Voltage drop increase the current?

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ok I'm going to look the exact data in theses nameplate fixture and I came back on Monday to the forum. thanks for all your responses is very helpful the knowledge that we can get here
 
I am very surprised that a 20 amp breaker is tripping at 21 or 22 amps. The product standard permits them to carry that load forever without tripping. In many cases I have seen 20 amp breakers that have carried 25 amps forever without tripping.
Yes, there are variations in the calibration that could account for tripping so close to the nameplate, but since the product standard requires that the breaker carry its handle rating forever in a 40°C ambient, I am surprised....not likely that the breaker is actually in a 40°C ambient and as the ambient goes down, the trip point goes up.
 
Has any one considered PF into this. The lamps rating at ?
Lamp is not the correct word, driver may be a better choice. I have seen to many driver coming on line at one time take out an OCD. Interesting thread!
 
I believe an acceptable solution has already been found, splitting the circuit and adding another home run. This thread is all about understanding what went wrong.

To HV+LV's point: LEDs themselves are not constant power devices. The devices being discussed here are LED lamps which include both the LEDs themselves and the necessary driver circuitry.

The question about what happens when voltage changes hinges on the specific nature of the driver circuit. However if the driver circuit is a 'multivolt' design (eg one which will work happily at any voltage from 100 to 277) then it is very likely constant power.

Jon
 
GoldDigger said:
A lighting load which uses an active driver circuit (LED, fluorescent, etc.) can be designed to draw a constant power to the lamp regardless of small fulctuations in input voltage. So a 5% drop in voltage at the fixture could cause a 5% increase in the current.
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For the ideal case wouldn't this cause a runaway feedback loop? The voltage drops, so the current rises, so the voltage drops some more, so the current rises some more...

Obviously real drivers must have engineered limits but it seems like a poor design principle.
 
jaggedben said:
For the ideal case wouldn't this cause a runaway feedback loop?
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Suppose you have a fixed voltage source V, and let's consider the real, linear case, so you have a transmission/source resistance A and a (variable) load resistance B. The load wants to adjust B to get some target power P.

The current in the circuit will be V/(A+B), and the total power dissipated will be V2/(A+B), of which B*V2/(A+B)2 will be dissipated in the load. A little calculus shows that the maximum load power dissipation occurs when B = A, in which case the load power will be V2/4B.

So if P is less than V2/4B, then the load will increase B above A to reduce the load power to the target P. If the P is larger than that, I'm not sure how a modern power supply would behave, but I doubt it will respond by lowering B to 0 to cause a short circuit (with current V/A).

Cheers, Wayne
 
don_resqcapt19 said:
I am very surprised that a 20 amp breaker is tripping at 21 or 22 amps. The product standard permits them to carry that load forever without tripping. In many cases I have seen 20 amp breakers that have carried 25 amps forever without tripping.
Yes, there are variations in the calibration that could account for tripping so close to the nameplate, but since the product standard requires that the breaker carry its handle rating forever in a 40°C ambient, I am surprised....not likely that the breaker is actually in a 40°C ambient and as the ambient goes down, the trip point goes up.
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In the next sentence after performance is investigated and marked for 40°C ambient, UL 489 and DIVQ prohibit continuous loads exceeding 80% of Amp rating.

"Unless otherwise marked, circuit breakers should not be loaded to exceed 80% of their current rating, where in normal operation the load will continue for three hours or more."

Since the rest of us would violate equipment listings loading breakers > 80% > 3hrs, the Don must be operating >1000 volts per 230.208(B), or using circuit breakers marked 100% rated per Exception in 210.20(A).
 
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infinity said:
In your opinion could VD contribute to increased circuit current?
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For normal resistive loads, I'd say no. But I don't know enough about commercial LED luminaire driver circuits to say whether or not they would demand more current if the voltage drops.
 
ramsy said:
In the next sentence after performance is investigated and marked for 40°C ambient, UL 489 and DIVQ prohibit continuous loads exceeding 80% of Amp rating.

"Unless otherwise marked, circuit breakers should not be loaded to exceed 80% of their current rating, where in normal operation the load will continue for three hours or more."

Since the rest of us would violate equipment listings loading breakers > 80% > 3hrs, the Don must be operating >1000 volts per 230.208(B), or using circuit breakers marked 100% rated per Exception in 210.20(A).
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I am just saying that they will carry their rating forever in a 40°C ambient.

Not saying you are permitted to do that by either NEC or the product standard.

In the real world, some breakers routinely carry above their nameplate rating forever because they are not actually running in a 40°C ambient, and because the calibration for breakers is not exact.

Which brings up another issue....breaker operation at low temperatures. In my area a 200 amp breaker installed outside will actually have a 250 amp or higher trip point for just over 5 months of the year, based on the trip curve shift because of ambient at or below 50°F
 
don_resqcapt19 said:
I am just saying that they will carry their rating forever in a 40°C ambient.



In the real world, some breakers routinely carry above their nameplate rating forever because they are not actually running in a 40°C ambient, and because the calibration for breakers is not exact.
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It may not be exact but it could also be slightly lower.

it could take hours for a breaker to trip at 21 or 22 amps.
possibly days if it is colder.
 
Hv&Lv said:

It may not be exact but it could also be slightly lower.

it could take hours for a breaker to trip at 21 or 22 amps.
possibly days if it is colder.
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In the real world, I would not expect a 20 amp breaker to actually trip at 21 or 22 amps even if left at that load for days, or weeks. Sure it might, but it appears to me that breakers typically operate closer to the maximum trip than to the minimum trip on the time current curves.
 
don_resqcapt19 said:
In the real world, I would not expect a 20 amp breaker to actually trip at 21 or 22 amps even if left at that load for days, or weeks. Sure it might, but it appears to me that breakers typically operate closer to the maximum trip than to the minimum trip on the time current curves.
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My first point on a test curve is 110% for a relay.
I may set up and test a magnetic breaker at 110% and time it out FTHOI..
If I do I’ll get back with the results.

I’ll have a hard time hitting the 40C mark..
too hot for me.
I bet it follows close to this. QPs are what I have at the shop..
 
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Hv&Lv said:
My first point on a test curve is 110% for a relay.
I may set up and test a magnetic breaker at 110% and time it out FTHOI..
If I do I’ll get back with the results.

I’ll have a hard time hitting the 40C mark..
too hot for me.
I bet it follows close to this. QPs are what I have at the shop..
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Yes and that is likely the reason that breakers in the real world will carry a few amps over nameplate forever as they are not operating in a 40°C ambient.
 
don_resqcapt19 said:
Yes and that is likely the reason that breakers in the real world will carry a few amps over nameplate forever as they are not operating in a 40°C ambient.
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I won’t be able to attain 104 on a test bench situation.
In an actual breaker panel 100+ degrees isn’t hard to attain, especially in the summer.
I infrared many panels and even in the winter I find several over 100.
It’s the main reason I refuse to use the 30C ratings on CTs.
Always 50C.
 
Hv&Lv said:
I won’t be able to attain 104 on a test bench situation.
In an actual breaker panel 100+ degrees isn’t hard to attain, especially in the summer.
I infrared many panels and even in the winter I find several over 100.
It’s the main reason I refuse to use the 30C ratings on CTs.
Always 50C.
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I have worked on a number of commercial buildings where loads have been added after the original installations. Often as part of a service call for "hot" conduits. In a number of these cases, there were lighting loads that were drawing a few amps over the breaker rating and the breakers were not tripping....no testing....just observation of real world installations.

The code and the breaker standard limit the continuous loads, not for any safety reason, but just as an attempt to limit breaker tripping...something no one really wants to have happen.
 
don_resqcapt19 said:
I have worked on a number of commercial buildings where loads have been added after the original installations. Often as part of a service call for "hot" conduits. In a number of these cases, there were lighting loads that were drawing a few amps over the breaker rating and the breakers were not tripping....no testing....just observation of real world installations.
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I'm having visions of maintenance employees, property-management employees, or the unsupervised employee of a licensed contractor.

How do you deal with this, since you were called to fix it?

don_resqcapt19 said:
The code and the breaker standard limit the continuous loads, not for any safety reason, but just as an attempt to limit breaker tripping...something no one really wants to have happen.
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What about the wire inside the "hot" conduit?

#12cu @ 20 Amps runs => 90°C with > 9 ccc's in the same pipe.
 
marcosgue said:
Hello all, this's my scenario,
Temporary panel 240V, single phase feeding lighting in construction commercial building, the lighting load is supply through 20A, single pole circuit breaker, the breaker tripping time to time.
I've checked and I got measurement 21-22amp in the circuit, seem to me evident overload. I've already fixed adding another home run and divide the total load in two circuits. When I told my supervisor about this situation, he says the breaker was tripped due to voltage drop because when the voltage decrease, the current increase and trip the breaker.
I think he's wrong and also I don't believe what he says is the best example to show the relationship between voltage and current.
Because we learn everyday in this forum I'd like hear the opinion of the experts.
Thanks in advance
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I see a lot of answers that suggest the operation of the 20 amp CB is a definite operating point. I would like to say that
in the USA, Standard UL 489, states that a circuit breaker less than 50 amp rated must trip between 12 seconds to a maximum of 2 minutes at 200% of its current rating and trip at 135% of rating in less than one hour. It is also necessary to understand how the current rating is arrived at. For a 30 amp circuit breaker the rating is arrived at by testing the circuit breaker in open ambient air of a maximum of 40 degrees C allowing a maximum degree C rise of 35 degrees giving a maximum operating temperature of 75 degrees C. Temperature is used as the defining parameter since it is a thermal strip that will cause the CB to trip. A specific degree C rise temperature indicates the maximum allowable differential in temperature between the circuit breaker and the ambient surrounding temperature. (It is noted here that the 30 amp rating is given under the condition of free air surrounding the CB, not with adjoining Circuit breakers on either side.) if the load on a circuit breaker is such that it causes a temperature rise in excess of 35 degrees C, the CB cannot dissipate heat quickly enough to keep it from tripping even though it is operating in an ambient temperature of less than 40 degrees C.

Based on the above, the circuit breaker may supply 30 amps without tripping as long as it is in free air, the maximum ambient temperature is a maximum of 40 degrees C. I also note that the NEC in the USA limits the maximum to 80% of the trip value when used in a panel board with adjacent circuit breakers. This is due to the inability of the 30 amp CB to dissipate heat in the same way in would in free air.

So you see there is a lot of room as to just when the 20 amp CB would trip. Also, LED lighting is a constant current system or constant current in steps for dimmable LEDS. If the voltage varies, the tot al energy the LEDs need remains the same and thus current draw from the supply will go up or down inversely with the voltage to a small degree. Linear loads follow the voltage, voltage up current up, voltage down current down. Motors are devices that supply (or attempt to supply) constant torque, thus within certain operating windows, voltage down, current up to supply the same torque. Hope this helps.
 
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