Grid Tied Breaker Heating Under Load

DanS26 · February 2013

Just want to bounce a question off the brain trust here on the PV Installers forum.

What is the acceptable heat gain that will be observed under maximum load for a grid tied breaker that is installed under NEC code?

Using a continuous load breaker, I am observing up to 40 degree gain over ambient room temperature when the solar system is producing at maximum. This is a 32 amp load on a 40 amp breaker located at the bottom of a 200 amp main distribution panel. I'm measuring this gain using an infrared heat measuring tool.

Specifically, I am observing temps of around 105 F on the tandem breaker in a 60 F ambient room. Should I need to be concerned?

BB. · February 2013

Re: Grid Tied Breaker Heating Under Load

It is not the worst thing in the world (I do too always like to see things run "cool"). I am not sure if that is "too much" heat or not.

However--I would pull the panel cover off and inspect/check temperature on the cable termination screws (proper torque, clean connections, correct AWG wire, look for signs of excessive temperatures/color change, etc.)--And if you want, pop the breaker out and inspect the contacts and bus bar mating surfaces.

Years ago I had a leak from the weather-head/roof flashing that dripped just a little bit of water from heavy rain storms right into the middle of the bus bar/breaker assembly. And cause significant corrosion over the years. Eventually, I had to replace the breaker panel.

Some information:

Underwriter Laboratories Inc. (UL) standards require that molded-case
circuit breakers rated at 125 amperes or less be marked with the conductor
insulation-temperature rating. Table 1 contains a listing of wire temperature
ratings for Square D circuit breakers. The wire temperature rating is
determined by testing the circuit breaker under full-load current with
conductors sized for the appropriate temperature rating—60°C or 75°C. The
temperature rise at the circuit breaker terminals must not exceed 50°C above
ambient per UL Standard 489.

Conductors with 90°C rated insulation can be used on circuit breakers rated
for 60°C or 75°C wiring only if their size is based on the ampacity of the lower
temperature-rated wire (reference Table 2). If the 90°C wire size were to be
selected based on the ampacity allowed in the 90°C column of Table 2, the
smaller resulting wire size would generate additional heat at the circuit
breaker terminals and possibly cause nuisance tripping.

And you are currently only seeing a 25C rise.

-Bill

DanS26 · February 2013

Re: Grid Tied Breaker Heating Under Load

Thanks Bill, that is good information.

In my case it is interesting that only one breaker in the tandem is showing the temperature rise. I'm measuring the top of the screw as you suggested. This leads me to believe that I may have a problem with that connection. I have torqued the connections to the proper specifications. What is interesting is that only one half of the tandem breaker is hot. This is a GE TQ breaker which I believe uses a thermal strip that heats under load and will trip when the strip expands too much. I have a feeling it is about to trip. I think I will replace with a new TH beaker. The existing breaker is over 25 years old.

Thanks again for your help.

icarus · February 2013

Re: Grid Tied Breaker Heating Under Load

Heat equals loss. My gut feeling is to do as
Bill suggests and check all the connection surfaces. You could also look for voltge drop across components, and measure the resistance of various components and compare to others. Failing that, change out the breaker just to be safe.

Tony

BB. · February 2013

Re: Grid Tied Breaker Heating Under Load

Solar power and battery connections usually operate at closer to maximum current for many hours on end vs the typical random home branch circuit.

Old breakers and fuses can and do fail... I have replaced quite a few water heater and electric Stove breakers after they hit a few decades of use.

-Bill

DanS26 · February 2013

Re: Grid Tied Breaker Heating Under Load

Just another observation that may or not be connected to the temperature rise in the breaker. I've noticed that as the current rises, the voltage also rises (as measured by my TED system). I always considered the voltage rise related to increased current, but now I'm thinking it could be related to the temperature rise (or increased resistance) of the breaker. Thoughts?

In full PV power (ie 32 amps) I see a 5 to 6 volt rise in the utility system. The voltage rise graph matches the power (ie volt amps) as the sun rises and falls. I'm think now that as current rises the resistance rises causing the voltage rise, which is really voltage drop. The inverter follows this utility voltage fluctuation as programmed.

I'm going to switch out the breaker and see if the voltage fluctuations diminish or disappear. This should be interesting.

drees · February 2013

Re: Grid Tied Breaker Heating Under Load

Well, a 5V rise at 32A would indicate that you are losing about 160W somewhere in the wiring to heat.

If all of that were in the breaker it'd melt for sure. But it does sound like at least a few watts of it could be in the breaker if it's hitting 105F.

solar_dave · February 2013

Re: Grid Tied Breaker Heating Under Load

I actually had one char up after a year of running at max 46 amps on 60 amp breaker. I replaced it and used some dielectric grease where it stabs the buss bar. Not sure if that was the cure but the second one seems to be surviving mich better.

inetdog · February 2013

Re: Grid Tied Breaker Heating Under Load

solar_dave wrote: »

I replaced it and used some dielectric grease where it stabs the buss bar. Not sure if that was the cure but the second one seems to be surviving mich better.

The OP's observation about one breaker section being a lot hotter than the other could just as well result from increased resistance in the bus stab as in the wire attachment screw. But a problem with the wire would be a lot easier to fix. :-)
I would not recommend touching the bus bars to see if the one connected to the suspect breaker is hotter! :-)

solar_dave · February 2013

Re: Grid Tied Breaker Heating Under Load

inetdog wrote: »

The OP's observation about one breaker section being a lot hotter than the other could just as well result from increased resistance in the bus stab as in the wire attachment screw. But a problem with the wire would be a lot easier to fix. :-)
I would not recommend touching the bus bars to see if the one connected to the suspect breaker is hotter! :-)

Agreed on the not touching the buss bar, unless of course the MAINS are OFF and you test it with a volt meter first! I actually moved mine to a different stab point as well. I will see if I can find the breaker and post a picture, I think it is out on top of the panel now. Yes the wire connection is easier to fix.

BTW I found it when the power company (I think) switched the AC disconnect off and when they pushed it back in didn't get a good connection on the switch, the inverters failed to start of course. They have it locked so I could not look inside the switch (beats me why). I had to pull the switch to the off position and slam it home to the on position to get it to work again. The charred breaker had not failed.

DanS26 · February 2013

Re: Grid Tied Breaker Heating Under Load

Measured the heat gain today again on the problem breaker. The phase B breaker is operating at 40 C which I believe is the maximum rating for a GE TQ breaker. I have just obtained new TH breaker and will install soon. Just hope the old one holds on for a few more days.

I will inspect the connections very carefully, looking for pitting, etc. Thanks for the advice.

mike95490 · February 2013

Re: Grid Tied Breaker Heating Under Load

For high current connections, there is copper and silver conductive paste that can be applied to the joints that helps reduce the losses.
McMasterCarr
Prevent corrosion and seizing while reducing the electrical resistance of your connections. These copper compounds seal out moisture, corrosive fluids, and gases. They simultaneously protect, lubricate, and enhance the conductivity of your cable strands, threaded connections, switches, lugs, and other connectors. They're easy to apply with the included brush, and will not run, drip, or harden. Temperature range is -50° to 250° F. UL listed.
1 1/2-oz. Container 2953K11 $6.68
8-oz. Container 2953K12 34.46
16-oz. Container 2953K13 49.93

DanS26 · February 2013

Re: Grid Tied Breaker Heating Under Load

mike95490 wrote: »

For high current connections, there is copper and silver conductive paste that can be applied to the joints that helps reduce the losses.
McMasterCarr
Prevent corrosion and seizing while reducing the electrical resistance of your connections. These copper compounds seal out moisture, corrosive fluids, and gases. They simultaneously protect, lubricate, and enhance the conductivity of your cable strands, threaded connections, switches, lugs, and other connectors. They're easy to apply with the included brush, and will not run, drip, or harden. Temperature range is -50° to 250° F. UL listed.
1 1/2-oz. Container 2953K11 $6.68
8-oz. Container 2953K12 34.46
16-oz. Container 2953K13 49.93

Thanks Mike, but I could not find the McMaster-Carr product you mentioned. I'm thinking about using this:

http://www.amazon.com/gp/product/B00447S32W/ref=ox_sc_act_title_2?ie=UTF8&psc=1&smid=AS0K3MKEU5H24

icarus · February 2013

Re: Grid Tied Breaker Heating Under Load

In indirect read, IR thermometer is a great (and pretty cheap) too to have on your bench. You can measure the break temp, as well as temp differences between live busses. Hand for other things like sticking brakes, or loose wire nuts or what have you.

Tony

DanS26 · February 2013

Re: Grid Tied Breaker Heating Under Load

icarus wrote: »

In indirect read, IR thermometer is a great (and pretty cheap) too to have on your bench. You can measure the break temp, as well as temp differences between live busses. Hand for other things like sticking brakes, or loose wire nuts or what have you.

Tony

Tony,

I use my IR tool for all kinds of things. It really is an all purpose tool and should be in every tool box. Finding where things are too hot or too cool is very useful.

Dan

mike95490 · February 2013

Re: Grid Tied Breaker Heating Under Load

1 1/2-oz. Container 2953K11 $6.68
8-oz. Container 2953K12 34.46
16-oz. Container 2953K13 49.93

Actual pn from catalog page - http://www.mcmaster.com/#catalog/119/948/=lm2khw nearly at the bottom of the page.

The chemtronics at amazon looks like they say the right stuff, but they don't mention corrosion inhibiting action. the mfg's ad at http://www.chemtronics.com/products/americas/TDS/Cw7100tds.pdf does mention it, and it's benefits at substations and high power connections. "just a dab will do ya". It's now on my amazon wish list!

DanS26 · March 2013

Re: Grid Tied Breaker Heating Under Load

Well, I finally replaced the tandem breaker with new GE THQL 40 amp. Inspected the panel mount contacts and all is well. I used silver conductive grease on the contacts which is rated for use on copper contacts.

The new breakers run about 20 deg F cooler at maximum continuous load which is about 32.5 amps. After a couple of hours at full load the new breaker is warm to the touch but not hot around 100 deg F.

I'm still wondering why there is any heat at all and if I should continue to investigate?

BB. · March 2013

Re: Grid Tied Breaker Heating Under Load

I am not having much luck in finding a catalog page for this GE Breaker--But many common breakers are thermal trip type... They have a "heater" inside them that when too much current flows, trips the breaker. So getting warm during heavy current flow is normal. How hot it should get--I am not sure.

Found it... They are Thermal Magnetic breakers--So, I would expect some heat from them. And solar power installations tend to run towards higher circuit current for many hours per day... Not as common for most house hold loads (cycling, much less load, on average, per circuit, etc.).

https://www.platt.com/CutSheets/GE%20Breakers/THQP.pdf

-Bill

Wally · March 2013

Re: Grid Tied Breaker Heating Under Load

My Utility requires a lockable OFF AC disconnect, so I am considering using a fusible one
similar to this type with a couple of 60 amp fuses for the back fed OCPD and avoid using
a back fed breaker altogether.
http://www.dale-electric.com/products/view/GHN322NW

I never see any examples of connecting that way --- is there a problem with doing this?

I should add my Utility Service entrance is on the outside of a detached garage and from
the meter/ base enclosure goes to a Siemens #WB2225 Outdoor Circuit Breaker Enclosure
with a 225 Amp max Rating and a 200 AMP breaker installed. This then feeds a Midwest
T1220 Terminal box which I will also be feeding from the fusible AC disconnect.

Planning on using a Fronius 11.4-1 inverter with a Max continuous rating of 47.5 Amps.
Any problems with doing it this way?

YehoshuaAgapao · March 2013

Re: Grid Tied Breaker Heating Under Load

Wally wrote: »

My Utility requires a lockable OFF AC disconnect, so I am considering using a fusible one
similar to this type with a couple of 60 amp fuses for the back fed OCPD and avoid using
a back fed breaker altogether.
http://www.dale-electric.com/products/view/GHN322NW

I never see any examples of connecting that way --- is there a problem with doing this?

I should add my Utility Service entrance is on the outside of a detached garage and from
the meter/ base enclosure goes to a Siemens #WB2225 Outdoor Circuit Breaker Enclosure
with a 225 Amp max Rating and a 200 AMP breaker installed. This then feeds a Midwest
T1220 Terminal box which I will also be feeding from the fusible AC disconnect.

Planning on using a Fronius 11.4-1 inverter with a Max continuous rating of 47.5 Amps.
Any problems with doing it this way?

I know SRP favors non-fused for load-side connections but is ok with fused. I believe fused disconnects are for supply-side connections (tapped in between the meter and main breaker). I have a fused and pre-sized for expansion because I know 2 inverters will not fit in the 120% of rating rule. max continuous sell amps <= ({120% of panel rating} - {main breaker rating}) * 0.8. At expansion, I could do a panel upgrade to a 225A main panel and keep the main and that would accommodate 50 sell amps, but I need a 125 amp breaker to service two Xantrex inverters/chargers (60 amps per inverter - to power loads and charge batteries simultaneously off of the grid) and I don't think they make those as regular 2-pole breakers for a residential panel. So I'll probably go supply side at expansion time.

For you though, being grid tie and not needing additional draw amps, just needing to support 47.5 sell amps, you can get by with either a supply-side or doing a panel upgrade to 225A and keeping the 200A main and using a 60A backfeed breaker (225*1.2-200)*0.8=56A; 60*.8=48A; 47.5A fits both). In Mesa no permits for grid-tie or bi-modal solar (do need permit for off-grid), but do need permits to upgrade the main panel or do a supply-side tap.

Grid Tied Breaker Heating Under Load

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