Breaker trip

[The electron man]

In the past i asked, if a breaker will trip if there is no neutral and ground bounding at the main

The answer I got is

In a line to line fault it will trip

But

In a ground fault it won't

My question is why won't it trip in a ground fault if not bonded

Won't the thermal trip kick in ??

 

[augie47]

 

[The electron man]

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I understand the main bonding jumper allows the current to return to the service neutral but why dose it trip on a line to line if not bonded ?

 

[Little Bill]

I understand the main bonding jumper allows the current to return to the service neutral but why dose it trip on a line to line if not bonded ?

Because a line to line fault is a dead short. The path is the conductors themselves. You have one leg of the 240V on one conductor, and the other leg on the other conductor. If they touch, it will create a short circuit and trip the breaker.

 

[The electron man]

Because a line to line fault is a dead short. The path is the conductors themselves. You have one leg of the 240V on one conductor, and the other leg on the other conductor. If they touch, it will create a short circuit and trip the breaker.

Got it , so the thermal trip only works for an overload right ?

 

[ptonsparky]

Got it , so the thermal trip only works for an overload right ?

Pretty much. Dependent on the amount of overload.

 

[infinity]

I understand the main bonding jumper allows the current to return to the service neutral but why dose it trip on a line to line if not bonded ?

For the same reason that it trips in a fault between the ungrounded and neutral conductor because there is a massive amount of current flow that is detected by the circuit breaker.

 

[jim dungar]

Got it , so the thermal trip only works for an overload right ?

No. The thermal element only responds to the current flowing through it via the line/hot conductor. It does not care what the return path is.

If the fault is line to ground but the ground is not bonded to the power source there is not a complete circuit so it is unlikely enough current would flow to put the protective device into its thermal region. See the second picture in post #2.

Ground fault tripping elements simply have lower tripping points than thermal elements but they still need a complete path for current to flow.

 

[The electron man]

No. The thermal element only responds to the current flowing through it via the line/hot conductor. It does not care what the return path is.

If the fault is line to ground but the ground is not bonded to the power source there is not a complete circuit so it is unlikely enough current would flow to put the protective device into its thermal region. See the second picture in post #2.

Ground fault tripping elements simply have lower tripping points than thermal elements but they still need a complete path for current to flow.

But there must always be a complete loop for a curcit breaker to work right ?

 

[jim dungar]

But there must always be a complete loop for a curcit breaker to work right ?

Yes there must be a 'loop' from the source through the protective device and then back to the source.

 

[Electromatic]

From the broader definition of "circuit": a roughly circular line, route, or movement that starts and finishes at the same place.