Testing elec breaker to verify trip
- Thread starter s219
- Start date
- Views: 4043
BertZegers
Gold Member
- Joined
- Jan 2, 2012
- Messages
- 259
- Location
- South-West Ontario
- Tractor
- Kubota L2900, Zetor 8011, Kubota KX41Excavator, John Deere 4400 Combine, Case 1816C skidsteer
A 15 amp breaker will carry 15 amps 24 hours a day 365 days a year and not disconnect. It will carry 20 amps a long time, before tripping, depending on heat dispensation of the breaker. If you throw out a 15 amp breaker if it doesn't trip within a minute loaded with 20 amps, you will throw out every breaker you buy.
It is all in the "AMPS - TIME graphic". You need to understand the graphic to understand the breaker!
NEVER test a breaker " short cutting" the breaker. The breaker is designed to disconnect in case of a short (and prevent fire), but can only do so a few times.
Testing a breaker can not be done at home, since you have to test Amps in relation to time over the whole band.
Bert, retired Electrical Contractor.
Paddy
Veteran Member
BertZegers,
You are correct, all based on current and time. We called it TCC, Time Current Curves. I was a large breaker design engineer 15 years ago, 15 kV to 27 kV breakers used in Substations. The number of times a breaker will trip is based on contact ware. High current= very few trips. The type test involved 100 short circuit interruptions, 20 at max and the rest at 20 and 50%. It was not uncommon for the contacts to weld. Every time a breaker opens, its random on the AC cycle. Arcing erodes until the current zero. Depending on the contact speed and where on the cycle open is started, over 8 ms arcing.
Why didn't the breaker trip? Either a bad breaker or it didn't reach trip levels? might have just acted as a mini arc welder and didn't exceed the ratings. I assume it blew out of the wall socket due to electromotive forces. I've seen 1.5 inch aluminum conductors rip out of clamps under 60kA SC testing.
European wall sockets are recessed so the plug is completely disengaged before the ends are exposed. Good idea with 220 v
You are correct, all based on current and time. We called it TCC, Time Current Curves. I was a large breaker design engineer 15 years ago, 15 kV to 27 kV breakers used in Substations. The number of times a breaker will trip is based on contact ware. High current= very few trips. The type test involved 100 short circuit interruptions, 20 at max and the rest at 20 and 50%. It was not uncommon for the contacts to weld. Every time a breaker opens, its random on the AC cycle. Arcing erodes until the current zero. Depending on the contact speed and where on the cycle open is started, over 8 ms arcing.
Why didn't the breaker trip? Either a bad breaker or it didn't reach trip levels? might have just acted as a mini arc welder and didn't exceed the ratings. I assume it blew out of the wall socket due to electromotive forces. I've seen 1.5 inch aluminum conductors rip out of clamps under 60kA SC testing.
European wall sockets are recessed so the plug is completely disengaged before the ends are exposed. Good idea with 220 v
aczlan
Good Morning
- Joined
- Mar 7, 2008
- Messages
- 16,985
- Tractor
- Kubota L3830GST, B7500HST, BX2660. Formerly: Case 480F LL, David Brown 880UE
Looking at the "AMPS - TIME graphic" posted above for a 15 amp Square D QO breaker, a 15 amp load should trip the breaker in just under 0.4 seconds and a 20 amp load should trip it in under 0.02 seconds.
Aaron Z
CobyRupert
Super Member
:thumbsup:
- Bert is correct, a 15 amp breaker will carry 15 amps all day. The numbers on the bottom of the "amps- time graph (a.k.a. time-current curve) represent the multiple of the breaker's rated current. Thus 15 amps is represented by the number "1". The above graph has the top of the curve cut off at a little over 10 seconds, but we can see that the curve needs a lot more time to even approach "1".
20 amps ( or 1.33 on the graph) is also off the top of the chart, but we can estimate from the graph, and from personal experience, that it's probably in the 15-25 second range.
Mendonsy
Veteran Member
AND .... there is a fairly wide range also. To get trip times of 1 second the QO breaker needs to see between 5 and 10 times the rated current. That means a 15 amp breaker would have to see somewhere between 75 to 150 amps to trip at 1 second.
I actually DO understand that every breaker has a time/current curve and do not trip simply on current alone. But please do tell me; what will be the temperature of the highest resistance point in my 14 gauge wiring on my branch circuit fed by that 15 amp breaker that is delivering 20 amps after "a long time"?
- Jay
Mendonsy
Veteran Member
According to the chart on page 3 of this PDF it should rise about 20 degrees C (68F) above the ambient temperature.
wire_and_cable_technical_data.pdf
wire_and_cable_technical_data.pdf
DarkBlack
Elite Member
Home circuit breakers are cheap. If you don't trust an old one, replace it with a new one. Don't short it out through your house wiring.
After you put n a new one, put a good load on it through the house wiring, like a hair dryer, and check the voltage at the outlet for drop.
After you put n a new one, put a good load on it through the house wiring, like a hair dryer, and check the voltage at the outlet for drop.
Mace Canute
Elite Member
Has anyone ever encountered a counterfeit breaker?
