Generator Power Cable Question


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Old 10-09-10, 07:16 AM
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Generator Power Cable Question

I have a small generator that produces 230V @15 amp. The neutral and ground are bonded, and each hot has a 15 amp breaker. It has an L14-20 4 prong plug.

I want to run a single cable from this plug into my basement and have an L6-20 3 prong 230V outlet for my well pump, and two sets of 115v outlets (one on each pole) for other stuff.

Question: Can I safely use 25' of 12-2 cable for the run from the generator to the basement?
 
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Old 10-09-10, 08:05 AM
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Welcome to the forums! I would guess your well pump will require a 20 amp service to begin with, so your generator will be inadequate. Check to be sure.
If your well pump is hooked to your house wiring, it must be separated using a Generac or similar switching system to isolate the generator from backfeeding the main circuitry. This is a MUST!! What type generator is it? I can't believe you have a generator with such a small output.
 
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Old 10-09-10, 10:34 AM
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Originally Posted by chandler View Post
Welcome to the forums! I would guess your well pump will require a 20 amp service to begin with, so your generator will be inadequate. Check to be sure.
If your well pump is hooked to your house wiring, it must be separated using a Generac or similar switching system to isolate the generator from backfeeding the main circuitry. This is a MUST!! What type generator is it? I can't believe you have a generator with such a small output.
I have a Generac 3250 Watt Portable Generator. BTW the breakers are 14 amp, not 15 amp.

I'll basically be running the pump motor and everything else from extension cords, so backfeeding is not an issue. The pump will plug into an L6-20 3 prong 230V outlet powered by the generator.

I haven't measured the current, but the motor is 1/2 hp and the plate says 5.4 amps max. Hopefully there will be enough juice to run the pump.

I think I can get away with 12-2 cable, since it's rated 20 amp, and the most current that would flow through any of the 3 wires is 14 amps before the breakers trip... right? I have a lot of 12-2 lying around, and would prefer to use it rather than spend the $$$ on new cable.
 
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Old 10-09-10, 02:00 PM
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Update: The 12-2 cable is working fine so far. The pump runs and the breakers don't trip. Next up: furnace.
 
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Old 10-09-10, 02:45 PM
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Good the pump runs!
What type of furnace are you going to connect?

If you have a furnace with an electronic board you need to consider that some cct boards do not like the dirty power from an inexpensive generator.
 
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Old 10-09-10, 04:05 PM
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Originally Posted by GregH View Post
Good the pump runs!
What type of furnace are you going to connect?

If you have a furnace with an electronic board you need to consider that some cct boards do not like the dirty power from an inexpensive generator.
It's a 15 or 20 year old oil burner, with two circulating pumps. I don't think it has much in the way of electronics. The furnace guy will be here in a couple of weeks to clean it and prep everything for winter. I'll ask him about running it off a generator. In the meantime, it'll be changed from hardwired to 115v plug in. It's on a 15 amp breaker.

Is there a line conditioner of some sort that can be placed between the generator and sensitive electronics?
 
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Old 10-09-10, 05:33 PM
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I think you were extremely lucky to get the pump motor started with that small generator. To ask that same generator to power your oil burner pumps and possibly start the well pump at the same time is a stretch IMO. I think you need a bigger generator.
 
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Old 10-09-10, 05:39 PM
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Some jurisdictions may require the oil burner be hardwired not plugged in. Is it currently plugged in or were you planing to change it to a plug?
 
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Old 10-09-10, 05:58 PM
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There are transfer switches/inlets made specifically to plug a furnace into a portable generator.. Much safer than changing the furnace to plug and cord, and code-compliant too!

 
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Old 10-09-10, 05:58 PM
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Originally Posted by CasualJoe View Post
I think you were extremely lucky to get the pump motor started with that small generator. To ask that same generator to power your oil burner pumps and possibly start the well pump at the same time is a stretch IMO. I think you need a bigger generator.
If the furnace and well pump cannot run at the same time... fine. We'll work that out. 5.4 amps max (not measured) for the pump should leave plenty left over on both poles for other stuff. It's a small generator, but If I can run the pump, furnace, refrigerator, freezer, lights, TV and a computer (not all at the same time) things will be peachy. The well pump is the biggest current draw, and it works, so I'm encouraged.
 
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Old 10-09-10, 06:04 PM
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Originally Posted by ray2047 View Post
Some jurisdictions may require the oil burner be hardwired not plugged in. Is it currently plugged in or were you planing to change it to a plug?
It is currently hardwired. I will change it to a plug. The furnace guy will be by here in two weeks. We'll see what he says about it. It can always be changed back to hard wired.
 
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Old 10-09-10, 06:19 PM
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Originally Posted by JerseyMatt View Post
There are transfer switches/inlets made specifically to plug a furnace into a portable generator.. Much safer than changing the furnace to plug and cord, and code-compliant too!

That's a pretty slick switch, I haven't seen one of those. What distributor handles them?
 
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Old 10-09-10, 06:25 PM
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Don't forget the start up amperage required by your motor(s). You are basing things on the running amperage which is fine, but getting the small generator to do what you want may be pushing the envelope.
 
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Old 10-09-10, 06:45 PM
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Originally Posted by chandler View Post
Don't forget the start up amperage required by your motor(s). You are basing things on the running amperage which is fine, but getting the small generator to do what you want may be pushing the envelope.
Here's what the plate on the pump motor:



5.4 amps is the startup current. Right?
 
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Old 10-09-10, 07:09 PM
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Nope, 5.4 amperes is the full load current when supplied by 240 volts. The starting current could be 3 to 6 times the running current.
 
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Old 10-09-10, 07:13 PM
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Originally Posted by furd View Post
Nope, 5.4 amperes is the full load current when supplied by 240 volts. The starting current could be 3 to 6 times the running current.
Yikes. Luckily the 14 amp breakers do not trip. We'll have to be careful starting up the pump.

Thanks.
 
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Old 10-09-10, 07:18 PM
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The starting surge only lasts for a small time, usually a fraction of a second. Circuit breakers also have a time-delay built in just for this purpose.
 
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Old 10-10-10, 04:31 AM
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Originally Posted by Sped2001 View Post
It's a small generator, but If I can run the ... TV and a computer (not all at the same time) things will be peachy.
Running sophisticated electronics may not be a good idea. That genny does not produce "True Sine Wave" power. Instead, it generates what's called a "Modified Sine Wave", which can damage the power supplies that are typically found in computers and newer TVs. If you must try it on the electronics, watch closely for any waivering on the screens, and check the power supplies for excessive heat. Damage can happen in a hurry.
 
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Old 10-10-10, 12:32 PM
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That isn't an inverter generator, so it can't be modified sine. Any cheap generator (including the one the OP said he has) produces true sine wave. The problem with them lies in the fact that the sine wave frequency is tied directly to the engine RPMs. So you wind up with one of two problems: if the governor on the engine is set improperly the frequency will be either high or low.. Or, when a heavy load kicks on (like the well pump) that maxes out the alternator, it puts so much drag on the (undersized) engine that the engine slows down, which causes the frequency to dip out of range until the engine can recover. THAT is what is ultimately meant by 'dirty power' when talking about a generator, and THAT is what will cause issues with your electronics. Line conditioners can help with over/undervoltages and noise, but they can't do anything to correct line frequency fluctuations.

That being said, I personally have never had any issues with my electronics or the controller in my furnace. But I use a 10kW generator for about 6kW max worth of load. It has a larger engine so it isn't badly bogged down when something turns on. I also don't have a well pump. It just powers lights, TV, computer, microwave, refrig, freezer, gas range, and gas high efficiency furnace. I've watched the output on a scope, and when something kicks on, the worst the frequency drops to is 57Hz (within spec for pretty much anything out there). Basically the bottom line is you have to oversize the generator for the application to make sure its output remains as clean as possible under starting surges.
 
 

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