Am I wrong?

[Steven Hockstein]

Mike, Thanks for the technical info. It is nice to know but I will never do this type of calculation as part of a home inspection. To me it is like calculating BTU requirements for a heating system and span ratings for floor joists as part of our home inspection. I specifically exclude technical analysis from a home inspection and offer more comprehensive analysis for an added cost.

The question is where is the line between what we do as a home inspection and technically analyzing the systems and structures in a home? I guess it is for each of us to decide where that line is for ourselves. We just need to be clear of what services we are providing for our clients and that we are meeting the standards or licensing requirements that govern our work.

When I noted that the electrical panel was overloaded I was referring to the fact that there was too much wiring stuffed into the panel box and what appeared to be an excessive amount of mini-breakers. Along with other electrical issues in the house, this triggered my concern about the quality of the electrical work. I punted to the electrician.

[hausdok]

Steve,

It arrived in my in-box. I'm just passing it on for folks to use it as they see fit. Me, I can't add a column of six single-digit numbers together five times in a row and get the right answer - I'm not kidding when I say I can't do second grade math - there's no way I'd attempt to do that calculating. I'd rather have my fingernails pulled out one by one verrrry slowwwwly.

[Marc]

I plan to use Holt's load calc article as an attachment to reports that recommend such a calculation. My boilerplate will say 'ask an electrician to complete a load calculation on the house, or do it yourself if you're up to it'

Any copyright issues with that?

Marc

[Jim Port]

Not to derail this thread, but what rule should be followed in this scenario?

150 amp panel 2 poles using this equation 150 Amp x 2 Poles = 300 / 10 = 30. There should only be 30 breakers.

The panel model number is rated for 40 breakers- qoc40uf.

Do you go off the equation or the manufacture label?

The panel listing is used, not an arbitrary formula that assumes a load of 10 amps per pole.

[mjr6550]

First, look at the panel diagram. These often show the allowable number of tandem breakers, and where they are allowed. That does not work with CH, because they do not use a diagram. Next, look at the panel model number. Usually in the model number you will see the amperage (100, 200) the number of slots (30, 40) and the number of poles. As an example, 200C3040 would be a 200 amp panel with 30 slots and room for 40 poles (i.e. 10 tandem breakers). 100C20 would be a 100 amp panel with 20 slots and no tandems. 100C2024, you get the picture. This may not be 100% accurate, but it seems to be true most of the time.

As far as anything pre-2008 and probably most panels you will see after that time, if it is a 40 or 42 slot panel, my bet it that it is highly unlikely that tandems are allowed. If they are I suspect the panel should look unusually large to accommodate the extra wiring.

[Jim Katen]

Not to derail this thread, but what rule should be followed in this scenario?

150 amp panel 2 poles using this equation 150 Amp x 2 Poles = 300 / 10 = 30. There should only be 30 breakers.

The panel model number is rated for 40 breakers- qoc40uf.

Do you go off the equation or the manufacture label?

The panel listing is used, not an arbitrary formula that assumes a load of 10 amps per pole.

I agree that the panel listing is the simplest and surest method. The formula, however, is not arbitrary. It's part of the UL listing for CTL designated panelboards and it can be useful if the panel listing isn't visible or if it's been destroyed.

[Jim Katen]

For those who are interested in doing a load calc, you can follow the guidelines directly from the NEC, use the info from Mike Holt, use the very easy form in Code Check, or get the "Resi Electrical Load Calc Pro" app for your phone.

After doing them by hand for years, I really appreciate the app. It's fast, easy, and accurate.

[Jim Port]

Thanks for posting that Jim. It seems outdated with 30 circuit 100 amp panels and even more so with the 42 circuit limit removed.

[kurt]

Any copyright issues with that?

Marc

Maybe, but I doubt he'd care as long as you credit him.

[Jim Katen]

Thanks for posting that Jim. It seems outdated with 30 circuit 100 amp panels and even more so with the 42 circuit limit removed.

Absolutely. But it's still useful for identifying pre-2008 panels.

[Speedy Petey]

Not to derail this thread, but what rule should be followed in this scenario?

150 amp panel 2 poles using this equation 150 Amp x 2 Poles = 300 / 10 = 30. There should only be 30 breakers.

The panel model number is rated for 40 breakers- qoc40uf.

Do you go off the equation or the manufacture label?

The panel listing is used, not an arbitrary formula that assumes a load of 10 amps per pole.

I agree. The number of breakers, in the same way that the sum of the installed breakers, is a meaningless number.

Most panels I install now are 40/80 panels. What does this formula say about 80 poles??

[John Dirks Jr]

I am sure the panel is not listed for all the circuit breakers that are installed! 40 circuits (more than likely) with the main counted as 2. As far as the "no limit on number of breakers now," that is correct, "as long as the panel is Listed" for the number of breakers that are installed. That rule change does not affect existing panels!

I had not been counting the main. Should I be doing that?

[Jim Port]

The main counts as two.

[palmettoinspect]

The main counts as two.

I've never counted the main either. If I did it would put a lot of panels over the CTL. Any literature on this?

[mjr6550]

I don't think the main counts. CH and probably others make 42 slot panels that also include a main, so they would have 44 poles. They existed pre-2008.

To clarify, I suppose you would count the mains in panels with back-fed mains.

[mjr6550]

I don't think I have seen a 40/80 slot panel yet. I just looked up two at HD. Eaton and Square D. The Eaton panel is about 49 inches high and the SD is about 40 inches high. As you would expect, they are a bit larger than a 40 slot panel.