time! I would
like it automated so if I am not here the wife only has to check no
excess loads in the house are still on, albeit not working due to power
outage, go outside and start the gennie, with no switches to fiddle with.
I intend to have an LED on the inside fuse box to allow her to see when
the mains is back, so she knows when to turn off the generator. Possible?
Schematics? Web site showing this? I am sure it must be a fairly common
thing for people living with iffy mains supplies.

Thanks. I am in the UK. Mains is normal 240v single phase.

--
Best Regards,
Chris.
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Jack Smith
 
Posts: n/a
Default Mains failure gennie switching

On Mon, 13 Oct 2003 12:35:34 +0100, Chris Wilson
wrote:

I am looking for advice on the easiest way to wire up a modified
electrical distribution panel here at home, to allow a generator to be
fired up and take over power supply to the house during one of our fairly
frequent mains failures. Ideally I would like a self powered contactor to
isolate the mains input to the board and make available a socket into
which the generator output is left plugged. Once power is re-established
from the mains this socket would be automatically isolated and the mains
takes over the running again. I need to (obviously...) avoid the scenario
where both mains and generator are connected at the same time! I would
like it automated so if I am not here the wife only has to check no
excess loads in the house are still on, albeit not working due to power
outage, go outside and start the gennie, with no switches to fiddle with.
I intend to have an LED on the inside fuse box to allow her to see when
the mains is back, so she knows when to turn off the generator. Possible?
Schematics? Web site showing this? I am sure it must be a fairly common
thing for people living with iffy mains supplies.

Thanks. I am in the UK. Mains is normal 240v single phase.


In the States, these devices are called "transfer switches" and a
Google search will show many designs. They are available in manual or
automatic versions, with the manual being cheaper. They are basically
a large DPDT switch. The automatic versions include power sensing and
delay hold functions.

If your generator is not an autostart model, then a manual transfer
switch is normally used. Autostart generators are installed with
automatic transfer switches.

The one used with my 25KW autostart generator is from PSP Products.
Their line of transfer switches can be seen at
http://www.pspproducts.com/body_transconnect.html . This page also
includes some introductory material that may help you understand
transfer switching.

I'm sure you can find something similar in the UK.


Jack Smith


  #3   Report Post  
Jack Smith
 
Posts: n/a
Default Mains failure gennie switching

On Mon, 13 Oct 2003 12:35:34 +0100, Chris Wilson
wrote:

I am looking for advice on the easiest way to wire up a modified
electrical distribution panel here at home, to allow a generator to be
fired up and take over power supply to the house during one of our fairly
frequent mains failures. Ideally I would like a self powered contactor to
isolate the mains input to the board and make available a socket into
which the generator output is left plugged. Once power is re-established
from the mains this socket would be automatically isolated and the mains
takes over the running again. I need to (obviously...) avoid the scenario
where both mains and generator are connected at the same time! I would
like it automated so if I am not here the wife only has to check no
excess loads in the house are still on, albeit not working due to power
outage, go outside and start the gennie, with no switches to fiddle with.
I intend to have an LED on the inside fuse box to allow her to see when
the mains is back, so she knows when to turn off the generator. Possible?
Schematics? Web site showing this? I am sure it must be a fairly common
thing for people living with iffy mains supplies.

Thanks. I am in the UK. Mains is normal 240v single phase.


In the States, these devices are called "transfer switches" and a
Google search will show many designs. They are available in manual or
automatic versions, with the manual being cheaper. They are basically
a large DPDT switch. The automatic versions include power sensing and
delay hold functions.

If your generator is not an autostart model, then a manual transfer
switch is normally used. Autostart generators are installed with
automatic transfer switches.

The one used with my 25KW autostart generator is from PSP Products.
Their line of transfer switches can be seen at
http://www.pspproducts.com/body_transconnect.html . This page also
includes some introductory material that may help you understand
transfer switching.

I'm sure you can find something similar in the UK.


Jack Smith


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Bob Shuman
 
Posts: n/a
Default Mains failure gennie switching

Since my 5KW gasoline generator is manual start only, I did not require an
automatic transfer switch. I also elected to go without the manual transfer
switch either and just use the 200A main breaker for this function (the
breaker needs to be switched off in case commercial power is restored while
the generator is operating). In my case, I ran a separate 30A 208VAC
breakered circuit to my garage. I can use this circuit for HD tools, but it
also provides me the ability to "backfeed" the main electrical panel so I
can distribute the available power to any of the house's 120VAC circuits
that I want (refrigerators, sump pump, gas furnace pilot & blower, etc.)

I've created a simple wiring diagram and specific step-by-step instructions
in case I am not around and the wife or older kids need to get this working
in my absence. If interested in a copy, send me email.

Bob

"Jack Smith" wrote in message
...
On Mon, 13 Oct 2003 12:35:34 +0100, Chris Wilson
wrote:

I am looking for advice on the easiest way to wire up a modified
electrical distribution panel here at home, to allow a generator to be
fired up and take over power supply to the house during one of our fairly
frequent mains failures.


In the States, these devices are called "transfer switches" and a
Google search will show many designs. They are available in manual or
automatic versions, with the manual being cheaper. They are basically
a large DPDT switch. The automatic versions include power sensing and
delay hold functions.

Jack Smith





  #5   Report Post  
Bob Shuman
 
Posts: n/a
Default Mains failure gennie switching

Since my 5KW gasoline generator is manual start only, I did not require an
automatic transfer switch. I also elected to go without the manual transfer
switch either and just use the 200A main breaker for this function (the
breaker needs to be switched off in case commercial power is restored while
the generator is operating). In my case, I ran a separate 30A 208VAC
breakered circuit to my garage. I can use this circuit for HD tools, but it
also provides me the ability to "backfeed" the main electrical panel so I
can distribute the available power to any of the house's 120VAC circuits
that I want (refrigerators, sump pump, gas furnace pilot & blower, etc.)

I've created a simple wiring diagram and specific step-by-step instructions
in case I am not around and the wife or older kids need to get this working
in my absence. If interested in a copy, send me email.

Bob

"Jack Smith" wrote in message
...
On Mon, 13 Oct 2003 12:35:34 +0100, Chris Wilson
wrote:

I am looking for advice on the easiest way to wire up a modified
electrical distribution panel here at home, to allow a generator to be
fired up and take over power supply to the house during one of our fairly
frequent mains failures.


In the States, these devices are called "transfer switches" and a
Google search will show many designs. They are available in manual or
automatic versions, with the manual being cheaper. They are basically
a large DPDT switch. The automatic versions include power sensing and
delay hold functions.

Jack Smith







  #6   Report Post  
 
Posts: n/a
Default Mains failure gennie switching

On Mon, 13 Oct 2003 15:12:53 -0500, "Bob Shuman"
wrote:

Since my 5KW gasoline generator is manual start only, I did not require an
automatic transfer switch. I also elected to go without the manual transfer
switch either and just use the 200A main breaker for this function (the
breaker needs to be switched off in case commercial power is restored while
the generator is operating). In my case, I ran a separate 30A 208VAC
breakered circuit to my garage. I can use this circuit for HD tools, but it
also provides me the ability to "backfeed" the main electrical panel so I
can distribute the available power to any of the house's 120VAC circuits
that I want (refrigerators, sump pump, gas furnace pilot & blower, etc.)

I've created a simple wiring diagram and specific step-by-step instructions
in case I am not around and the wife or older kids need to get this working
in my absence. If interested in a copy, send me email.

Bob


Just be careful that this type of arangement is illegal in many areas
as it can possibly backfeed to external powerlines. Most proper
solutions are designed to physically prevent this.

If you proceed with this, I highly recommend putting a sign next to
the breaker panel with instructions on shifting power, so that your
wife/kids know how to safely operate this setup. For example:

1. Kill main breaker
2. Kill genset breaker
3. Shutoff HW heater and other high draw appliances
4. Start generator, let it warm up
5. Energize genset breaker

Also be very careful of the plugs you use, to avoid the possibility of
having a cord with 120/208 on exposed prongs (sometimes called a dead
mans cord for obvious reasons).

In reality, backfeeding the grid is not as big of an issue as the
power company makes it. Attempting to backfeed to your neighborhood
will usually stall your generator. Even if you do manage to
backfeed, you stand a good chance of frying your genset when the power
comes back on (fire/electrocution hazard). Linesmen take precautions
even if a line is supposed to be dead. But still, that very slim
chance of energizing lines and presenting a danger to lineworkers is a
concern. That concern is expressed in electrical codes as a
requirements to not install equipment that can backfeed.


All that said, I would still recommend a transfer switch for it's
simplicity

-Chris
  #7   Report Post  
James Sweet
 
Posts: n/a
Default Mains failure gennie switching


In reality, backfeeding the grid is not as big of an issue as the
power company makes it. Attempting to backfeed to your neighborhood
will usually stall your generator. Even if you do manage to
backfeed, you stand a good chance of frying your genset when the power
comes back on (fire/electrocution hazard). Linesmen take precautions
even if a line is supposed to be dead. But still, that very slim
chance of energizing lines and presenting a danger to lineworkers is a
concern. That concern is expressed in electrical codes as a
requirements to not install equipment that can backfeed.


All that said, I would still recommend a transfer switch for it's
simplicity



Definitly worth it, it only takes once of someone forgetting to kill the
main breaker, or forgetting to disconnect the generator before switching it
back on. Your generator will be running out of phase with the grid,
connecting it on accident can do very bad things.



  #8   Report Post  
David Lesher
 
Posts: n/a
Default Mains failure gennie switching



While large DPDT transfer switches are expensive; it's not hard to
get DPDT surplus relays with 30A contact ratings.


to line CB1 NC NO CB2 to genset

---------o o----|/|-----O---------||---------o o-------
|
|
|
|
\/ to load.


You could repeat the above on each circuit. The hard part will be a
2nd breaker box for the generator, and how to feed each leg of
CB2 from a separate source.

Use a small relay with a NO pushbutton to control it:

NO
[/\/\/\/\]--.-| |-.-----to gen
/ | |
| -| |-
| NO PB

The relay will latch up through its own contact, until the generator
runs out of fuel or otherwise shuts down. Use a 2nd contact on this
to run the mains contactors.

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433
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