Calculating Load for a Generator?

[roger]

Re: Calculating Load for a Generator?

Dave, I have always let a manufacturer calculate the generator size. There are a number of things to consider besides what has been touched on. For example, typically a LP or NG generator is sized larger than a diesel, altitude comes in to play, for just a couple more.


Tell these people that even hospitals with million dollar Gen sets don't run everything in power outages. I know, not what they want to hear.

Roger

 

[davedottcom]

Re: Calculating Load for a Generator?

Originally posted by roger:
Dave, I have always let a manufacturer calculate the generator size. There are a number of things to consider besides what has been touched on. For example, typically a LP or NG generator is sized larger than a diesel, altitude comes in to play, for just a couple more.


Tell these people that even hospitals with million dollar Gen sets don't run everything in power outages. I know, not what they want to hear. I've been doing that for years! I often tell my customers there are millions of ways to wire something wrong, but I'm not willing to do any of them. If they can't afford to do it right, they simply can't afford it.

Let the manufacturer calculate the size! Good idea! Take the burden off me...I could use one less straw on my back!
Yes, I'm also aware of the difference in output between LP and other sources, actually I didn't know that until about 1 week ago, very interesting.
The problem is still mine since the customers buy the generators FIRST then look for someone to rig, I mean hook it up. So by the time I get there, they've been promised the world and they look at me to deliver. That is when I need to be able to do a calculation to determine if it can be done with the existing generator or not.

Dave

 

[rick hart]

Re: Calculating Load for a Generator?

Kick was a wonderful scientific term I came across today in Engineers Wannabe Word for the Day calendar......maybe not.
KVA would be a better term- how many amps are required at nominal voltage. Total connected load needs to be considered when sizing a generator. But if you size a generator by only the motor's Full Load Ampere on the nameplate, the motor will likely not start especially if it has a high code letter.

 

[davedottcom]

Re: Calculating Load for a Generator?

I just spoke to a very knowlegeable & helpful woman at Generac. After explaining the chaos I'm finding everywhere we had a good laugh about all of the morons out there hooking these things up wrong.
She said "I deal with those morons everyday!"
...anyway...
She seemed reluctant at first, but once she realized I was one of the "Good guys", She confirmed very quickly that most homes will need at least a 25kw generator if they expect thier HVAC systems to operate.
She also added, they only warranty the generators that are installed by thier "certified" installers. Basically, have it installed correctly or at your own risk.
Like I said before, if you can't afford to do it correctly, you simply can't afford it.

Thanks for all the input guys.
Dave

 

[vasparky27]

Re: Calculating Load for a Generator?

It's getting fun here in VA beach area too.
so far in the last year I have helped too install 4 15kw generators 1 10 kw generator and 2 7kw
currently working on a 25kw THIS THING IS A BLAST!
125A breaker at the unit 1/0 subfeed underground in pipe is as far as I've gotten so far and the home owner wants too feed his WHOLE 300a service!

I'll keep ya posted on the fun
any suggestions on the 25kws? never installed one b4
THANKS

 

[benaround]

Re: Calculating Load for a Generator?

ddc,

Have you looked at Annex"D" example D2(a) at the back of NEC? This would also be good to show customer what's going on.

frank

 

[davedottcom]

Re: Calculating Load for a Generator?

Excellent point Frank, D2(c) says (see 220.82) which 220.82(C) clearly requires the "largest" of the HVAC loads to be figured at 100%.



Dave

 

[luke warmwater]

Re: Calculating Load for a Generator?

Dave,
I take it that you are not a certified Generac installer?
I'm not. Although I have about 6 messages from them wanting me to join them.

I personally think that the Cutler Hammer standby generators are better.

Ir this link works, it is a CH generator sizing chart:
CH link

There are differences between the 2 manufacturers.
Also, from what I remember, the 15kw Generac is not a true 15kw.

 

[luke warmwater]

Re: Calculating Load for a Generator?

That link didn't work.

Click HERE and then click on the 'generator sizing calculator' link.

 

[davedottcom]

Re: Calculating Load for a Generator?

Luke, Very cool link, thanks.


No, I'm not a "certified" installer for Generac....not yet! I'm definitely thinking about it. I wanted to get my (virgin) install under my belt to get a handle on the whole set up, and to see what kind of time it actually takes.
My 1st install: 6 hours! :roll:

I'll check out the C.H. Equipment sometime. Everything I've seen down here (FL)is Generac/Gaurdian.

What's the "benefit" of being one of their "Certified" installers?

Thanks again Luke,
Dave