Square D is what my electrician buddy insisted on when I started stringing wire for this house. And, since he works part time for the electrical inspector, I took it as gospel. Around here, you can get Square D and Usually GE at every Hardware. Beyond that you take your chances on ever being able to get new breakers.
As long as I've got folks here who know their way around a breaker box... did I see a "Universal" breaker? I was in somewhere and I though I saw a "Universal" breaker that would fit several manufacturer's products. It occurs to me that this is either a fire waiting to happen, or several brands are actually made by the same manufacturer.
<font color="blue"> Allen Bradley Motor Control Centers </font color>
Cool stuff huh? I worked a summer as an intern at an industrial automation warehouse. We sold Allen Bradley. The motor drives, PLCs etc. Really fun to see it installed at a factory. One of the most interesting customers was the State Prison, they used it for their HVAC.
[img]/forums/images/icons/tongue.gif[/img] The Allen-Bradley MCCs have some of the best auxillary contact setups for adding on controls and of course the PLCs are superior to anything else out there. As always, there are a few weaknesses here and there in the AB stuff, but overall they are quite bulletproof. They have a conductor between the bus clip and the top of the breaker that in certain size panels can be a problem. The braided conductor is crimped into a lug that has inadequate crosssectional area for the amperage. [img]/forums/images/icons/crazy.gif[/img] Here is a question that will tweak your brain: "Why is it unwise to use one or more cells in an MCC to feed over to another smaller MCC or maybe even a process room?" Let's say you use a spare bucket that has a 150 AMP breaker in it to feed over and run a process room that needs about 120 AMPS? Or maybe you use a cell (bucket) with a 100 AMP breaker to run a transformer or some lighting that requires 80 AMPS. What's the problem here? [img]/forums/images/icons/crazy.gif[/img]
<font color="blue"> Why is it unwise to use one or more cells in an MCC to feed over to another smaller MCC or maybe even a process room?" Let's say you use a spare bucket that has a 150 AMP breaker in it to feed over and run a process room that needs about 120 AMPS? Or maybe you use a cell (bucket) with a 100 AMP breaker to run a transformer or some lighting that requires 80 AMPS. What's the problem here?
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I'm stumped. It's been a while and I'm a mechanical engineer, not electrical so I'm a bit rusty. What's an MCC?
[img]/forums/images/icons/tongue.gif[/img] The big mistake that is so often made by plant operators is using an MCC for a DISTRIBUTION PANEL, which it isn't. The cells in an MCC are designed to feed motor circuits, and as such they are engineered for MOTOR CURRENT LOADS. If the cell has a 150 AMP breaker in it, THAT ASSUMES that the cell will be feeding a 75 HP motor (breaker size is roughly two times the HP on 480 volts)....and the RUNNING CURRENT of that 75 HP motor is just 96 AMPs, not 150. So the cells are not made to deliver anything like 150 AMPs of continuous rated current and will burn down if you try it. A genuine DISTRIBUTION PANEL that is intended to feed to remote loads like a process room or a remote MCC has a breaker size and bus work that is designed to deliver rated current and stay under 100 degrees (unless it is in a boiler room). I just could not tell you how many MCC cells I've found that were desperately overheated because the operators mistook them for distribution panels when the KEY WORD in the name was "motor"....as in Motor Control Center. [img]/forums/images/icons/crazy.gif[/img] Would you like another brain teaser that's simple, yet tricky, and speaks to the basics of current handling? [img]/forums/images/icons/smile.gif[/img]
OK....here it is: Lem N. Squezins owns and operates: "Lem's Body & Fender Repair" and of course they need lots of air for paint guns and so forth so over the years as the business grew, Lem has added a second compressor. His original compressor ran just fine for YEARS on a 40 AMP 220V breaker and his backup ran for YEARS on a 20 AMP 220V breaker, both running at the same time, NO PROBLEM. [img]/forums/images/icons/smile.gif[/img] The compressors FINALLY wear out, and Lem has to replace them. A local parts house has ONE unit that can do the work of both of the existing units, and by having a single large unit, they save money and precious floor space. Lem voices his concern about the power supply, but the parts house salesman explains that the new unit will run on a single 60 AMP breaker no problem. So in actuality, nothing has changed from an input power standpoint. So Lem buys the unit; they pull the 40 AMP breaker; pop in a 60 AMP; and then pull the remaining 20 AMP and discard it altogether. SO far so good. The next day Lem notices that the shop circuit breaker panel seems warm; in fact it is HOT where the 60 AMP breaker is. What's the problem? [img]/forums/images/icons/crazy.gif[/img] The connected load has not changed, the total horsepower is the same, the amps are the same. [img]/forums/images/icons/crazy.gif[/img] Why is the panel suddenly hot? [img]/forums/images/icons/tongue.gif[/img]
<font color="blue"> Why is the panel suddenly hot? </font color>
While installing the new compressor they accidential bumped the thermostat to high?
Doesn't take much to tease my brain [img]/forums/images/icons/frown.gif[/img] I'll try a wag guess.
The second breaker (60 amp) was physically identical to the 40Amp breaker with respect to it's steady state thermal dissipation capability. The resistive losses in the breaker went up by the square of the current demand in the ratio of 60x60/40x40 = 3600/1600 (more than twice) The 60 amp breaker could not conduct the heat away from itself any better than the 40 amp, but it had ~twice as much to do.
Maybe we could get a new topic opened, Puzzles and Wag's.
[img]/forums/images/icons/smile.gif[/img] You are rubbing up against the answer, and you have a good grasp of what physical size has to to with handling current without overheating. THE ANSWER IS:.....with the two compressors Lem was pulling rated current off the bus with SIX BITES ON THE BUS. Now with the single breaker he only has THREE bites, and the contact area is insufficient to transfer the current. This is why you NEVER want to put in a panel where the MAIN BREAKER is a plug-on to the bus. It's a matter of area. The three things needed to transfer current are: Cleanliness, Area, and Contact Pressure. Lem lost area when they went to a single breaker. [img]/forums/images/icons/mad.gif[/img] VERY FEW electrical guys can answer that question; and I have asked it probably over a hundred times. [img]/forums/images/icons/tongue.gif[/img] Want another electrical question that might tweak you some more? You did pretty good on that one. [img]/forums/images/icons/crazy.gif[/img]
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