Circuit Breakers

Does anyone know which specific 60A circuit breaker is included in the kit?

Are they single, double or triple poled?

What is the voltage rating, and what type is it?

The 60 amp breaker that comes in your kit is in a grayish box with yellow & blue print on it and roughly 4" x 3 1/2" x .75". There is a picture of it with all the details in the kit of parts section of the rule book, which you can access right on line at the USFIRST.ORG site. You can buy a replacement from your local SquareD distributor. The phone book may list Brands with the yellow page ad for “electrical distributors.” Otherwise call any electrical distributor and they can tell you where to get one if they don’t have it.

Tim Gates
Team #288

So how many teams have tripped it in competition?

we have, so now we need to turn off parts of our robot before ramming/pulling other objects on the field. :stuck_out_tongue:

In the Elimination Rounds at the Buckeye Regional, a number of teams, including Chief Delphi, had problems with the 60 Amp circuit breaker tripping.

I have been one of the voices saying that teams should not have any problems so I am especially anxious to get the word out on this issue to set the record straight.

Here is my story:

I knew we should have been okay on that breaker. There is no way we pull more than an average 100 Amps during a match, no almost no matter what we are doing. The charts tell me at 100A the breaker should take 2 minutes to trip. Yet we were going dark about ½ way through the match! What gives?

I thought perhaps it was a bad breaker but tests on the breaker we took out of our machine (thinking it might be bad) showed that it did not trip in less than 2 minutes when we tested it at 100A constant.

Shock turned out to be the explanation. If we just tap the breaker on the side of the housing with the handle of a screw drive (and not too hard either), the break time is effectively cut in half. This was found to be true at several different test conditions.

When we reviewed the tapes of our matches, in every match that we tripped the breaker, the robot took a hit right at the moment the beacon went dead.

I think we have found the smoking gun…

Bottom line: Teams that can figure out a way to keep their breaker from getting an impact load may be able to extend the trip time of their breaker by a factor of 2.

This is a important bit of news that we plan on implementing at the Great Lakes Regional this week.

Stay tuned for more results as the story continues…

Joe J.

Our 60A breaker tripped when we took a particulary hard hit during the qualifying matches at VCU.

Michael D.
Team 602

*Originally posted by Joe Johnson *
Bottom line: Teams that can figure out a way to keep their breaker from getting an impact load may be able to extend the trip time of their breaker by a factor of 2.

Would putting a clip on the breaker help? I know that many of the breakers in my house have a clip on them (which, i guess, turns them into auto-reset breakers), but would such a clip be legal in competition? If so, where would I get such a clip? Also, would it be legal to wire in a toggle switch if the breaker is locked?

hmm, maybe that’s why our breaker blew a few times, for now reason at all. well, i think we’ll still turn off none vital parts of the robot before we ram/push/etc. other things on trhe field. doesn’t hurt to play it safe.

Joe, we had the same problem in training before ship. I remember someone saying that the breakers should be cable-tied in the ‘on’ position during matches to avoid tripping from shock, but I’m not sure that would help.

Our immediate solution was to first replace the offending breaker, and second, mount the new one vertically so as to avoid the largest part of the shock when we smash into the goals.

It also seems like someone might be clever enough to figure out the internal geometry of the breaker, and mount it so that the forces from the increased current are cancelled out by the forces from the impact, allowing you an instantaneous current peak.

Ok, so maybe that last bit was a little far-fetched.

One more issue, though - if the failures you’re having are not shock-induced, current spikes can trip these breakers in very short time frames. So you don’t need to average 100A if you have a 200A instantaneous spike. The spike will trip the breaker magnetically.

A clip would not make it auto reset since you need to switch it to on then off then on again (and probally against the rules), the best way to avoid shock tripping is to mout the beraker perpendicular to the force ie. not parallel to the floor. This way the shock wont effect the tripping mechinism. Also if you suspend it with taught rubber tubing it should buffer out the major shocks.

I’m not sure on this, but I think that the breaker will trip even if the switch is forced in the on position constantly. Even if it could be “kept on”, it would defy the whole purpose of the 60 Amp breaker, which is to prevent overheating and a potentially major fire hazard.

I hadn’t thought about shock affecting the breaker, but it makes sense now that I think about it. Often, the biggest amp load is when the robot runs into something and the motors are pushing hard, which also happens to be a big physical shock. Bad combo for the 60 Amp circuit breaker.

You can download the technical documentation on the breaker at this site:

Download document 0720CT9401, “QOU Miniature Circuit Breakers and Switches”.

Tripping mechanisms are shown on pages 1 & 2 - both the thermal (inverse time) and the magnetic (instantaneous).

Thr trip curve is the right-hand one on page 14. It shows both the “inverse time” characteristic of the thermal mechanism, and the “instantaneous” magnetic mechanism.

Look at figure 1 on page 2. Of course a breaker on the verge of tripping will trip off when “mechanically agitated”. It really wouldn’t matter much what the mounting orientation is, either. It’s ready to trip, it gets hit, it trips.

Once you look at, it appears very simple - deceptively so. Many such things will come back to bite you in your engineering career.

Beware of using equipment in applications outside the design basis. Very few electrical distribution cabinets move. Even the best of us (i.e., Dr. Joe) can be fooled on occasion.

Here is Square D’s responce about shock impact:

There is no technical information on this application. QOU breakers are
susceptible to shock
or a large impact. Suggest locating the breaker where it won’t receive that
shock or large
Sherry Glass
CIC Tech Support

On the subject of the 60 amp breakers, I do not believe that any team can trip this breaker on current overload. The breaker has been tested and has predictable trips when run at 120 volts AC and 45 volts DC. Even though the battery at full charge is capable of delivering 450 amps, the terminal voltage at that current would be low enough to reset the robot controller before the circuit breaker would have a chance to react. These circuit breakers are very susceptible to impact trips, however. (try it yourself by tapping on the circuit breaker on either side the wires enter, you will be surprised at how little it takes.)They are especially sensitive to shocks from the sides, where the the wires are attached. For this reason, circuit breakers should not be firmly mounted in the robot such that any shock to the robot is transmitted directly to the circuit breaker. Teams have been successful in adding a few inches of extra #6 wire when installing the breaker. This allows the wire to absorb most of the shock and keeps the breaker from shock tripping.
We add a small block of plastic to the breaker that is wider than the body by 1 inch on both sides. (This allows us to tywrap the #6 wires to prevent flex failures in the wire at the breaker.) Then we bend the wires back so that there is several inches before they are attched to a frame member. That extra wire then absords the impacts to the frame.
I saw several impact trips at Great Lakes this weekend.
Hope this helps,

P.S. The clips on circuit breakers (in a distribution panel) are to prevent someone from turning them off accidently. They do not prevent the breaker from tripping on either current overload or impact.

my robot took numerous hard hits philly to the side the breaker is on and so on, we never blew out once. Is it possible there is just a batch of bad breakers out there?

No, all circuit breakers exhibit this phenomena. Consider yourself really lucky…so far. Remember though, the circuit breakers are most sensitive to side impact, i.e. where the wires enter and exit.
Good Luck

*Originally posted by Al Skierkiewicz *
On the subject of the 60 amp breakers, I do not believe that any team can trip this breaker on current overload.

Unfortunately, I think it is quite clear that our robot DID trip our breaker multiple times solely on current overload. We were running six-motor drive, and we continued to trip the breaker even after gearing down, providing better ventilation to the breakers, fixing some faulty wiring, and allowing the breaker to be supported in mid-air by its own wires only (and cushioned by surgical tubing in case it moved too far).

Also, our breaker tripped mainly during sustained pushing matches, such as continuous low current being used to keep two goals stationary in our scoring zone. We eventually had to make the painful decision to disengage the drills from our mobility gearboxes, which has so far solved the tripping problem but has noticeably reduced speed and torque.

What seemed to happen sometimes is that one motor would trip its own 30 amp breaker, and while that motor was not receiving power the other two would be driving it, increasing the load on them and exacerbating the problem.

-Ian Mackenzie
Team 188
Woburn Robotics

Are you coming to Midwest regional? I would really like to take a look at your robot and talk to you about the tripping. You kind of imply that one of the 30 amp circuit breakers tripped out and stayed that way. The 30 amp breakers reset pretty quickly and on a sustained fault have been known to buzz as they repeatedly trip and reset. You did not mention if your controller was rebooting, did that happen as well? Let me know.
Good Luck All

Yeah, and which motors are tripping the 30A breakers?


First of all, no, we will not be at the Midwest regional, although we will be at the nationals (and by that time we will have competed in the Canadian Regional, during which we might discover something else). I confess that I don’t know which motors were tripping the 30 amp breakers; in the heat of competition, we believed that it was better to make a drastic change (taking out two motors) that would definitely solve the problem than to take our time investigating and fine-tuning individual breakers and speed controllers. The latter seemed to be, as we say, “building to tolerance”. Actually, I couldn’t confidently say that the breakers were tripping at all; we never really got conclusive evidence of it, so we may very well have been grasping at straws.

I don’t believe our controller lost power, because I never remember the light turning off temporarily (I have seen the controller shut off during practice back in Canada, usually when our battery was running low, so I think I would have recognized it if it happened in competition).

-Ian Mackenzie
Team 188
Woburn Robotics