# Testing main breaker ampacity



## Ashokan1 (Apr 11, 2013)

HI everyone, my first post here.

I'm working on a house that has way too many circuits and load on a 200A main service. We are changing the circuits to dramatically lessen the load by eliminating the electric furnace, sauna, oven and stovetop by going to propane. The service has been overloaded for years but the homeowners have never experience a tripped main. So is there an easy way to test the reliability of the main circuit breaker? I'm thinking just load it up and see if it trips but I'm not too sure I want to overload the feeders for such a test. Any other suggestions? Thanks.


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## Fibes (Feb 18, 2010)

Ashokan1 said:


> HI everyone, my first post here.
> 
> I'm working on a house that has way too many circuits and load on a 200A main service. We are changing the circuits to dramatically lessen the load by eliminating the electric furnace, sauna, oven and stovetop by going to propane. The service has been overloaded for years but the homeowners have never experience a tripped main. So is there an easy way to test the reliability of the main circuit breaker? I'm thinking just load it up and see if it trips but I'm not too sure I want to overload the feeders for such a test. Any other suggestions? Thanks.


 
How was it determined that the service was overloaded? Did someone put a Data Logger on it for a period of time?


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## Zog (Apr 15, 2009)

Ashokan1 said:


> HI everyone, my first post here.
> 
> I'm working on a house that has way too many circuits and load on a 200A main service. We are changing the circuits to dramatically lessen the load by eliminating the electric furnace, sauna, oven and stovetop by going to propane. The service has been overloaded for years but the homeowners have never experience a tripped main. So is there an easy way to test the reliability of the main circuit breaker? I'm thinking just load it up and see if it trips but I'm not too sure I want to overload the feeders for such a test. Any other suggestions? Thanks.


You don't want to do that, they have test sets for testing breakers that use a low voltage, controllable current and a timer. Typically you would apply a 300% overload and compare the trip time to the breakers time current curve. 

Keep in mind a small overload may never trip the breaker or would take several minutes at a constant overload to trip. 

It really isn't worth the time and expense (If you don't have the equipment) to test a small breaker like that, if in doubt just replace it.


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## Ashokan1 (Apr 11, 2013)

No I did a load calculation and simple observation as I was spec'ing the job for a generator installation.

It's a 200A residential main single phase service for 2500 sq ft house. The circuits included a 3 stage electric furnace that draws 143A/leg when fully engaged, a 50A sauna, a 50A hot tub, 40A electric stovetop, 30A oven, supplemental baseboard heat, dryer, hot water, 3 small freezers, well pump, and all the ordinary household receptacles and lighting. 

Instead of a service upgrade the homeowner is opting for converting much of it to propane. I would like to keep the original main panel to save money but wonder about the integrity of the main with such a load on it for many years.


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## dronai (Apr 11, 2011)

Your heater load seems too high ? for your main CB, turn on all loads and put an amp clamp on there. Also some of those other loads don't draw 100% nameplate rating.


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## drumnut08 (Sep 23, 2012)

Ashokan1 said:


> No I did a load calculation and simple observation as I was spec'ing the job for a generator installation.
> 
> It's a 200A residential main single phase service for 2500 sq ft house. The circuits included a 3 stage electric furnace that draws 143A/leg when fully engaged, a 50A sauna, a 50A hot tub, 40A electric stovetop, 30A oven, supplemental baseboard heat, dryer, hot water, 3 small freezers, well pump, and all the ordinary household receptacles and lighting.
> 
> Instead of a service upgrade the homeowner is opting for converting much of it to propane. I would like to keep the original main panel to save money but wonder about the integrity of the main with such a load on it for many years.


I have a customer with a similar issue and is teetering on the brink of tripping his 200 amp main this summer . I recommended a larger service before his last subpanel , but some people refuse to listen , lol ! What amperage readings are you getting to question the reliability of the breaker ? Cycle it to make sure it operates ok , but aside from that , chances are , it's fine . If it has been tripping several times throughout the years , I'd be more concerned .


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## Ashokan1 (Apr 11, 2013)

Yes I realize the loads aren't the same as the nameplate rating but i just wanted to give you a broad idea of the load. It's not even close to working within the limits of a 200A service. Yet it was like this for years. 

The furnace had an additional stage installed years ago. It was really surprising when I measured the load on the furnace alone. The homeowner is eliminating the furnace and going with a heat pump, eliminating the sauna, the cooktop/oven and maybe the electric hot water. That will get me well within the load capability of a 200A service. It's less expensive and more practical to replace these appliances than upgrade the service.

Probably just makes sense to replace the panel but I'm curious about the test equipment Zog refers too. I do mostly residential work so I have little knowledge or need for that type of testing gear. How expensive is it?


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## drumnut08 (Sep 23, 2012)

dronai said:


> Your heater load seems too high ? for your main CB, turn on all loads and put an amp clamp on there. Also some of those other loads don't draw 100% nameplate rating.


I prefer an actual connected ( running ) load test over a calculation any day too .


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## Ashokan1 (Apr 11, 2013)

The furnace draw of 143A/leg and the hot tub draw of 23A/leg put me well above a 160A continuous load rating for a 200A service. Not to mention the other circuits. So how they never tripped the main is beyond me.


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## Bbsound (Dec 16, 2011)

143 amps is a LOT of heat for a 2500 sq ft house. 

I'll bet all 3 stages never came on.


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## Ashokan1 (Apr 11, 2013)

I think the control wiring was altered or miswired so all the stages came on at once. It is a 20 year old mountaintop house with lots of windows facing a windy view. Plus there was 20+ feet of supplemental electric baseboard heat in bedrooms and baths. They must have had significant heat loss to need such heating capability. The HVAC guy thought it was crazy too.


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## 99cents (Aug 20, 2012)

If you suspect the main breaker is getting tired, replace it. It's cheaper than getting it lab tested and probably cheaper than the time you spend screwing around with it.


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## BBQ (Nov 16, 2010)

99cents said:


> If you suspect the main breaker is getting tired, replace it. It's cheaper than getting it lab tested and probably cheaper than the time you spend screwing around with it.


I agree 100%.


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## 99cents (Aug 20, 2012)

BBQ said:


> I agree 100%.


Well, it's an extra you can charge money for and completely justified by a professional electrician. It provides the customer with peace of mind, which is usually a very easy thing to sell.


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## knowledge29 (Nov 6, 2010)

why not plug in a P.Q.A. And get actual readings on real time then you'll be able to see whats going on power wise.


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## Deep Cover (Dec 8, 2012)

You are either a really good salesman or your customer didn't ask the correct questions. I would have demanded to see the actual load on the service rather some numbers on a sheet of paper. From your responses, it doesn't seem like you even metered the load.


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## Ashokan1 (Apr 11, 2013)

The load was metered at 143A/leg with just the electric furnace load. 156A/leg with just some minor things running in the house. Doesn't need much more metering to determine a hot tub, electric stovetop and oven, hot water heater, sauna, dryer, washer, well pump, kitchen appliances (microwave), 2x additional freezers, supplemental baseboard plus recepts and lighting for a 2500 sq ft house clearly exceeds the ampacity of a 200A service. NEC Article 220.10 makes it pretty clear how to calculate load so at some point calculations do matter.


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