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Joined: Jul 2004
Posts: 9,923
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G
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Reno I agree your method may sound like common sense but I am not sure it satisfies 702.5(b)(2)(a).
The IAEI guys were really banging this around a while ago. I will go see what they came up with.
I do remember they said you can allow the user to do load management on a manually switched genny but when it was auto, they were more leaning toward total attached load. That would be the load calc for the house if this switched at the service disconnect ... I think.
That is how I remember it. I will see if that is right.


Greg Fretwell
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Joined: Jul 2004
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G
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This was the last word on the discussion and the participants seemed to agree.

Quote
Seems to me the first question to ask the customer is do they want to have their generator start automatically or are they wanting to transfer it manually. If they select a manual transfer then we should be able to connect any size generator to the "whole house" and the customer can then micro manages their loads.

If they select an automatic system (and most will) then the generator should at least be able to handle any loads that are on the system when no one is home, the A/C, refrigerator, pumps, etc. So a whole house back up may not include the washer, dryer, range, oven, etc.

Typically when sizing a generator for a customer I would add the starting kW of the largest motor together with the running load of any other motors to be backed up and then add the kW of any non-motor loads, and then adding 20% at the end.

Educating the consumer is the key, if they are going to own their own power supply then there should be some responsibility on their part to understand the system.

To me the issue is not so much the customer having a professionally installed system but the one buying a portable at the last minute and backing up his house through the dryer receptacle.
_________________________


Greg Fretwell
Joined: Jan 2005
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Cat Servant
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Greg, I must admit that even I'm not sure my method complies with the code as written. In this instance, I will fault the code, rather than the method.

After all, these are optional systems - that is, 'nice to have' systems. So what if the system fails? Just as important, what's the worst that can happen? The genny stall and quit running? That's not that big of a deal with an optional system.

I can see where you might want to be more thorough in the design of a genny for backing up critical systems, but that's not what we're talking about here.

Just as important -as I've already explained- is that an ordinary load calc will result in your having too large of a generator, and that's worse than if the generator were too small. Our 3 watts/sq. ft. figure is a lot of power alone, an amount that's rarely fully used.

I really hope the 2011 cycle addresses this section; it's bad code.

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