Analogy

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tryinghard

tryinghard

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What would be a good analogy (word picture) to give someone that doesn?t believe knowing the actual load is necessary to size a standby backup generator? These type of people believe guessing is just fine. I on the other hand believe a load calculation is always appropriate.
 
tryinghard said:
What would be a good analogy (word picture) to give someone that doesn?t believe knowing the actual load is necessary to size a standby backup generator? These type of people believe guessing is just fine. I on the other hand believe a load calculation is always appropriate.
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Sizing a standby generator is like sizing an engine for an airplane. If it don't have enough output, you don't get off the ground!
 
Would you run a whole building on one car battery/inverter ????? No..... then why undersize the generator. If thats the case go buy the 1000 watt honda.
 
I'm going to buy your house, and I'm going to guess how much you want for it and place this wad of cash in an envelope without you knowing the amount, and we sign the contract. At the settlement table, after the transfer, you get to open up the envelope and count your money, and you hope it's at least what you needed.

kent
 
You guy's got me going now. :)

It?s the same as assuming interstate traffic should be fine on a rural highway. You can regulate who uses the highway at certain times, even regulate what type of vehicle, but this doesn?t change the demand for the interstate and it does not eliminate the potential clogs.
 
tryinghard said:
...knowing the actual load is necessary to size a standby backup generator?...
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If you believe their result will be undersized, you have a point and can easily prove it.

If you believe their result would be grossly oversized, possibly because they are using max rated loads or max circuit design data without regard to actual and future usage of the built-in electrical capacity, you would also have a point, but it might come down to a judgement call. One aspect is that running a generator at very low amounts of it's rated load capacity usually invites problems.

But, if you believe their result is slightly oversized, I would accept it.

kent
 
tryinghard said:
What would be a good analogy (word picture) to give someone that doesn?t believe knowing the actual load is necessary to size a standby backup generator? These type of people believe guessing is just fine. I on the other hand believe a load calculation is always appropriate.
Click to expand...

No idea what sixe we are talking about but lets assume there is a $20,000 generator and a $30,000 generator. You go with the $20,000, and pay to have it installed, say $5,000. Then after the next power outage, you find out you generator is too small. $5,00 to remove it, $30,000 for the new generator, $5,000 to install. You just paid $60,000 for a $30,000 generator. A $1,000 load study would have saved you $29,000.
 
zog said:
No idea what sixe we are talking about but lets assume there is a $20,000 generator and a $30,000 generator. You go with the $20,000, and pay to have it installed, say $5,000. Then after the next power outage, you find out you generator is too small. $5,00 to remove it, $30,000 for the new generator, $5,000 to install. You just paid $60,000 for a $30,000 generator. A $1,000 load study would have saved you $29,000.
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zog, if i give you my boss' phone number would you explain this to him, he wont listen to me.
 
tryinghard said:
What would be a good analogy (word picture) to give someone that doesn?t believe knowing the actual load is necessary to size a standby backup generator? These type of people believe guessing is just fine. I on the other hand believe a load calculation is always appropriate.
Click to expand...

Trying-
You didn't tell us if the application is Residential, Commercial, Industrial, nor do we know the magnitude. In most any case, I'm with you that a load calc is "always appropriate". Here is an example of where I wouldn't care: Household plugin standby - buy anything you want.

However, there are a lot of people on this forum that think "Rules of Thumb' are okay. To me, "guessing" and "ROT" are the same thing.

So, question for those who think ROTS are okay:

Using the information Trying gave us, is using an "ROT' or "guessing" okay? If not, why not?

cf
 
dropping the clutch

dropping the clutch

THe best way I describe a electrical startup load is to compare it a to 3/4 ton pick-up truck. I tell them that closing the switch (inrush) on a electric motor is like dropping the clutch. Most people can't fathom that a 5hp generator will not start a 2HP air compressor.. I also go onto explain - a motor load is compable to- truck loaded down -will the sqaut on it, add a 20 ft trailer loaded also, then stick it in 3rd gear rev-it-up to about 3000rpm and dump the clutch. (farm-boys get the analogy ) .
 
It's like ordering food for a party but you don't know how many people are coming, you

know you can feed some of them or maybe all of them and have leftovers or maybe run

out real fast and look stupid.
 
Generators have a purpose just like a gas jug has a purpose. The gas jug is purposefully designed to hold gasoline and the likes at a particular volume. If its uses are within its intended design then all is well; but if not, well then things may not be so good and it?s the not so good that will be situational.

A good analogy can often help the questioner better understand because they usually need something to relate to and electricity?s uses can be elusive to them.

It?s really not up to a qualified journeyman to explain why something done wrong has not hurt someone, caught fire, or is inadequate rather I think we?re most suited to explain how it can be rather than how it can?t; permissive like the NEC.
 
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