PDA

View Full Version : Transfere Switch Power Cord



rbertalotto
08-29-2011, 12:56 PM
My transfer switch is going to be mounted 75' from where the generator is going to be placed (in my garage).

I want to hard wire a cable from the transfer switch to a 30-Amp (4-Prong) Power Inlet Box to plug the generator into.

Is this length an issue and what size should the wire be?

SGW
08-29-2011, 01:43 PM
Although there may be code details I don't know about, I'd say you need 3-wire #10 with ground. I think you'll also need a circuit breaker at the socket end, otherwise, that 75' is not protected against overload.

I don't think 75' is enough to require a larger wire size, especially since use will be (hopefully) occasional and of short duration.

But there are better electricians than me on this board who may know stuff I don't about generator wiring requirements.

Rosco-P
08-29-2011, 01:52 PM
75' of #10 copper wire in PVC conduit will result in a 2.3% voltage drop. An acceptable value.

How are you going to pipe the exhaust outside?

rbertalotto
08-29-2011, 03:19 PM
I haven't worked out the exhaust yet, but for now I place the generator at the opening of my garage and leave the door open 2 feet for air circulation and exhaust.

I will most likely install a thru-wall exhaust port and a big muffler to keep the noise down.

I found a 75' pre-made cord for hooking the genset and the transfer switch. And it is indeed 10g. You guys know your stuff!

http://www.gen-tran.com/eshop/10Expand.asp?ProductCode=RJB10475

THANKS!

Jim Caudill
08-29-2011, 03:42 PM
Really think this thru as you designing the generator operating location. Maybe have a simple enclsoure that is well-vented to the outside. A couple of years ago, in an area not far away from me, a couple bought a house that had been unattended for a while and the power had been "turned off". We were experiencing heavy rain, and the basement had a sump pump, and the sump would collect water. They setup a portable generator and let it run in the basement. The generator ran out of gas, and had been sitting there for some time (hours? days?) when the man went to see how the basement was doing. He entered the basement and did not return, his wife/girlfriend went to check on him, and she did not return. Finally, a neighbor alerted the proper folks, and they found both of them dead in the basement. They essentially descended into a "gas chamber" filled with Carbon Monoxide. With no generator running, they didn't realize the danger.

I have a motorhome with a generator mounted under the bed. It doesn't bother me as I know the installation well, and I have a CO detector under the bed as well. I also have a combination detector about 6 feet away in the galley area.

I'm just saying, think it thru.

Carld
08-29-2011, 04:26 PM
I would not put the generator in a garage ESPECIALLY if it's an attached garage. Even a separate garage can fill with fumes and kill you.

Last winter a couple was killed here with a generator in their garage attached to the house.

Also, I would use 4 conductor #8 wire to go 75' because if your pulling almost 30A for any period it may cause issues with #10 wire.

Black_Moons
08-29-2011, 04:30 PM
Put the generator out into a doghouse, Far away from the real house.

Forrest Addy
08-29-2011, 04:31 PM
Did I miss what size generator? You need to size the wire for the generated amps. How can anyone offer advice on sizing a wire to feed a transfer switch without knowing the size of the generator?

99% of packaged home emergency power systems have incorporated in them circuit protection in the form of a main breaker on the control panel of the generator itself. Is that breaker present in the generator's panel? If so OK. That's done. If not you need a local breaker or disconnect within sight of the generator or however the Code is worded. Look it up.

You should find in the information packet that came with the generator detailed instructions and specifications for connecting the generator to the transfer swithch, wiring the transfer switch into the home electrical panel, etc. If the generator is a current model you may be able to find the info on line. Get that information. It will save you from a lot of engineering.

For example, here the Generac web page for their owner's manuals: http://www.generac.com/Service/ManualSearch/

I see 8 and 12 KW gen sets in the big box stores. This is serious capacity that may require # 6 or #4 load conductors. What does your local code and NEC have to say? Local code and NEC are the minimum requirements any elecrical installations have to comply. They supercede popular opinions found on message boards and coffee shop anecotes. You want an electrical system that will pass local inspection and be reliable and simple to maintain over the years, pose no fire and safety hazards, start instantly and change over promptly in the dark by your wife or older more responsible kid when they're still half asleep.

Ideally, the generator should be provided its own little doghouse. Better check local code about running a generator in a semi-enclosed space even in a detached garage - NEVER in an attached structure or partly enclosed deck with a door or window opening on them. Carbon mobnoxide you know. Besides the hazard the exhaust smell will permeate every surface and persist - even when running from LPG or natural gas.

Too bad home generator sets are never designed for heat recuperation. For very watt of power generated there are 4 watts of heat wasted. That's 4 watts of heat you are paying good money for that could heat domestic water, dry clothes, space heat, etc. What a waste.

Don Young
08-29-2011, 10:55 PM
I too have thought about how nice and easy it would be to install my generator in my attached garage where there is natural gas and an outside wall for the exhaust. However, I have decided that it is too hazardous and is basically forbidden by safety codes. Mine will go outside in its own shelter and I strongly suggest you do the same. Don't just think about normal conditions, think about what could go wrong.

Rosco-P
08-30-2011, 11:44 AM
My transfer switch is going to be mounted 75' from where the generator is going to be placed (in my garage).

I want to hard wire a cable from the transfer switch to a 30-Amp (4-Prong) Power Inlet Box to plug the generator into.

Is this length an issue and what size should the wire be?

From the above info. one can conclude that the voltage is 220vac, the run is 75 feet and the current is 30A. For the purposes of the voltage drop calculation, the conductors would be copper.

PixMan
08-30-2011, 01:57 PM
I too have thought about how nice and easy it would be to install my generator in my attached garage where there is natural gas and an outside wall for the exhaust. However, I have decided that it is too hazardous and is basically forbidden by safety codes. Mine will go outside in its own shelter and I strongly suggest you do the same. Don't just think about normal conditions, think about what could go wrong.

You should consider going to a natural gas fired generator, as it sounds like you're already close to being set up right for it. Sell off the gasoline powered one or keep it for powered tools you need to use away from the house.

I have natural gas in the the house, but right now don't have the funds to buy and install the 20Kw unit I'd like.

Scottike
08-30-2011, 02:25 PM
If your Hardwiring the run from your genset to the transfer sw. why do you need a $200 extension cord?
Hardwiring presumes a permament installation, ( ie: conduit, through walls, buried, etc.) save some money and use the properly sized romex or indvidual stranded conductors properly marked to id whick is which. Available from any electrical supply house.

rbertalotto
08-31-2011, 05:13 PM
I only referenced the extension cord to validate the 10ga suggestion.........

rbertalotto
08-31-2011, 05:14 PM
I have a kit to convert the generator to multi-fuel, Gasoline - Propane - Natural Gas.

Just need time to plumb the house.............

lakeside53
08-31-2011, 05:38 PM
If you go with natural gas, you may need the gas company to upgrade your meter or pressure regulator. Many standard house regulators cannot supply the generator demand. And you only get about 70-80% of the power verses gasoline.

rbertalotto
08-31-2011, 07:04 PM
The kit I have is called a "Low Pressure Propane / Natural Gas" kit. It says that a standard residential gas pressure is sufficient.

You are correct about the power loss, but on constant RPM motors like a generator, it might not make as big a difference.

I've talked to folks that did the conversion and they noticed no change in generator performance.

lakeside53
08-31-2011, 09:35 PM
In that case they aren't loading their generator above 70-80% of the rating ;)


As for the regualror - it depends on your generator size, existing house load and house regulator. In my case, I can't run my 16hp (18?) generator without a larger flow (not higher pressure) regulator from the gas company. When the generator is running, you still need to run the existing gas appliances, some of which are gas hogs - like a furnace.