Portable generators

[Norm Frechette]

I survived Tropical Storm Irene with flying colors (nothing missing on my mobile home) but still out of power.

I am considering buying a portable generator and was wondering what size would be appropriate for a mobile home.

Does anyone has a setup they can recommend?

Thanks in advance,

Norm

[JD]

When under emergency generator power, you would want to limit power usage as much as possible. I wouldn't use an electric oven at all for instance. You can either get a smaller unit just to run certain appliances with extension cords or a larger unit to supply the whole home from the lifeline at the utility pedestal. A plug adapter would probably be needed. Nothing should be powered directly to the breaker box. The generator must be isolated from the direct home wiring so emergency crews won't be accidentally shocked when working on lines in your area. Using all extension cords of appropriate gauge direct to appliances or connecting at the lifeline isolates the generator when a mobile home is set up properly.

You are really looking at the amount of power that would be required simultaneously. Electric motors also need to have an additional initial surge power wattage, which has to be considered in adding up needed watts. Lot's of reserve power overhead is the safe way to go. I found the following link with a google search on "surge power requirement generator", without the quote marks (boolean operators). It answers your question well. Here it is.

http://www2.northerntool.com/generator-buyers-guide.htm

[Greg]

Well norm, I'm sure that I have people I know working to get power restored in your area. The best man at my wedding is one of the Emergency coordinators for National Grid in Syracuse, when I talked to him last week be fore the storm he knew he would be somewhere, just not sure where.

As JD said, you need to figure how much of your home you want to be able to run. If you want 100% I would guess somewhere in the 10-12KW range, if you have electric heat or stove possibly more. Now the other thing you need to think about is fuel for the generator. For a fixed standby unit I would go with a natural gas unit, storms don't usually interrupt the gas supply. Remember that gas stations need power to pump gas to power your generator. A gas generator can suck 5 gallons in 8 hours with no problem, in a week's time that can be a lot of gas.

Greg

[cmanningjr]

Here's an example for you. If you buy a 8000kw generator. ($800 model at lowes)

Take the 8000 and devide it by 120V (normal appliance/lighting power)
You will get 66.6 something AMPS. this is under max running load.


One 60 watt light bulb pulls .5 amps
Read back of appliances to see what they pull and DON'T go over 60 amps(Using example generator)

It's HIGHLY unlikely you will be able to run your stove or ac. Keep in mind that everything you turn on adds to it. We would turn everything off at night and turn on the water heater so we would have hot water for showers. And turn it off durring the day for TV and Microwave.

DON'T use cheap extension cords. THEY ARE DANGEROUS. Get professional to connect it for you and be careful.

I'm a licensed electrician and recommend you getting a professional to connect it and TURN THE MAIN BREAKER OFF if not using a transfer switch.

[JD]

Great post cmainningjr. I really like the water heater suggestion.

[cmanningjr]

Thanks JD, our water heater would hold hot water for 2 days, enough for quick showers.

It's all about the math and timing when running a portable generator. They can bring some normalcy back durring an emergency situation. Also keep in mind that they run more efficent under max load.

[Eric_v]

Cmanningjr is incorrect. It's 8000 / 240v. It would be a 30A generator. For 60a you would need a 16kw generator and them puppies are far from portable.

I should clarify. He is correct that under 120v you would indeed have 60amps. BUT, for a electric hot water heater it runs of 240v so you would have to divide by 240 not 120. Electric ranges, dryers, cooktops, furnaces, etc. Any device that operates at 240v you divide the wattage by the voltage so...

[cmanningjr]

I was not incorrect. I gave the example for 120 amp devices. So, 8000 divided by 120 would be 66.666. THEN I gave an example for what I did durring the April 27th storms WITHOUT calculations for the waterheater.

[Eric_v]

But you are incorrect. Any 8000 watt generator has a hookup for 240v which supplies 30amps across each "leg". So when you put a outside generator receptacle to "back feed" into your panel you will wire the panel as 240v which only gives you 30amps per "leg".

My proof is in the installation. No electrician in their right mind would put a 2pole 60a breaker for a 8kw generator. It would in fact be a 2pole 30.

[cmanningjr]

My proof is in the math. 30 + 30 = 60 Where did I say what size breaker to use?

I did NOT give an example of how to connect it. I said to get a professional to do it.

You apparently know how to do this BUT you didn't fully read what I wrote.

[Eric_v]

Agreed, 30 + 30 = 60 but you will not have 60amps running through one extension cord you will only have 30 and that's IF the generator has a 120v 30a receptacle. Most generators I've came across have 2 GFCI's rated at 20a each and one 30A 240v connection point for the 'backfeeding' cord.

Maybe I am misreading what you are saying but I don't want someone reading this and taking away from it what I thought you were saying and that they would have 60amps running through a single connection.

So my apologies if I upset you but to me it read like you were saying you'd have 60amps over one connection.

[cmanningjr]

It is hard to explain how to figure out what size generator someone would want/need to run durring an outage. Plus take in the factor how much someone would want to spend.

My example wasn't inteded to be used as a guide to connect a generator. I took the cover all of getting a professional to install it. And still stand on that. Believe me, I've seen some scary stuff. (I like backfeeding with a twistlock) Good luck finding one after a storm.

But I do see what you are saying. Now worries. WE are just here to help.

Wire size and overcurrent protection is VERY important as Eric was saying. And is determined on what method is used to connect the generator to the home.

[Greg]

From where I sit I think that you are both saying the same thing only differently. A 220 v line is actually 2 110v lines. if the TOTAL is 30amps @220 then it is 2 110v lines @15amps.

This is the reason we really do not allow a lot of electrical advise here. One mistake or wrong advise and someone's dead.

Back feeding is dangerous, I work an Ice storm on Long Island doing tree work in the 90's. I was with the line crews, one of the line men grabbed a wire that was visibly on the ground broken at both ends and got knocked. The unknown variable - the house in the middle had a generator back feed without pulling the mains.

Greg

[Norm Frechette]

thank you for answering my question but it seems that i have stirred up a hornets nest. that was never the intention. i only was asking because i thought maybe some home owners might have gone through a similar situation and added a generator for emergency purposes.

i did no know that these types of questions are not allowed.

it appears to me that this was not the best place to ask my question and i would be best served to contact a local licensed electician to resolve my generator problem.

good luck on your forum

norm

[Greg]

Norm, it's not that they are not allowed, but we try to give a more general answer. Our thinking is that if someone has to ask specific questions concerning Electrical work, they really shouldn't be messing with it. As I said, one wrong move or bad advise could lead to a death, And no one here wants that.

Greg