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Old 02-10-2010, 09:34 AM   #1
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Do I need to upgrade my electrical service?


I was thinking about buying the 60 gallon Campell Hausfeld air compressor from Lowes and in order to install it in my house I would need to run a 240V line to the garage. Not a problem of knowing how to do it, but my breaker box was full so I started thinking about how I wanted to go about this. However, in the process of investigating all of my options, I noticed my main breaker is only 100A.

I don't know if these two things are related, but in the summer my lights will dim when the A/C turns on (I put a hard start kit on it, but I feel like I shouldn't need to do that) and sometimes it even happens when the refrigerator compressor turns on.

Some details about my house:
Gas furnace
Gas water heater
Gas stove
4000 sq. ft. w/ multiple adults and kids
built in 2001
tons of electronics and tools...

It's a pretty normal setup, I know, and I also didn't think it would be a problem when I first thought about it because of the major appliances being gas instead of electric. I still wanted to ask though as I plan on upgrading my third garage port into a woodshop with several large tools and I don't want to constantly reset breakers if I try to use my CNC router at the same time as my air compressor and air conditioner. My gut says 100A is too small but I don't really know.

Any advice would be appreciated.
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Old 02-10-2010, 09:45 AM   #2
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Do I need to upgrade my electrical service?


If you are adding a wood shop with large tools I would go to 200a

BUT, this depends upon how much power they use, if more then one will be on at the same time
Heat/AC needed out in the shop

Have you performed a whole house electric calc to see how much power is currently "used" by devices ?
By code if the power calc goes over your service you should upgrade
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File Type: zip Electrical_Load_Calculator blank97.zip (7.1 KB, 140 views)
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Old 02-10-2010, 10:39 AM   #3
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Do I need to upgrade my electrical service?


Your fourth paragraph should tell you what to do.
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Old 02-10-2010, 10:40 PM   #4
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Do I need to upgrade my electrical service?


I have four major projects - the building of a detached garage/workshop, the conversion of attached garage into a hobby room, a major renovation of the house proper, and the addition of a new master bedroom suite - the first three are completed. Before I started any of the projects I planned for electrical needs and upgraded the existing 100a panel to 200a with ample circuit capacity - it's worked out great. Sounds like you should do so as well.
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Old 02-11-2010, 10:42 AM   #5
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Do I need to upgrade my electrical service?


I've been working on doing a load calculation in my own home. It's been daunting to try to figure out the correct way to do this to say the least. I've got two reference guides that try to break down the process for you, but each attempts to do it differently. I looked at the above referenced spread sheet, and it too seems to be different from the other things I've read.

So I tried to read over NEC 2008 section 220.12, 220.14, and some of the sections they reference. As best as I can tell, the above spread sheet seems to be doing the final calculation wrong.

For example, I would try to summarize what the spreadsheet says to do is this:

1. Sum up all of your gross loads.
2. Use the 1st 10,000 watts of the gross load at 100%
3. Use the remainder of your gross load at 40%.


But so far, I can't find anything in the code that indicates that is the proper way to do it.

What I can find is Table 220.42 that indicates you should use 100% of the 1st 3,000 watts of your LIGHTING load, and 35% of the remainder (25% for really huge loads). Other wise, it seems like you should be using 100% of the gross load.

This logic seems to play out in this spread sheet
http://www.mikeholt.com/documents/ca...lculations.xls
I found reference here: http://forums.mikeholt.com/archive/i...p/t-54024.html

Which is correct?
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Old 02-11-2010, 11:45 AM   #6
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Do I need to upgrade my electrical service?


Quote:
Originally Posted by HooKooDooKu View Post
I've been working on doing a load calculation in my own home. It's been daunting to try to figure out the correct way to do this to say the least. I've got two reference guides that try to break down the process for you, but each attempts to do it differently. I looked at the above referenced spread sheet, and it too seems to be different from the other things I've read.

So I tried to read over NEC 2008 section 220.12, 220.14, and some of the sections they reference. As best as I can tell, the above spread sheet seems to be doing the final calculation wrong.

For example, I would try to summarize what the spreadsheet says to do is this:

1. Sum up all of your gross loads.
2. Use the 1st 10,000 watts of the gross load at 100%
3. Use the remainder of your gross load at 40%.


But so far, I can't find anything in the code that indicates that is the proper way to do it.

What I can find is Table 220.42 that indicates you should use 100% of the 1st 3,000 watts of your LIGHTING load, and 35% of the remainder (25% for really huge loads). Other wise, it seems like you should be using 100% of the gross load.

This logic seems to play out in this spread sheet
http://www.mikeholt.com/documents/ca...lculations.xls
I found reference here: http://forums.mikeholt.com/archive/i...p/t-54024.html

Which is correct?
They both are: the first one you reference is the optional method you may use for single family dwellings; the second is the standard method for all structures.
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Old 02-11-2010, 10:27 PM   #7
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Do I need to upgrade my electrical service?


Quote:
Originally Posted by HouseHelper View Post
They both are: the first one you reference is the optional method you may use for single family dwellings; the second is the standard method for all structures.
Thanks, I found it now and just hadn't read far enough. It also makes sense why two guide books published within the last year each have a different method: one followed 220.40, the other followed 220.82.
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