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  #1  
Old 8/18/11, 5:04 PM
Peter C. Russell's Avatar
Peter C. Russell Peter C. Russell is offline
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Default 90 amp breaker

for a sub panel with three 20 amp and 2 15 amp breakers.
Any ideas? concerns?
Main panel is 100 amp. sub panel is for second floor bedrooms/bath.
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Russell Inspection Services LLC
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www.newenglandthermalimaging.com
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  #2  
Old 8/18/11, 5:21 PM
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Default Re: 90 amp breaker

Are you asking why a 90 amp CB? What size conductors are within that SE cable feeding the sub?
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  #3  
Old 8/18/11, 6:13 PM
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Default Re: 90 amp breaker

I wonder if the OP is thinking that 3x20=60 + 2x15=30 60+30=90 and the panel is maxed out.
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  #4  
Old 8/18/11, 6:16 PM
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Peter C. Russell Peter C. Russell is offline
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Default Re: 90 amp breaker

The size of the conductor is OK, just trying to figure out the rational



Russell Inspection Services LLC
New Hampshire state license # 57
Level I Thermographer, ITC
Building Science Thermographer, ITC
Building Analyst, BPI
Commercial Inspector, ITA
Certified Septic Evaluator, GSDI #148

www.newenglandthermalimaging.com
www.russellinspectionservices.com
www.nhsepticinspection.com

Serving Alton, Alton Bay, Wolfeboro, Laconia, Gilmanton, Gilford, Meredith, Center Harbor and the entire Lakes Region
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  #5  
Old 8/18/11, 6:44 PM
Jim Port Jim Port is offline
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Default Re: 90 amp breaker

The rational as in why 90?

Most likely it is more capacity than was needed vs something like maybe a 60 amp feeder that might be undersized. Sounds like good design to me. Without knowing the calculated loads it is a guess.

You do not add breaker ratings to determine the actual load on a panel.
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Old 8/18/11, 6:55 PM
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Peter C. Russell Peter C. Russell is offline
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Default Re: 90 amp breaker

Unfortunately I think that is what was done here. Homeowners wiring. There was a water heater removed and the 30 amp breaker could have been used for the second floor. It has been disconnected at the main panel. It's 3 small bedrooms and a bath. 100 year old home with minimal outlets/lights.



Russell Inspection Services LLC
New Hampshire state license # 57
Level I Thermographer, ITC
Building Science Thermographer, ITC
Building Analyst, BPI
Commercial Inspector, ITA
Certified Septic Evaluator, GSDI #148

www.newenglandthermalimaging.com
www.russellinspectionservices.com
www.nhsepticinspection.com

Serving Alton, Alton Bay, Wolfeboro, Laconia, Gilmanton, Gilford, Meredith, Center Harbor and the entire Lakes Region
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  #7  
Old 8/18/11, 7:24 PM
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Default Re: 90 amp breaker

Quote:
Originally Posted by Jim Port View Post
I wonder if the OP is thinking that 3x20=60 + 2x15=30 60+30=90 and the panel is maxed out.

Since they're all single phase, 120 volt circuits in the sub the available current at 120 volts is actually 180 amps not 90 amps. But this is all pretty hypothetical.

The feeder should be sized according to the load which in this case is smaller than 90 amps. The OCPD is sized according to the SER cable feeding the sub panel. What is the size of the conductors in the SER cable?
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Old 8/19/11, 9:40 AM
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Default Re: 90 amp breaker

I agree it does seem a little strange and rubs me the wrong way too. May be Harry Homeowner wiring, who probably added up the subpanel breakers to come up with a 90A feeder breaker.

Not that there is automatically anything wrong with a 90A subpanel ... it depends on the actual load for the 100A service. You said its a small house, but it does look like there are a number of 240V loads/appliances. Did they install a gas/oil WH for the electric one that was disconnected? Gas/oil heat?

When I see stuff like this that may have been done by Harry I look very carefully at the wiring (secure cable attachment, floating neutrals with bond strap removed, neutrals separated and individually terminated, correct branch wires, no nicked wires at insulation cuts, etc).

I am also curious about the feeder and size (#1 or 1/0 AL 3W+G SE Cable?), and how did they terminate the subpanel feeder neutral in the service panel? Haircut or split wire?



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  #9  
Old 8/19/11, 1:46 PM
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Default Re: 90 amp breaker

Why would one suspect that this was done by a homeowner, is it because of the 90 amp CB? Actually #2 SER is a standard size and at 75░ C is rated for 90 amps under the 2005 and earlier NEC cycles. Under the 2008 and 2011 that same #2 Al SER is only good for up to 80 amps since it must now be used at it's 60░ C ampacity.
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  #10  
Old 8/19/11, 4:35 PM
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Default Re: 90 amp breaker

90A double pole CB feeding a few circuits in a 2nd floor, while the rest of the house is on a 100A service. If an electrician did it, he needs to retake the exam. The circuits that are in that sub panel are not likely rated at 100% load unless they connect to baseboard heaters. You don't rate a panel at the sum of all the breaker sizes.
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  #11  
Old 8/19/11, 10:26 PM
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Default Re: 90 amp breaker

Quote:
Originally Posted by Mark Connor View Post
90A double pole CB feeding a few circuits in a 2nd floor, while the rest of the house is on a 100A service. If an electrician did it, he needs to retake the exam. The circuits that are in that sub panel are not likely rated at 100% load unless they connect to baseboard heaters. You don't rate a panel at the sum of all the breaker sizes.
Care to elaborate on what the specific problems there are with a 90 amp feeder to a sub panel?
And what does 100% load mean?
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  #12  
Old 8/20/11, 7:26 AM
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Default Re: 90 amp breaker

Quote:
Originally Posted by Robert Meier View Post
Why would one suspect that this was done by a homeowner, is it because of the 90 amp CB?
I typically only see that breaker used for heat pump toaster wires, and the subpanel breakers just happen to add up to 90A. Im guessing there is an issue with terminating the feeder neutral too. The wire looks larger than #2 AL



Robert O'Connor, PE
Consulting Engineer & Inspector
LIU CW Post Adjunct Professor
NACHI Education Committee
www.reporthost.com/-rjo

I am absolutely amazed sometimes by how much thought goes into doing things wrong ...

Last edited by roconnor; 8/20/11 at 9:19 AM..
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  #13  
Old 8/20/11, 7:49 AM
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Default Re: 90 amp breaker

Quote:
Originally Posted by roconnor View Post
I typically only see that breaker used for heat pump toaster wires, and the subpanel breakers just happen to add up to 90A. Im guessing there is an issue with terminating the feeder neutral too. The wire looks larger than #2 AL

As I stated earlier, and as you know, adding of the CB values is not a reliable method of determining anything. And also in this case at 120 volts you would have 180 amps of available current so the 90-90 amp comparison is irrelevant.

I do agree that from the photo it does appear that the neutral is terminated improperly. Just for clarity in this discussion maybe Peter will check back in with the size of the SER cable.
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  #14  
Old 8/20/11, 9:24 AM
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Default Re: 90 amp breaker

Quote:
Originally Posted by Robert Meier View Post
As I stated earlier, and as you know, adding of the CB values is not a reliable method of determining anything. And also in this case at 120 volts you would have 180 amps of available current so the 90-90 amp comparison is irrelevant.
We know that, but Harry Homeowner doesn't ...

And maybe my eyes are going bad, but that subpanel feeder wire looks just a bit larger than the service entrance cables, which are likely #2 AL for a 100A service panel. That would be another clue.

JMO & 2-Nickels ...



Robert O'Connor, PE
Consulting Engineer & Inspector
LIU CW Post Adjunct Professor
NACHI Education Committee
www.reporthost.com/-rjo

I am absolutely amazed sometimes by how much thought goes into doing things wrong ...

Last edited by roconnor; 8/20/11 at 9:29 AM..
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  #15  
Old 8/20/11, 2:12 PM
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Peter C. Russell Peter C. Russell is offline
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Default Re: 90 amp breaker

Hi guys, the service cable is #2 and the neutral was split.
This home was built in 1910 but has been renovated. No electric heat. electric dryer, 220. Electric stove. The water heater was removed and a new oil fired boiler supplies the hot water. Thats why I couldn't understand why they didn't take that circuit to feed the 5 circuits on the second floor. The 30 amp double pole breaker is shut off and not being used.

Thanks for your comments.



Russell Inspection Services LLC
New Hampshire state license # 57
Level I Thermographer, ITC
Building Science Thermographer, ITC
Building Analyst, BPI
Commercial Inspector, ITA
Certified Septic Evaluator, GSDI #148

www.newenglandthermalimaging.com
www.russellinspectionservices.com
www.nhsepticinspection.com

Serving Alton, Alton Bay, Wolfeboro, Laconia, Gilmanton, Gilford, Meredith, Center Harbor and the entire Lakes Region
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