I had a customer call with a breaker melted to the bussbar. this was the second or third breaker that has done this according to him.the bussbar was fine but the breaker fell apart I installed a new breaker and it made good tight connection and the amp load was in range. any Ideas? I think it was a g&s panel with challenger breakers.

Load up the circuits and check the voltage drop from the feed conductor to the load conductor terminations. You'll be looking for voltages around 100 ma on the low end to about a volt, depending on the load and the size of breaker. Compare readings for the various breakers for an idea about what is normal in that panel. If the voltage drop seems high, move the probe from the feed wire to the bussbar by the breaker, then the metal part of the breaker.

It's the equivalent of checking the temperature of the connection points, but it's faster and easier to pinpoint the problem because voltage drop doesn't migrate the way heat does.

Do you have a non contact thermometer? They are getting cheap enough for the mortal man and will let you further track down this heat thing. TWH is right about starting with your meter to see where the leak is.

Check for corrosion on the Aluminum bus...

Repeat problem and the buss doesn't seem damaged? That doesn't make sense.

However ...

1) Water dripping, condensing on the breaker might;

2) Some load that was not available to you (like a space heater) might; and,

3) the customer's own actions (not shared with you) might.

thanks for the input. The bussbar was damaged from a previous breaker but the breaker I removed did not appear to have damaged the buss.I did sand the buss and applied corrosion inhibiter with the new breaker. The breaker is feeding 15 kw heat strips and is pulling 60 amps on each leg.

15kW strip heaters drawing 60 Amps per phase??
What voltage are you running at?

If you can't re-locate that breaker to an undamaged part of the buss - perhaps swapping places with a much smaller one - then you really need to replace the busses.

Is this a bolt-in or push in CB? 'sanding' the buss may not have been a good move. The contact tension on the push in type CB may be compromised, resulting in failure over a period of time.

If you are running 208 volt, 3 phase, with a 60 amp CB and 15KW of heat you also have an issue with the 'continuous load' (80%).

Conductor size?

Like Greg said, see if you can get your hands on an IR unit, you may have a heating issue due to the design.

Since your load is linear my idea that it may be related to non linear loads is not going to explain it.
A 3 phase 15 KW load on a 60 amp breaker should be around 42 amps so the breaker looks correct for 3 phase, Single phase would be a 90 amp breaker and a 72 amp load, Note that the 90 amp breaker is actually 1/8th of an amp too much load for the 90 amp breaker but most inspectors would give that much away.

it is single phase 239 volts, conductors are #2 copper, it is a push in breaker and it made a good snug fit when installed.buss was not damaged where i installed breaker

Did you amp clamp both legs on each circuit while under load?
Is there a neutral in the circuit?
Did you put the new breakers in where you filed down?

239 volts, single phase, 15KW load, equates to 69.7 amps of load. That (69.7) is approx. 15% overload by math. Hence, over a period of time....the CB will fail. You need a minimum 90 amp cb! Perhaps the first person that replaced the CB saw "60" instead of "90"??

I have seen breaker failure when 2 breakers of high amperage were on the same buss bar. Just on opposite sides. For example a double oven was on breaker(s) 1/3 and the dryer was on breaker(s) 2/4. Both breakers drew high amps and one of the breakers started to melt.

I'm with Harold on this. I prefer to place all of my multi-pole breakers for larger loads down one side of the panel and the single-pole ones end up on the other side. If I have the luxury of plenty of space in the panel, I'll even leave two pole spaces between each two-pole breaker just in case, to help with heat dissipation.

I start with the highest-amperage circuits (like the furnace, etc.) located closest to the main breaker. I then sort the remaining ones in order of anticipated continuous loads. The dinky loads, like the cook top, end up closer to the bottom.

The single-pole circuits on the other side would be hard-pressed to cause enough heat to damage the bus bar or individual stab position.

I feel that this minimizes the amount of current that actually flows through the bus bar. This also keeps heavy load breakers from being face-to-face, thus sharing the same stab position.

Despite the fact that manufacturers of panels state that all stabs are rated for X amount of load per the panel's label, I don't trust them. Many bus bars are made of questionable materials, that when coupled with paint over spray or corrosion, these 'ratings' quickly go down the drain.

If that is the case, the breakers should trip before they melt unless they are junk breakers to start.

Mike, per code, a 15k heating load is considered a continious load which requires a 125 demand factor. Per 15k heater requires a minimum of an 80 amp breaker (15,000/240x1.25= 78.125). However, 424.22(B) limits the OCPD to 60 amps. Is it possible to split up the loads to keep load to 11.5K per cicuit so the OCPDs are at 60 amps or less? What are they heating with such a big heater?

Here in AZ where summertime air conditioning loads can become continuous loads we do see breaker meltdowns. However, the bus always gets damaged and it will spell death for any subsequent breaker installed on the same stabs. Even cleaning/sanding them is no help for very long. Some of the buses are plated, and the plating burns thru. Many times the whole panel will melt down. Interesting note though, every panel I have ever seen that melted down was a Siemens. Never seen any other brand melt down. Not trying to badmouth Siemens, just an observation.

Sparkyak:

The 'math' amperage /voltage is just 'math'. Real world the strip heaters could be drawing less amperage, high resistance at connections (buss to brkr stabs) may result in a 'lower' amp draw.

I have seen quite a few CBs over the years that 'held' at the rating, or at a small percentage above the rating. A steady resistave load that has no 'peaks' is what I'm describing. A sudden 'line-line', or grd short would cause the CB to trip.



If this is a famous 'old' brand .....no issues with tripping at all.

I agree however code is code and with size of loads continuously does heat the breakers up. Breakers do not respond well and over time I'm sure there is degradation of there reliability

BigB,


I have to think about this, the time I saw that breaker melt was many, many years ago. However I do think it was a Siemens panel though.

I remember the thin GE 120/240 volt, and Murray/Bryant types, having burn-out issues, back in the day.

Aluminum busbars have a tin plating that is less than .0006".

Be careful when sanding busbars, or you'll sand right through this plating

Six ten-thousandths would be very, very difficult to not damage.

From what I can see, simply installing the push in breakers looks like it is enough to scratch the coating on the aluminum busses. IDK, maybe that is the manufacturer’s intent. The salt air on the water front around here just seems to annihilate those aluminum panel busses.
Seems some manufacturers make the effort put a little dab of inhibitor or grease on their CB pressure contacts, while others leave theirs completely dry. I would think that the inhibitor should help keep out moisture and make more of a so called oxygen free connection, but maybe not.
I will still install the Siemens panels with the aluminum buss, but will usually try and get them with the copper buss if possible, since the price isn’t that much more.

KJay...

I've witnessed the effect of near-ocean air on aluminum bussing: it's tremendous.

One can observe 2-4% voltage drops right there.

The heat from this is not trivial.

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FYI: Chlorine attacks aluminum VERY vigorously. That is why aluminum can't be used for Ufers.

In some Nevada locations ground salts are so intense you have to stay with copper for everything. ( It used to be at the bottom of the ocean -- hence the salt flats in Utah and Nevada. )

If the installation is near the ocean just forget about using aluminum bussing -- aluminum anything.

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Try this: place an old aluminum lug in a glass of salted water.

Let it sit and watch just how fast it is destroyed. Any acid will REALLY speed the effect up.

Im working on a siemans panel in the bay area whwere the fog seems to come in HO called that the washer/dryer was having trouble and she had some guy out who checked a few things and went away. problem was still was intermittant, would lose power to run and the LG electronics on the units would start flashing wildly. I came out and the interior cover from the main outside panel was missing, they said its been like that ever since they moved in 3 years ago, the buss was corroded something awful and the suspect breaker was almost welded to the buss, the circuit wiring was new since they had the furnace and water heater moved.....its a ite panel at least that is the maker on the 100 amp main this is the older panel where the buss is against the outside wall. newer ones theyve moved it to the main/load divider partition. any experience with these panels and loose breakers or under thickness buss some breakers seem a little loose? CRS

CRS, I would imagine a coastal environment juxtaposed to a missing panel cover would warrant it's replacement

~S~