wiring generator

[Robert A. Cibiras]

I am interested in wiring a generator to my home
via transfer switch. It is a portable unit, not
built in. My plan is to run a wire in the attic
about 80', from the breaker box/transfer switch,
to an outlet in a waterproof box under a covered
patio, then use a double male "extension cord"
from the outlet to the generator's 50 amp plug,
for about another 45'.

My question is this. What size wires should be
used to safely move the power that distance? I
have been told everything from 4 AWG to 10 AWG,
mostly by alleged electricians who at least appear
to make a living at it.

During the last storm, I was using 100', 12/3
extension cords to run individual freezers and the
like, with no problem.

I am looking to be safe about it. I am not
interested in the cheapest thing, and I am
definitely not interested in burning my house
down. I'd like a little overkill, but on the other
hand I don't necessarily want to spend a bunch of
excess money for nothing.

Understanding that obviously the larger the wire
the better, without going totally overboard, what
would be a reasonable and very safe wire size for
this project?

Is 6/3 w/ ground SER for the 80' run in the attic,
and 6/4 SO for the 45' "extension cord" suitable,
or is 4/3 SER and 4/4 SO needed, or is there
something totally different out there?

I am not planning on doing this myself, but I do
want to be able to make an educated decision
regarding what materials to use, and who to use to
put it together. Seems like some people may cut
corners on materials to get the bid.

Many thanks.

Robert

 

[ehsjr]

I am interested in wiring a generator to my home via transfer switch. It
is a portable unit, not built in. My plan is to run a wire in the attic
about 80', from the breaker box/transfer switch, to an outlet in a
waterproof box under a covered patio, then use a double male "extension
cord" from the outlet to the generator's 50 amp plug, for about another
45'.

You are unsafe there - double male - regardless of wire size.

Use a hard wired male attached at the waterproof box on a
short whip, and make a male/female extension for the run from
the generator to the box to address that. You'll need to keep
the male plug out of the weather, too, so that it doesn't sit
there corroding month after month.

You should use #4 copper for the attic run, and #4 SER
for the other run to keep the voltage drop within 5%.
Here's the math:

You need to keep the voltage drop to 5% or less, (6 volts
on a 120 volt circuit). You have a 160 foot run (hot + neutral)
in the attic and a 90 foot run outside.
#6 copper is .491 ohms per 1000 feet.
#4 copper is .308 ohms per 1000 feet.
#4 alumium is .508 ohms per thousand feet.
(From Table 8 Conductor Properties in the 2005 National
Electrical Code)

Using SER aluminum for the 45 foot run (90 feet total wire):
#4 aluminum is .508 ohms per 1000 feet. .508/1000*90 = .04572
ohms. At 50 amps, it will drop 2.286 volts. That leaves a
maximum of 3.714 (6 - 2.286) volts that can be dropped in the
160 feet of wire in the attic, which means the total resistance
of the 160 feet of wire must be 3.714/50 = .07428 ohms or less.
At 160 feet, that means .07428/160 = .00046425 ohms/foot or
..46425 ohms/1000 feet, which makes #6 too small. You'll have
to go with #4 copper in the attic at .308 ohms/1000 feet. It
will have .04928 ohms total resistance, (.308/1000*160 = .04928)
which means it will drop 2.464 volts. The total drop will be
4.75 volts - about a 4% drop which is within the limit.

You need to address "physical safety" of the extension cord
such that cars don't roll over it and damage it, people don't
trip on it - that kind of thing.

It would be best if you dug a trench and used permanent wiring
to the generator site, and had the male plug on its short whip
inside a weatherproof box there. Then a short male/female
extension from the generator to the male plug. (My plug is on
a 2 foot whip in the garage, and I use an 8' extension to the
generator. I run a 30 amp generator, and the wiring is 80 feet
(160 in the computation, hot + neutral) of #6 copper.)

Now *if* you are going to trench it, and *if* there is
a possibility of using a bigger generator in the future,
you should go to a bigger wire size. It will yield no
real benefit now and will cost more for the wire, but
you *don't* want to dig an 18" deep 45 foot trench more
than once.

Ed

 

[Charles Perry]

You are unsafe there - double male - regardless of wire size.

Use a hard wired male attached at the waterproof box on a
short whip, and make a male/female extension for the run from
the generator to the box to address that. You'll need to keep
the male plug out of the weather, too, so that it doesn't sit
there corroding month after month.

You should use #4 copper for the attic run, and #4 SER
for the other run to keep the voltage drop within 5%.
Here's the math:

You need to keep the voltage drop to 5% or less, (6 volts
on a 120 volt circuit). You have a 160 foot run (hot + neutral)
in the attic and a 90 foot run outside.
#6 copper is .491 ohms per 1000 feet.
#4 copper is .308 ohms per 1000 feet.
#4 alumium is .508 ohms per thousand feet.
(From Table 8 Conductor Properties in the 2005 National
Electrical Code)

Using SER aluminum for the 45 foot run (90 feet total wire):
#4 aluminum is .508 ohms per 1000 feet. .508/1000*90 = .04572
ohms. At 50 amps, it will drop 2.286 volts. That leaves a
maximum of 3.714 (6 - 2.286) volts that can be dropped in the
160 feet of wire in the attic, which means the total resistance
of the 160 feet of wire must be 3.714/50 = .07428 ohms or less.
At 160 feet, that means .07428/160 = .00046425 ohms/foot or
.46425 ohms/1000 feet, which makes #6 too small. You'll have
to go with #4 copper in the attic at .308 ohms/1000 feet. It
will have .04928 ohms total resistance, (.308/1000*160 = .04928)
which means it will drop 2.464 volts. The total drop will be
4.75 volts - about a 4% drop which is within the limit.

You need to address "physical safety" of the extension cord
such that cars don't roll over it and damage it, people don't
trip on it - that kind of thing.

It would be best if you dug a trench and used permanent wiring
to the generator site, and had the male plug on its short whip
inside a weatherproof box there. Then a short male/female
extension from the generator to the male plug. (My plug is on
a 2 foot whip in the garage, and I use an 8' extension to the
generator. I run a 30 amp generator, and the wiring is 80 feet
(160 in the computation, hot + neutral) of #6 copper.)

Now *if* you are going to trench it, and *if* there is
a possibility of using a bigger generator in the future,
you should go to a bigger wire size. It will yield no
real benefit now and will cost more for the wire, but
you *don't* want to dig an 18" deep 45 foot trench more
than once.

Ed

Don't forget the approved transfer switch. Thousands of linemen will thank
you when you don't accidentally electrocute them.

Charles Perry P.E.

 

[SQLit]

I am interested in wiring a generator to my home
via transfer switch. It is a portable unit, not
built in. My plan is to run a wire in the attic
about 80', from the breaker box/transfer switch,
to an outlet in a waterproof box under a covered
patio, then use a double male "extension cord"
from the outlet to the generator's 50 amp plug,
for about another 45'.

My question is this. What size wires should be
used to safely move the power that distance? I
have been told everything from 4 AWG to 10 AWG,
mostly by alleged electricians who at least appear
to make a living at it.

During the last storm, I was using 100', 12/3
extension cords to run individual freezers and the
like, with no problem.

I am looking to be safe about it. I am not
interested in the cheapest thing, and I am
definitely not interested in burning my house
down. I'd like a little overkill, but on the other
hand I don't necessarily want to spend a bunch of
excess money for nothing.

Understanding that obviously the larger the wire
the better, without going totally overboard, what
would be a reasonable and very safe wire size for
this project?

Is 6/3 w/ ground SER for the 80' run in the attic,
and 6/4 SO for the 45' "extension cord" suitable,
or is 4/3 SER and 4/4 SO needed, or is there
something totally different out there?

I am not planning on doing this myself, but I do
want to be able to make an educated decision
regarding what materials to use, and who to use to
put it together. Seems like some people may cut
corners on materials to get the bid.

Many thanks.

Robert

The others have pointed you in the right direction. Sounds as if you have
not gotten the transfer switch yet... So look into a 4 pole switch, so you
can switch the neutral. The reason I suggest this is because of the distance
between the generator and the service.
What have you done to ground your generator effectively?

Running four wires will assure that everything will work correctly. The
generator creates a new neutral. Hence the reason I like the 4 pole transfer
switches. Nothing says this as to be an automatic switch you could use a 4
pole double throw switch as long as it was service rated.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7530853583&category=66982&ssPageName=WDVW&rd=1

This one is used and over sized for your application. Offered as a hint what
to look for. If your generator is only 50 amps you would be able to install
a 60 amp switch. CH used to make some residential stuff. I never used it or
installed it.

 

[operator jay]

| The others have pointed you in the right direction. Sounds as if you have
| not gotten the transfer switch yet... So look into a 4 pole switch, so you
| can switch the neutral. The reason I suggest this is because of the distance
| between the generator and the service.

Are you also suggesting switching the EGC in addition to the neutral,
or did I miss the OP saying his home was on three phase power?

Would it be proper (compliant with code, and actually safe) to have
a 4-pole disconnect on a single phase (line, line, neutral, ground)
service entrance? I get enough heat from people by merely suggesting
that I might disconnect the neutral (in addition to the 2 hot lines).

http://ka9wgn.ham.org/ |

--------------------------------------------------------------------------

---


I'd suggest sketching a 5-line diagram (as opposed to a single-line).
Sketch out a couple areas of the distro using five lines representing hot,
hot, neutral, bond, misc metal connections (such as equipment cases,
conduit*, structural metal). *Your conduit could be part of your bonding,
at least here it could. I find this handy to determine what will (and
won't) happen -- make sure neutral current won't be returning on bonding or
other connections, check whether a switched neutral or EGC would still leave
everything safe, allow devices to trip that are supposed to trip, etc.

j

 

[SQLit]

| The others have pointed you in the right direction. Sounds as if you have
| not gotten the transfer switch yet... So look into a 4 pole switch, so you
| can switch the neutral. The reason I suggest this is because of the distance
| between the generator and the service.

Are you also suggesting switching the EGC in addition to the neutral,
or did I miss the OP saying his home was on three phase power?

OOPS,, fat fingered that one I meant 3 pole.

I am pretty sure that disconnecting the ground execpt in testing situations
is not allowed.

Sorry for the confusion

Would it be proper (compliant with code, and actually safe) to have
a 4-pole disconnect on a single phase (line, line, neutral, ground)
service entrance? I get enough heat from people by merely suggesting
that I might disconnect the neutral (in addition to the 2 hot lines).

http://ka9wgn.ham.org/ |

--------------------------------------------------------------------------

---

 

[Mike Lamond]

The others have pointed you in the right direction. Sounds as if you have
not gotten the transfer switch yet... So look into a 4 pole switch, so you
can switch the neutral. The reason I suggest this is because of the
distance
between the generator and the service.
What have you done to ground your generator effectively?

Running four wires will assure that everything will work correctly. The
generator creates a new neutral. Hence the reason I like the 4 pole
transfer
switches. Nothing says this as to be an automatic switch you could use a
4
pole double throw switch as long as it was service rated.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7530853583&category=66982&ssPageName=WDVW&rd=1

This one is used and over sized for your application. Offered as a hint
what
to look for. If your generator is only 50 amps you would be able to
install
a 60 amp switch. CH used to make some residential stuff. I never used it
or
installed it.

The transfer switch has to be sized for the larger of the generator capacity
or the
utility side circuit feeding it. If the switch is going to be installed on
the service
entrance, ahead of the main circuit panel, it will have to be 100 or 200
amps.
A 60 amp switch feeding a subpanel would limit the emergency circuits to a
60
amp feeder.

Mike

 

[Robert A. Cibiras]

The OP would be well advised to use a generator inlet box such as the
ones shown at
<http://www.electricgeneratorsdirect.com/catalog/default.php?cPath=21_27>
They provide a fixed male plug installed in a weather proof box.
--
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison

Thanks for all the info. I have obtained 4AWG wire
for the project. The final piece of the puzzle to
avoid the double male plug is a replaceable female
receptacle for one end of the extension cord to
plug into the inlet box refenenced above. The male
ends are a dime a dozen at Lowes, Home Depot, etc.
The female is not. I have located 50 amp extension
cords for RVs, though generally only with 6AWG
wire, and no more than 30' long, which have the
female end on them, so I know they exist. I have
found replacements for a 30 amp female receptacle at

http://www.progressiveindustries.net/TT30R.asp

, but no 50's.

Anybody know where I can locate such? I have tried
the electrical supply houses in town, and have
found the closet thing on the internet on RV sites.

Thanks

Robert

 

[ehsjr]

Thanks for all the info. I have obtained 4AWG wire for the project. The
final piece of the puzzle to avoid the double male plug is a replaceable
female receptacle for one end of the extension cord to plug into the
inlet box refenenced above. The male ends are a dime a dozen at Lowes,
Home Depot, etc. The female is not. I have located 50 amp extension
cords for RVs, though generally only with 6AWG wire, and no more than
30' long, which have the female end on them, so I know they exist. I
have found replacements for a 30 amp female receptacle at

http://www.progressiveindustries.net/TT30R.asp

, but no 50's.

Anybody know where I can locate such? I have tried the electrical supply
houses in town, and have found the closet thing on the internet on RV
sites.

Thanks

Robert

You're looking for something like this?
http://www.passandseymour.com/products/product.html?c=CS6364
Give your electrical supply house the information.
You want a "50 amp cordset connector, Pass & Seymore model CR6364"
or equivalent. Perhaps they can order it for you.

Two good sites:
http://www.marinco.com/swdhome.htm
and
http://www.tiptopelectronics.com/pdfs/industrial/MARINCO 2003.pdf

You can order it online for $70.00 here (watch out for line wrap):
http://www.kennedypower.com/catalog...id=78&osCsid=687fd4625d896450af3db0b133178e82
or here for $45.00
http://www.nooutage.com/rjbc6364.htm
or here for $43.00 (watch the line wrap)
http://www.northerntool.com/webapp/...erformics&cm_pla=Performics&cm_ite=Performics

Check all the sites to make sure of what you are getting.

Ed