over current device

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I agree with the other Charlie, of course. But I wonder where you are going with this line of question. Just please do recognize that the 70 amps that leaves the breaker on one leg will return to the breaker on the other leg (or perhaps it may return to the source on a neutral wire). But you don't add the 70 to the 70 and conclude that you are dealing with 140 amps total.
 
To carry this a bit further, if you had a 20 ampere two pole circuit breaker with NO internal connection and just a handle tie. Further, you remove the handle tie and use it as two single pole circuit breakers to feed two separate circuits, it would have the capability of 20 amperes each at 120 volts. If the handle tie was not removed and it fed a 240 volt piece of equipment, each circuit breaker would carry 20 amperes but at 240 volts between the circuit breakers.

I hope I didn't confuse the answer. :smile:
 
Over current device

Over current device

No, you did not confuse the answer at all. To the contrary, that is quite clear. I have a 70 amp 2P breaker running a heating load (head bolt heaters) and the actual dynamic amp load is 40 A, 23 A, and (34 A on the neutral). However the breaker keeps tripping. I am thinking now perhaps it is tripping on imbalance or perhaps I need a new 70 amp breaker.

At any rate I just wanted to know for sure that one does not add the amp readings together because if that is the way it worked then it would be obvious why the 70 amp breaker is tripping as it would have 97 amps on it.

Thank you Charlie B. and charlie E.
 
Arcticsparky,


Where is the breaker phisically located?

I ask, because if it is in a boiler room, then that is the ambient temperaturre to the breaker.

If it is outside, and it's cold (have had 35 amps of heater not trip a 20 amp breaker for months on end at 20 below zero)

Hope you have an extra 70A 2P breaker laying around to try the fix.
 
Over current device

Over current device

Yes it is located in a boiler room. However the boilers is a direct vent Weil McClain 310 and the panel is cool to the touch. When the temp teaches 70 below here I think you could rum 70 amps on a # 12. I should be able to borrow a spare breaker to test with.
 
Any chance that you're on a cat train heading for Pt Thompson?

I know, if you tell me, you'll have to kill me. Wait, there are some thugly looking characters knocking at the door right now!
 
arcticsparky said:
No, you did not confuse the answer at all. To the contrary, that is quite clear. I have a 70 amp 2P breaker running a heating load (head bolt heaters) and the actual dynamic amp load is 40 A, 23 A, and (34 A on the neutral). However the breaker keeps tripping. I am thinking now perhaps it is tripping on imbalance or perhaps I need a new 70 amp breaker.

At any rate I just wanted to know for sure that one does not add the amp readings together because if that is the way it worked then it would be obvious why the 70 amp breaker is tripping as it would have 97 amps on it.

Thank you Charlie B. and charlie E.
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Is the 70A CBer supplying a panel? Or is it directly supplying the heat?
 
How old is the CB on this heating load..and how old are the head bolt heaters..because when a head bolt heater starts to fail it gets a hair line crack in it and when it gets hot the crack expands..at first the heater is okay but as the insulation material breaks down it starts to trip the breaker and proceeds to get more frequent over time..so you could actually have 2 problems hear..
 
arcticsparky said:
. . . the actual dynamic amp load is 40 A, 23 A, and (34 A on the neutral). . . .
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There is a formula that relates the neutral current to the current on the other phases, and these numbers are consistent with what that formula is telling me. So my guess is that you have a breaker that has failed, and the solution should require nothing more than a new breaker.

However, there are other possibilities, other possible causes for which you might not have noticed the symptoms. One is that there may be a fault within the equipment being served. Another is a breakdown in the insulation of one of the wires. In a boiler room, there is not only heat, but vibration. Suppose a conductor had been free to vibrate over the years, and had rubbed part of its insulation off. It might, from time to time, bump up against a nearby metal part, and cause a short circuit that will trip the breaker, even though the measured load currents were well below the breaker's setpoint.
 
arcticsparky said:
I am thinking now perhaps it is tripping on imbalance or perhaps I need a new 70 amp breaker.
Click to expand...
Normal circuit breakers (those without electronic components) do not trip on current imbalance.

How long does the breaker stay on before it trips?
 
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