ECN Forum Forums General Topics of the Trade General Discussion Area breaker meltdown

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.