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-   -   Generators and AMPS (http://www.diychatroom.com/f18/generators-amps-13464/)

DaveSherman 11-15-2007 06:29 PM

Generators and AMPS
 
Hello Experts:

I purchased a Honda 5000W generator. When I made the purchase I was only concerned with wattage.

I am getting ready to purchase a gen-trans switch, my concern is this:

There are 2 120 volt 20 amp receptacles on the generator and one 240 volt 20 amp receptacle. The only 30 amp receptacle is for 120 volt power.

4 of my users inside the panel of my home are 240 volt 30 amp.

Will I damage the appliance pumping 20 amps into a user protected by a 30 amp breaker?

I plan on using a 25' #8 or #6 wire from the generator to the transfer switch.

Thanks in advance!

Sammy 11-15-2007 07:29 PM

How much do each of the 30 amp circuits in the breaker box now actually draw? [sum of the appliances on each circuit]

Backfeed into the electrical service when the power is out is also a major concern to be aware of.

DaveSherman 11-15-2007 07:37 PM

Hello Sammy:
 
I don't know, the only 30 amp circuit I am planning on using is a well pump, I know it is 3.5HP I will dig through my files (just moved) and get that for you.

By the way, what is backfeed? I was planning on turning off all breakers unless we were going to be powering that branch circuit, and when we drew water I was going to have them all off save for the well.

Sammy 11-15-2007 08:25 PM

Backfeed is where your generator feeds back thru your breaker panel into the power line leading to your house and could be deadly to a utility worker repairing a line.

If your not running a direct line from your generator to whatever applicance your running [like with an extension cord] versus wiring into your panel, you probably should consult a qualified electician.

My math is a little rusty but I think a 3.5 HP motor would consume around 2600 watts. I'm sure Andy and Stubbie will correct me though...

frenchelectrican 11-15-2007 08:52 PM

I hope you are not kidding with 3.5 HP pump motor that do draw a bit serious amout of power during start up.

for 3.5 HP single phase motor wired on 240 volt it will draw roughly about 4 KW easly.

and the 5 KW genny you have there let me tell you one thing i am sure it will do one thing surefire is stall the genny fast when try to start up the well motor like that big.

the starting current is anywhere from 3X to 6X of running current to get the motor up to the speed and i dont think your generator have much surge wattage something like 6500 surge wattage and the well motor starting i am sure it will nail it fast,

i did see it happend before.

but you can try to test it by running a tempory wire/ cord set up and see if the generator can take full load which i doubt becuse the 20 amp repctale you have there it will get over the limit fast.

and you have 30 amp 120 v repctale from that generator that was designed in instering way.
do that generaor have 120 or 120/240 volt switch ? if so sometime it called full power switch which it do is change the windings to useation both winding on 120 volts.

my rough thumb of rule 2.25 KW per hp [ single phase ] that how i sized the generators.

Merci, Marc

spebby 11-15-2007 11:34 PM

The way a transfer switch prevents backfeed is you move the circuits to be powered by the generator to the transfer switch from your existing breaker panel. You also supply the transfer switch with power from the meter. When the power goes out, the transfer switch can be switched to the generator with a "break before make" switch. This prevents power from the generator from reaching the transmission lines.

With a 5000 watt generator you can have a total load of 40 amps at 120 volts (4800 watts) or 20 amps at 240 volts (4800 watts). The actual circuit breaker in your breaker panel is sized to protect the wire, it does not mean the load on the circuit. To determine the actual load you would need an Amp meter.

This link may provide you with more info.:

http://mayberrys.com/honda/generator/html/transfer.htm

DaveSherman 11-16-2007 07:16 AM

Out in field today
 
Hello Speby, Marc & Sammy:

WOW! I can't thank you enough for this information.

I will be in the field today but will look tonight tomorow am for the well pump specs. We live on a mountain so the well is 850' deep in solid granite! I remember for sure they ran #6 wire 350' from house to well and then 600' more down the hole.

I do believe they said it was a 3 phase motor and I know there is a controller in the basement that tells the pump the demand, apperently it is different then pumps we had, one flush, one hand wash and the pump comes on, a shower really gets it pumping.

Anyway once I locate the box of stuff I got from the well guys I will post the info I have.

Again, THANKS for this info so far!!!!!!!

elkangorito 11-16-2007 12:30 PM

Is the generator 3 phase or single phase? I will assume single phase (probably incorrect). If it is single phase, you will not be able to run a 3 phase pump by it.

Anyway, the OP has 2 x 120 volt 20 amp receptacles, 1 x 240 volt 20 amp receptacle & 1 x 120 volt 30 amp receptacle available on his generator. According to my calculations, he can only use at any one time, one of the following;

1] the 2 x 120 volt 20 Amp (40 Amps) receptacles or,
2] the 1 x 240 volt 20 Amp receptacle or,
3] the 1 x 120 volt 30 Amp receptacle.

Marc, although I generally agree with you, I disagree about starting currents. Assuming that 1 HP = about 750 Watts, 3.5 HP = about 2600 Watts. At 240 volts & assuming a Power Factor of 0.8 (for a motor), this equals about 13.5 Amps Full Load Current. Unlike yourself, I assume a starting current of between 4x to 8x the FLC. Assuming the minimum (4x), 4 x 13.5 = 54 Amps. 54 Amps x 240 volts x 0.8 = 10.4kW, which is well above the generators capacity (double). I'd doubt that it (the generator) could cope with such a high starting load...especially intermittently.

In answer to the OP's question, "Will I damage the appliance pumping 20 amps into a user protected by a 30 amp breaker?". Well, I don't know. This cannot be clearly answered because you must supply us with the details about what you want the generator to supply. Ie you must give the wattages and/or currents & respective voltages of each piece of equipment to be supplied. Not only this, you must also give the electrical technical details of the generator. Until this information is provided, a clear & concise answer cannot be given.

In the meantime, your generator is not able to supply your pump without sustaining damage (reduced life). While supplying this pump, it (the generator) must not supply anything else.

frenchelectrican 11-16-2007 03:18 PM

Quote:

Originally Posted by elkangorito (Post 74288)
Is the generator 3 phase or single phase? I will assume single phase (probably incorrect). If it is single phase, you will not be able to run a 3 phase pump by it.

Anyway, the OP has 2 x 120 volt 20 amp receptacles, 1 x 240 volt 20 amp receptacle & 1 x 120 volt 30 amp receptacle available on his generator. According to my calculations, he can only use at any one time, one of the following;

1] the 2 x 120 volt 20 Amp (40 Amps) receptacles or,
2] the 1 x 240 volt 20 Amp receptacle or,
3] the 1 x 120 volt 30 Amp receptacle.

Marc, although I generally agree with you, I disagree about starting currents. Assuming that 1 HP = about 750 Watts, 3.5 HP = about 2600 Watts. At 240 volts & assuming a Power Factor of 0.8 (for a motor), this equals about 13.5 Amps Full Load Current. Unlike yourself, I assume a starting current of between 4x to 8x the FLC. Assuming the minimum (4x), 4 x 13.5 = 54 Amps. 54 Amps x 240 volts x 0.8 = 10.4kW, which is well above the generators capacity (double). I'd doubt that it (the generator) could cope with such a high starting load...especially intermittently.

In the meantime, your generator is not able to supply your pump without sustaining damage (reduced life). While supplying this pump, it (the generator) must not supply anything else.


Elk:

true but for the well pump the OP gave to us this is not a common size what i know of 3.5 HP and i used my normal motor amparge chart and it just don't " line up " with the facts unless that OP did have 3 with the conveter and have to keep in mind if the OP give us the 3 motor rating but possible a oversight that if going from 1 to 3 have to use the 1 figures to get the correct amp rating so see if it will " fly " with this patair size genny.

but before it get out of the hand with 3 motor issue there is other possiblty that the 1 motor is a 3 wire motor instead of 2 wire motor so we will wait until the OP get the all the facts in first before we can give the correct answer.

Merci, Marc

DaveSherman 11-16-2007 06:44 PM

Hello:
 
Wow, i feel pretty stupid as my brain hurts trying to wrap my mind around this.

I contacted the well driller this morning and got this reply back, I hope it is of help.

This is a 3 HP motor.
230 volts.
8.1 amps when running.
Start will be higher.
A 5000 watt generator should start and run this unit.

Thanks in advance!

Andy in ATL 11-16-2007 08:16 PM

The running part, maybe. It is that pesky starting part...:whistling2:

Edit to add... That seem big to me(the motor) Seems like the few I've wired were 1 to 2 A. Maybe I'm wrong . OOPS 850 foot deep well. The only thing that Genny is going to be running is the well pump?? That being said...The well driller very well may know what he is talking about. But dang that is a big ole pump on a little genny!

frenchelectrican 11-17-2007 12:33 AM

Quote:

Originally Posted by DaveSherman (Post 74365)
Wow, i feel pretty stupid as my brain hurts trying to wrap my mind around this.

I contacted the well driller this morning and got this reply back, I hope it is of help.

This is a 3 HP motor.
230 volts.
8.1 amps when running.
Start will be higher.
A 5000 watt generator should start and run this unit.

Thanks in advance!


ok but hate to " debate with you " i came up two completly diffrent numbers and it dont even get close to the numbers i came up and i will give you the typical amp rating with common one

single phase 230 v 17 amp

three phase 230v 10.4 amp

this is a typical amparage between the two

but the main condersation i have some issue you will see it is during start up time when the motor crank up to the speed it will draw a bit of current to get it start

like example you say 8.1 amp running but starting amp i am talking about anywhere from 24 to 64 amp starting amp [ that will just last a few seconds to get up the speed]

and with your 5 KW genny it might barely make it if your surge wattage is over 6500 watts you might squeak by.

if more question just ask us

Merci, Marc

DaveSherman 11-17-2007 05:00 AM

Hello:
 
Yes it is a deep hole!

We will only run this circuit when we need water.

Marc, I'm not certain on the amperage I last posted, that was a cut and paste from the well drillers email on the motor specs question...

My biggest concern is that I am only able to plug in on a 20 amp plug do you think this will be an issue now that we have the specs on the motor?

Thanks, Dave

J. V. 11-17-2007 02:11 PM

Start the generator BEFORE you load anything. The breakers on the generator will trip if the load is to high. No worry about the generator if the breakers operate as they are designed.

This pump must be 3 phase. 8.1 amps at 240 volt indicate this is three phase motor. A single phase motor at 240 volts would draw 17 amps. How lucky can you get. 3 phase power. I'm jealous.

The distance to the pump and the starting current is my issue. You have almost 1500 feet of wire. If it worked before great. They are correct about starting current. I use 8xFLA = starting current
Have you thought about an interlock kit instead of the expensive transfer switch? It's not automatic so you would have to manually transfer. $60-$150 bucks.

DaveSherman 11-17-2007 02:18 PM

Hello JV:
 
I never heard of an interlock switch but I am going to get one, the cost is super, I can't thank you enough!!

Yup off the house power the pump has been working great!! "Knock wood"

I am 99.9999% certain that they told me it is a 3 phase pump, I used to fly and I remember thinking oh, that is like the inverters in the plane (becuase I really know very little of electricalal stuff.)

What is FLA?

Take care,

Dave


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